JET IMPINGEMENT DRYING OF A MOIST POROUS SOLID

This paper investigates the thermal characteristics of a continuous in dustrial drying process for semi-porous textile composites. The conser vation of mass, momentum and energy are written for a partially satura te porous fiber layer attached to a solid-backing layer. The numerical solution of the one-dimensional and transient conservation equations provides the temperature, volumetric saturation and gas phase pressure distributions in the moist porous solid and the temperature distribut ion in the solid-backing layer. During the wet region drying period, c ontinuous liquid exists in the pore space, the moisture transport with in the solid is described by the Darcy form of the momentum equation. The moisture transport in the sorption region is described by a bound liquid diffusion and gas phase transport. For the jet impingement type dryer, it is assumed that the penetration of the flow field into the porous solid is small (assumed valid due to the presence of the solid backing). The enhanced transport coefficients al the drying surface ar e estimated with the use of the Kolmogoroff theory of isotropic turbul ence. This theory provides correlations for the heat and mass transfer coefficients from the fluid properties and the turbulent energy dissi pation rate in the fluid. The model results of the continuous industri al drying process are compared to independent experimental temperature and global moisture content measurements taken in an operational indu strial dryer. From the model analysis and experimental data, the heat flux conditions at the drying surface dictate the manner in which the solid is dried. The heat transfer coefficients considered are in the r ange of 20-130 W m(-2) K-1 and necessarily affect the manner in which moisture transport occurs within the solid. It is seen that the lower heat transfer coefficients more accurately represent the internal tran sport phenomena occurring during the drying process and the heating of the solid. The transport coefficients are compared to previously obta ined empirical results.