University of Hawaii, USA
Dr. Soojin Jun
A 2D numerical model using COMSOL codes was developed to validate uniform heating of particulate foods in a continuous flow microwave (MW) and ohmic (OH) combination heater. Uniform heating of particulate foods is a serious challenge because individual solids and liquids are so discrepant in terms of thermal, electrical, and dielectric properties. To achieve the challengeable uniformity in heating of particulate foods, a new cylindrical microwave chamber equipped with an ohmic tube was designed and fabricated for testing in a continuous flow mode. Due to model complexity, previous studies associated with continuous ohmic and microwave heating did not fully combine all partial differential equations to govern the multi-physics occurring in the system were not integrated into one numerical code. However, the developed model was integrated with an electric field, electromagnetic field, incompressible laminar flow, forced-coupling method (FCM), heat transfer and arbitrary Langrangian-Eulerian (ALE) moving mesh technique. Three representative solid particles were simulated to experience hydrodynamic viscous drag and pressure forces resulting from their motions relative to fluid. The stress tensors of forces exerted on the particle surfaces were successfully formulated by use of the FCM module. The large deformation and movement of geometric mesh containing trajectories of particles inside the feeding tube were accurately predicted in an unsteady state. The simulated outlet temperatures of particulate foods had a good agreement with experimental data within the prediction error of 4%.