Numerical investigations of heat transfer and skin effect characteristics within rods located in a 48-rod Siemens reactor heated by AC

Abstract

Abstract In the polysilicon reduction furnace, all the energy is supplied by the heat generation on silicon rods which are heated up by the passage of electric current. The alternating current (AC) produces the alternating magnetic field, and the oscillating magnetic field induces the corresponding eddy current in the conductor, which causes the phenomenon of skin effect. In the present paper, the coupling model of thermal and electromagnetic field for the silicon rods has been developed by coupling Joule heating equation controlled by frequency and heat dissipation (radiation, convection and reaction energy). Comparing the calculated results with the industrial data, it is found that the average relative errors of the current intensities of the inner, middle and outer ring silicon rods are 7.55%, 5.55% and 7.43%, respectively, indicating that the model calculation results are accurate and can be used to accurately analyze the thermoelectric behavior of the silicon rods. Based on the Joule heating process of silicon rods in a 48-rod polysilicon reduction furnace, the influences of AC frequency on temperature and current density profile within rod arranged in different rings have been studied. The interesting results show that the high frequency current sources can generate an even temperature profile and an isothermal region inside the rod can be obtained when the RF increases to 10. Therefore, utilizing the high frequency current sources can decrease the temperature gradient within silicon rod effectively, which provides a method for producing larger diameter silicon rod. Furthermore, the voltage-current curves of low frequency (50 Hz) and high frequency (10 kHz and 50 kHz) can be predicted by the present Joule heating model, at the same time, a hybrid heating process of low frequency and high frequency is proposed.