Experimental and Numerical Study of a DC Induction Heater Prototype With an Adjustable Air Gap Structure

To improve the poor efficiency of conventional ac induction heaters, which is usually below 50%, a high-temperature superconducting (HTS) dc induction heater has been proposed as a candidate solution. In previous researches, the air gap structure is fixed, which leads to a less controllable magnetic field distribution along the axial direction of billets, hence a less controllable temperature distribution along the same direction. However, an adjustable temperature distribution along the axial direction of billets is required in the aluminum extrusion industry. In order to solve this problem, a novel adjustable air gap structure is proposed and fabricated in our laboratory-scale prototype of the HTS dc induction heater. To validate the method, heating experiments for uniform and gradient temperature distribution were performed with different air gap structures. In addition, a novel adjustment method, i.e., unilateral adjustment, for air gap structure was proposal and tested, which simplified the adjustment method. A finite-element method model of the heater was built to analyze the temperature distribution and the theoretical availability of adjustable air gap structure.