Mathematical Modeling of the Heating of Liquids in Stirred Tanks Assisted by Microwaves

Abstract

One of the most widely used technologies for food heating today is the use of microwaves. This procedure is applied daily at the domestic level but shows difficulties in industrial designs; one of them is the non-uniformity in the distribution of temperatures. This phenomenon is caused by an inhomogeneous distribution of the electromagnetic fields within the control volume, depending on the dielectric properties of the material and the geometry of the system. In this work, the microwave heating of a liquid product inside a tank (reactor) with and without mechanical agitation was analyzed. To this purpose, a mathematical model was developed that includes the resolution of the microscopic energy balance in which a source term is used to consider the interaction between food and microwaves. The electromagnetic distribution was obtained through the resolution of the Maxwell equations for the product and the oven-cavity. In the case of the stirred tank, the microscopic momentum balance was coupled to the non-stationary energy balance to solve the distribution of velocities within the tank. The Maxwell equations and the energy and momentum balances with the initial and boundary conditions were solved using the finite element method through the commercial software COMSOL Multiphysics. From numerical simulations it was possible to evaluate the effect of the agitation rate, the position and number of the microwave-generators inside the cavity in the temperature profiles of the liquid products.