Effects of Dry-bulb and Wet-bulb Temperature on the Drying Time of Spherical Porous Material in High Temperature Gas Flow

Abstract

The effects of humidity on drying kinetics and drying time for convection drying of porous material, taking into account steam condensation onto the material at the early stage of drying, were investigated. Mass and core temperature changes of a sample porous material, spherical red brick, were measured using a test apparatus in which the dry-bulb and wet-bulb temperature of the drying medium could be controlled. These were set at 160-240°C and 44-100°C, respectively. The experimental results showed that the critical moisture content decreased and the amount of steam condensation increased at higher wet-bulb conditions. The time required for drying to less than critical moisture content was much the same under all wet-bulb conditions at higher dry-bulb temperature, regardless of steam condensation. In addition, material mass and core temperature changes and drying time were estimated by numerical calculation using a simple calculation model based on receding evaporation plane model and reverse process model. The results obtained from these calculations were in agreement with the experimental results. Factors which determine drying time, such as amount of steam condensation in the pre-heating period, constant drying rate, critical moisture content and falling drying rate, were summarized, and a prediction method for drying time was proposed on a simple calulation model using the values of these factors.