Analysis And Research On The Heat Transfer Characteristics Of The Heat Exchanger Of The Vehicle-mounted ORC System

In order to effectively recover and utilize the waste heat of automobile exhaust gas,in this paper,a heat exchanger suitable for on-board Organic Rankine Cycle(ORC)system is designed,and its heat transfer characteristics are theoretically calculated and numerically simulated.The main research contents are as follows:1.The working principle and thermodynamic cycle characteristics of ORC system,water vapor circulation system and Carnot cycle system are compared and analyzed,which proves that ORC system has certain advantages in waste heat recovery.By simplifying the calculation conditions,the fonnula for calculating the thermal efficiency of the on-board ORC system is derived;using thermal efficiency analysis methods,optimized selection of four hydrofluorocarbon(HFC)working fluids R245fa?R134a?R236ea and R227ea that meet the requirements,the results show that the thermal efficiency and net work of the working fluid R245fa are the best working fluids for the on-board ORC system of the four HFC working fluids.2.Using automobile exhaust as residual heat source,combined with thermodynamic properties of organic working fluid,Select a plate-fin heat exchanger with low back pressure,compact structure,light weight and high heat exchange efficiency to design the heat exchanger of the on-board ORC system.The design steps and calculation methods of plate-fin heat exchangers are analyzed,and the structural parameters of the heat exchanger suitable for the on-board ORC system are optimized by using the simple algorithm module of the heat exchanger calculation tool HTFS.MUSE.3.The phase change characteristic original function of working fluid are programed by using C++,import the compiled program into CFD software for numerical simulation,the phase change heat transfer analysis of working fluid from liquid phase to gas phase can be achieved.Numerical simulation of on-board ORC system heat exchanger under variable working conditions,the results show:the working fluid R245fa is the best working fluid for heat transfer performance,which is basically consistent with the theoretically calculated heat transfer performance of the heat exchanger.4.Analysis of heat transfer mechanism based on fins of plate-fin heat exchanger,an optimized design scheme for rectangular flat fin structure is proposed,numerical simulation of fins based on SIMPLE algorithm of FLUENT software;the polynomial fitting of the numerical simulation value and the Kays test value is carried out,and the relationship between j,f and Re is obtained,comparative analysis showed that:Kays test values and numerical simulation values are consistent with the overall trend,explain that this numerical simulation method has certain accuracy and feasibility;the numerical simulation analysis of the fins of different structural parameters in the three optimization schemes of rounding treat,ment,baffle treatment and round hole treatment shows that the fin rounding design is the optimal design.