Rimental And Theoretical Investigations On Thermophotovoltaic System

Thermophotovoltaic (TPV) technology can be used to convert infrared radiation from the high temperature heat source directly into electric energy by semiconductor p-n junctions. TPV system has a high energy output density and theoretical efficiency with the advantages of various forms of heat source, portable, quiet operation, low maintenance cost, safety, no pollution and cogeneration. All those make TPV applications in the field of industry, commerce, military and aerospace very promising and attractive.At present, research on TPV has been gradually transferred from the optimization design of individual components to the design of overall system. In this work, a TPV system based on a porous medium burner was built. The experimental Ⅰ-Ⅴ characteristics of a single GaSb cell, a single Si cell and their modules in a TPV system using a SiC radiator were investigated. The influence of the radiator temperature and the radiator-cell distance on the output performances of a single cell and its module was analyzed. The results demonstrate that increasing the radiator temperature or decreasing the radiator-cell distance would both lead to the increasing of the short-circuit current density, but the decrease of the open-circuit voltage due to the rise of cell temperature counteracts the increment of output power density. At the same conditions, the output power density of GaSb cells is higher than that of Si cells. Moreover, the cell performance calculated using the ideal diode model is in good agreement with the experiment in the trend, but the error is large. And the power generation efficiencies were less than1%because of the low radiator temperature (<1000℃) and no spectrum control technology.Another TPV system with a high-temperature electric furnace was built to increase the radiator temperature which can be up to1300℃. The performance parameters of TPV system made up by a selective radiator (Er2O3or Yb2O3) with different PV cells (GaSb or Si) were analyzed. Because the infrared radiation is inhibited by the Er2O3or Yb2O3spectral selectivity, the cell temperature is lowered effectively and the thermoelectric efficiency is improved. But the output power of the cell is reduced. The structure design flaws and low-efficient spectral efficiency make the thermoelectric efficiency of the system small. Moreover, an actual diode model and light tracking method were used to establish a new physical mathematical model to improve the above-mentioned theory model. A higher accuracy was obtained in the prediction of open voltage and maximum output power, and the error of the predicted short circuit current was greatly reduced.Based on the experiment investigations of the above two TPV systems, a lot of experience for establishing a large burner TPV system are accumulated. In view of using gaseous hydrocarbon fuels as the heat source of the system, the influence of combusion-radiator on the whole system performance is very important. Therefore, a theoretical model with the tungsten antireflection coating proposed by Fraas was established based on several kinds of commercial combustion-radiators provide by Kanthal Company. The influences of CH4mass flowrate, recuperator efficiency, air/fuel ratio and geometrical size on the performance of the combustor-emitter of the thermophotovoltaic system were analyzed. It is found that the chemical-radiant energy conversion efficiency and the radiant surface temperature can be rasied noticeable by using recuperator; the optimized air/fuel ratio and CH4mass flowrate are20.64:1.00and0.988kg/h, respectively. Based on the above conditions, the optimized combustor-emitter performance can be obtained when the inner diameter and wall sickness of the inner/outer tube are27.2mm/38.5mm and7.0mm/3.5mm, respectively. The optimal parameters for the average surface temperature, the radiant surface power density and the chemical-radiant energy conversion efficiency are1523.8K,11.99W/cm2and73.7%.The above calculated results also show that the regenerator can significantly improve the surface temperature of the radiator and the conversion efficiency of chemical energy to radiant energy, and then improving the performance of the TPV system. Therefore, it is necessary to investigate the regenerator using theoretical and experimental methods. Considering the compact structure of the TPV system, a rotary regenerator with solid regenerative fillers is chosen as the heat transfer equipment. It was found that the deviations of the theoretical results from the experimental ones decrease with the increase of the period of rotation. To the TPV system of10kW combustion power, the deviation is3.5%when the rotation period is3s; while the deviation decreases to1.5%when the rotation period increases to15s. The deviation could be mainly attributed to the cold and hot fluids carryover loss which was not considered in the model. With a new model taking account of the carryover loss established, the predicted results were greatly improved. Based on the modified model, the influence of geometrical parameters of rotary regenerator on the effectiveness was analyzed for TP V systems of various combustion power. The results demonstrate that the effectiveness increases with the increase of the rotary regenerator diameter and height, while fluid carryover loss increases at the same time, which weakens the impact of geometrical parameters.In the end, a large burner TPV system was established. The geometric position between the cells and the radiator is improved; the cell modules are around the outside of the radiator in the form of hexahedron. The experiment result of the Si cell modules with SiC radiator indicates that the output power density has been improved to that of the TPV system with the high-temperature electric furnace. The output power density is0.087W/cm2when the radiator temperature is1473K. In the experiment with the GaSb cells, the output power density is0.307W/cm2when the SiC radiator temperature is1243K. When Er2O3selective radiator is used, the output power density decreases to0.208W/cm2.