Mass transport across a flowing gas

Transport across tire direction of flow can be determined using Pick s hrst law of diffusion for dre flux of material in particles/cm sec in a steady, time-independent state 

For a gas in laminar flow over a condensed phase sample of length L, the mass transport across the boundary layer, in terms of the flux of molecules from the sample to die gas phase, is therefore 

The mass transport coefficient in tlris example can be related to the properties of the flowing gas by the equation 

The dimensionless numbers in tlris equation are the Reynolds, Schmidt and the Sherwood number, A/ sh. which is defined by this equation. Dy/g is the diffusion coefficient of the metal-transporting vapour species in the flowing gas. The Reynolds and Schmidt numbers are defined by tire equations 

The advantage of the use of dimensionless numbers in calculations such as these is that they may be applied independent of the physical size of the system being described. 

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