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Low, Elaine (2024) Performance study on a membrane absorber-evaporator component of a solar-driven membrane-based absorption heat pump (MAHP). PhD thesis, University of Nottingham.

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Abstract

The membrane-based absorption heat pump (MAHP) is a compact-sized, thermally-driven absorption refrigeration system (ARS) that recovers low-temperature renewable or waste heat from a refrigerant stream. MAHP can be used for absorption heating, cooling, or desiccant dehumidification applications operating at a smaller scale. As the solution film thickness in the existing falling film absorbers is inconsistent during operation, using membrane modules can help to mechanically constrain the solution film by forming membrane microchannels with consistent thickness. Besides, the use of membranes also significantly increases the membrane-fluid interfacial area, which is conducive to improving heat and mass transfer performance.

The first part of the thesis focuses on the performance study of the integrated membrane absorber-evaporator component of a parallel-plate MAHP system. By operating the MAHP system in a semi-open cycle configuration with an integrated component, the evaporator unit is eliminated, enabling further scalability for applications that require higher compactness.

To investigate the conjugate heat and mass transfer performance of the MAHP, a three-dimensional, steady-state mathematical model is developed, and numerical simulations are obtained via the finite element method (FEM). The simulation results are experimentally validated with a general discrepancy of within 10%. Parametric studies involving the variation of operational and geometrical parameters are further assessed via scaling analysis and simulation case studies. The effects of these variations on the heat and mass transfer dimensionless parameters, and fluid flow behaviour within the membrane microchannels are analysed. The performance improvements via the inclusion of air-gap and internal cooling are also determined, as the air-gap minimizes sensible heat loss by retaining more latent heat of absorption, whereas internal cooling helps to remove absorption heat and maintain the absorption strength of the absorbent solution. The findings of this study provide insights into the aspects essential for performance enhancement in the MAHP system.

In the second part of the thesis, the feasibility of utilizing renewable solar heat in the MAHP system as the main heat source for its most energy-intensive process – absorbent solution regeneration is determined. The pinch-based Cascade Analysis (CA) method is proposed to optimally size the capacity of the solar thermal system (STS) by matching the intermittent availability of solar irradiation with the fluctuating solution regeneration heat demand. Cascade Analysis is a simplistic approach for decision-makers to assess the feasibility of implementing solar heat recovery in MAHP systems for their intended use, which includes small-scale absorption cooling, heating, or air-conditioning applications.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Law, Chung Lim Show, Pau Loke
Keywords:	membrane absorption heat pump, MAHP, absorber-evaporator component, solar, cascade analysis
Subjects:	T Technology > TP Chemical technology
Faculties/Schools:	University of Nottingham, Malaysia > Faculty of Science and Engineering — Engineering > Department of Chemical and Environmental Engineering
Item ID:	78459
Depositing User:	LOW, ELAINE
Date Deposited:	27 Jul 2024 04:40
Last Modified:	27 Jul 2024 04:40
URI:	https://eprints.nottingham.ac.uk/id/eprint/78459

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