2026 Volume 52 Issue 4 Pages 73-76
Non-steady state diffusion process is separated as the former part called penetration period (PP) and the latter one called regular regime (RR). In the case of the constant diffusion coefficient assuming a parabolic equation on the concentration profile, linear driving-force approximation (LDF model) gives a simple relation between mean concentration and its changing rate with time during the non-steady state process. The LDF model gives an equation similar to the solution during RR, and it is not suitable for PP. In this study, an approximate solution for the short time solution during PP was proposed and an extended LDF model that is available for the whole range of the non-steady state process was introduced by a combination of the approximate solution and the solution during RR. In addition a useful correlation equation was proposed. Numerical simulations were performed about a sorption process in a paper using the LDF model, the extended one and the correlation equation, and the result of the simulations were compared together.
