| Since the reform and opening up, the original extensive, high energy consumptionmodel of economic development has gradually exposed its drawbacks with the rapideconomic development and industrialization process of our country. In the automotiveindustry in China, about1/3of oil energy is consumed by the cars. In the automobileengine combustion process, there is only about25%of the energy were used for theautomobile and accessories,30%for the energy consumed to heat sink mode, but alsoabout40%for energy in exhaust loss to the environment. Recovering the waste heat energyfor utilization will be helpful to improve not only vehicle dynamic performance and fueleconomy, but also save oil resources, reduce greenhouse gas emissions. Thus, it has a goodeffect on the environmental protection. Based on this situation, the automobile exhaustwaste heat recovery and utilization technology has become one of the hot researchdirection today.The convection heat transfer enhancement method was one of the key technologies inthe automobile exhaust waste heat recovery technology. With the devlopment of enhancedconvection heat transfer technology, it had a great significance for the automobileenergy-saving and emission reduction. However, less research focused on the heat transfersurface strengthening mechanism and structure optimization of automobile exhaust heatrecovery exchanger. Based on the analysis of the current situation of the development athome and abroad, the ribs of the discrete double inclined rib tube was redesigned andinstead by an new streamline-shaped ribs. The heat transfer enhancement mechanism wasdiscussed by the field synergy angle. The paper show the reason for better performance ofDISR tubes. The results provided the theory basis for the future simulation and experiment.The circular inner rib tube and square inner rib tube were meshed and simulated by the computational fluid dynamics software: ANSYS/ICEM-CFD and FLUENT. The law ofcomprehensive heat transfer enhancement varies with the changing sizes of differentinternal ribbed tube were studyed, and finally the optimal size of the ribs were obtained.Its shape includes ribs length l, ribs inclined angle, ribs height h and ribs pitch P. Theoptimal structure parameters within the circular inner rib tube heat exchanger was:l=38mm,=45°, h=2.5mm, P=60mm, the heat transfer enhancement index PEC was up to1.396. The optimal structural parameters of square inner rib tube heat exchanger was:l=38mm,=45°, h=2.5mm, P=60mm, the heat transfer enhancement index PEC was1.07.According to the results of simulation, three heat exchange tubes with different sizesand smooth square tube were choosed as the experimental object. The gas-water heattransfer enhanced experimental system for automobile exhaust heat recovery device wasdesigned and built. In different conditions, the gas velocity and temperature of inlet andoutlet, the fluid temperature of inlet and outlet, velocity and static pressure in the heattransfer tubes were measured. The Nusselt numbers and PEC numbers were obtained. Theexperimental results showed that, compared with the smooth square tube, internally ribbedheat transfer tubes had higher Nusselt numbers which meaned better heat transfer effect.By comparing the scale of PEC numbers, three internal finned heat transfer tubes wereranked. The results of experimental and simulation were in good agreement, which meanedthat the method for simulation is reliable.The simulation and experiments for DISR tube were finished in this paper. The resultsprovided a basis for the application of automotive exhaust heat recovery device with fieldsynergy theory. |
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