Temperature profiles in microwave heated solid foods of slab geometry: Influence of process parameters

Abstract

A simple 1-D mathematical model for prediction of local temperatures in a layer of solid material during microwave heating (Houšová et al. 1998) and a sensitivity analysis were used to evaluate the influence of process and material parameters on vertical temperature profiles in a layer of material during heating. The results of calculations are presented in graphs and discussed. The incident microwave power and heat capacity and density of heated material are parameters with great effect on all local and average temperatures and local and average heating rates. The shape of temperature profile is influenced only to a small extent by a change in the value of applied microwave power and also in the value of heat capacity or density of heated material. The whole profiles shift to higher or lower temperature values when the incident microwave power is changing. The distribution of applied microwave power between the upper and bottom layer surface very much influences the shape of the profile and the values and position of the highest and the lowest temperature in the layer. Depth of penetration and thermal conductivity of heated material influence on the shape of temperature profiles and the temperature spread in the layer (evenness of temperature distribution). Effect of penetration depth also depends on the relation to the layer thickness – its effect increases with the increasing layer thickness. At the low values of penetration depth relative to the layer thickness, an uneven temperature profile is to be expected. Effect of thermal conductivity value on temperature profile depends on the time of heating. Because of a short time of microwave heating, the effect of this parameter on temperature distribution is smaller compared to the conventional heating methods. At the beginning of heating its influence is quite negligible. Temperature of the air surrounding the layer and intensity of heat exchange between the air and layer surface are parameters with only small local effect on temperature distribution.