Which dimensionless number is used to describe convective mass transfer relative to diffusion in mass transfer analysis?

Which dimensionless number is used to describe convective mass transfer relative to diffusion in mass transfer analysis?

• A. Sherwood Number
• B. Reynolds Number
• C. Prandtl Number
• D. Nusselt Number

Answer: (A)

This is about quantifying how much convection enhances mass transfer compared to diffusion using a dimensionless group. The Sherwood number does exactly that: it compares the convective mass transfer rate to the rate that would occur by diffusion alone across a boundary layer, often defined as Sh = k_m L / D_AB or Sh = h_m L / D_AB, with L a characteristic length and D_AB the diffusion coefficient. A larger Sherwood number means convection is substantially boosting mass transfer beyond diffusion, while a value near 1 indicates diffusion-dominated transfer. The other numbers describe different transport phenomena: Reynolds is inertia versus viscous forces in flow, Prandtl is momentum diffusivity versus thermal diffusivity, and Nusselt is convective heat transfer versus conductive heat transfer. So the Sherwood number is the appropriate descriptor for convective mass transfer relative to diffusion.

This is about quantifying how much convection enhances mass transfer compared to diffusion using a dimensionless group. The Sherwood number does exactly that: it compares the convective mass transfer rate to the rate that would occur by diffusion alone across a boundary layer, often defined as Sh = k_m L / D_AB or Sh = h_m L / D_AB, with L a characteristic length and D_AB the diffusion coefficient. A larger Sherwood number means convection is substantially boosting mass transfer beyond diffusion, while a value near 1 indicates diffusion-dominated transfer. The other numbers describe different transport phenomena: Reynolds is inertia versus viscous forces in flow, Prandtl is momentum diffusivity versus thermal diffusivity, and Nusselt is convective heat transfer versus conductive heat transfer. So the Sherwood number is the appropriate descriptor for convective mass transfer relative to diffusion.