Coupled unsteady computational fluid dynamics with heat and mass transfer analysis of a solar/heat-powered adsorption cooling system for use in buildings

Abstract

Abstract In recent years, considerable interest has been given to the application of solar-powered cooling technology for use in buildings. Solar cooling systems look like to be a suitable substitution to the traditional vapour-compression electrical-driven machines. Solar systems have the advantage of using harmless working fluids, especially water. They also have the capacity to decrease the peak loads for electricity utilities and can contribute to a substantial reduction of the harmful CO2 emissions, which produce the notorious greenhouse effect that in turn is responsible for global warming and its devastating consequences. Amongst cooling technologies, low-temperature, solar-powered adsorption chillers/heat pumps are arising as a sustainable alternative to electrical vapour-compression systems. This study aims at examining the impact of design and operating factors on an adsorption cooling system’s performance in a residential application. An unsteady Computational Fluid Dynamics (CFD) combined with a heat and mass transfer model of the adsorption cooling system using adsorbent/water pair, was created in order to predict the following: (1) Flow behaviour; (2) Pressure; (3) Temperature; and (4) Water adsorption distributions. For possible adsorbents, both silica gel and zeolite 13X were considered; however, it is worth mentioning that silica gel was used at a lower working temperature range, as required by the operation. This makes silica gel an efficient option for solar/heat driven residential cooling applications. For the CFD model implemented equations, two geometries found in literature were employed for validation. Validation of the unsteady simulation results with experimental data found in literature showed favourable agreements. In a parametric study, various computation cases underwent simulation over the duration of the adsorption mode, which considered the following set of factors: heat transfer fluid (HTF) velocity (v); adsorbent bed thickness (lbed); heat exchanger tube thickness (b); and adsorbent particle diameter (dp) in order to perform a detailed investigation for main geometrical and operating parameters’ influence upon system performance. Results obtained from CFD disclosed the significance of v, lbed and dp whereas b was found having relatively minor modifications within the system performance. Additionally, the development of CFD combined with heat and mass transfer model serves as an effective tool for both simulation and optimisation of adsorption cooling systems as well as for performance predicting purposes.