Determination of Heat and Mass Transfer Coefficients during Drying by Using High Velocity Multiplier Air Jets

Abstract

High velocity impact air jets are widely used in industrial heating, cooling and drying processes. In this study, the drying behaviour of a textile dryer, the ram machine, in which multiplier air jets were used was experimentally investigated. Experiments were carried out in a 10-cabinet ram machine using a fabric with 95% Cotton + 5% lycra contents at three different drying air temperatures (110-130-150 °C) and at a fabric feed rate of 0.500 m/s. The fabric that is dried in the calculations is regarded as a flat plate. For each drying condition, it has been found that the flow type on the flat plate is turbulent throughout the boundary layer between the fabric surface and the drying air, taking advantage of the thermodynamic properties of moist air. Heat transport and mass transport coefficients have been reached with mean Nusselt and Sherwood numbers developed for turbulent flow in forced convection on a flat plate. Accordingly, for each of the above-mentioned drying conditions, it is determined that the average heat transfer coefficients varied respectively between 69.53-74.07-92.96 W/m2K and mass transport coefficients 0.064-0.071-0.093 m/s.

Keywords: Drying, Ram machine, Chilton-Colburn analogy, Heat and mass transfer with convection