Principles of Unsteady-State and Convective Mass Transfer

Principles of Unsteady-State and Convective Mass Transfer 

In Chapter 6 we considered various mass-transfer systems where the concentration or partial pressure at any point and the diffusion flux were constant with time, hence at steady state. Before steady state can be reached, time must elapse after the mass-transfer process is initiated for the unsteady-state conditions to disappear. 

In Section 2.3 a general property balance for unsteady-state molecular diffusion was made for the properties momentum, heat, and mass. For no generation present, this was 

In Section 5.1 an unsteady-state equation for heat conduction was derived, 

The derivation of the unsteady-state diffusion equation in one direction for mass transfer is similar to that done for heat transfer in obtaining Eq. (5.1-10). We refer to Fig. 7.1-1 where mass is diffusing in the. x direction in a cube composed of a solid, stagnant gas, or stagnant liquid and having dimensions Ax, Ay, and Az. For diffusion in the x direction we write 

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Chap. 7 Principles of Unsteady-State and Convective Mass Transfer... 

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