Modeling of an Integrated Internal Heat Exchanger and Accumulator in R744 Mobile Air-Conditioning Applications

Carbon dioxide (CO₂ or R744) is a promising next-generation refrigerant for mobile air-conditioning applications (MAC), which has the advantages of good heating performance in cold climates and environmental-friendly properties. This paper presents a simulation model of an integrated internal heat exchanger (IHX) and accumulator (Acc) using the finite volume method. The results are validated by a group of experimental data collected with different transcritical R744 mobile air-conditioner and heat pump (MHP) systems, and the error was within ±10%. The impacts of refrigerant mass flow rate and operating temperatures on the heat transfer rate of the IHX, improvement on refrigeration capacity and the liquid level in the Acc were studied. Results show that the net benefits of IHX are significant in AC mode, while it helps preventing flooding of the compressor in MHP mode. Also, the IHX heat transfer performance is more sensitive to evaporator exit quality and operating temperatures than it is to relative mass flow rate. The flow and liquid level in the accumulator is also described by the model.