The Sherwood Number is defined as what?

• A. Ratio of diffusive mass transport to convective mass transport
• B. Ratio of viscous forces to inertial forces
• C. Ratio of thermal diffusivity to mass diffusivity
• D. Ratio of convective mass transport to diffusive mass transport

Answer: (D)

The Sherwood number tells you how strong convection is compared with diffusion for moving a species between a surface and the surrounding fluid. It quantifies the actual mass transfer rate by convection relative to what would happen if diffusion alone did the job. The standard definition is Sh = kL / D_AB, where k is the overall mass-transfer coefficient, L is a characteristic length, and D_AB is the diffusivity of species A in B. Put simply, it’s the ratio of the convective transport rate (kL) to the diffusive transport rate (D_AB). When the flow carries a lot of material with it, convection dominates and Sh becomes much greater than 1; when diffusion dominates, Sh approaches 1. This concept is analogous to the Nusselt number in heat transfer, showing how much convection enhances mass transfer beyond pure diffusion.