Research And Optimization On Thermoelectric Generation Using The Waste Heat Of Water Heater Flue Gas

With the energy and environmental problems becoming more and more serious, how to maximize the improvement of energy efficiency on the premise of no hazard to the environment has become the concern of countries in the world. Researchers around the global have given unprecedented attention to the research on themoelectric technology. About seventy percent of the energy in the existing energy system is disspated to environment in the form of waste heat that is a great waste of energy. On the other hand, it has large energy-saving space to take use of the waste heat. Thermoelectric generation technology is friendly to the environment. It is a solid-state energy conversion means and has no noise, no wear, no pollutant emission, small size, light in weight, portable, long life and no maintenance. Particularly it has no limit to temperature so the unique advantage makes more and more people see its potentiality in the waste heat recovery field. Thermoelectric conversion efficiency is not high because of the limitation of thermoelectric materials and it has few studies on the match of various parts of thermoelectric generators, so it is necessary to conduct a much deeper study on thermoelectric. This paper introduced the worldwide research on thermoeletric technology, analysed the potentiality of thermoelectric generation system in application of waste heat recovery. The main research work and conclusions include the following:(1)Testing platform of thermoelectric generation system has been established on the basis of the basic theory of thermoelectricity. The heat chip which designed by ourselves works as the heat source, and the cold side heat is dissipated by the heat sink. Testing the uniformity of temperature distribution of heat chip surface by experiment combined with Infrared thermal image technology, and the results show that temperature in the center of the heat chip was higher than the surroundings and temperature difference increased while the heater power increased. However, the temperature difference is still acceptable in our experiment. Then we select four kinds of common commercial thermoelectric modules and the relationship of thermoelectric generation system performance with temperature difference between hot and cold side, load resistance, converting efficiency and energy efficiency, dynamic internal resistance and reliability of thermoelectric module have been studied. The phenomenon that matching resistance of modules differs from reference value is explained by the dynamic internal resistance method. And the performance of the cold side heat sink was investigated with the multi-parameter experiments. And the optimized heat sink length, heat sink height and the base thickness are 140mm, 31mm, 4mm respectively. (2) The thermoelectric uicouple analytical model, which includes the Peltier effect, Seebeck effect, Fourier effect and Joule effect, has been firstly developed in order to simulate the performance of the thermoelectric system with the variation of kinds of influenced factors. The theory and simulating results has been compared in order to investigate the reliability of the model. The output power and converting efficiency of the system at different load resistance has been studied.The comparation between the simulating and experimental results inspects the drawback of the system. And it sets up the theoretical basis for the sake of improving the experimental accuracy. The variations of thermoelectric generator with hot and cold side temperature have been investigated. Then a optimization design has been done on the length and the cross width of the thermoelectric legs. And the optimized length and the cross width are respectively of 1.5mm, 2.0mm where gets the highest converting efficiency.(3) We put the thermoelectric generator system into application of the recovering of exhaust heat produced by Gas Water Heater. The specific install area of the thermoelectric generation system has been fixed by the temperature distribution testing experiment.Plus, the output power of the thermoelectric generation system at different water flow and gas pressure has been tested. The comparision of the two manners of module connections with the output power effects shows that: series is better than in parallel.The regularity for change of output power,converting efficiency and energy efficiency of the thermoelectric generation system has been studied with the working conditions like different load resistance,temperature difference and so on with the experimental approach in this paper. The study of the heat recovering of Gas Water Heater system with thermoelectric system has enriched the research content about thermoelectric generation on heat recovering and some practical methods and conclusions about low heat recovering of thermoelectric generator has been shown.