Analysis of the heat transfer characteristics of blackberries during microwave vacuum heating

Microwave vacuum heating of blackberries was carried out to investigate the effects of microwave power and vacuum degree on the temperature of blackberries during the heating process, and the distribution of the temperature field was observed. Using numerical simulations, a combined electromagnetic and heat transfer model was established. The simulations can be used to observe the locations of hot spots and cold spots during heating. The appropriate microwave power and vacuum could also be selected using the simulation to reduce the temperature difference of the locations of hot spots and ensure uniform heating. The results show that, for blackberries heated for 2 min at a microwave power of 400 W and vacuum degree of −80 kPa, the temperature of the hot spot was maintained at about 60 °C and the temperature difference was about 0.27; thus, the heating was uniform, meeting the industrial drying requirements for blackberries.