Steady state one dimensional flow model for a pneumatic dryer

Abstract

A one-dimensional steady-state mathematical model for dilute phase flow in a pneumatic dryer is presented. The model takes into account mass, momentum and heat transfer between the gas and the particle phases. The model was applied to the drying process of wet PVC particles in a large-scale pneumatic dryer. The rate of drying was controlled by a two-stage drying process. In the first drying stage, heat transfer controls evaporation from the saturated outer surface of the particle to the surrounding gas. At the second stage, the particles were assumed to have a wet core and a dry outer crust; the evaporation process of the liquid from a particle is assumed to be governed by diffusion through the particle crust and by convection into the gas medium. As evaporation proceeds, the wet core shrinks while the particle dries. The drying process is assumed to stop when: the moisture content of a particle falls to a predefined value; or when the particle riches the exit of the pneumatic dryer. The one-dimensional pneumatic drying model was solved numerically and two operating conditions, adiabatic and given pneumatic dryer wall temperature, were simulated. The prediction of the numerical simulation was compared successfully with experimental results of drying of wet PVC particles conveyed with air in a large-scale pneumatic dryer.