Micro-mechanism And Optimization Study On Thermodynamic Performances Of Vehicular Typical Heat Exchangers

With the development of the modern vehicular technologies, it is required that vehicular cooling system play an escort role for improving the performances of economic, emission, safety and comfort of vehicles.That is, modern vehicular cooling system is demanded to meet the need of heat dissipation under various operation conditions and guarantee the normal operation of key parts, simultaneously, it must reduce energy loss and improve thermodynamic efficiency of vehicluar system.There is no doubt that performance optimal design of heat exchangers in cooling system is the foundation of realizing advanced cooling system, and the principles and performance effecting mechanisms of fluid flow and heat transfer are the key points to performance optimal design of heat exchangers and even systems. Recently, various enhancing heat transfer technologies are developed and applied, however, it must be at the cost of more flow resistance. As a result, the imperfect flow and heat transfer principles and unclear effect micro-mechanisms are the bottlenecks to research and develop ideal cooling systems.Following the trend of subtle analysis and precise computation of fluid flow and heat transfer, this thesis investigated the thermodynamic performance effect factors and analyzed the effct mechanisms, and carried out temperature field visualization experiments of heat transfer units to authenticate the numerical methods used in the thesis. The main contents are as follows:Temperature contour visualization experiments:establishing a numerical platform for thermodynamic performance simulation, setting up test-rig and carrying out temperature field visualization experiments of heat transfer units to authenticate the numerical simulation method.Thermodynamic performance analysis of typical heat transfer units:the thermodynamic performances of three kinds of typical vehicular heat transfer units were investigated, and the performance effect factors and mechanisms were analyzed, the optimal matching of turbulators and fins and were determined and the structural parameters of fins were optimally designed.The thermodynamic performance analysis of heat exchangers:the thermodynamic performances of two kinds of vehicular heat exchanges were numerical simulated, the performance effect mechanisms were analyzed and the structure of a heat exchanger was optimally designed. Nanofluid was used as coolant to improve the performance. Experiments were carried out to verify the above simulation results.The thermodynamic performance analysis methods:artificial neural networks, parameters sensitivity analysis and multi-objective optimization methods were combined with numerica simulation to analyze the thermodynamic performances.The main conclusions were as follows:(1) Infrared camera technology was combined with thermodynamic performance experiments to realize the temperature field visualization of heat transfer units which is the authentication of numerical simulations.(2) The optimal matching of turbulator and fin was determined by simulating the thermodynamic performances of typical vehicular heat transfer units. The effect mechanisms of structural parameters of fin on performances were analyzed and the parameters were optimized.(3) The performance effect factors and mechanisms were investigated by simulating the thermodynamic performances of heat exchangers. The location of inlet and outlet of a heat exchanger, the fin arrangement and coolant were important factors to improve the performance.(4) Artificial neural networks, sensitivity analysis and multi-objective optimization methods can be usde in thermodynamic performance analysis combined with numerical simulation results, which can broaden the research ideas and improve the analysis efficiency.Numerical simulation method combined with some experiments was used in the thesis to investigate the thermodynamic performance of typical and vehicular heat transfer units and heat exchangers. The work analyzed the performance effect factors and mechanisms and carried out performance optimal design from several different aspects, which will guide the optimal design directon of vehicular heat exchangers.