Thermodynamic performance and heat and mass transfer analysis of air source absorption heat pump for heating

Abstract

To lower CO2 emission and obtain better heating efficiency compared with conventional gas boilers, this paper proposed a solar air source absorption heat pump (SAAHP) with falling film heat exchanger for district heating. The thermodynamic model is established to analyze the performance of the proposed system. The falling film generator as the key heat exchange component has been designed carefully, and then the numerical models of the falling film generation process which include one and two-dimensional numerical models are developed. According to the thermodynamic analysis, the primary energy efficiency (PEE) and heating capacity of the system are 1.65 and 45.02 kW at the generation temperature of 190 °C and ambient temperature of −7 °C, respectively, which can save 41.69 t of CO2 emissions from heating. The two-dimensional numerical model indicates the main heat and mass transfer occur between the falling film height x = 0 mm and x = 200 mm, and the interface heat transfer decreases from 74.6 kJ/(m2·s) to 40.5 kJ/(m2·s) in a typical vertical falling film generation process. In addition, the energy transfer as the inter-diffusion is corrected in the energy equation which improves the prediction accuracy by about 1.5% of the two-dimensional model. The research provides a reference for the optimization design of the generator, where one-dimensional models can quickly guide the design and selection of equipment, modified two-dimensional numerical models and Computational fluid dynamics (CFD) models can provide references for the refined optimization design, which attributes to the improvement of thermodynamic performance of the solar absorption heat pump system.