Conveyor-Belt Dryers with Tangential Flow for Food Drying: Development of Drying ODEs Useful to Design and Process Adjustment

Abstract

The mathematical investigation presented in this paper concerns the conveyor-belt dryer with tangential flow operating in co-current. This dryer is bigger than the continuous through-circulation conveyor dryer but has the advantage of better preserving the organoleptic and nutritional qualities of the dried product. In a previous work a mathematical modeling of the conveyor-belt dryer with tangential flow was carried out to offer guidelines for its optimized design. The last of those design guidelines indicated the need for an optimized adjustment of the dryer to ensure the constant maintenance of the final moisture content of the product. The fast and very precise measurement of the moisture content as the first step in the feedback chain was therefore necessary. Considering the difficulty of this type of measurement, two specific ordinary differential equations (ODEs) were obtained with the mathematical investigation of this work. Their solution became a relationship between the final moisture content of the product, the outlet air temperature, and other quantities that could be easily implemented in an automatic dryer control system. Therefore, the fast and accurate and much less expensive measurement of the temperature of the air leaving the dryer, owing to the relationship found, replaces the measurement of moisture content for the adjustment system. The experimental verification of the relationship highlighted the need to introduce a modification by which the relationship was finally validated.