COMBINED CONVECTIVE AND INFRARED DRYING OF A CAPILLARP POROUS BODY

Conventional convective drying processes being energy intensive and relatively slow, other techniques are being more intensively studied to minimize of offset these limitations. Among these, the use of I.R. (infrared) heating has significant advantages for industrial drying applications: direct transfer of heat to the product; low thermal inertia of the I.R. heat source; high heat flux intensity (up to 60 kW/m[sup 2]); choice of the emitter wavelength to match the product absorption characteristics; accurate local application of the heat flux only where needed; heating homogeneity due to radiation penetration (small thickness); and ease of combination with other heating modes (convection, conduction). Despite such advantages, the design of the combined convective-I.R. drying oven still relies largely on experiments very often obtained with free convection-I.R. heating (no forced flow present) or with a full scale oven. Additionally, no drying models have been tested over the wide range of drying conditions encountered in the combined process. Thus, the objectives of this study were the following: to build a reliable experimental facility to study the high temperature combined convective-I.R. drying process; to evaluate the effect of I.R. heating on the convective heat and mass transfer coefficients; to determine the influence of combined convective andmore » I.R. drying parameters on the critical moisture content of a model material (soda lime glass beads; 90-105 [mu]m diameter range); and to test the applicability of a drying front model for the case of convective as well as combined convective-I.R. drying of a capillary porous medium.« less