安全火花试验电极热场致发射模型和温度效应的数值模拟研究

Research on Numerical Simulation of Thermal Field Electron Emission and Temperature Effect for Safety Spark Test Electrode

研究安全火花试验装置的镉盘试验电极温度分布和热场致电子发射特性为研究感性电路分断放电特性和揭示其电弧放电机理奠定理论基础。根据量子理论,热场致电子发射电流密度主要取决于阴极表面温度和外加电场等因素。因此基于椭圆积分法,推导出阴极电子穿透率的数学表达式,得出热场致电子发射电流密度与温度及外加电场之间的关系表达式;综合考虑试验电极的微观表面形貌、发射电流密度、焦耳热和热传导效应,数值计算阴极微凸起的表面温度变化规律。实例模拟仿真结果表明:当镉盘阴极表面温度在熔点和沸点范围内时,热场致电子发射电流密度随外电场和阴极表面温度的增大而非线性增加;在不同外加电场下,阴极微凸起温度随放电时间呈非线性增长,且增长率越来越大;阴极微凸起顶端温度在极短时间(ns级)内上升到熔点,从而引起其顶端局部发生微爆炸电子发射。这为进一步研究感性电路分断放电的微观机理和本安非爆炸性评价奠定了理论基础。

The temperature distribution of cadmium electrode and thermal field electron emission(TFEE)properties based on safety spark test apparatus are studied to lay the foundation for studying the inductor-disconnected discharge characteristics and revealing the mechanism of arc discharge.According to quantum theory,the TFEE current density depends largely on such factors as the cathode surface temperature and applied electric field.Therefore,with the elliptic integral method,the mathematical expression of cathode electronic penetration rate was deduced.The relational expression between the TFEE current density,the cathode surface temperature and the applied electric field was derived.Considering the microcosmic surface morphology of the test electrode,the TFEE current density,joule heat and heat conduction effect,the temperature on the micro-protrusion of the cathode surface was computed with numerical method.The simulation results show that,the TFEE current density increases nonlinearly with the increase of the applied electric field and cathode surface temperature between the melting point and boiling point of cadmium electrode.Under different applied electric fields,the temperature of micro-protrusion increases nonlinearly with discharge time,and the growth rate increases.The temperature of micro-protrusion top rises to the melting point in a very short time(ns-grade),and thus the local micro-explosion electron emission occurred.It has laid a theoretical foundation for further research on the micro-mechanism of inductor-disconnected discharge and the evaluation of the non-explosive intrinsically safe performance for the inductive circuit.