A calibration approach for the bulk temperature estimation from container surface temperature during microwave heating processes

Abstract

Microwave dielectric heating has been demonstrated to have substantial advantages over traditional heating procedures. Nonetheless, the sample temperature must be continuously monitored during the microwave irradiation procedure. Despite the fact that various sensors exist to directly obtain the sample temperature, this is still an issue for microwave-heating processes. The sample temperature is typically measured with the use of a calibrated external sensor capable of monitoring the surface temperature of the sample container from a predetermined distance. Nonetheless, significant limits have been identified, implying that monitoring the container temperature is insufficiently accurate in many scenarios. In this paper, we present a case study of a calibration approach for estimating sample temperature from pyrometer records during microwave-heating processes in a multimode cavity. Various thermal properties have been determined to explain the errors that tend to take place when monitoring the temperature of the container surface instead of that of the sample. However, some discrepancies were found in calculating the bulk temperature. Furthermore, the estimation of the bulk temperature became more inaccurate at the beginning of the experiments, particularly at high power-to-mass ratio levels. Nonetheless, if low power-to-mass ratios are applied, bulk temperature at specific points can be properly estimated.