| Abstract: | A theoretical model for drying of a thin gel film is presented. The model is based upon the premise that as solvent is removed from any portion of a gel structure which is permeable by the solvent, the structure shrinks locally to fill the voids left by the solvent. The diffusion coefficient of solvent through the gel film is assumed to be an exponential function of concentration and temperature. The governing equations for the model indicate that for nonisothermal drying, the results of drying and shrinkage rates are functions of 13 independent dimensionless system variables. These results are obtained with the help of a computer solution of the proposed model. The computer results indicate that, except under extreme temperature conditions, the drying and shrinkage rates are most influenced by dimensionless groups M, P, and P?, defined by eq. (9) of the paper. Furthermore, the drying and shrinkage rates are essentially independent of groups M and P for the values of M and P greater than approximately 100 and 10, respectively. The effect of variable solvent diffusivity on approximate time to achieve the steady-state drying and shrinkage rates is approximately handled by defining a dimensionless time variable τ in terms of average solvent diffusivity. Finally, some experimental data on drying and shrinkage rates of isothermal drying of lyphogel film under natural convection condition are obtained. These data are found to be in qualitative agreement with similar computer predictions by the proposed model. |
