Design of an H2O-LiBr absorption system using PCMs and powered by automotive exhaust gas

Abstract

• The thermal performance of the absorption system driven by the exhaust gases is proposed. • The multiple PCMs increase the heat transfer and speed up the melting rate. • The new generator can drive the absorption system at low engine speeds. • There is a valuable increase in COP values and output performance at low engine speeds. The main challenge of the absorption cycle in automobile air conditioning (A/C) systems is the use of exhaust energy to drive the system at low engine speeds. To obtain a continuous supply of cooling energy from the absorption cycle, the present study highlights a proposal for a numerical investigation of a novel generator design in an absorption system using an H 2 O-LiBr solution as the working fluid. The generator heat exchanger (H.EX) was divided into several cells filled with multiple types of phase change materials (PCMs) acting as a storage unit. A comprehensive thermal model was developed and validated with experimental data from the literature. The effects of multiple types of PCM, coefficient of performance (COP), and solution temperature were studied at low (1500, 1750, and 2000 rpm) and high (2250, 2500, and 2750 rpm) engine speeds. The results demonstrated that using multiple types of PCM could improve the heat transfer capability, thereby accelerating the melting rate of the PCM. At low engine speeds, exhaust energy could drive the absorption system with COP values of 0.767 and 0.778, while in the case without PCM, exhaust energy could drive COP values of 0.284 and 0.763 for engine speeds of 1500 and 2000 rpm, respectively. At high engine speeds, the system performance was roughly stable with a slight increase in COP values.