Size effect on temperature distribution of instant rice during microwave reheating process

In order to improve the performance in food microwave reheating and avoid the “cold spots”, real time determination of sample temperature by the optical fiber probe, combined with axis analysis and temperature variation coefficient calculation was used. The effect of sample size on the temperature distribution of instant rice during the microwave reheating in a microwave workstation was investigated. The results showed that hot-spot temperature of rice with the same radius shifted from the geometric center region to the surrounding border over the increase of L/D ratio. When the L/D ratio was equal or less than 0.75, the increase of radius led the hot point to focus on the center area. Hot-spot temperature transferred to the edge and surface regions as the radius increased under the L/D ratio range of 0.75 to 1.25. Coefficient of variance (COV) of temperature derived from standard deviation was used to analyze the temperature uniformity. Rice cylinder with 4 cm in radius and 4 cm in height exhibited the best uniform temperature distribution during microwave reheating. Numerical simulation of temperature distribution in the rice microwave reheating process showed that the predicted data with determination coefficient (R2) of 0.990 to 0.999 matched with the experimental results.