Numerical Simulation And Experimental Study Of Heat Transfer Of Thermionic Energy Conversion

The thermal electronic energy converter is an electric vacuum device which converts heat energy directly into electric energy.It is based on the development of the thermionic emission phenomenon that electrons will evaporate from the surface of the emitter at high temperature.It depends on the emitter hot electron emission and the collector's positive contact potential difference output current.Such a device can turn the energy of the heating emitter into a low voltage and high current DC output.The structure of a simple thermionic converter needs only one emitter and one collector.When the emitter with a higher function is heated,the electrons are emitted from the surface of the metal and captured by the collector anode,when the load is connected to the emitter and the collector can produce the current.The efficiency of the ideal thermal electron energy conversion is affected by the following three processes: the research on the thermionic converter is generally carried out from two directions,one is to increase the temperature of the emitter,and the two is to reduce the working temperature of the emitter to extend the range of the thermionic ion.In order to obtain high efficiency at low temperature,the emitter material of low escape work can be found,and the space charge effect is neutralized by reducing the distance between two electrodes and introducing the positive cesium ion.The output characteristics of the thermionic energy converter are analyzed from the heat transfer angle,and the influence of heat conduction,convection heat transfer and radiation heat transfer on the output characteristics of the thermionic energy converter is analyzed.Two different models of thermionic energy converter are built to improve the thermionic energy converter.Through numerical simulation,the factors affecting emitter temperature and output characteristics of thermionic energy converter are studied and analyzed.The results show that the smaller the thermal conductivity of the receiving pole and the insulation material is,the greater the heating power is,the greater the reflective film is,the higher the emitter temperature,the output current density and efficiency,and the main factor affecting the emitter temperature and efficiency in the heat transfer process is the heat conduction between the solid.Generally speaking,adequate illumination,reasonable receiving size and insulation measures can effectively improve the output characteristics of thermionic energy converters.For TEC,the emitter temperature has an important influence on its output power and efficiency.The experimental device is mainly divided into three parts,the laser heater and the heat absorbing device and the temperature measuring part.The effect of different factors on the emitter temperature is explored by changing the output power of the laser and the vacuum degree of the vacuum insulation device.The results show that the higher the heating power is,the higher the emitter temperature is,but with the increasing of the heating power,theincrease of the emitter temperature is becoming smaller and smaller;the higher the vacuum degree,the higher the vacuum degree,the higher the emitter temperature,because the energy lost through the heat conduction is reduced,but the effect is not obvious.Using the oxide cathode and six lanthanum boride thin film as the poles,a thermoelectric conversion experimental system was established.The system characteristics were explored by changing the input power and applied voltage.The experiment shows that with the increase of heating power,the output current and conversion efficiency of the thermoelectric conversion system also increase,and the trend is more and more obvious.In a certain range,changing the applied voltage will affect the output current and efficiency of the system,but there is a critical value.