Experimental and simulation study of high-voltage molten salt electric heating tubes for large-scale electric-to-thermal energy conversion

Electric heaters are essential for converting electrical energy into thermal energy. High-voltage electric heaters enable efficient voltage distribution across hundreds of heating units, allowing for higher power output while maintaining low current levels. To achieve high-voltage electric heating, the thermal conduct ability and insulation properties of the filling powder are crucial. This study selects aluminum nitride, boron nitride, silicon nitride, and electrical-grade- magnesium oxide as filling powders to manufacture electric heating tubes, the breakdown voltage and thermal conductivity were tested. The aluminum nitride-tube shows the best breakdown voltage at 2.9 kV, and the magnesium oxide-tube shows the best thermal conductivity at 1.4 W/(m & sdot;k). Numerical simulation works are conducted to verify the accuracy of the thermal conductivity calculation results and simulate the heater's temperature field. The results show that the temperature of the surface and resistance wire decrease as the heat transfer coefficient increases, and the heat transfer coefficient between the molten salt and the electric heating tube cannot be less than 3000 W/m2 & sdot;K when the power density of the resistance wire is 24.27 W/cm2 to keep the surface temperature below 570.43 degrees C. Overall, this article verifies the feasibility of aluminum nitride as a filling material for high-voltage electric heating tubes through experiments and simulations, and investigates the effects of power and heat transfer coefficient on the temperature distribution within the heating tubes with numerical simulations.