Influence Of The Internal Heat Exchanger On Performance Of Automotive Air Conditioning System

With the contradiction between the increasing demand for energy saving and environmental protection of automobile consumers and the large energy consumption of automotive air conditioning system becoming more and more serious,people pay more attention to the improvement of energy saving and refrigerating capacity of automotive air conditioning system,and the technological change of automobile industry is continuously upgraded.Adding an internal heat exchanger(IHX)to the system is an economical and effective energy saving ways.The length of the IHX is mainly determined by the layout of the front cabin of the vehicle,so the actual shape of the IHX will show different lengths,different curvatures and different ways of internal heat transfer enhancement according to different models,but their thermodynamic principles are common.Increasing the length of the IHX can effectively increase its internal heat transfer area between gas and liquid refrigerants.At the same time,the length of the IHX also depends on the size of the equivalent diameter,the structure and type of the IHX selected and the refrigerating capacity of the system to be lifted.These variables also correspond to different gas-liquid side pressure drop,super-heat and sub-cooling increments and refrigerant mass flow rate.The application of IHX at home and abroad will be briefly introduced in this paper.The development status of IHX at home and abroad is introduced comprehensively.The research achievements and shortcomings of scientific research institutions and enterprises in universities are described.The work of this paper are pointed out.The thermodynamic theory of cycle with IHX is analyzed.The basic governing equation of flow and heat transfer in IHX is analyzed,and the applicable scope of different heat transfer enhancement measures is distinguished emphatically.The automotive air conditioning system with IHX is experimentally studied in theenthalpy difference room.The purpose is to verify the benefits of IHX on improving the refrigerating capacity of automotive air conditioning system.A total of 9 working conditions were tested.Variables of experimental parameters included the speed of compressor,with/without IHX and the super-heat of thermal expansion valve(TXV).The one-dimensional and three-dimensional simulation of the IHX is carried out,and the one-dimensional simulation analysis of the IHX is carried out in the Graphical User Interface(GUI)interface of MATLAB.Three types of IHXs with different structures are studied.The geometric model and physical model are identical with the actual ones.Then with the help of STAT-CCM+ software,the internal flow state and changes are theoretically analyzed.According to the actual engineering requirements,the factors affecting the refrigerating capacity of IHX are analyzed and optimized.Computational Fluid Dynamics(CFD)simulation analysis is used as the basis of optimization research.The effects of four key factors including Twist Degree of inner tube,Helical groove depth of inner tube,rib number and rib thickness,on the performance improvement of IHX are studied.This study provides a reference for the refinement of the internal design of IHX,provides some ideas on how to improve the performance of IHX and the refrigerating capacity of the whole system,meanwhile the direction of follow-up research is pointed out.Through the combination of CFD simulation and experiment,different types of IHXs are evaluated,and it is concluded that adding IHX can improve the performance of automotive air conditioning system.At the same time,the direction of follow-up research is also pointed out.Designers need to optimize the matching of the whole automotive air conditioning system,there is a huge space for the improvement of the internal structure of the IHX unit itself.