Characterization of Spatial Non-Uniformity in Microwave Reheating of High Loss Foods

In order to characterize the non-uniformity of microwave heating when power deposition can be approximated as simple exponential decay, a correlation was developed between temperature non-uniformity and the significant parameters, such as surface microwave flux, penetration depth and the duration of heating. An index of temperature non-uniformity was developed as the difference between the average temperatures of the hottest 5% of the volume and the coldest 5% of the volume. Temperatures calculated using a numerical solution to the energy equation were used to develop the correlation. Experimental verifications were carried out using both a fiberoptic temperature measurement system and an infrared thermal imaging system. Results are provided in terms of a simple expression that can be used to estimate the expected non-uniformity of heating in product and process development, by knowing the dielectric and the thermal properties of a food material.