Research On The Performance Of Micro-channel Automotive Air-conditioning System With HFO-1234yf

The EU regulations (DIREVTIVE2006/40/EC) legislated that any newly developedautomotive air-conditioning system cannot use a refrigerant with GWP greater than150after2011, and all newly produced vehicles will be forbidden to use refrigerants with GWPgreater than150by2017.To decrease the influence of global warming due to refrigerants, anew refrigerant, HFO-1234yf has been developed.This paper first reports on the thermodynamic properties of HFO-1234yf.The models ofevaporator and condenser have been built by1D programming.The relevant conclusionsdraw from the comparison of the models and the experiment.1D simulation has been set asheat transfer boundary conditions for solving three-dimensional simulation.Two-phaseboiling heat transfer in micro-channel with HFO-1234yf is researched by the finite elementanalysis method.The empirical correlations have been matched by estimated value of pressure, density,enthalpy and entropy from230K to360K.The existing temperature range has been enlarged.The relative error is0.35%between the result and REFPROP9.0.The model of micro-channel evaporator with HFO-1234yf is described by NTU and LMTD(logarithmic mean temperature difference).Chen’s heat transfer correlation is thehighest accuracy of the six correlations in this paper.The error of the1D simulation value ofHFO-1234yf micro-channel evaporator comparing with the experiment is less than5%.Themodel of HFO-1234yf micro-channel condenser is built by the same way.The applicabilityof the heat transfer correlation in two-phase condensation is compared.To verify the reliability of the1D simulation,the proven experiments is conductedinclude evaporator monomer test and condenser monomer test.According to the steps ofrefrigerant development, the bench test,the compatibility test and the stability test ofHFO-1234yf in automotive air-conditioning systems have been conducted.If R134a isdirectly replaced by HFO-1234yf in the refrigeration performance test, the refrigeratingcapacity of HFO-1234yf was reduced8%in the worst case, and reduced about4%instandard working conditions. The superheating temperature in HFO-1234yf systems isgenerally1-2℃higher than that in R134a systems.In standard conditions (evaporator temperature is27°C, condenser temperature is35°C), the refrigeration capacity ofHFO-1234yf in an optimized automotive air-conditioning system increased by2%.Therefrigeration capacity of automotive air-conditioning systems with HFO-1234yf can reach98.9%of that of R134a systems. In other conditions, the refrigeration capacity differencebetween the two refrigerants is within4%. In low-load conditions, the refrigeration capacityof the HFO-1234yf system is much closer to that of the R134a system.The models of HFO-1234yf and R134a micro-channel evaporator have been analyzedby finite element software COMSOL Multiphysics.The modules of porous media,non-isothermal flow and phase-change heat transfer have been selected.The modules usegeometric added Lagrangian. Comparing with R134a evaporator, the uneven temperaturedistribution area in the surface of the HFO-1234yf evaporator is lager.