The combination of external mass transfer and internal diffusion

5 The Combination of External Mass Transfer and Internal DifFusion 

We have seen in Sec, 6.3 that the rate of transport of A to the outside surface of a pellet can be expressed as kc(a — a,). If A diffuses into the pellet at the same rate, the appropriate boundary condition for the diffusion and reaction equation will be 

using the flat plate geometry we have the same Eq. (6.4.16) with dajdx = 0 at X = 0 and the boundary condition Eq. (6.5,1) at x = . Once more we have the solution Eq. (6.4.4) and M = 0 by the condition at the center. Thus 

It must be remembered that fl with no suffix denotes the concentration of A in the free stream. If there were no resistance to mass transfer of any 

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