Indirect Measurement Method for Effective Work Function of Electrode in Thermionic Energy Converter

In the thermionic energy conversion of Cs-charged, the work function of the electrodes, especially the effective work function of the electrode material in the Cs-absorbing state, has a decisive impact on its power generation performance. However, it is difficult to measure the work function in the high-temperature Cs environment for the test method at this stage, so establishing relevant experimental methods to evaluate the work function of the electrode material in the real environment is necessary. Based on the energy balance equation of electron flow between electrodes in thermionic energy conversion, combined with the local characteristics of electrode influence in the thermoelectric conversion process, the indirect measurement method of the effective work function of the emitter and collector was established by processing the current-volt characteristic curves under specific operating parameters. Furthermore, the data processing program was compiled by Matlab language, then the effective work function of the electrode material at different temperatures could be directly output. A series of current-volt characteristic data were obtained by using the current-volt characteristic program in the literature, and the current-volt characteristic data of Ni with only changing the temperature of the collector were tested by using a self-built plate-electrode experimental device. The parameters such as current density, voltage and electrode temperature in the current-volt characteristic results were substituted into the effective work function calculation model. The effective work functions of W emitter and Ni collector under different power generation currents under specific operating conditions subsequently were calculated separately, compared with the test values of the Cs-absorbing work function tested in the literature, which not measured under arc conditions during power generation. The results show that the effective work function of the emitter is approximately positively correlated with the Rasor index, decreasing with the increase of current density, which is caused by the Schottky effect. The changes of the effective work function of the collector with the working condition are consistent with the change trend of the influence of the collector temperature on the output power. Furthermore, there is an optimal collector temperature, in the vicinity of which the effective work function is the lowest. The average relative errors of the effective work functions of the emitter and collector and the literature values of the Cs-absorbing work function are 5.74% and 3.86%, respectively. The indirect measurement results of the effective work function can be consistent with the power generation characteristics of the thermionic energy conversion, which could be reflected in the previous test results of the Cs-absorbing work function.