Electromagnetic effects and accurate wall-temperature measurement method under directly electric heating mode

Abstract

By directly imposed electrical energy on metal materials with low voltage but high current to generate Joule heat is an effective energy conversion method. The corresponding temperature will quickly reach the predetermined value. It is also an effective way to achieve homogeneous heating or local non-uniform heating in the heterogeneous conductive elements, thus directly electric heating is widely used in scientific experiments and industrial practices. However, direct electrical heating method may effect by electromagnetic effect (skin effect or proximity effect) and interfere on the sensor, results in inconsistent temperature distribution or inaccurate temperature, even under the condition with power frequency (f = 50 Hz or 60 Hz). In the present paper, a comparative experimental investigation on temperature distribution of multiple parallel blocks at steady and transient process under DC and AC heating mode have been measured by infrared camera and thermocouples. It is found that the temperature measured by AC heating is always lower than that measured by DC heating under the same apparent power applied effected by electromagnetic effect. Three different sensor installations used for temperature measurement is also discussed and found an effective installation method. The electric field and temperature field in parallel blocks is further analyzed by electromagnetic-thermal coupling multiphysics solver after model verification. Moreover, another experiment discovered that the imposed external DC potential will generate a non-linear interference to the measured temperature, the temperature sensor with a good insulation can get more accurate result. These result can provide a technical guidance for direct electrical heating scientific researches and industrial application.