| Thermionic energy converters（TECs）are solid-state thermoelectric conversion devices with extremely high output power per unit area and theoretical conversion efficiency.They have the characteristics of no phase change,no movement,simple structure and have broad application prospects.However,the actual performance of the device is much lower than the ideal value,which is restricted by the space charge effect and heat loss.In this work,the structural design and optimization basis of the high-performance thermionic energy converter by constructing a theoretical model has been explored.Then an experimental system was built and the prototype experiment has been completed.Based on the basic theory of thermionic converter,the influence of basic parameters（the work function of the emitter and the collector,the operating temperature of the emitter and the collector）on the output characteristics of the device were analyzed to provide a design basis for the upper limit of the ideal performance.On this basis,the performance evaluation and comparison of the TECs devices that can be constructed by advanced electrode materials were made and the electrode combinations suitable for forming high-performance devices were pointed out.Subsequently,a calculation program was written based on the theoretical calculation method of the current density weakened by the space charge effect.The influence of the electrode spacing and the space charge effect on the output characteristics of the device was studied.Based on the theory of microscale heat transfer and near-field radiation,the heat loss caused by the structure between the electrodes was studied.Combined with the space charge effect calculation program,a comprehensive model of energy transfer between the electrodes was constructed to explore the effect of the distance between the electrodes and the proportion of the support structure on the actual device performance.The research showed that there is an optimal spacing interval between the electrodes that makes the device operate in a more efficient state.For the device with tungsten as the electrode substrate,when there is a support structure between the electrodes,the heat conduction of the support structure is the dominant factor of heat loss,and the electrode spacing interval for the higher actual efficiency of the device is 0.5μm to 1.2μm.When there is no support between the electrodes in a suspended state,the interval between the electrodes to make the actual efficiency of the device higher is0.3μm to 0.6μm.Finally,the thermionic energy converter experimental system was designed and built,including vacuum environment,contact temperature measurement,non-contact temperature measurement,capacitance measurement.The thermionic energy converter prototype test process was explored.The experiment used Mo emitter and Ta collector to build a device prototype.The spacing between the electrodes is 5.13μm through the separation of Al2O3particles.Under the conditions of emitter temperature of 1467K and collector temperature of444K,the maximum output power per unit area is 2.296μW/cm2.The electrical efficiency is35.44%at the peak power. |
