| Energy-saving and environmental protection are a serious problem the all mankind facing in the21st century. In recent years, with the rapid development of national economy, China’s energy, especially oil and gas dependence on foreign continue to rise, energy security situation is increasingly grim. To this, The People’s Republic of China Energy Conservation Law point out the energy conservation is a long-term strategy policy in the state development economic, is also the primary way to solve the today’s energy problem. The twelve five state plan is clearly put forword:green development, building a resource-conserving and environment-friendly society, promoting the energy conservation, spreading the advanced energy-saving technologies and products.Thermoelectric power generation technology can directly conver the heat energy to electricity power using the materials Seebeck effect. It has the advantages of compact structure, no wear, no leaks, no noise, clean, long life, high reliability. It is a new, green power generation technologies and can reasonably use of solar energy, geothermal energy, industrial waste heat and other low-grade waste heat energy. Many science and technology developed countries have classified the thermoelectric power generation technology as a long-term energy development plan. China is rich in solar energy and industrial waste heat. Every years, land surface receives the solar radiation energy is equivalent to170billion tons of standard caol. The waste heat accounts for17%of total fuel consumption to67%, of which,60%recyclable. If these low-grade energy can be converted to electricity by the thermoelectric power generation technology, which will have huge economic and social benefits.Domestics researches on thermoelectric power generation technology started relatively later, and mainly in the studies of new thermoelectric material preparation and its properties. As for the heat transfer mechanism of thermoelectric generation, there are less researches. Based on the basic theory of heat transfer and through the thermal resistance network method, the theoretical analysis and experimental research of the heat transfer processes mechanism within thermoelectric generation was carried out. The thermal resistance analytical models of thermoelectric generatior and thermoelectric modules connected in series and parallel are built. Numerical simulation of the waste heat thermoelectric generator was carried also. In all, the main works and conclusions are as follows,(1) Based on the thermal resistance network method, the heat transfer process within thermoelectric generatior was analysed in theory. A thermoelectric performance test platform was built to study the distribution and variation of thermal resistance. The heat transfer enhancement of generator cold side has significantly affect on the heat transfer control region: as compared with the air natural convection, the air-forced convection and the water cooling modes enhance the heat transfer between the heat sink fins and the ambient and reduce the temperature and thermal resistance on the cold side, and that the main thermal resistance changes from the convectional one between the heat sink fins and the ambient to the contact one between the generator as well as the heat source and the sink on the cold side. When the heat flux of the heat source keeps constant, strengthening the heat transfer on the cold side of the generator may decrease the temperatures of the heat source and the hot side, while the temperature difference between the hot and the cold sides of the generator has no significant improvement. When the heat flux of the heat source is low, strengthening the heat transfer on the cold side of the generator can not dramatically increase the output power of the generator. When the heat flux of heat source is high, strengthening the heat transfer on the cold side may greatly increase the output power of the generator. Moreover, at a heat flux of50W, the output power in air-forced convection cooling and water cooling respectively increase by27.9%and39.5%, as compared with that in air natural convection cooling.(2) The numerical simulation research of waste heat thermoelectric generatior was studied by Fluent software. A larger temperature difference can be obtained by increasing the cold and hot fluid rate and strengthening the heat transfer within the cold and hot side heat exchanger, thus the generator get better performance. But when the heat transfer control region changes, by further increasing the cold and hot fluid rate to improve the generator performance, the effec become poor. At this point, it should be focused on reduce the heat transfer resistance of heat transfer control region to solve the problem.(3) Based on the non-equilibrium thermodynamics theory and thermal resistance network method, the output power and efficiency thermal resistance analytical models are derived. The models comprise the thermal resistance θH between the thermoelectric module and the heat source, the thermal resistance θC between the thermoelectric module and the cold source, the P-N thermoelement legs thermal resistance θTE, the number of thermoelement legs m, the Seebeck coefficient αP-N and resistance r of the materials used in thermoelement legs, the loop current I, the hot source temperature T1and the cold source temperature T0, and so on. The accuracy of the models were verified by the experiment. The models can accurately predict the performance of the generator, so as to provide a theoretical basis for the assembly of the high-performance generator.(4) The series-parallel connection of thermoelectric components can adjust the thermoelectric module internal resistances and thermal resistances, thereby regulating the generator output voltage, current and power, so that the generator can provide electrical energy for the different loads. The thermoelectric generation system with series-parallel connection of thermoelectric components was investigated, and the thermal resistance analytical model for system output power was derived. In addition, the effect of total number of thermoelectric components, number of components with parallel connection, thermoelectric module as well as thermal resistance at both hot and cold ends of the module on the system performance was discussed. The results show that there is a matching relationship between the system resistance and load resistance. Moreover, the thermal resistance of thermoelectric module and the thermal resistance at both hot and cold ends of the module also exhibit a matching relationship. Therefore the maximum output power can be obtained for the system. With increasing the number of components with parallel connection, the maximum output power and loop current get enhanced, while the output voltage of the system decreases. The present results can provide the theoretical reference for the reasonable assembly and performance optimization of thermoelectric generation system.(5) The study on the optimization of thermoelectric leg structure size. The relationship between the generator output power and thermoelectric leg aspect ratio is derived. The matching relationship between the load resistance and aspect ratio, and which between the external thermal resistance and aspect ratio are obtained respectively. With the aspect ratio increase, both the matching load resistance and the matching external thermal resistance are firstly falling sharply. While the aspect ratio increase to1-1.5x10-3m, the decline leveled off. The maximum output power increases with the increasing aspect ratio.The studies on the heat transfer mechanism of thermoelectric generator have enriched the thermoelectric power generation technology theory. This study not only shows the performance optimization direction on thermoelectric generator or system, but also provides the necessary theoretical and experimental evidence for developing the new and high performance thermoelectric generator or system. |
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