| Author: | Yao, Yao |
| Title: | Numerical and experimental study of novel inline bidirectional micro hydro turbine for hydropower harvesting from water supply pipelines |
| Advisors: | Yang, Hongxing (BEEE) Lu, Lin (BEEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Water-power Water-pipes Water -- Distribution Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Building Environment and Energy Engineering |
| Pages: | xxxv, 262 pages : color illustrations |
| Language: | English |
| Abstract: | With the continuous expansion and development of cities, the water supply pipe network in urban areas is developing into an enormous and complicated system, especially for a large city such as Hong Kong. Annually, Hong Kong channels approximately 1.2×10⁹ m³ of water for residential and commercial purposes across various urban sectors via its water distribution pipelines, a number projected to escalate by almost 10% until 2030. However, a significant portion of this infrastructure grapples with degradation issues, attributed to over four decades of operational wear and tear. It is postulated that annual freshwater wastage due to pipeline leakages in Hong Kong hovers around 15% of the total capacity. In order to reduce and prevent water leakage, a modern Water Intelligent Network (WIN) with real-time detecting and monitoring as well as data transmission aroused attention. Realization of the WIN requires installing a large number of accompanying sensors and control devices, which need to be continuously and stably powered to enable their uninterrupted operation and data transmissions. Chemical batteries are usually adopted due to their short-term use, cost-efficient and reliability. However, the battery needs to be frequently replaced due to its limited capacity and life. In contrast, the kinetic energy present in water flow within pipelines represents an untapped potential energy source for inline hydro power generation due to oversized design. Past reported studies related to micro hydropower technologies have rarely considered the actual application conditions of main urban water supply pipes. Compared to the regional or branch-line water supply pipes, the main water pipes have much more stringent application conditions for the micro hydropower harvester. The main water pipes feature a high real-time unsteadiness of water flow velocity and uncertainty of flow direction for demands of field operation and water supply regulation. Consequently, the primary objective of the thesis is to develop a micro-hydropower technology specifically tailored for urban water supply pipelines, aiming to furnish the WIN with a consistent and dependable power source. This thesis presents a comprehensive and systematic study of inline bidirectional micro hydro turbine for hydropower harvesting. The foremost objective of this research and development of hydro-turbines is to achieve stable power generation for the WIN without excessively depleting the water head within a water pipeline system. To address the intricacies of water conditions within urban pipeline networks, the proposed hydro-turbine models and design methodologies have undergone extensive optimizations and refinements. This rigorous process has led to a notable enhancement in the overall performance capabilities of the turbine. In response to the regular flow velocities observed in urban pipelines, an inline bidirectional micro crossflow turbine with bell-mouth block has been proposed and subsequently refined through both numerical analyses and empirical methodologies (Chapter 3). Given the fluctuating flow velocities inherent in urban pipelines, a self-adaptive bidirectional micro crossflow turbine with unilateral bypass is conceived, with the subsequent research emphasizing the mechanistic impact of adaptive deflection apparatus on the turbine performance (Chapter 4). Based on the developed novel turbine configurations, an investigation into the influence of a bilateral bypasses structure equipped with an adaptive deflection apparatus on the turbine performance is executed. Comparative evaluations of the three proposed turbine designs are subsequently drawn, grounded on the empirical data acquired from on-site experiments (Chapter 5). Firstly, in response to the regular flow velocities observed in urban pipelines, a novel inline bidirectional crossflow turbine (BTB) integrated with bell-mouth guide blocks is developed. Specifically, the configurations and geometries of the proposed BTB were designed for large-size pipelines, and four schemes of water blocks in BTB were investigated based on the computational fluid dynamics method to determine the optimal configuration. A hydraulic test rig in the laboratory and a field test system integrated with an electricity storage module were developed. The BTB, after numerical optimizations, was fabricated and tested to validate its overall performance of power generation, water head loss, and long-term operating stability. The results showed that the designed centrosymmetric bell-mouth guide blocks significantly contribute to the efficient conversion of water flow energy into mechanical energy by the turbine. The BTB prototype had the best efficiency of 2.6 % at the water flow velocity of 1.3 m/s, which was capable of providing stable and sufficient electric power with a daily electricity generation capacity of 470 Wh. Additionally, the water head loss was effectively restricted within 6.1 m at the higher water flow velocity of 3 m/s. These technology metrics of the BTB exhibited superior overall performance and met the power requirements of the WIN system used in the main urban water pipelines. Secondly, given the fluctuating flow velocities inherent in urban pipelines, a self-adaptive bidirectional micro crossflow turbine with unilateral bypass (SBTU) is designed to be more adaptable to the complex water conditions of urban water supply systems. Specifically, the adaptive deflection apparatus is developed, utilizing torsion springs to adjust the angular position of rotary deflector at varying flow velocities, thereby dynamically modifying the bypass channel to regulate the flow passing through the turbine blades. The accuracy of the employed numerical simulation methods is verified through a comparison with experimental outcomes. Subsequently, numerical simulations are conducted for six cases, each featuring different angular orientations of the rotary deflector, and the outcomes are juxtaposed to evaluate relative turbine performance and flow field characteristics. Through an in-depth analysis of fluid velocity, turbulence attributes, pressure distribution and path line characteristics, the study dissect the impact mechanism of the adaptive deflector apparatus on the fluid flow, culminating in the identification of the optimal angular orientation for the rotary deflectors under specific design points. Further, a prototype of the hydro turbine is fabricated and subjected to empirical testing on an updated test rig to assess its overall performance at different flow velocities. Experimental results ascertain that the hydro-turbine is capable of generating an output power range of 23.57 W to 280.05 W under varying flow rates of 1.0 m/s to 3.5 m/s. The corresponding hydraulic head loss oscillated between 1.22 m and 7.52 m. Notably, the peak efficiency of the hydro-turbine is observed to reach as high as 4.09%. In comparison to the BTB, the SBTU not only broadens the applicative flow velocity range but also reduces water head losses, thereby enhancing power generation efficiency. These refinements collectively lead to a significant elevation in the SBTU overall efficiency, and the daily average power generation experienced a remarkable upswing of 323%. This amplifies the suitability of SBTU for deployment in pipelines characterized by intricate water conditions. Finally, based on the impact mechanism of the adaptive deflector apparatus on the internal fluid flow within the pipeline, a self-adaptive bidirectional micro crossflow turbine with bilateral bypasses (SBTB) has been newly designed. Specifically, a bidirectional adaptive deflector apparatus is introduced which, compared to the previous design, increases the bypass area. Primarily, fluid mechanical models are devised for two distinct scenarios: complete closure and opening of the bypass area, succeeded by simulation analyses. The numerical outcomes are juxtaposed with those of the SBTU, investigating the repercussions of bilateral bypasses from vantages of hydro-turbine output power, water head loss, output efficiency, and flow field characteristics. The findings denote that when the rotation angle of the rotary deflection plate is small, thereby amplifying the bypass area, the dual bypasses exert a notable impact on the hydro-turbine's performance. Subsequently, hydro-turbine prototypes with diverse torsion spring stiffness coefficients are fabricated and empirically examined, discerning that the hydro-turbine exhibits optimal electric generation performance when the stiffness coefficient is constituted at 8 N·m. Founded on this, a prototype of the SBTB is developed and subjected to experimental scrutiny. The experimental findings indicated that the SBTB, within a flow speed ambit of 1.0 m/s to 3.5 m/s, could engender a minimum output power of 15.89W, a maximum hydraulic head loss of 2.69 m, and peak output efficiency of 6.45%, representing a 246.44% enhancement relative to the BTB. In summary, this research, tailored to the intricate hydrological conditions inherent in urban water supply pipelines, introduces novel hydro turbine configurations to harness surplus hydraulic head within the pipelines for energy provision to the WIN system. Distinct strategies, namely BTB and SBTB, have been proposed and advanced respective to the regular and fluctuating flow velocities within the pipes. An adaptive deflection apparatus, which is incorporated through the development of SBTU, serves as a pivot in enhancing the turbine performance. This scholarly endeavor furnishes pivotal guidance for the design and application of such turbines under varied operational conditions. |
| Rights: | All rights reserved |
| Access: | open access |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/13558