The Investigation Of Heat Transfer Enhancement For Exhaust Thermoelectric Generator System Based On Non-smooth Surface

The availability of fossil fuels such as petroleum for commercial exploitation is limited.With the increasing shortage of energy and pollution of atmosphere,it is imperative to find some ways to improve energy efficiency and reduce energy consumption.For vehicle thermoelectric generator(TEG),heat energy in exhaust will be directly transferred into electricity by thermoelectric modules(TEMs),which can power for electrical equipment to improve the vehicle fuel economy.However,an insurmountable problem is that the heat exchanger for extracting heat in TEG brings a large back pressure to the exhaust system.The additional back pressure hinders the normal work of the engine and increases the fuel consumption rate.The major characteristics for non-smooth surface structure include high heat transfer coefficients and low flow resistance.When the non-smooth surface structure is arranged in the heat exchanger,the back pressure of TEG can be well controlled.In this thesis,the heat transfer enhancement of heat exchanger with non-smooth surface has been investigated by theoretical analysis,numerical simulation and relevant experiments.By using the non-smooth structure containing dimples and cylinder grooves to improve the internal structure of heat exchanger,the convective heat transfer coefficient between exhaust and wall is enhanced with minimal pressure drop which shows a great advantage to fins.Comparing the overall performance of TEG,dimples show the best balance between power generation,thermal resistance and back pressure.The heat transfer performance over dimpled surface is studied.The heat transfer capacity in terms of Nusselt number and flow friction in terms of Fanning friction factors of the exchanger were compared.Optimization of heat exchangers with dimpled surfaces is conducted to improve the performance in TEG using a Kriging surrogate model.With an optimal design of channel structure,the temperature uniformity can be greatly improved compared with the initial exchanger,and the additional pressure loss is also controlled.A simulation platform containing four TEG systems the same with real car situation is constructed.And the simulation results are verified by the experimental results to provide a strong data support for current study.The heat exchangers with random fins in are replaced by the optimized heat exchangers with dimpled surfaces.The simulation results show that non-smooth surface could greatly improve the heat transfer and power generation in TEG.Finally a TEG system which has quite good heat transfer and high power generation with minimal pressure drop is obtained.