화학공학소재연구정보센터
KAGAKU KOGAKU RONBUNSHU, Vol.23, No.1, 37-46, 1997
Integral form of diffusion equation and its application to the calculation of concentration dependent diffusion coefficient for desorption (isothermal drying)
The integral form of the diffusion equation for a slab with a constant surface concentration based on the dissolved solid coordinate is derived, which presents the relation between desorption rate and integral average diffusion coefficient by the ratio of the 0 and 1 st moments of concentration distribution. The relation between the 0 and ist moments is quite insensitive to the concentration distribution governed by the diffusion equation with the concentration dependent diffusion coefficients and is satisfactorily estimated by the ratio of average to center concentration at the starting point of the regular regime. From these equations, one desorption curve is quantitatively transformed to the integral average diffusion coefficients as a function of center concentrations. The diffusion coefficient is calculated as a function of concentration by differentiating the integral average diffusion coefficients. As an example, the isothermal drying data of skim-milk aqueous solution are analyzed.