Analysis of diffusion equation based on steady state assumption：Ⅰ.the process of steady state approximation

The Fick diffusion equation is widely used to describe mass transfer in a particlea droplet or a liquid layer in a chemical reactorwhere the definition domain of the diffusive equation is limitedbecause it is decided by the scale of those particles or droplets.The diffusive equation with a definition domain of certain length has no analytic solutions unless the series solution.Soto obtain approximate solutions of a diffusive equation is of theoretical and practical significance.After an assumption of constant concentration variance ratio is made and substituted for the presumption of constant concentration frequently used in kinetics of multi-phase reactiona detail process to deal with diffusion equation based on steady state approximation is givenand the approximate solutions of the diffusive equation with the second boundary condition and the third boundary condition are obtained in the meantime.The method to deal with diffusion equation by steady state approximation may be applied to many fields in engineering.