Heat and mass transfer and deformation parameter model of minced Antarctic krill during microwave drying

Microwave drying is a technology for rapid dehydration of materials, which is widely used in the food industry. Compared with traditional convection drying, microwave drying for food has been found to result in improving the drying rate and final quality. However, microwave drying lead to a non-uniform temperature distribution in some instances, which can over-dry and even destroy food and its texture. Intermittent microwave drying can overcome these adverse effects and improve product quality. Although there are many experimental studies on microwave drying, there is no complete model of heat, mass transfer and shrinkage for microwave drying of Antarctic krill mince available in the literature. Therefore, in this paper, the simulation model was studied based on electromagnetics, multiphase transport and deformation using minced Antarctic krill as media. Microwave drying was carried out in a household microwave oven with a power of 100 W (rated power of 1 000 W). The results of the simulation were obtained by solving electromagnetic equation, energy and momentum conservation and deformation equation by COMSOL Multiphysics. The model included multiphysics of Maxwell's electromagnetic heating, energy conservation, Darcy's velocity, solid mechanics, mass conservations of water and gas, and phase change of melting and evaporation of water 6 s as one cycle was adopted in the simulation. The strategy for each cycle was that the first step was to calculate the electromagnetic field; the second step was to calculate the temperature, pressure, moisture concentration and vapor concentration by using the heat source term; the third step was to calculate the solid mechanics module based on the moisture concentration. After each cycle, the last calculation result was taken as the initial condition of the next calculation, and the dielectric property, thermophysical property, porosity and material size were updated for the next cycle (30 cycles in total). It could save calculation time by using the method to separation and circulation. Infrared thermal imager was used to photograph temperature distribution on the surface of the sample, and optical fiber sensor was used to measure the instantaneous temperature in the point of the sample. The spatial temperature distribution, transient temperature curve, moisture content and volume ratio were in good agreement with the experimental values during intermittent microwave drying for 180 s, and the RMSE of temperature and moisture content without considering shrinkage model are 9.42℃ and 0.08, respectively. Microwave simulation of microwave drying was feasible. In addition, the temperature and moisture content of minced shrimp treated as deformable material were significantly different from that of rigid material during microwave drying simulation, and the former was closer to the experimental value. Water loss was the main factor of material deformation. Intermittent microwave drying allowed the distribution of moisture, pressure and temperature within the material uniform. The sensitivity analysis of the input parameters including intrinsic permeability of water and gas (±50%) and water absorption expansion coefficient (±50%) showed that the water content was more sensitive to the intrinsic permeability of liquid water (RMSE=0.089), less sensitive to the intrinsic permeability of gas (RMSE=0.023), and the volume ratio was very sensitive to the water absorption expansion coefficient. © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.