A boundary‐layer model of fluid‐particle mass transfer in fixed beds

The process of fluid‐particle mass transfer in fixed beds at Reynolds numbers less than 1,000 is viewed in terms of transient molecular diffusion within a boundary layer which is developed and destroyed repeatedly as the fluid journeys through the bed. Literature data support the j factor derived from the premises of the model. The theory predicts a Schmidt number exponent of 2/3 for N Sc ≧ 1; however this exponent should approach 1/2 for N Sc < 1.