Constant Drying Rate of Wet Granular Beds by Far Infrared Radiation

Abstract

Since for infrared drying, drying materials are heated by radiant heat, their optical properties are important factors. In this paper, focusing on such optical properties as emissivity and reflectivity of the drying materials, we selected three kinds of wet granular beds as model foods, whose optical properties are different each other. These beds consisted of each one of the three kinds of powders (alumina, silver and stainless steel) and water. The emissivity of alumina is the highest among them and that of silver is the lowest. Based on far infrared drying experiments of these beds, a drying model for the granular beds by far infrared radiation was discussed to calculate the drying rate and the material temperature in the constant rate period. We introduced the optical properties of the drying materials (emissivity of powder, emissivity and reflectivity of water) to the model. The drying rate and the material temperature in the constant rate period for the alumina beds are the highest of three beds. The values calculated for each bed by the model agreed with the experimental values.