Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Building Environment and Energy Engineering | en_US |
| dc.contributor.advisor | Lu, Lin (BEEE) | en_US |
| dc.creator | Gao, Yu | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/13289 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Investigation on air gap membrane distillation for liquid desiccant regeneration and portable water production in air-conditioning systems | en_US |
| dcterms.abstract | The currently widely used falling film regeneration has certain drawbacks including energy waste for air heating, desiccant loss, low surface wettability, corrosion of air ducts and so on. Moreover, water collection from regeneration process is a promising solution for drinking water supply in buildings. In this context, the present thesis aims to integrate air gap membrane distillation into hybrid air-conditioning systems for the purpose of simultaneous liquid desiccant regeneration and freshwater collection. | en_US |
| dcterms.abstract | Firstly, a compact liquid desiccant cooling system is proposed and investigated, where the solution self-circulation design is introduced for energy savings. Based on the energy matching strategy, a model-based parametric study is conducted to demonstrate the effects of various influencing factors. The results show that there exists an optimum solution self-circulation ratio to achieve the maximum COP under a given condition. Moreover, a reduction of 29.68% in energy consumption and an improvement of 42.20% in COP are achieved under the ambient condition of 30 ℃ temperature and 20 g/kg humidity ratio. Furthermore, a correlation analysis is used to reveal the association strength and direction between any two main operation and performance parameters. | en_US |
| dcterms.abstract | Secondly, a prototype of an air gap membrane distillation (AGMD) regenerator is designed and fabricated, and then is experimentally examined using response surface methodology based on collected data from a self-built test rig. Regression models are developed to correlate response variables and operating variables for generating response surfaces. The two-factor analysis shows that increasing feed temperature leads to a significantly improved water production rate and thermal efficiency. By contrast, coolant temperature has a minor influence on water production rate but an impressive impact on thermal efficiency. Moreover, increasing feed flow rate can result in a dramatic improvement in water production rate and thermal efficiency, with mitigated polarization effects. Additionally, the effect of coolant flow rate on water production rate appears to be negligible. Nevertheless, decreasing feed flow rate can obviously enhance thermal efficiency. | en_US |
| dcterms.abstract | Thirdly, the air gap membrane distillation regenerator coupled with an external heat exchanger is numerically evaluated in terms of regeneration capacity and energy performance. The comparison of flow patterns demonstrates that counter-flow is preferable than parallel-flow. The parametric analysis shows that feed temperature is the most dominant one among operating parameters and membrane length also has a remarkable impact. Additionally, it is found that narrowing the air gap from 3 mm to 1 mm can improve regeneration capacity and energy efficiency by 69.9% and 50.1% respectively. Moreover, the heat recovery by the coolant channel is proved to save nearly 8% of energy input under the involved conditions. Finally, the NSGA-II based multi-objective optimization is performed to obtain the Pareto front for maximizing regeneration capacity and minimizing energy demand. | en_US |
| dcterms.abstract | Finally, AGMD is compared with direct contact membrane distillation (DCMD) regarding potential for liquid desiccant regeneration. Based on a thermodynamic model, the performance of two solar-driven MD systems are systematically evaluated from an energetic, exergetic and economic perspective. The results show that AGMD is preferable at a low operating temperature or solution flow rate compared to DCMD system in terms of regeneration capacity, energy efficiency and cost-effectiveness. Furthermore, AGMD is more competitive in handling highly saline desiccant than DCMD since the latter suffers from increasingly remarkable driving force reversal with the rise in concentration. As for the design parameter, AGMD exhibits a linear trend in regeneration capacity with extending membrane length, while for DCMD there exists an optimal membrane length at which it can yield the highest regeneration capacity. The seasonal analysis indicates that the availability of DCMD ranges between 60.7% and 88.9% during summer in Hong Kong, lower than that of AGMD. | en_US |
| dcterms.abstract | Overall, this thesis makes the first attempt to use air gap membrane distillation for liquid desiccant regeneration. The findings help deepen the understanding of membrane distillation-based regeneration process and pave the way for applications of air gap membrane distillation in hybrid air-conditioning systems. It is hoped that this research will make a significant contribution to energy savings and water supply in buildings. | en_US |
| dcterms.extent | xxii, 223 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2024 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.LCSH | Air-gap membrane distillation | en_US |
| dcterms.LCSH | Air conditioning -- Equipment and supplies | en_US |
| dcterms.LCSH | Air conditioning -- Energy conservation | en_US |
| dcterms.LCSH | Hong Kong Polytechnic University -- Dissertations | en_US |
| dcterms.accessRights | open access | en_US |
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