Research On The Performance Of Internal Heat Exchanger Used In HFC134a Mobil Air Conditioning

With the global attention to the energy problem, the energy saving andenvironment protection issues of mobile air conditioning (MAC) becomes the focusboth for the MAC industry and the Car companies. The European Union hadlegislated that the MAC system using the refrigerant which global warming potential(GWP) is larger than 150 will be forbidden for new platform from 2011 . Butalternatives are still in discussion. Therefore, it is important to improve currentHFC134a system. Adding an internal heat exchanger (IHX) in the MAC system is oneof the most efficient ways. Under this background, performance of IHX and effects onHFC134a MAC system are studied in this thesis. The main contents and conclusionsare as followings:1) A MAC system simulation model is established for thermal physics cycleanalysis. The numerical models of refrigeration components including IHX are set up.Differences between the baseline refrigeration cycle and improved cycle underdifferent temperatures at evaporator inlet and compressor RPMs are studied insimulation method. It can preliminarily prove that IHX can enhance systemperformance and COP.2) An IHX heat transfer performance simulation model is established. Thesimulation model has a good agreement with the experiment results within error of±10%. With the data of simulation and experiment, the impacts of fin number, tubelength, distribution way and bending method on heat transfer performance of IHX arestudied. Taguchi method is used to analyze the weight of different structureparameters on heat transfer performance of IHX. Results show that fin number affectaccounts for 33.23%, tube length affect accounts for 41.85% and distribution wayaffect accounts for 24.96%.3) The impacts of IHX on HFC134a MAC system's performance areexperimentally studied. The test results show that the IHX can obviously improve thesystem performance. Especially at idle conditions with high ambient temperature, theimprovement of cooling capacity and COP are 14.7% and 20%, respectivelycompared with the system without IHX. A real vehicle with IHX system is also testedin environmental chamber. The vent temperature in a real vehicle with IHX is about 1℃less than that without IHX.4) TEWI (Total Equivalent Warming Impact) of the MAC system with IHX isanalyzed. Results show that IHX can help reduce refrigerant charge and enhance COPof the system. The TEWI is 6.36% reduced by adding IHX in the MAC system.