The Sherwood number is the dimensionless quantity that represents the ratio of which two types of mass transfer?

• A. Convective mass transfer to diffusive mass transfer
• B. Heat transfer to mass transfer
• C. Diffusive flux to convective flux
• D. Mass transfer coefficient to area

Answer: (A)

The Sherwood number measures how effective convection is compared to diffusion in moving a species through a boundary layer. It is defined as Sh = k_L L / D_AB, where k_L is the convective mass transfer coefficient, L a characteristic length, and D_AB the diffusivity of A in B. This ratio directly compares the convective flux to the diffusive flux across the same interface: a larger Sh means convection dominates, while a smaller Sh means diffusion plays a bigger role. It’s the mass-transfer analogue of the Nusselt number for heat transfer. So the dimensionless quantity represents the ratio of convective mass transfer to diffusive mass transfer.