Abstract: An "instantaneous thin layer" model for transnormal mass transfer is brought forward in this paper. In transnormal mass transfer,there is an interface existing in the medium,which divides the object into two parts:the "instantaneous thin layer",which is a thin layer region around the mass disturbance position,and the other part of the object. Mass transfer in the "thin layer" is governed by non-Fick law, while that in the other part still complies with the Fick's law approximatively. Mass transfer on the boundary surface of the "thin layer" region satisfies the continuous boundary conditions (i.e.the fourth kind of boundary conditions). An example of one-dimensional transnormal mass transfer, resulting from a pulsed mass disturbance source,is presented in this paper,too. The hyperbolic non-Fick mass transfer equation,which is similar to the hyperbolic non Fourier heat conduction equation,is used to describe this transnormal mass transfer,and the finite-difference method(FDM) combined with MacCormack's predictor-corrector schems is used to solve it. Ultimately the correlativity of the thickness of the "instantaneous thin layer" to the mass relaxation time, mass diffusivity and the mass disturbing source is obtained.

Key words: non-Fick mass transfer, hyperbolic mass transfer, mass wave, numerical solution, non classical heat or mass transfer