Energy utilization and heating uniformity of multiple specimens heated in a domestic microwave oven

Abstract

To improve the energy utilization and quality of multiple specimens heated in a domestic microwave oven, we developed a theoretical model that considered the electromagnetic, heat, mass and momentum fields and phase change. Specimens with different distances, volumes and shapes were compared and discussed. The state parameter distribution uniformity and concentrative degree were described by the coefficient of variation (COVE, COVT, COVM and COVP), the microwave focusing degree (MFD) and thermal runaway. The energy utilization efficiency was quantified by the specific power absorption efficiency (SPAE). Microwave focusing, hot spots, and dry and wet spots occurred during the process and were influenced by the electric field distribution, mass and heat transfer and certain geometries. When the distance between the two specimens was approximately one wavelength (in free space), the energy utilization was higher, but the uniformity was worse. The SPAE of the specimens with larger volumes was lower due to energy attenuation, which gave rise to a lower average temperature, lower phase change rate, higher average moisture content and better moisture distribution uniformity. The distribution uniformity of the electric field and temperature of the cylindrical specimens were the best.