【作者】 周泽广；

【导师】 朱冬生；

【作者基本信息】 华南理工大学 ， 化学工程， 2013， 博士

【摘要】 节能与环保是21世纪全人类共同面临的严峻问题。近年来，随着国民经济的快速发展，能源安全形势日益严峻。对此，《中华人民共和国节能法》指出：节能是国家发展经济的一项长远战略方针，也是解决当今能源问题的首要途径。国家“十二·五”规划更是明确提出：绿色发展，建设资源节约型、环境友好型社会。要求大力推进节能降耗，推广先进节能技术和产品。温差发电技术利用材料的塞贝克效应，可将热能直接转换成电能，具有结构紧凑、无磨损、无泄漏、清洁、无噪声、寿命长、可靠性高等一系列优点。它是一种新型的、绿色环保的发电技术，可以合理利用太阳能、地热能、工业余热废热等低品位热能。许多科技发达国家已将发展温差发电技术列为中长期能源开发计划。我国太阳能和工业余热资源丰富，陆地表面每年接收到的太阳辐射能相当于1700亿吨标准煤；而余热资源约占燃料消耗总量的17%~67%，其中可回收率达60%。若能结合温差发电技术在低品位能源利用上的独特优势，把这部分能源转化为电能，必将产生巨大的经济效益和社会效益。温差发电技术在国内的研究起步比较晚，主要集中在新型热电材料的制备及其性能研究。针对温差发电器内热量传递的机理、机制问题的研究则相对较少。本文基于热量传递基本理论，通过热阻网络法对温差发电器内热量的传递过程机理进行理论分析和实验研究，建立温差发电器热阻解析模型以及温差电组件串并联连接的热阻解析模型，并通过数值模拟对余热温差发电器进行了模拟研究。主要研究工作和结论如下：（1）基于热阻网络法对温差发电器内热量的传递过程进行理论分析，同时搭建温差发电器性能测试平台对其内各部分热阻的分布和变化规律进行了实验研究。发电器冷端散热的强化对其内部传热控制区域有显著影响：与空气自然对流相比，空气强制对流和水冷散热方式强化了散热器翅片与环境之间的传热，降低了发电器冷端的温度和热阻，发电器内的主要热阻由自然对流时的散热器翅片与环境间的对流换热热阻转变为温差电组件与热源和冷端散热器之间的接触热阻；当热源提供的热流量恒定时，强化发电器冷端传热的同时也降低了热源和发电器热端的温度，发电器热冷两端的温差并无显著提高；当热源热流量较低时，强化冷端的传热并不能显著提高发电器的输出功率；当热源热流量较大时，强化冷端的传热将大大提高发电器的输出功率；热源热流量为50W时，强制风冷和水冷方式下的输出功率比自然对流方式下的分别提高了27.9%和39.5%。（2）采用Fluent软件对余热温差发电器进行了数值模拟研究。增加冷、热流体的流速，强化温差电组件冷端和热端换热器内热量的传递，均可获得更大的温差，发电器因而获得更好的性能。但当发电器内传热控制区域发生变化之后，再进一步增加冷热流体的流速，对提高发电器性能的效果变差了。此时，应把解决问题的重点放在降低传热控制区域的热阻上。（3）基于非平衡态热力学理论和热阻网络法导出了包括温差电组件与热源和冷源之间的热阻θH和θC、P-N电偶臂自身热阻θTE、电偶臂数量m、电偶臂所用材料的塞贝克系数αPN和电阻r、回路电流I以及热源温度T1和冷源温度T0等参量的输出功率和发电效率热阻解析模型，实验验证了模型的准确性。根据该模型可以较精确地预测发电器的性能，从而为高性能发电器的组装提供理论依据。（4）温差电组件的串并联连接可调节热电模块的内部电阻和热阻，从而调控发电器的输出电压、电流和功率，以便为具有不同电阻值的负载提供电能。对温差电组件采用串并联连接方式的温差发电系统进行了研究，导出了系统输出功率的热阻解析模型，探讨了温差电组件总数量、并联组件数量、热电模块及其热端和冷端的热阻等对系统性能的影响。结果表明，系统电阻与负载电阻、热电模块热阻与其热端和冷端的热阻之间存在匹配关系，能使系统获得最大的输出功率；随着并联组件数量的增加，最大输出功率和回路电流得到了提高，但系统的输出电压却降低了。研究结果为温差发电系统的合理装配及性能优化提供了理论参考。（5）电偶臂结构尺寸的优化设计研究。导出了发电器输出功率与电偶臂面长比的关系式，获得了负载电阻及外部热阻两者分别与面长比的匹配关系。随着面长比的增加，匹配的负载电阻和外部热阻都是先急剧下降，当面长比增大到1～1.5×103m之后，其下降幅度趋于平缓。最大输出功率随面长比的增加而增大。本文关于温差发电器内热量传递过程特性及机理的研究丰富了温差发电技术的理论体系。该研究不仅为温差发电器或温差发电系统性能的优化指明了方向，更为新型高性能温差发电器或系统的开发和研制提供必要的理论和实验依据。更多还原

【Abstract】 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.更多还原