Performance Analysis Of Electrogasdynamic Power-cycle System

Nowadays, with the intense contradiction of energy and environment, the demand for utilizing the low grade energy is surging at an unprecedented pace, especially the usage of medium or low temperature geothermal energy resources. Combined with the characteristics of electrogasdynamic(EGD) converter, the electrogasdynamic power-cycle systems are established to recycle and in-depth utilize the low-grate energy recourses in the subcritical state. The electrogasdynamic power-cycle systems contain two combined systems, which are thermoelectric system with electrogasdynamic converter and trigeneration system with electrogasdynamic converter. Those two systems not only can promote the development and utilization of geothermal resources, but also can increase and optimize the traditional way to producing the electricity. In addition, high voltage and small current are the significant characteristics of the electrogasdynamic conversion, so it can be widely used in some certain occasions.According to a large number of literature investigations and also the actual situation, the specific defining is as follows. It defines that the geothermal fluid of higher than 493.15 K is high-temperature geothermal fluid, 393.15 to 493.15 K is called medium-temperature geothermal fluid and below 393.15 K is low-temperature geothermal fluid. In this thesis, the exergy efficiency, energy utilization coefficient, output power and exergy loss rate of the system are selected as the objective functions, and seven pure working fluids are chosen to comprehensively investigate and analyze the important characteristics of those objective functions in the evaporating temperature range of 333.15-493.15 K, including evaporating temperature, pinch point temperature difference and heat source inlet temperature. These results show that the electrogasdynamic power-cycle systems are different from the traditional power-cycle systems. In the subcritical state, the output power evidently elevates with the increase of the evaporation temperature. It is found that the inlet temperature of heat source has significant impact on the exergy efficiency. For the same pinch point temperature difference, there exists maximum exergy efficiency when inlet temperature is not higher than twice of pinch point temperature difference compared to the critical temperature. Otherwise, the exergy efficiency keeps rising with the increase of heat source temperature. In addition, it can reduce the exergy loss rate of geothermal fluid injection and improve the exergy efficiency effectively if the heat source temperature of the system is appropriate, which refers to the inlet temperature of heat source is higher than twice of pinch point temperature difference compared to the critical temperature and the evaporation temperature changes next to the critical temperature of working fluids. For these working fluids with low critical temperature, such as R134 a, the exergy efficiency of system can be greatly improved by choosing the lower heat source temperature. And when the evaporation temperature is lower than 370 K, for the others with higher critical temperature, the exergy efficiency of system can be also greatly improved in the way above. Besides, in order to making the mixture gas with enough kinetic energy to get through the diffusive tube and ensure the nozzle exit pressure higher than or equal to the condensing pressure, the evaporation temperature should not be lower than a certain value on the condition of the corresponding ejector entrainment ratio.The results provide some valuable guidance for screening working fluids and further optimizing the electrogasdynamic power-cycle system for the utilization of medium or low temperature geothermal resources, promoting the new recognition and in-depth study of electrogasdynamic technology.