| Author |
Ku, Chung Yee |
| Title |
A study on fire hazard and smoke control in large railway interchange stations |
| Department | Dept. of Building Services Engineering |
| Year | 2017 |
| Subject |
Hong Kong Polytechnic University -- Dissertations Local transit -- Fires and fire prevention Fire escapes |
| Degree |
Ph.D. |
| Pages | 244 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/99102195 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8983 |
| Abstract |
In a busy city like Hong Kong, railway interchange stations are obliged to cope with the growing population and the expansion of the railway network. As of now, a number of new railway lines are, or will soon be, in operation. Within the integrated railway network, the design of the new railway stations with smoke control via a smoke management system is becoming more and more complicated. Likewise, a timeline analysis of the Available Safe Egress Time (ASET)/Required Safe Egress Time (RSET) and a fire hazard assessment based on the architectural design and smoke management system must consider the effects of different fire scenarios, fire loads, and occupancy factors. Complicated station designs and the integration of the railway stations with other transport facilities, including Public Transport Interchanges, can produce problems in the evacuation of passengers in the event of fire. Due to complicated station designs, the standard prescriptive code on fire safety cannot be directly applied to all stations. Clearly, the station configuration built nowadays is commonly very complicated in terms of the building size, building height, and method of construction. In order to justify that the railway station is safe for use, it is necessary to adopt the performance-based fire engineering approach to work out a solution. In the design and planning of the railway station, especially one with a Public Transport Interchange, a fire evacuation strategy has to be developed based on the consideration of a number of important factors. As a general rule and design requirement, passengers within the fire incident place should be able to leave the place before becoming unduly affected by the fire and smoke; passengers in an area remote from the fire should be given sufficient and clear information to enable them to react according to the instructions from the station staff or clear announcements broadcast in the station. The prescriptive building codes deal with the provisions for escape based on the lengths of escape routes, width and number of exits, the time for evacuation, and the evacuation path. By using the Fire Dynamics Simulator (FDS), a Computational Fluid Dynamics (CFD) software simulation model, and the data obtained from experimental results, the fire hazards in relation to the smoke control system in the large railway stations can be assessed, and the ASET can be determined. The railway stations with complicated architectural layouts and evacuation route arrangements can be justified by the performance-based fire engineering approach of analysis. A smoke management system is a method of controlling the smoke generated by fires in railway stations. The objective of the smoke control system is to keep the smoke at high levels, thus facilitating the fire-fighting process and passenger evacuation. In this study, the smoke layer height and the ASET will be estimated via FDS simulation. With sufficient data collected from the CFD simulation results and experimental results from the scale model of a tilted enclosed space, the CFD simulation results can be compared, and the ASET from the CFD model by FDS can be validated. A fire safety management plan based on the validated results can then be developed to accommodate the railway station design. In large railway interchange stations, the main concourse areas are often connected to horizontal passenger subways, slightly tilted passenger corridors, and even tunnels for trains due to a construction alignment. In order to study fire characteristics in large railway interchange stations, a scale fire model of an enclosed space similar to the configuration of a tunnel, with the ratio of 1:40 and angles of 0°, 2°, 4°, and 6° to the horizontal, is created and studied. The fire source is modelled by the use of containers in different sizes in the 1:40 scale model of an enclosed space. A 37-mm-diameter pool fire is created to represent the Heat Release Rate (HRR) of 5 MW from a bulk of burning luggage. It is conventional in Hong Kong and many countries worldwide to adopt the convective heat flow as the steady-state design fire for smoke control calculations. The experimental results indicate that the flame-bending angle increases while the flame height decreases with an increase in the inclination angle of the enclosed space, as additional force is acting along the longitudinal direction with the gravitational force. It is also observed that the flame colour is independent of the tilted angle. Flame colour remains yellow at different tilted angles due to the supply of oxygen maintaining the reaction of the emissions of small carbon-based particles. Different tilted angles produce fires with different characteristics involving the flame pattern, gas temperature, and flame height. Fire engineers should take these factors into consideration in the design of fire and smoke control systems in large railway interchange stations. The use of timeline analysis in the performance-based fire engineering approach should be reviewed by fire engineers with knowledge in fire dynamics. In terms of railway station designs, exit arrangements should be carefully reviewed with the aid of a predictive evacuation model. Further systematic studies on human behaviour including a proper interpretation of fire and evacuation predictive models with the RSET data supported by the field measurements of crowd movements are recommended. |
| Author |
Qu, Lu |
| Title |
A study on fire safety provisions of public transport interchanges in well-developed cities |
| Department | Dept. of Building Services Engineering |
| Year | 2012 |
| Subject |
Local transit -- Fires and fire prevention. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xiii, 150, [123] leaves : ill. ; 30 cm. |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2615877 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/6979 |
| Abstract |
With the requirements for better and more efficient transport systems in well-developed cities, public transport interchanges (PTIs) are built. As several catastrophic fires occurred in the transport system of dense urban areas in the past years in many places over the world, life safety and smooth operation of PTIs have to be ensured. PTIs with both building characteristics and occupant loading are different from other buildings. Fire safety problems have to be addressed differently and will be discussed in this thesis. The thesis starts with a review on the fire safety aspects of PTIs. Fire hazards in possible areas, long evacuation routes and high transient passenger loading were identified. Performance-based design fire engineering approach was commonly applied to provide fire safety of PTIs. Relevant standards, codes and other investigations were reviewed. Hardware provisions of fire safety such as the construction characteristics and fire service installations were investigated. Fire safety management is proposed to be enhanced as software provision. Detailed investigations on the fire risks in PTIs, evacuation of passengers, and smoke movement characteristics in long corridors were carried out to develop the fire safety strategies. Performance of ventilation and smoke control system is very important to prove fire safety. Smoke exhaust system is evaluated in an example public transport interchange including a subway station and a bus terminal under different fire scenarios. Train fire, luggage fire on platform and retail shop fire with different ventilation operations were simulated numerically to identify if there is a tenable environment for the evacuation of passengers. Computational fluid dynamics (CFD) model - Fire Dynamics Simulator (FDS) Version 5 was used to predict smoke spread and the available safe egress time during the fire. It is demonstrated that mechanical exhaust system is useful in delaying the spread of smoke. Platform screen door (PSD) systems are starting to be popular in underground railway stations. There is a concern that PSDs would affect passenger movement during emergency particularly during rush hours. Effect of PSDs on emergency evacuation under crowded conditions was studied based on the surveyed passenger flow characteristics. As the passenger loading is important for the evacuation simulations, a field survey on the transient passenger loading of selected PTI in Hong Kong was carried out. It was observed that the transient passenger loading can be very high in rush hours. Evacuation times under different passenger loadings from a train vehicle were estimated by empirical equations. Simulations on train evacuation under normal and fire conditions were then carried out using the computer software FDS with evacuation. Several scenarios with different opening conditions of PSDs were considered. There are many long corridors built underground in many PTIs. Design of smoke control systems in such areas requires a good understanding of the smoke mass flux at different parts of the building. A density jump might occur when the smoke released by the fire flows along the ceiling. FDS was used to simulate the characteristics of the density jump along a long corridor. Characteristics of density jump to horizontal smoke movement underneath the ceiling induced by a fire were studied. Numerical experiments on density jump controlled by different types of smoke barriers in a long corridor were reported. From the predicted fire environment in a long corridor, the effect of smoke control system on density jump was identified. Fire safety problems on hazards due to density jump were then pointed out. Characteristics of density jumps with different Froude number in a long corridor were also studied numerically. Timeline approach was commonly applied in performance-based design for many big construction projects. Timeline analysis was carried out on construction projects with difficulties to comply with the prescriptive fire safety codes such as the public transport interchanges. An underground transport station was selected as an example to illustrate the common practice in performance-based design. Both the Available Safe Egress Time (ASET) and the Required Safe Egress Time (RSET) were estimated and then compared. Different fire scenarios with different fire sizes were identified. Fire simulations were carried out to predict ASET. Evacuation simulations were carried out to predict RSET. However, the conclusion will be entirely different with larger fire size and higher occupant loading. The challenges on applying the timeline analysis in performance-based design in crowded areas were pointed out. |
| Author |
Liu, Jing |
| Title |
A study on fires and associated provisions in open kitchens in small residential units of tall buildings |
| Department | Dept. of Building Services Engineering |
| Year | 2016 |
| Subject |
Kitchens -- Fires and fire prevention. Dwellings -- Fires and fire prevention. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xix, 107, 8, 73, 3, 10 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2925525 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8694 |
| Abstract |
Open kitchens are adopted in small residential units in tall buildings to make room spacious. These residential flats characterized by small floor area and high fire load density in tall buildings pose serious fire hazards. In this thesis, the fire hazards associated with open kitchens were first studied. Then, fire resulting environments of kitchen fires were examined. And at last, the application and effectiveness of water mist fire suppression system in these kitchens were evaluated. Fire hazards originating from cooking area were reviewed and analysed. The leading cause of home cooking fires was identified. A scenario with special hazards was also identified. When frozen food is dipped into hot oil, the water turns into steam instantly and can violently explode hot oil in many directions with large volume of flames. In this case, the fire may spread out of the cooking area and ignite surrounding combustibles, resulting in a big fire. Water and ice were used to simulate the water content in frozen foods and experiments were conducted under varying ratio of water or ice to oil to evaluate the associated hazards. In the experiments, an induction cooker was used to heat the oil which is allowed to use in open kitchens. Temperature and characteristics of flames were obtained and discussed. Flashover is a big concern in small units with a high fire load density. Nonlinear dynamics was applied to study flashover in flats with an open kitchen. Evolution equation was developed based on a two-layer zone model. The upper smoke temperature was taken as the system state with selected control parameters. The effect of heat release rate, floor geometry, thermal properties of wall material and other parameters on the occurrence of flashover was investigated. It was proved that flashover can be demonstrated by the model developed, though the results are sensitive to the parameters selected. Kitchen fires were then investigated numerically by the Computational Fluid Dynamics software Fire Dynamics Simulator (version 6.0). Fire source was determined based on the plate size of the induction cooker and heat release rate per unit surface area of canola oil. Common household furnishings in a typical layout were input to the model. Then, the fire environment was evaluated under various scenarios. The presence of combustibles in the immediate vicinity of the cooker, state of the exhaust hood fan, fire barrier required to install adjacent to the exit and wind effect were taken into consideration. The extinguishment of cooking oil fires is very challenging. Water mist fire suppression system is one of the alternative protection measures in open kitchen. The effectiveness of water mist fire suppression system depends on the fire scenario. Full-scale fire extinguishment experiments were conducted in a mock-up open kitchen. The suppression performance of water mist system was examined under different types of nozzle head, various system operating conditions and different oil depths. Parameters such as free burning time, discharge duration, extinguishing time, quantity of water used and temperatures were recorded and measured. The suppression of cooking oil fire by water mist was also numerically studied. The cooking oil fire was modelled in different ways and the water mist system was modeled with varying spray characteristics. The numerical results were compared with the experimental data. |
| Author |
Dong, Xue |
| Title |
A study on fire suppression mechanism in tall halls by long-throw sprinkler |
| Department | Dept. of Building Services Engineering |
| Year | 2016 |
| Subject |
Fire extinction. Fire sprinklers. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xv, 238 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2904148 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8572 |
| Abstract | Designing fire suppression in tall and large spaces is a challenge. Tall and large spaces typically contain large fire loads that can lead to a rapid increase in temperatures during an accidental fire. Conventional fire suppression systems are not able to extinguish fires in tall and large atria. The water droplets distinguished from sprinkler systems can either be vaporized or carried away by the fire-induced hot air currents in tall and large spaces. In this thesis, the fundamental principles of rapid and effective fire extinguishment, the major findings and limitations of existing sprinkler systems widely used were identified first. A side-wall long-throw sprinkler system is then proposed. The characteristics of the system including their structure, flow coefficient, operating pressure, sprinkler head distance and installation height were then studied. The experimental portion of the study was started by establishing the key experiment parameters for the long-throw sprinkler, including the use of a 10 MW fire. Appropriate wood cribs were selected as the experimental fire in this study. The heat release rate characteristics for different arrangements of wood cribs with different numbers of wood cribs and placements were explored. Tests were conducted on the water distribution qualities of sprinklers in a hall with different installation heights of 6 m, 8 m and 10 m under operating pressures of 0.2 MPa, 0.35 MPa, and 0.5 MPa respectively. The results were used to justify numerical simulations. Experimental results are then correlated with the most desirable water distribution characteristics for proposing design practices. The Computational Fluid Dynamics (CFD) model Fire Dynamics Simulator (FDS) was then used to study the performance of proposed side-wall long-throw sprinkler systems. Two sets of four scenarios on sprinkler fire were adopted for CFD-FDS simulation. The size distribution of water droplets, sprinkler flow effectiveness, sprinkler head design, fire extinguishing system activation time and heat transfer characteristics between smoke and sprinkler water droplets were studied. For medium hazard classes, sprinklers with flow coefficients 115 and 161, installation heights higher than 10 m and operating pressure of 0.5 MPa are found to be appropriate for extinguishing fires. Full-scale experiments were conducted on sprinkler fire for justifying CFD-FDS predictions. Important technical requirements for designing sprinkler for tall and large halls are the proportion of large water droplets discharged from the sprinkler system reaching the fire. The concept of Actual Delivered Density and Required Delivered Density were applied to evaluate the performance of sprinkler systems. Results from full-scale experiments are consistent with those from the mathematical models. |
| Author |
Qi, Ronghui |
| Title |
Study on heat and mass transfer of internally heated liquid desiccant regeneration for solar-assisted air-conditioning system |
| Department | Dept. of Building Services Engineering |
| Year | 2013 |
| Subject |
Solar air conditioning. Air conditioning -- Energy consumption. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xxxii, 299 leaves : ill. ; 30 cm. |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2653090 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/7289 |
| Abstract |
Traditional air-conditioning (AC) systems have several limitations, such as the poor humidity control, energy wastage, and the creation of wet surfaces that become breeding grounds for mildew and bacteria. The problems become more serious in warm or hot and humid climates. As an energy-saving and environmental-friendly alternative, the Liquid Desiccant AC System (LDAC) becomes a good solution to remove the extra moisture of air by desiccant absorption. Its major energy required is low-grade thermal energy, such as the solar thermal energy provided by solar collectors. To improve the system performance and to utilize the thermal energy efficiently, the internally cooled/heated dehumidifier/regenerator has drawn many attentions recently. Furthermore, due to its low possibility of droplets carried by the air and low pressure drop, the falling film dehumidifier/regenerator has become a promising type for liquid/gas contacting. As most energy consumes for regenerating the solution, this research focused on the regeneration process. However,'the study of literature shows that previous investigations on this system were insufficient. This research aimed to investigate the heat and mass transfer of the internally heated liquid desiccant regeneration experimentally and theoretically by considering the change of wetted area, film thickness and mass transfer coefficient under the insufficient wetting conditions, and to develop a 3-D theoretical model for predicting the fluid characteristics and system performance more accurately. Based on the buildings' load profiles and weather data of Hong Kong, the dynamic operation performance of the whole Solar-assisted LDAC (SLDAC) was evaluated, and several system optimizations were proposed and studied to reduce the energy consumption. The wetted area and mass transfer coefficient are key parameters affecting the system performance, and also indispensable parameters in the system evaluation. By testing a single channel internally heated regenerator, the influencing factors of wetted area, film thickness and mass transfer coefficient were investigated experimentally, as well as their effects on the mass transfer performance. The film sizes under different operation conditions were recorded by a thermal camera, and LiCl was chosen as the solution. The increase of wetted area benefits the mass transfer performance greatly, while the performance reduced with the increasing film thickness. The initial width of the film was affected by the solution distributor thickness most greatly, and changed significantly with the contact angle and solution mass flow rate. When the surface was pre-wetted to be hydrophilic, the initial width dramatically increased, and the contraction of falling film was effectively weakened. The film contraction was also reduced with the higher working surface temperature, while it was aggravated with the increase of solution temperature. Furthermore, under insufficient wetting conditions, the mass transfer coefficient decreased with the increase of solution mass flow rate. It also decreased with the increase of solution distributor thickness and solution temperature, and increased with the increasing air mass flow rate. Additionally, the contact angle of solution was experimentally found to be determined by the surface roughness, solution concentration and temperature. Based on the experimental results, a theoretical model with an analytical solution was developed for accurately calculating the wetted area of the internally heated regeneration, by describing the transverse flow caused by the Marangoni effect. The model could be divided into three parts, including the model for initial wetted width, the model for contact angle and the model for contraction distance along the flow direction. The calculation results were compared with the experimental ones with small average errors of 8.8%, 12.3% and 10.8% respectively for the three parts. The film thickness, plate surface temperature, and solution temperature, concentration and contact angle were numerically found to significantly influence the wetted area. An empiric formula of mass transfer coefficient was also developed with the multi linear regression, showing an acceptable error compared with the experiments results. Then, a 3-D model with a numerical solution of internally heated regeneration was developed for describing the heat and mass transfer among the air, solution and extra hot water in all three directions. The insufficient wetting condition, the change of film thickness due to the mass transfer and film deformation, and the effect of contact angle were considered. The calculation results were compared with those obtained by other existing theoretical models, and showed a closer trend to the experimental data, especially in the prediction of the influences of solution mass flow rate, hot water temperature and working plate surface temperature. The parameter study showed that the thickness of solution distributor has the greatest impact on the moisture removal rate, and the change of inlet solution temperature results in the most obvious change of the regeneration efficiency. The changes of solution concentration and hot water temperature also significantly affect the system performance. Though the increase of mass flow rates of solution, air and hot water benefits the mass transfer, the effect of excessive mass flow rates are slight. Although the model was developed based on the internally heated regeneration, it is also suitable for the adiabatic system by introducing of plate surface temperature. Furthermore, the new model could also be applied for the dehumidification process considering the similar heat and mass transfer mechanism between the dehumidification and regeneration of liquid desiccant. Though the 3-D model could predict the system performance more accurately, it is complex and inconvenient for investigating the dynamic operation performance. A simplified numerical model of internally cooled/heated dehumidifier/regenerator was developed accordingly by defining three kinds of effectiveness, i.e. enthalpy effectiveness, moisture effectiveness, and temperature effectiveness. With the multi linear regression, the statistical correlations of effectiveness were developed by using the heat and mass driving forces and other related parameters as variables. The results were compared with those by the 3-D model with an acceptable error of 14.7% for dehumidifiers and 7.1% for regenerators. With the simplified model, to evaluate the operation performance and energy potential, a dynamic simulation of the SLDAC was conducted by employing four nested iteration calculation loops. As a case study, the AC load profiles of three typical commercial buildings in Hong Kong were investigated. Results showed that only up to 12.5% of electricity consumption could be saved annually if the cooling tower is used as the only cooling source of the dehumidifier due to the high dehumidification demand in summer. But, by introducing an extra cooling coil for the dehumidifier and a heat exchanger for the regenerator, the electricity saving percentage could be significantly improved to 36.7%. Additionally, the energy consumption of solar-assisted systems is affected by the installation area of solar thermal collectors, and the energy saving could not be achieved until the area is larger than the minimum required value. For our case, the minimum installation area is 0.22 m2/kW (peak load) for office buildings. Academically, this research contributes a 3-D theoretical model for predicting the heat and mass transfer of falling film liquid desiccant system more accurately by employing the newly developed models for the wetted area and mass transfer coefficient during the dehumidification/regeneration process. It provides a useful reference for researchers and engineering to improve the wetted area, to enhance the heat and mass transfer, and to optimize the system performance. Furthermore, as the falling liquid film are widely employed in many industrial applications, such as vertical condensers, film evaporators, absorption towers and heat exchangers, our results could also be applied for the performance evaluation and optimization in these areas. |
| Author |
Zhang, Wenke |
| Title |
Study on heat transfer surrounding pile foundation ground heat exchangers with groundwater advection |
| Department | Dept. of Building Services Engineering |
| Year | 2015 |
| Subject |
Heat pumps. Ground source heat pump systems. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xxxv, 212 leaves : illustrations (some color) ; 30 cm |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2816416 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8168 |
| Abstract |
Currently, the ground-coupled heat pump (GCHP) technology has gained more and more attentions due to its outstanding high performance characteristics in energy saving, environmental protection and associated benefits. The development of investigations have led to a new type of ground heat exchanger (GHE) entitled "energy pile". In brief, it is proposed for spiral heat exchange tubs to be enclosed in the pile foundation of buildings, thus integrating the bearing structure of buildings with a heat transfer component. A certain proportion of the heating load or cooling load can be met in this way; thereby reducing the initial cost of the whole cooling and heating system.A range of research studies have been conducted on the pure conduction of pile foundation GHE, however, little references or documentation exists in the literature concerning the influence exerted by groundwater flow. It should be recognized that varying degrees of groundwater seepage phenomena exist below ground. As the depth of the pile is usually more than ten meters or even many more meters, the underground hydraulic gradient inevitably leads to the groundwater flow. Accordingly the heat transfer involving conduction and groundwater advection should be taken into account when considering the role of seepage. The study presented in this thesis includes corresponding studies on simulation models for an energy pile with groundwater advection, and each type of model consists of both infinite and finite length sources. Heat transfer experiments were then conducted to indirectly verify the seepage models. In addition, a reasonable methodology to obtain the groundwater velocity is also proposed. The models were investigated and then further developed to be more advanced from some classical models such as line and hollow cylindrical heat sources. Firstly, a new model, referred to as the "solid" cylindrical source model, is initially proposed. In this model, the pile diameter is much thicker and the depth is usually shorter than in the case of the borehole, and the spiral coils are disposed in the vicinity of the pile circumference. The cylinder is filled with medium identical to that out of it; thus, the interior heat capacity of the pile cannot be ignored. Analytical solutions for the solid cylindrical models while groundwater flows through it were obtained. Secondly, the ring-coil model is put forward to represent the configuration of spiral coils set inside the pile by a more appropriate method. The solid cylindrical model only regards the pile foundation GHE as a uniform surface heat source and thus the coil intervals are not considered. Compared to the solid cylindrical model, the ring-coil model is relatively advanced because it takes into consideration the discontinuity of the heat source along the depth. This heat source is deemed as a series of separated coils arranged along the z-direction so that focus is on the impacts of the coil pitch. If groundwater goes through the energy pile with spiral coils, the temperature response induced by conduction and groundwater advection at any point except the heat source can be achieved. Thirdly, focus is on comparing the solid cylindrical and ring-coil models with an improved model. An attempt is made to reduce the deficiencies of the former two by introducing a spiral line, hence proposing the spiral heat source model. The improvement is the fact that a spiral line replaces the separated coils and thus a succession of connected coils with a certain diameter are distributed down the depth of pile. Accordingly, not only the coil pitch but also the helix angles are dealt with. Thereby, the spiral heat source seepage model efficiently shows the thermal transfusions with greater accuracy and precision at the time of the combined contributions of both conduction and groundwater advection.However and regrettably the on-site heat exchange experiments of energy pile have not yet been conducted to validate the theoretical models. Next, the significant experiments based on the actual engineering projects were conducted to check the heat transfer ability and verify the conduction model of the pile foundation GHE. The experiments conducted in this study focused on the pure conduction of energy piles, and two groups of trials were conducted and the heat transfer superiority of the energy pile is shown by comparing pile foundation GHE with borehole GHE. The pure conduction model can then be validated by the experimental results. The combined heat transfer models including pure conduction and groundwater advection are indirectly proven because it derives from the pure conduction case. Thus, the combined model could be certificated indirectly in the event of the pure conduction model being confirmed.Lastly, the groundwater velocity is a vital parameter embodying the influence degrees of seepage, the comprehension of both value and orientation of velocity is becomingly increasingly important. To avoid the huge difficulties of directly measuring the velocity by means of the test equipments, a significant methodology named "back calculation" is suggested. The conditional extreme values of the sum of the variance and the corresponding derivatives combined with the theoretical models were put to use when the target functions had been established. By this means, the groundwater velocity can be obtained based on the temperature responses at different points around a borehole GHE.In summary, all models involving both energy pile and groundwater advection developed and presented in the thesis are introduced one by one on the simple to complex principle. The spiral heat source model is the optimum case from the perspective of academic study as it most approximately simulates the energy pile with groundwater advection. However, other models can still be employed to provide theoretical basis for some situations such as engineering projects and so on, because in these cases the requirements for calculation accuracy are not too high. The application of energy piles can reduce the initial cost of meeting a building's need for heating and cooling. Groundwater advection does improve the heat transfer performance of energy piles as it enables heat accumulation around the pile to be alleviated, therefore the temperature difference between GHE and the surrounding underground medium is maintained or even increased. Thermal transmission is further promoted and accordingly heat exchange quantity is enlarged. The flow velocity including its value and orientation can be deduced when the back calculation method is employed. The pure conduction experiments have produced satisfactory effects, and an aim of the future work is the implementation of the heat transfer experiments with groundwater advection to directly validate the groundwater seepage models. Full understanding of groundwater advection is helpful to emphasize not only the significance but also the popularization of energy pile technology. |
| Author |
Lau, Kwai Wing |
| Title |
A study on installing water curtain system at refuge floor of supertall buildings in Hong Kong |
| Department | Dept. of Building Services Engineering |
| Year | 2015 |
| Subject |
Fire detectors. Tall buildings -- Fires and fire prevention. Tall buildings -- Safety measures. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xix, 157 leaves, 97 variously numbered pages : illustrations (some color) ; 30 cm |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2806850 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/7925 |
| Abstract |
Local code of practice for fire safety in buildings issued by Buildings Department (BD) requires supertall buildings over forty storeys high to provide a refuge floor for every 25 storeys in residential/commercial buildings. However, the protection to external wall openings on refuge floor by a drencher/water curtain system falls within the jurisdiction of the Fire Services Department (FSD). There is a concern on the trend for flatted units in supertall buildings to have large window/glass panes design so as to have more sunlight and a better view. The result is that this design increases the impact of the ventilation factor, which in turn steps up the heat release rate for flashover and fire development in compartment fires. Another concern is the external wall opening sizes on the refuge floor vary greatly in different types of buildings. The differeence in the ratio of the area of an external wall opening to the area of the external wall of the refuge floor greatly affects the effectiveness of cross-ventilation on that floor. For a better understanding, a survey of building plans including 44 building lots (51 blocks) of residential and non-residential buildings was conducted. As statistics from FSD reveal that about 80% of structural fires occurred in government housing estates and private residential buildings, my study focuses on these types of buildings. Detailed inspections of building plans of 29 building lots (31 blocks) were conducted to obtain and analyze, for each of the building, the ratio of the area of an external wall opening to the area of the external wall on the refuge floor, the ratio of the window opening area to the external wall area as well as the ratio of the window opening area to the floor area of the flatted unit immediately below the refuge floor. The trend of refuge floor designs and the cross-ventilation requirement stipulated in the relevant local building code were also analysed. To determine the minimum amount of heat released for flashover in a compartment with large window panes, 31 supertall residential buildings were selected and the Babrauskas method for flashover was adopted. The results showed that the average minimum heat release rate for flashover was 15.3 MW for an unit having an average window opening area of 15.1 m2. To evaluate the effectiveness of a water curtain system in achieving heat reduction, radiation attenuation and smoke reduction from entering the refuge floor, Computational Fluid Dynamics (CFD) model Fire Dynamics Simulator (FDS) was adopted. Before working on the CFD model, a pre-study in four main subject areas was conducted: (1) comparing the simulation results of the FDS model with another CFD model called “SIMTEC and also with the results of full-scale burning test from literature; (2) selecting appropriate fuel types as an input parameter in FDS simulation; (3) comparing the performance of the sprinkler system and the water curtain system; and (4) making FDS trial runs covering different locations of fire seat, domain model geometry and fire sizes, etc. Simulation results from my pre-study showed that the results generated by the FDS model were comparatively more conservative in subject area 1 (i.e. lower temperture reduction and lower radiation attenuation) and agreed well with burning test results from literature (at least in the veocity of outflow gases) and with temeprature profile of the fire plume. In the selection of the appropriate fuel type for FDS simulation study, my prime objective was to look for the adverse effects in the combustion of propane, wood, polyurethane (PU) and polyvinyl chloride (PVC) . Simulation results including outputs of temperature, visibilities, carbon monoxide concentrations and radiation heat fluxes from different scenarios were evaluated. The highly hazardous properties of burning PVC and PU in producing large amounts of carbon monoxide and very low visibilities within a short period of time were carefully considered. The sprinkler system is commonly used in fire protection but this is not the case in the protection of external wall openings on the refuge floor. To compare the performance of the sprinkler system with that of the water curtain system in defined scenarios, the FDS model was adopted. Simulation results showed that the water curtain system performed better in of temeprature reduction and radiation atttenuation. To simulate the performance of the water curtain system on refuge floor external wall openings, a two-storey building model consisting of a fire room measuring 11m (length) x 9 m (width) x 3m (height) on the ground floor with a refuge floor immediately above it was designed. A fire was assumed to be spreading from the fire room after a flashover fire with flames ejecting through broken windows and spreading upwards along the external wall and wall openings of the refuge floor. An in-depth simulation study using FDS in different scenarios and design parameters including different fire sizes, opening widths of the fire room, wind speeds and scenarios with and without the water curtain system were conducted. The results showed that the water curtain sytem performed well in temeperature reduction, radiation attenuation and visibility enhancement on the refuge floor. Attenuation of thermal radiation by the drencher/water curtain system and relevant parameters such as water flow rates, water pressures, spacing of drencher nozzles, water droplet sizes and water density were studied using FDS simulation. Theories of Beer-Lambert's law and its analogy were adopted and simulation data analysed. The relationship between the parameters and the ratios of radiation intensity for scenarios with and without water curtain protection was established. A generalized equation to calculate the maximum attenuation of thermal radiation by a water curtain system was formulated using multiple regression analysis. The introduction of a building fire safety management system to monitor building fire safety based on the total fire safety concept together with an ultimate building fire safety audit system to ensure overall building fire safety has been developed. Methods and procedures in the evaluation of building fire safety levels are also presented. The thesis concludes that in the scenarios studied, the water curtain system performs well in temperature reduction, radiation attenuation and visibility enhancement on the refuge floor; and offers recommendations on how to improve the design of the water curtain system. Limitations of the study and suggestions on further work on the adequacy of ventilation requirement on the refuge floor are also given. |
| Author |
Tong, Hang Fa |
| Title |
A study on modern container terminal efficiency |
| Department | Dept. of Logistics and Maritime Studies |
| Year | 2018 |
| Subject |
Hong Kong Polytechnic University -- Dissertations Container terminals -- Management Container terminals -- Cost effectiveness Container terminals -- Economic aspects |
| Degree |
Ph.D. |
| Pages | 202 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/99102210 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/9401 |
| Abstract | This thesis focuses on terminal efficiency in the modern container shipping industry, addressing three principal research questions: 1) How is a modern container terminal's efficiency, as commonly represented by the annual throughput volume, determined in principle during the different planning and operations stages in a terminal? 2) What are the hidden influences on terminal efficiency performance and how can they be accounted for in possible berth allocation solutions when vessel schedules fluctuate severely? 3) What is the effect on terminal efficiency and the best berth allocation arrangement when additional vessels are added to the original vessel set? In Chapter 2, four key determinants are proposed after a detailed literature review on the topic. The effect of each determinant on terminals is elaborated. Together forming a comprehensive efficiency development space, the four key determinants are integrated container terminal design, terminal information system, customer service strategy, and operations planning and execution. A clear understanding of terminal efficiency in terms of costs, time, and quality is offered. In Chapter 3, the first hidden influence on efficiency is introduced. The concept of vessel workload waiting time is defined and modeled for an effective solution, called "vessel reberth arrangement," in the berth allocation process for the best operational performance. Exceptionally long vessel berthing periods are reduced and terminal operational efficiency is effectively increased using the proposed solution. In Chapter 4, the second hidden influence on efficiency is introduced. The concept of additional vessel workload demand is defined and modeled for another permanent solution, called "spare vessel window management," in the berth allocation process for the best operational and business performance. Additional vessel workload demand is reviewed, and how it can be served at the lowest operational cost and causing the highest business profit without adversely affecting regularly operated vessels is determined. This study contributes to the literature on container terminal efficiency in several ways. First, it identifies the four key determinants that form the efficiency development space for all types of container terminals. The impact of an improvement in one area on the overall strategy can be measured using these four key determinants. Second, the vessel workload waiting time problem is solved using the proposed reberth modeling strategy without the requirement of additional capital resources or staff. Terminal efficiency is not only improved at the quayside but also in the storage areas and along container movement routes. Third, the additional vessel service request problem is solved using the proposed spare window modeling, again without the requirement of additional capital resources or staff. Increased business profit is ensured when the optimal vessel berthing arrangement is employed. Terminal efficiency is improved with high flexibility and reliability. In practical terms, this study can help different players in the terminal and shipping industry to obtain a better understanding of modern terminal efficiency and how it can be improved without extra investment in capital or human resources, resulting in higher resource utilization and business profit. |
| Author |
Ma, Tao |
| Title |
Study on renewable energy systems with different energy storage solutions for power supply in remote areas |
| Department | Dept. of Building Services Engineering |
| Year | 2015 |
| Subject |
Renewable energy sources Energy storage Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xxxi, 302 leaves : illustrations (some color) ; 30 cm |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2806853 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/7928 |
| Abstract |
At present, more than 1.3 billion inhabitants worldwide still lack access to grid electricity. Most of the people live in remote areas, such as islands, mountain areas and isolated villages, all some distance from the utility grid. Grid extension to such remote communities is both uneconomical and technically difficult owing to dispersed population or rugged terrain. As a result, their electrical demand is normally met by use of diesel power or there is no power supply at all. Fortunately, such areas, although remote, are usually rich in renewable energy (RE) resources, thus making it worthwhile to explore such local RE resources with the objective of producing much needed electricity. In recent years, the unpredictability of diesel costs, falling RE generation costs as well as technological improvements have encouraged a wider adoption of renewable energies in such areas. Stand-alone renewable energy power generation systems have been the target of substantial research over the past decades. However, the focus on comprehensive renewable energy power supply solutions for remote areas, together with the identification of effective and low-cost technologies is limited. In addition, one significant technical challenge for those stand-alone RE systems, such as solar and wind energy, is the fluctuation of their output. This feature prevents the RE from being fully reliable for remote areas. In this context, the development of some effective energy storage solutions, to keep energy in excess for use in time of need, is an essential requirement. Currently battery must be a front-runner for use in remote RE systems. However, it has well known limitations, such as high cost, short lifespan, possibility of environmental damage and explosion, and difficulties for maintenance in isolated areas. Pumped hydro storage (PHS), usually used for conventional power plants, shows a great potential to replace batteries in standalone application, but to date few studies have reported the micro PHS for remote RE systems. The aim of this thesis is to study the options of power supply and energy storage for remote areas. One remote inhabited island 20 km off the coast of Hong Kong is taken to act as a test site for the proposed RE systems and storage technologies. To achieve the objectives of the study, a detailed study of different energy technologies for remote electrification was conducted, including system development, mathematical modeling, simulation, optimization, techno-economic evaluation, and sensitivity analysis. Different energy storage technologies, i.e. batteries, PHS, super-capacitors and their hybrids, are investigated via theoretical analysis, numerical simulation and experimental validation. The operational performance of a real PV-battery system on this example island was evaluated. Firstly, the RE potential and load demand of the selected island were assessed. Mathematical models for each RE technology were developed, and system evaluation criteria discussed. In particular, a novel simulation model for PV devices, offering a good compromise between accuracy and simplicity, was developed in Matlab to fit the I-V curves and predict PV power output. The model was solved using an integrated analytical and numerical method, then validated through field measurements in a real grid-connected and a standalone PV system. A detailed study on the use of a traditional energy storage technology, battery, to support a remote area power generation system has been conducted. System configurations of possible combinations of solar energy, wind energy, diesel generator and battery bank were developed. Hourly simulations for a wide variety of configurations were performed to achieve an optimal one based on techno-economic analysis. Two representative systems, the 100% RE and hybrid RE-diesel, were selected for deeper analysis. Emphasis was also placed on examinations of the effects of the PV, wind turbine, diesel generator, and battery bank capacity on the system's reliability and economic performance. The results demonstrated that the island could be powered by a 100% RE system, although it is possible that the energy cost provision will be quite high. The addition of a back-up diesel generator would make the hybrid system, i.e. solar-wind-diesel-battery, a more economically viable option. The problems which were observed concerning batteries limit a wider and future application of the battery-based RE systems. Thus as an alternative, a small PHS unit was proposed to support the remote area RE power supply systems at a few hundred kW scale. Of interest is the development in this study of a novel operating principle and design process for PHS-based RE systems. With the simulation program developed in this study, the system was simulated for a whole year. The genetic algorithm, along with the Pareto optimality concept, was then employed for system optimization, i.e. to identify the maximization of power supply reliability and minimization of system cost. The optimized system configuration under zero loss of power supply probability (LPSP) was then investigated. In addition, the system performance of hybrid solar-wind, solar-alone and wind-alone systems with pumped storage under LPSPs from 0 to 5% were compared. Sensitivity analysis on several key parameters was also performed to examine their effects on system performance. This study proposed a new concept of energy storage to compensate the intermittent nature of renewable energy applications. Even though the overall efficiency of the micro-scaled pumped storage system is not high, a sustainable and environmentally friendly power supply solution is able to be provided, indicating that the pumped storage is one future ideal partner for remote area RE power supply systems. Further investigation of the battery-based and PHS-based RE system indicates that the use of more than one storage technology will give a better performance as regards complementing fluctuating RE outputs and dynamic power demands. Therefore, a new hybrid energy storage system (HESS), which combines battery for long-term energy management and supercapacitor for fast dynamic power regulation, was proposed. The mathematical models of the passive connected HESS were developed, and then implemented in Matlab/Simulink for numerical simulations. An electric inductance was further introduced to improve the performance of the HESS. In addition, an experimental test bench was developed to validate simulation results. It was demonstrated that the HESS can stabilize energy provision, not only for intermittent RE, but also for other fluctuating load applications. Finally, the benefit of another kind HESS, a combination of pumped storage and battery energy storage system, was analyzed and the system was experimentally studied, as an illustration of the operation states of such hybrid energy storage technology. The operating data of a 19.8kWp solar PV-battery system on the island was collected and evaluated for the following aspects: the PV array, inverters, the battery bank and overall system. This evaluation enables a detailed understanding of the operating performance of the existing PV system from the technical point of view. It also provides useful reference data for further system extension. A comprehensive study of stand-alone RE power supply system using different energy storage solutions for remote areas with useful research outputs has been outlined above. The results provide researchers, engineers and policy makers with choices regarding the use of local RE resource, which could be aligned with the characteristics of individual remote area of interest. It is believed that the findings have provided a good reference for the selection of suitable RE and energy storage technologies, and the methodology presented can also be viewed as a starting point for planning and designing RE systems for remote communities around the world. |
| Author |
Yau, Pui Shan |
| Title |
Study on ship emissions and its impact to air quality in Hong Kong |
| Department | Dept. of Civil and Environmental Engineering |
| Year | 2012 |
| Subject |
Air -- Pollution -- China -- Hong Kong. Combustion gases -- Environmental aspects. Ships -- Environmental aspects. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xiii, 182 leaves : ill. (some col.), col. maps ; 30 cm. |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2551295 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/6804 |
| Abstract | Hong Kong is one of the busiest ports in the world, but it is lacking in sophisticated maritime emission inventory and air quality assessment inside or near the port area. Most of the shipping activities in Hong Kong waters occur within a couple of kilometers from the community, and the emissions from ships may cause adverse health effects on the public. The current research focuses on two areas: (i) developing emission inventory on ocean-going vessels (OGVs) and (ii) investigating the contribution of ship emission to the air quality of a community near the international container port. The speed profiles of vessels on different shipping routes in Hong Kong waters were determined with Automatic Identification System. Compared with the emissions estimated using the speed limits of control zones, the ship emissions estimated using vessel speed profiles could provide results with up to 88% higher accuracy. Uncertainty analysis and sensitivity of the model demonstrated the significance of improvement of vessel speed resolution. The vessel speed profiles derived were applied to the ship emission estimation. Based on maritime emission inventory developed with activity-based approach in the current study, the total ship emissions from OGVs in 2007 were 17097, 8190, and 1035 tonnes accounting for 17%, 11%, and 16% of total emissions of NOx, SO₂, and PM₁₀ in Hong Kong, respectively. From the emission spatial allocation, the shipping route along the East Lamma Channel and the berthing location of the Kwai Chung and Tsing Yi Container Port were the regions with the highest emissions. The OGV emissions in Hong Kong contributed 0.07% NOx, 0.05% SO₂, and 0.06% PM₁₀ out of the global total shipping emissions in 2007. Fine particulates (PM₂.₅) was collected near the Kwai Chung and Tsing Yi Container Terminals (KTCT) during the two study periods, i.e., (1) 14 August to 2 October 2009 for summer and (2) 26 January to 1 March 2010 for winter. The average PM₂.₅ concentration was 30.5 μg/m³. The chemical composition of the PM₂.₅ collected was characterized. The dominant species was determined to be sulfate (34%), followed by organic matter (19%) and elemental carbon (12%). The major PM₂.₅ sources, with particular emphasis on those associated with ship emissions, were identified using positive matrix factorization (PMF). The emissions of residual oil combustion and marine diesel oil combustion from ship engines contributed 12% (3.6 μg/m³) and 7% (2.3 μg/m³) of the total PM₂.₅ in the area near KTCT. The secondary sulfate associated with ship emission was determined, and its contribution to PM₂.₅ was 6% (1.8 μg/m³). Together with the primary ship emissions, the total ambient PM₂.₅ mass associated with ship emissions at the sampling site was 7.6 μg/m³ (25%). |
| Author |
Li, Yutong |
| Title |
Study on solar liquid desiccant dehumidification and regeneration for central air-conditioning applications |
| Department | Dept. of Building Services Engineering |
| Year | 2009 |
| Subject |
Hong Kong Polytechnic University -- Dissertations. Air conditioning. Energy conservation. |
| Degree | Ph.D. |
| Pages | xxi, 174 leaves : ill. ; 30 cm. |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2306437 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/3858 |
| Abstract | Dehumidification of air conditioning is traditionally accomplished with vapor refrigeration equipment. The disadvantage of this air handling process is that the temperature of the air must be cooled below its dew-point which is deemed to be energy expensive. An open cycle liquid desiccant dehumidification system driven by solar energy was emerged as a potential alternative to a conventional vapor refrigeration system for humidity control in an air conditioning system. This system can utilize solar energy and can provide cooling more efficiently. Application of the open cycle solar collectors/regenerators (C/R) is an effective way to utilize low-grade solar thermal energy to concentrate desiccant solution for air-conditioning. This project is to study how efficiently the solar desiccant dehumidification and regeneration can be used for central air-conditioning in hot-humidity weather area like Hong Kong. This thesis, firstly, presents the numerical simulation results of an open cycle liquid desiccant dehumidification system, attempting to obtain the optimum configurations of the solar assisted air-conditioning system and to validate the feasibility for using the liquid desiccant dehumidification system to handle the latent load and improve energy efficiency of central air-conditioning systems in a building. Secondly, a simplified simulation model for analyzing the coupled heat and mass transfer process on an open cycle solar C/R is introduced. Within narrow ranges of operating conditions, linear approximations were made to find the dependence of an equilibrium humidity ratio on the solution temperature, constant properties and coefficients. New parameters, which represent the heat and mass transfer driving forces, were defined and the basic differential equations were rearranged to obtain two coupled non-homogeneous linear equations. The climate conditions, such as solar radiation, air temperature, humidity ratio and wind speed, were treated as non-homogenous parameters for direct evaluation. In order to measure the performance of an open cycle and forced flow solar regenerator over a hot summer day for simulation validation purpose, an experiment using H2O/LiBr solution as working fluid was performed. The effects of ambient temperature, ambient relative humidity, forced air velocity and solar radiation intensity on the regeneration of the liquid desiccant have been experimentally observed. The simulation results were used to validate the simplified simulation model and develop the heat and mass transfer coefficient correlations. Unlike other types of solar utilization methods for which solar radiation is the only dominant weather parameter, the performance of the open cycle solar desiccant dehumidification system is also closely related to the ambient humidity and temperature significantly. To better predict its performance, a stochastic simulation approach is adopted to syntactically generate a series of meteorological parameters by using 15 years of real weather conditions of Hong Kong (between 1979-1988 and 1996-2000). Specifically, a first-order multivariate Markov chains model was developed to represent ambient temperature, humidity and solar radiation. The static properties of real weather data, like mean value, standard variance and persistence of a certain climate, are well preserved in the syntactically generated weather data and the inter-dependence of the solar radiation, ambient temperature and humidity are well reflected. Using the synthetic series of weather conditions, the annual performance of the open cycle liquid desiccant dehumidification system was analyzed. The energy saving, compared with a conventional vapor compression system, is in the range of 40-50%. More energy saving can be achieved if the ventilation load contains higher portion of a latent load. Besides, the economical aspect for using the open cycle solar desiccant dehumidification/regeneration system in Hong Kong is also discussed based on the system simulation and experimental results. |
| Author |
Luo, Hongsheng |
| Title |
Study on stimulus-responsive cellulose-based polymeric materials |
| Department | Institute of Textiles and Clothing |
| Year | 2012 |
| Subject |
Polymeric composites. Nanocomposites (Materials) Smart materials. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xxvi, 224 p. : ill. ; 30 cm. |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2551280 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/6792 |
| Abstract |
Cellulose is the most abundant natural polymeric material and has been widely used by human beings for several thousands of years. Exploration of novel and new materials based on the "old" material is of great academic and industrial significance. This thesis presents the first attempt to explore stimulus-responsive polymeric materials based on the natural cellulose by physical and chemical approaches, namely polymeric nano-composites, blending/semi-interpenetrating network and chemical modification. The thermal, structural, mechanical and morphologic properties of the samples were comprehensively investigated by Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), Wide angle X-ray Diffraction (WXRD), Dynamic Mechanical Analysis (DMA), tensile tests, Scanning Electron Microscope (SEM) and so on. Two categories, five types of stimulus-responsive polymeric materials were exploited based on the natural cellulose. Water-sensitive shape memory effect (SME), programming-structure-property relationship and underling mechanisms were emphasized in this study. Some new concepts, such as heterogeneous-twin-switch, path-dependent multi-shape, rapidly switchable water-sensitive SME were established. For the first category, cellulose nano-whiskers (CNWs) were incorporated into crystalline shape memory polyurethane (SMPU) and thermal plastic polyurethane (TPU). The CNW-SMPU nano-composites had heterogeneous twin switches, i.e. the thermo-sensitive switch due to the PCL crystals and the water-sensitive switch due to the percolating cellulose network (PCN). The water-sensitive switch was further hypothesized to divide into the shielded and the naked parts. Triple-and multi-shape effects were achieved for the CNW-SMPU nano-composites by applying into appropriate thermal-aqueous-mechanical programming. When the composites were in the dry state, the thermally triggered shape recovery was tuneable according to the PCN content. Furthermore, theoretical prediction along with numerical analysis was conducted, providing evidence on the proposed microstructure of the CNW-SMPU nano-composites. The CNW-TPU nano-composites were found to possess rapidly switchable water-sensitive SME due to the PCN whose hydrogen bonding was able to be reversibly regulated by water. A novel mechanism model was established based upon systematic investigation of the composites in terms of the morphological, thermal, structural and mechanical properties. The explored stimulus-responsive cellulose-based polymers in the second category consisted of cellulose-polyurethane (PU) blends, cellulose-poly(acrylic acid) (PAA) composites and modified cellulose with supramolecular switches, featuring the requirement of homogeneous cellulose solution in the synthesis process. The reversible behaviours of the cellulose-PU blends in wet-dry cycles as well as the underlying shape memory mechanism were characterized and disclosed. The micro-patterns of the blends were found to be self-similar and have fractal dimensions. As for the cellulose-PAA semi-interpenetrating networks, the emphasis was put on the mechanical adaptability in wet-dry cycles. A thermally reversible quadruple hydrogen bonding unit, ureidopyrimidinone (UPy), was used to react with the cellulose as pendent side-groups, which may impart the modified cellulose with thermal sensitivity. The findings in this project are beneficial for extending the potential application of cellulose in smart materials field. Moreover, it contributes to the development of shape memory polymers. The combination of multiple disciplines in this study also benefits the applications of nanotechnology and supramolecular chemistry in materials field. |
| Author |
Wang, Kai |
| Title |
Study on structural behaviour of high strength steel s690 welded H- and I-sections |
| Department | Dept. of Civil and Environmental Engineering |
| Year | 2018 |
| Subject |
Hong Kong Polytechnic University -- Dissertations Steel, High strength Steel, Structural |
| Degree |
Ph.D. |
| Pages | 378 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/99102214 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/9516 |
| Abstract |
Motivation
High strength S690 steel material possesses a yield strength of 690 N/mm² which are double or triple to those of normal strength steel materials, i.e. S235 and S355 steel materials. In recent years, massive production of these high strength steel (HSS) materials was realized in modern steel mills, and many successful applications of HSS in machinery, equipment and structures have been reported. Hence, advantages of excellent strength-to-self-weight ratios and high levels of economy of HSS have been widely recognized by researchers and engineers. It is also realized that drawbacks such as reduced ductility, stringent welding requirements as well as insufficient design guidance should be overcome. Up to the presence, wide application of HSS is hindered, particularly for building construction. Hence, it is highly desirable to experimentally understand structural behaviour of S690 welded sections. Moreover, suitable design methods should be developed to facilitate safe and efficient design for HSS structures. Objectives and scope of work In this research project, a systematic experimental and numerical investigation into structural behaviour of S690 welded H- and I-sections is conducted. This research project is comprehensive in which material properties of S690 steel material and its residual stress patterns induced by welding were accurately measured, and structural behaviour of these S690 welded H- and I-sections is examined experimentally and numerically. The scope of work covers the following tasks: - Task 1: Stocky columns of S690 welded H-sections under compression To examine section resistances of stocky columns of S690 welded H-sections through experimental and numerical studies. - Task 2: Slender columns of S690 welded H-sections To carry out a numerical investigation into overall buckling behaviour of slender columns of S690 welded H-sections. - Task 3: Restrained beams of S690 welded I-sections To examine local buckling behaviour of restrained beams of S690 welded I-sections with various section compactness through experimental and numerical studies. - Task 4: Partially restrained beams of S690 welded I-sections To examine lateral torsional buckling behaviour of partially restrained beams of S690 welded I-sections through experimental and numerical studies. The areas of interest include: - Deformation characteristics of HSS S690 welded H- and I-sections under i) compression and ii) combined compression and bending; - Comparison of welding-induced residual stresses in S690 and S355 welded H- and I-sections, and effects of residual stresses on structural behaviour of S690 welded sections; - Establishing a double Y-shaped finite element model which employs shell elements to facilitate accurate predictions on structural behaviour of welded H- and I-sections; - Applicability of current design rules in EN 1993-1-1 by comparing design resistances with measured and predicted resistances of S690 welded sections. It should be noted that four different cross-sections of welded H-sections, namely Sections C1 to C4, and six different cross-sections of welded I-sections, namely Sections B1 to B6 are fabricated with S690 steel plates of 6, 10 and 16 mm thickness. Moreover, plate thicknesses up to 40 mm are incorporated into numerical studies in order to cover a wide range of practical applications. Within this research framework, advantages of S690 steel materials and their wide application are elaborated systematically. Research methodology and key findings Based on a series of experimental and numerical investigations, all the four tasks have been successfully completed. It should be noted that: - Task 1: Stocky columns of S690 welded H-sections A total of 20 stocky columns of S690 welded H-sections were fabricated, and they were tested as follows: i) 12 stocky columns under compression, and ii) 8 stocky columns under combined compression and bending. Section resistances and deformation characteristics of the test specimens were successfully obtained. It was shown that predicted section resistances based on EN 1993-1-1 could be readily attained by all 20 test specimens. Large deformation capacity ratios as well as significant strength enhancement were obtained in S690 welded H-sections with high section compactness. Verified residual stress patterns of S690 welded H-sections are incorporated into structural finite element models of stocky columns. Generally, entire load-shortening curves of stocky columns were accurately predicted with calibrated models. Moreover, enhancement of section resistances which was highly dependent on material properties and plate local buckling was closely examined. The design rules given in EN 1993-1-1 are shown to be applicable to evaluate cross-section resistances of those stocky columns of S690 welded H-sections. In addition, it is also found that certain conservatism is embedded in interactive design curves for H-sections under combined compression and bending. - Task 2: Slender columns of S690 welded H-sections Calibrated double Y-shaped model is employed to predict overall buckling resistances of slender columns of S690 welded H-sections. Verification of the model is conducted against benchmark tests conducted by Wang et al. Through direct incorporation of residual stresses into H-sections, predicted load-shortening curves of these slender columns were found to compare very well with those of measured data. In general, current design rules in EN 1993-1-1 and -12 were found to be applicable to predict member resistances of these slender columns of S690 welded H-sections. Owing to significantly reduced compressive residual stresses in those cross-sections comparing with those in S355 steel sections, buckling curve c should be replaced by possibly curve b or even curve a based on parametric studies. Therefore, an improved design efficiency is achieved. - Task 3: Restrained beams of S690 welded I-sections In order to determine section resistances of restrained beams of S690 welded I-sections, a total of 6 beams under single-point loads were tested. Local buckling in the flange outstands was observed in all test specimens. With different cross-sectional compactness, steel sections generally attained full plastic section resistances against bending based on EN 1993-1-1. And various strength enhancement levels were obtained in steel beams, depending on section classification of these sections. Extensive studies based on verified models were conducted, and it was found that section classification rules in EN 1993-1-1 were applicable to restrained beams of S690 welded I-sections. Moreover, in order to achieve improved structural efficiency, new design criteria and methods are proposed according to numerical results of the comprehensive parametric studies. - Task 4: Partially restrained beams of S690 welded I-sections In order to investigate lateral torsional buckling of partially restrained beams of S690 welded I-sections, a total of 12 beams under single-point loads were tested. Different failure modes, including lateral torsional buckling and plastic section failure were observed in the test specimens. It was shown that partially restrained beams are readily assessed with buckling curve b instead of curve d as suggested in EN 1993-1-1. All numerical studies were carried out successfully incorporating effects of residual stresses. It is shown that partially restrained beams of small to moderate slendernesses tend to be significantly affected by residual stresses, when compared with those of high slendernesses. Moreover, a certain conservatism embedded in the current design method in adopting curve d was highlighted according to numerical results of the comprehensive parametric studies. Key findings and their significances The major academic merits of this research project are: - A whole-process simulation on temperature distribution, residual stress distribution and structural behaviour of S690 welded sections was fully established and verified to enable effective use of S690 welded sections; - Residual stresses in S690 welded H- and I-sections were systematically investigated, and their effects on structural behaviour of columns and beams of S690 welded sections have been identified; - Current design rules in EN 1993-1-1 were justified for designing S690 welded sections according to both experimental and numerical results. Moreover, current design rules with suitably selected design parameters were proposed for improved structural design efficiency; and, - Application of HSS S690 steel materials in columns and beams were fully validated through comprehensive experimental investigation, and they are technically ready for wide application in steel structures. |
| Author |
Kim, Ken Ri |
| Title |
A study on structural optimisation and colour mixing systems of digital Jacquard textile based on full-colour compound structure |
| Department | Institute of Textiles and Clothing |
| Year | 2014 |
| Subject |
Textile design -- Computer-aided design. Jacquard weaving. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xix, 191 leaves : illustrations (chiefly color) ; 30 cm |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2757519 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/7517 |
| Abstract |
Digitalisation technology has created a novel environment for Jacquard textiles in which computerised weaving technology and digital Jacquard CAD system make the design process convenient and time for fabrication efficient. The warps in an automatic weaving loom are hired in continuous styles and consist thousands of yarns. Since each of them is hooked up in an individual heddle, replacing them every time is nearly impossible. Although weft yarns are flexible to change, applicable yarn numbers are substantially limited. Diverse textile designs are now possible to be realised in woven Jacquard forms by utilising digitalisation technology. Yet, with limited yarns, the production of highly refined designs with a great number of colours remains difficult. Creation and reproduction of Jacquard fabrics of picturesque designs rely on both colour patterns and weave structures. Since Jacquard colour creation is based on optical colour mixing, the conditions of thread colour surrounding and interlacement distribution are explored through compound structure forms to achieve refined colour representation and to maintain structural balance. Numerous derivatives of weaves are created based on basic weave forms: plan, twill, satin and sateen weave. In order to achieve natural colour presentation, the forms of shaded weaves are designated to realise continuous tones of colour shades. In Jacquard textiles, the colour systems involve the aspects of rendering colour patterns as well as assorting a filling yarn group. The classification of the primary colour alignment of colour systems is crucial in assigning individual figuring threads to floats in defined regions to emulate the projected colours. The additive and subtractive colour models used to reproduce colours are thus examined to expand weave colour gamut through juxtaposing the primary coloured yarn groups. Jacquard textiles have been extended their application into a wide range of home furnishings and ornamentations. Yet many complicated designs are still being confined to but design concepts since intricate weave structure formations and unique features of colour realisation are still practical barriers in realising more complicated designs. It is where innovative design concepts are introduced in this study to expand the technical knowledge of the weave structure and pattern optimisation. Using the principle of establishing shaded weave structures, a new silhouette of shaded weaves is introduced. These structure formations are possible not only to generate gradual colour deviations, but also to render a distinctive textural effect on the surface of Jacquard fabrics. In addition, by applying a blurring effect in digitised colour patterns, {176}watercolour{174} effect which is originally formed when pigments defuse into each other can now be realised in woven fabrics. This study explored, examined, evaluated and identified the conditions of weave structures and colour systems for optimal colour representation of full-coloured designs with which new design concepts in Jacquard textiles are introduced. Designs previously considered difficult to be realised in Jacquard textiles are made possible in this study, which in turn has greatly expanded the creative scope, dimension and applications of Jacquard textiles. |
| Author |
Luo, Yimo |
| Title |
Study on the coupled flow, heat and mass transfer processes in a liquid desiccant dehumidifier |
| Department | Dept. of Building Services Engineering |
| Year | 2014 |
| Subject |
Air conditioning -- Energy conservation. Solar air conditioning. Cooling load. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xxx, 239 leaves : illustrations (some color) ; 30 cm |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2762975 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/7765 |
| Abstract |
At present, a large amount of energy is needed to create a livable indoor environment. It is estimated that the buildings sector consumed 28% ~ 30% of the total final energy in China. Among all the power-driven equipment in buildings, chillers for air conditioning are well-known for their high power consumption in buildings. This study concentrates on solar energy based liquid desiccant air-conditioning to reduce latent cooling load of central air-conditioning systems. Due to the separate control of temperature and humidity, a liquid desiccant air conditioning system can save up to 40% of energy compared to a conventional vapor compression system. Thus, it has drawn more and more attention. Even though many researches have been carried out about the dehumidifier by simulation and experiment, there are still some limitations. It has been found that most of the previous researches focus on the macroscopic parameter changes of the fluids and the effect of various operating parameters. However, the flow situations and their impacts on heat and mass transfer in the dehumidifier interior are seldom studied. Therefore, this thesis aims to study the coupled flow, heat and mass transfer processes in a typical dehumidifier numerically and experimentally. Firstly, numerical predictions were conducted to investigate the flow dynamics in the liquid desiccant dehumidifier with the CFD software Fluent. The developed model was validated by existing data from literatures. With the model, the mechanism of the gas-liquid flow in the dehumidifier was illustrated. The velocity profiles, the minimum wetting rate, the effective interfacial areas between the solution and air, the average and local film thickness at different conditions were investigated. Based on the calculation results, it was concluded that the simulation model could predicate the dynamic and local flow conditions in the dehumidifier interior microscopically. It was found that the counter-flow air did change the velocity profile of the LiCl solution along the film thickness due to the drag force. And when the air inlet velocity reached 3.0 m s⁻¹, the impact became very distinct. Under that situation, the air became the dominated factor to decide the velocity field at the interface. Meanwhile, the importance of a suitable solution and air flow rates could be highlighted. The results also explained the reason of the enhancement of mass transfer with film flow. Then, by adding suitable sources files to Fluent, the coupled flow, heat and mass transfer processes were described comprehensively. In the model, the effect of the velocity field on the heat and mass transfer process has been considered. Meanwhile, the variable physical properties of the desiccant and air, which were taken as constant in almost all existing models, render the simulation more in line with real conditions. In addition, the penetration mass transfer theory was employed to make it possible to observe the dynamic process in the dehumidifier interior. With the established model, the parametric studies were conducted in a range of different flow conditions. Through the simulation, it was found that the air velocity played a critical role on the performance of the dehumidifier, which had to be matched with the channel geometric size for optimization. Besides, titling the plate to keep certain mass transfer gradient in the channel was also essential. Meanwhile, the coupled flow, heat and mass transfer phenomenon was also analyzed. Secondly, to investigate the hydrodynamics of falling film in the dehumidifier experimentally, the film thickness was measured by a capacitance probe and the flow morphology was captured by a camera. The wetting area under different solution flow rates and plate surface temperatures were investigated. It was found that the minimum solution flow rate to prevent the breakout of the falling film was 0.068 kg m⁻¹ s⁻¹, which was of the same order of magnitude of the simulation results (0.071 kg m⁻¹ s⁻¹). The local and temporal film thicknesses under different air velocities were recorded and analyzed for both the upper and lower parts of the falling film. The results showed that the wave was intensified along the flow direction, which also agreed well with the simulation results. In addition, the influence of the air velocity on the film thickness was also investigated. The average film thicknesses were calculated and compared with those of the Nusselt empirical formula. It was found that the Nusselt empirical formula underestimated the film thicknesses in present condition. In addition, the pattern and shape of the typical film flow were presented in the thesis. Experiments were also designed to investigate the real dehumidification process in a single channel internally-cooled dehumidifier. The absolute humidity change and overall mass transfer coefficient were chosen as the indices to evaluate the performance of the dehumidifier. The influences of various parameters were analyzed in depth. It was found that the overall mass transfer coefficient was higher than that reported in the previous literature due to much higher humidity of the inlet air in the present work. The result fully demonstrated the feasibility and advantages of adopting liquid desiccant dehumidification in Hong Kong. The increase of air velocity in the dehumidifier resulted in the increase of the overall mass transfer coefficient and yet the decrease of the absolute humidity change. The experimental results showed the same tendency with those of the simulation model, which verified the correctness of employing the penetration mass transfer theory. Academically, the numerical research provides a novel simulation model to predict the coupled flow, heat and mass transfer processes in a liquid desiccant dehumidifier in this thesis. The model considered the effect of the flow and the variable physical properties of the fluids on the dehumidification process, and enabled the dynamic observation by adopting the penetration mass transfer theory. Secondly, a single channel experimental setup was fabricated to investigate the performance of the dehumidifier. The hydrodynamics of the falling film was studied by investigating the local and temporal film thickness and the flow patterns. Then the effects of various parameters on the performance of the dehumidifier were analyzed in depth. The experimental results verified the correctness of the simulation model to some extent. Thus, the engineers and researchers can employ the model to predict the wetting situation, optimize the operation conditions and design dehumidifiers. |
| Author |
Liao, Xian |
| Title |
A study on the developmental characteristics of Hong Kong primary students' ability to integrate textual information in narrative text reading |
| Department | Dept. of Chinese and Bilingual Studies |
| Year | 2015 |
| Subject |
Reading (Primary) -- China -- Hong Kong. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xii, 214 pages : illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2823802 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8125 |
| Abstract |
Integration is one of the key constituents of students' reading ability. However, systematic investigations have rarely been reported in this field worldwide. As international assessment programmes (e.g. PIRLS) and local public examinations (e.g. Hong Kong Territory-wide System Assessment) on reading have shown that Hong Kong primary students’ integration ability in reading is yet to be developed, it is of great theoretical and practical importance to get a deeper understanding of this ability. Therefore, the aim of the present study is to explore the developmental characteristics of Hong Kong primary students' integration ability in reading and factors that influence the development. The present study was conducted among Grade 4 and Grade 6 students in Hong Kong who were at the stage of "read to learn". Using narrative as a sample genre, the present study aims at finding out: (1) what are the characteristics of integration performance of Hong Kong Grade 4 and 6 primary students in reading narrative text? (2) What are the differences between integration performance of Grade 4 and Grade 6 students? (3) What are the differences between integration performance of boys and girls? (4) What are the factors that influence the development of students’ integration ability in reading? To answer the research questions, the present study adopts multiple methods to triangulate the findings, including reading integration test, semi-structured interviews with teachers and students and student questionnaire survey. Specifically, a "six integration skills" is first proposed, which includes identifying a referent of pronoun (IRPN), identifying relationships between adjacent sentences (IRS), identifying main idea (IMI), identifying relationships among paragraphs (IRP), abstracting specific information (ASI) and summarising the whole text (SWT). A reading integration test was then designed according to these skills and 352 Grade 4 students and 371 Grade 6 students participated in the test. Upon completion of the test, all participants completed a questionnaire designed to investigate potential factors that influence the development of students' integration ability. In addition, the researcher interviewed 24 students to explore the process of how they answered items in the test and 7 teachers were selected randomly for interviews to investigate teachers' perceptions of students' integration ability development and their teaching methods. The present study has reached some conclusions based on the statistical analysis of quantitative data and text analysis of qualitative data. The major findings are: (1) Primary students in Grade 4 and Grade 6 have attained preliminary integration ability in reading but still have room for further development. Students in both grades performed best in IRS and worst in ASI; (2) In general, students in both grades performed better in integration skills relying on "straightforward inference" (IRS, IRPN and IMI) than in those skills requiring complex inference and language transformation (IRP, ASI and SWT); (3) Grade 6 students performed significantly better in individual integration skills than Grade 4 students. Compared with Grade 6 students, Grade 4 students were unable to identify complete information referred by pronouns and had difficulties in identifying the relationships between adjacent sentences and between paragraphs and locating topic sentences. Also, Grade 4 students were not capable of summarising specific abstracted information in a complete and brief way. Therefore, Grade 4 students performed worse in terms of complicity and accuracy in integrating information of the whole text than Grade 6 students; (4) In general, girls performed better than boys in total integration score and individual integration skills, which indicates that girls' develop their integration ability earlier than boys. However, boys may gradually catch up with girls' performance in some easier skills such as IMI and IRS; and (5) Three factors play important roles in development of students' integration ability in reading, use of reading strategy, extensive reading and reading attitude. In sum, the present study has revealed some developmental characteristics of students' integration ability in the context of Chinese teaching. A series of implications of Chinese curriculum, teaching and assessment are drawn from the results of this study in order to improve students' integration ability. |
| Author |
Lui, Po Ying |
| Title |
A study on the effects of electronic games on musculoskeletal health and aerobic fitness in school-age children and adolescents |
| Department | Dept. of Rehabilitation Sciences |
| Year | 2016 |
| Subject |
Video gamers -- Health and hygiene. Electronic games -- Health aspects. Physical fitness for children. Physical fitness for youth. Musculoskeletal system. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xx, 255 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2925497 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8682 |
| Abstract |
Today school-age children and adolescents are exposed to a wide range of screen-based devices, particularly various electronic games (EG) systems. High exposure and intensive use of these devices may have negative health impacts on the musculoskeletal system and aerobic fitness. The purposes of this thesis were: a) to examine the pattern of EG device usage, sedentary behaviours and physical activities among school-age children and adolescents, and their association with musculoskeletal discomforts (MSDs); b) to investigate the biomechanical loading and the oxygen consumption during play of two types of EG devices (small-screen handheld and active game system), as well as MSDs and aerobic fitness related to EG play. This thesis involves two studies. Study 1 involved a survey on the usage of EG devices among Primary 4 to Secondary 3 students of four schools in Hong Kong. The survey was conducted from November 2009 to May 2010. Two primary and two secondary schools participated, returning 1,590 questionnaires (out of 2,000, the response rate was 79.5%) for analysis. The mean age of the 1,590 children surveyed was 12.49±2.03 years and the age range was 8-18 years; 23.7% reported high-level use of EG devices (more than four hours daily), and amongst these high-level EG device users, more boys were large-screen based device users while small-screen handheld devices were used by more girls. More secondary school students were associated with the habit of high-level EG use than primary school students (32.2% versus 9.3%). The survey found students spent long hours (≥4 hrs/day) in computer use (30.7%) and television viewing (27.2%). Only 18% of students had a habit of physical activity more than 60 minutes daily. Participants were asked to indicate their bodily discomfort related to EG play. 19.5% and 23.8% of students had neck discomfort and upper limb discomfort, respectively. Univariate logistic regression analysis of the data illustrated that high EG use (≥4 hrs/day) was associated with neck discomfort (odds ratio=1.400, 95% CI=1.083-1.811, p=0.010) and upper limb discomfort (odds ratio=1.687, 95% CI=1.307-2.177, p=0.001). Study 2 investigates the biomechanical loading on the musculoskeletal system (Part A) and on oxygen consumption (Part B) during play sessions with two types of EG devices: the small-screen handheld Sony PlayStation Portable® (PSP) and the active game system the Nintendo Wii® (Wii), in the same group of subjects (aged 10-14 years). Specifically, Part A examined in 36 subjects, the electromyographic and kinematic responses of the neck and upper limb region during 20 minutes of EG play, and its association with subjective musculoskeletal discomforts. Surface electromyography (EMG) was conducted to measure the muscle activity of the cervical erector spinae (CES), upper trapezius (UT), extensor carpi radialis (ECR), flexor carpi ulnaris (FCU), and abductor pollicis brevis (APB). Head-neck angle and wrist joint movements (posture and angular acceleration) were measured by inclinometer and 2-D electrogoniometers, respectively. The results showed that there was constantly high loading to the CES during EG play, possibly due to the need to stabilize the head in a flexion posture during PSP play. The variability of ECR and FCU muscle activity and the range of wrist movement were very low, suggesting static muscle tension and static wrist posture. During Wii play, which involves more dynamic arm movements, maintaining the head in an erect posture and high neck muscle activity were recorded. The high ECR and FCU activity and high wrist angular acceleration could be beneficial to young people as this may promote musculoskeletal development in the forearm. Part B of the study involved indirect calorimetric measurement of oxygen consumption during a play session with the PSP and Wii in the same group of subjects. Subjects' maximal aerobic capacity (VO2max) was estimated by a submaximal stress test - the ‘three-minute step test'. Results of this study showed that the physical activity level of playing both games were less than 3 metabolic equivalents (METs) thus the physical activity level is "light". The estimated VO2max were compared by the effect of high-level (≥4 hrs/day) and low-level (<4 hrs/day) of EG devices usage and the results were not significant. In conclusion, the findings of this study show school-age children and adolescents have a daily habit of intensive EG use. The results of the experimental studies confirm a sustained poor neck flexion posture, and with high static muscle loading to the neck and upper limb regions during small-screen handheld EG use. Playing a Wii game is considered by some to be an active exercise; however, its energy cost does not meet the recommended guidelines for the healthy growth of young people. The work of this thesis provides preliminary evidence relating to the impact of EG playing on the musculoskeletal health and aerobic fitness of children and adolescents. This useful information may contribute towards the development of ergonomic guidelines for school-age children and adolescents during the use of EG devices. Further research should investigate the cause-and-effect relationship among the EG devices use, bodily discomfort, and the musculoskeletal responses. |
| Author |
Lau, Chin Keung Brandon |
| Title |
A study on the emotional labor of tour leaders in Hong Kong |
| Department | School of Hotel and Tourism Management |
| Year | 2017 |
| Subject |
Hong Kong Polytechnic University -- Dissertations Tour guides (Persons) -- China -- Hong Kong Employees -- Psychology Tourism -- Personnel management Employee motivation |
| Degree |
DHTM |
| Pages | xiv, 196 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/99102204 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/9274 |
| Abstract | Further to Goffman's (1959) study of dramaturgical perspectives to examine the structure of social interaction that one emerges when people are in one another's presence, Hochschild (1979, 1983) adopts his dramaturgical approach and applied the term emotional labor to paid employment. The construct of emotional labor was introduced by Hochschild (1979) who continued to develop the conceptualization of emotional labor. Although the study of emotional labor of front-line service providers commenced some 30 years ago, it is a comparatively new topic for the travel industry in Hong Kong and the study of the emotional labor of tour leaders is lacking. Focus groups, in-depth interviews, participant observation and documentation analysis are used in this qualitative study to examine the key factors affecting the performance of emotional labor by tour leaders; assess how the individuals' and companies' emotional labor strategies can improve tour leaders' performance and triangulate the validity of the findings. The findings of this study are significant to tour leaders, customers and the travel industry; they also contribute to the scholarly literature on emotional labor literature in the travel industry. This study found that customer satisfaction and job satisfaction are ranked as low priorities by tour leaders, whereas these are the most major factors to customers and travel companies. This study adds previously undiscussed factors--physical fatigue, finance and family to the scholarly literature. These factors are closely related to the career development and the well-being of tour leaders. The conceptual framework of emotional labor of tour leaders developed in this study explains the positive outcomes and negative consequences of emotional labor of tour leaders through the application of different emotional labor strategies. Both the new factors and the conceptual framework can be added to the literature on emotional labor. For the industry, it is recommended that emotional labor of tour leaders should be included in the curriculum of the tour leaders' examination course to upgrade the quality of customer service of new tour leaders who plan to join the industry. This study has created new insights on the emotional labor of tour leaders; however, by using qualitative methods, the number of targeted interviewees and the sample size was comparatively small. For future research studies, it is recommended that quantitative methods which can generate a sizable sample be used to examine the relations among factors that affect emotional labor of tour leaders in other countries. |
| Author |
Leung, Cheuk-wai |
| Title |
A study on the flame spread over partition materials |
| Department | Dept. of Building Services Engineering |
| Year | 2007 |
| Subject |
Hong Kong Polytechnic University -- Dissertations. Flame spread. Building materials -- Fire testing. |
| Degree | Ph.D. |
| Pages | xxix, 148, [261] leaves : ill. ; 31 cm. |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2094037 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/890 |
| Abstract | Flame spread over partition materials is one of the key driving forces in the fire growth in a compartment. An appropriate test method should be selected which is the key subject of this thesis. The study includes three major areas. The first area includes review of flame spread mechanisms, local legislative requirements on flame spread and use of construction materials. Partition materials with high flame spread hazard were identified. The likelihood of flashover in a typical small room covered by those materials was predicted using an empirical equation based on ventilation factor. Standard flame spread tests were reviewed and compared. Possible correlations of the tests were made. The second area is a series of full-scale burning tests on common partition and lining materials carried out in collaboration with the Harbin Engineering University in Northeast China. Wood partitions, fire retardants and plastics were tested in three groups of tests in a room calorimeter similar to ISO 9705. Heat release rate, time to flashover and flame spread rates were measured. Tests included a fully-lined room under a 45 kW small fire located at the room corner, products covered on one side of the room under a 100 kW growing fire and tests of the products under a 2.3 MW flashover fire. Results showed that products with limited flame spread and heat release rate under the small growing fire tests would give out much more heat and even fully consumed in the flashover fires. Taking plywood partitions treated with fire retardant as an example, testing under a 45 kW fire would reduce the peak heat release rate by 90 %. Onsetting flashover might be prevented. The same fire retarded partitions gave faster flame spread rate by 26 % than untreated plywood under the 100 kW growing fire. Under the flashover fire, the partition was burnt and reached over 500 kW within 200 s and released over 49 MJ within 400 s. Testing under flashover is proposed to evaluate the actual contributions of the materials in a fire. Such approach is recommended to the local Authority on assessing flame spread over partition materials. In the third area, mathematical flame spread models were reviewed as alternatives to assess flame spread over materials. A new model was developed in which the radiation from the flame, treated as a two-dimensional homogeneous gas/particulates medium, is described using a gray soot model with an absorption coefficient. The model is used to predict the radiative heat transfer, flame front and burnout front of an opposed flame spread problem in the Lateral Ignition and Flame spread Test (LIFT) setup using data from the Cone Calorimeter. Limitations of the models were identified and further improvements were suggested. |
| Author |
Xia, Liang |
| Title |
Study on the heat and mass transfer taking place in a direct expansion (DX) air cooling and dehumidification coil |
| Department | Dept. of Building Services Engineering |
| Year | 2010 |
| Subject |
Hong Kong Polytechnic University -- Dissertations Air conditioning -- Equipment and supplies Ventilation -- Equipment and supplies Air quality management |
| Degree | Ph.D. |
| Pages | xxii, 187 leaves : ill. (some col.) ; 30 cm. |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2343021 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/5707 |
| Abstract |
Direct expansion (DX) Air Conditioning (A/C) units are commonly seen in small to medium sized buildings. In the evaporator of a DX A/C unit, or a DX air cooling coil, usually simultaneous heat and mass transfer, in the form of cooling and dehumidifying of the warm and humid air flowing through the cooling coil, takes place, when the surface temperature of the DX cooling coil is lower than the dew point temperature of the air stream. The use of a DX A/C unit having a single-speed compressor and air supply fan, normally relies on on-off control to only maintain indoor dry-bulb temperature, resulting in an uncontrolled equilibrium indoor humidity, and leading to a reduced level of thermal comfort, poor indoor air quality (IAQ) and low energy efficiency. Hence, DX A/C units having variable-speed compressor and air supply fan are increasingly used for pursuing a thermally comfortable indoor environment at a higher energy efficiency. Therefore, it is important to study the performance of the simultaneous heat and mass transfer taking place in the DX air cooling coil of a DX A/C unit having a variable-speed compressor and air supply fan, which has been inadequately investigated. This thesis begins with addressing the calculation of an important dimensionless parameter, i.e., steady state Equipment Sensible Heat Ratio (SHR) of a DX air cooling coil, which is defined as the ratio of the output sensible cooling capacity to the total output cooling capacity from the DX cooling coil. The determination of Equipment SHR is essential because a satisfactory indoor thermal environmental control in a space requires not only a match between the total output cooling capacity from the DX A/C unit serving the space and the total space cooling load, but also a match between unit's Equipment SHR and an Application SHR which is defined as a ratio of the space sensible cooling load to the total space cooling load. A Calculation Method for the Equipment SHR of a DX cooling coil has been developed and reported. The calculation method was validated through a comparison between its results and the experimental results from different operating conditions, i.e., different combinations of compressor speed and air supply fan speed, and different inlet air conditions to the DX cooling coil. With the Method developed, the effect of refrigerant evaporating temperature at fixed inlet air conditions on Equipment SHR was theoretically analyzed. Secondly, the thesis presents an experimental study on estimating on the dehumidification effect on the airside of the superheated region (SPR) in a DX cooling coil. Previously when investigating the heat and mass transfer taking place in DX cooling coils, a dry airside in a SPR was normally assumed without validation. This assumption conflicted with the experimental observation from an operating DX cooling coil. Therefore, an experimental study has been carried out to examine the validity of such an assumption under different operating conditions. A lumped parameter calculation procedure was developed specifically for processing the experimental data. The experimental results suggested that the airside surface of the SPR in a DX air cooling coil was either fully or partially wet under all experimental conditions. Consequently assuming a dry airside in the SPR could lead to an underestimated total amount of water vapor condensed on the entire airside of the DX cooling coil. Thirdly, the thesis reports on the development of a modified Logarithmic Mean Enthalpy Difference (LMED) method for evaluating the total heat transfer rate in a wet air cooling coil operating under both unit and non-unit Lewis Factors (Le² /³) conditions. The development stemmed from the inaccurate assumption of Lewis Factor being unit in the existing LMED method, which has been extensively applied to modeling the combined heat and mass transfer taking place in both DX and chilled water cooling coils. The assumption resulted in calculation errors when non-unit Lewis Factors were encountered, which has been however observed by many researchers. A modified LMED (m-LMED) method has been therefore developed for calculating the total heat transfer rate under both unit and non-unit Lewis Factors. Although the m-LMED method was validated by comparing its prediction of the total heat transfer rate to that from numerically solving the fundamental governing equations of the heat and mass transfer in a wet chilled water cooling coil, the m-LMED method can also be applied to the DX cooling coils. Finally, the analytical solutions for evaluating the heat and mass transfer in both a wet DX cooling coil and a wet chilled water cooling coil, respectively, have been developed and are reported. The analytical solutions were validated by comparing their predictions with those from numerically solving the fundamental governing equations of the heat and mass transfer taking place in wet air cooling coils. With the analytical solutions, the distributions of air temperature and moisture content along the air flow direction in either a wet DX or a wet chilled water cooling coil can be evaluated. The analytical solutions can be a low-cost replacement to numerically solving the fundamental heat and mass transfer governing equations. |