Research On Heat Transfer Characteristics And Multi-Field Synergy Mechanisms For Exhaust Gas Recirculation Shell-and-Tube Heat Exchanger

As global energy shortages and environmental pollution problems become more and more serious,the introduced emission regulation for cars has become stricter all over the world.In control of engine exhaust NO_X,the Exhaust Gas Recirculation technology is more common.At partial load,part exhaust gases is introduced into the intake pipe by EGR system,then blends with fresh air into the cylinder.The intake pipe pressure and total amount of circulating gas are improved,the cylinder temperature is lower and oxygen concentration of the combustion chamber is higher at the same time.The effect of energy conservation and emissions reduction has been achieved.However,with the increasingly stringent emission regulations,it is also necessary to cool off the waste gas that is involved in the recirculation process.The cold EGR,namely in front of the EGR valve equipped with cooler,the waste gases are cooled at first then taken into the intake pipe.EGR cooler is the key component in the cold EGR system,and its performancehasveryimportantinfluenceonthefunctionofEGR system.Therefore,based on theory of heat transfer and fluid dynamics,the flow field and heat transfer characteristics of EGR cooler have been simulated,which have important theoretical significance and application value for the improvement of the performance of the cold EGR system in diesel engine.For this purpose,the thesis is supported by National Natural Science Fund Project[51176066].The flow field and heat transfer characteristics of EGR cooler are investigated by numerical simulation and field synergy principle.The main research contents and innovation points for this paper are as follows:(1)The mathematical model of EGR cooler heat transfer is established,the internal flow field and heat transfer characteristics of EGR cooler under different inlet mass are studied and analyzed.The heat transfer and flow law of EGR cooler under different inlet mass flow is revealed.(2)The heat transfer characteristics of EGR cooler with eight different baffle structures under different inlet mass flow are analyzed and compared with the original model.The heat transfer and flow characteristics of EGR coolers with better baffle structure are obtained.(3)The synergy mathematical model of EGR cooler heat transfer process field is established,and the field synergy effects of EGR cooler with different baffles are compared.The synergy law of velocity field and temperature gradient field of heat transfer process of EGR cooler with better baffle structure is obtained.