An analysis of transient flow of heat and moisture during drying of granular beds

Abstract

The transient process of drying granular materials in fixed packed beds is analysed, and equations expressing moisture contents and temperatures of material and drying medium as functions of time and location in the bed are derived. While moisture content of the granules may be expressed in terms of ordinary exponential functions of these variables, humidity and temperature of the drying medium additionally require numerical solutions. The theory is developed for materials drying in four stages—one stage at constant rate, one at increasing rate, and two at falling rates—and should be applicable to numerous products in the chemical and food industries, with wider applicability if suitably modified. Application of the theory is demonstrated for through-drying of a granular bed of wheat, using published data to evaluate transfer parameters appropriate to special drying conditions and employing a CDC3200 digital computer to calculate the moisture content of grains as a function of time and location. The Fortran programme written for this computation may be used to predict the progress of drying other materials within the category of the present analysis.