The Schmidt number is defined as the ratio of kinematic viscosity to the diffusivity.

The Schmidt number is defined as the ratio of kinematic viscosity to the diffusivity.

• A. The ratio of kinematic viscosity to the diffusivity
• B. The ratio of density to viscosity
• C. The ratio of velocity to viscosity
• D. The ratio of inertial to viscous forces

Answer: (A)

It measures how quickly momentum diffuses compared with how quickly mass diffuses. The Schmidt number is Sc = ν / D, where ν is the kinematic viscosity (ν = μ/ρ) and D is the diffusivity of the species. This dimensionless quantity tells you whether momentum transport or mass transport dominates: a large Sc means momentum diffusion is faster than mass diffusion, while a small Sc means mass diffusion is relatively faster. The statement that the Schmidt number is the ratio of kinematic viscosity to diffusivity is correct. The other ratios described correspond to different concepts (for example, density to viscosity is not a diffusion ratio, velocity to viscosity is not dimensionless, and inertial to viscous forces is the Reynolds number).

It measures how quickly momentum diffuses compared with how quickly mass diffuses. The Schmidt number is Sc = ν / D, where ν is the kinematic viscosity (ν = μ/ρ) and D is the diffusivity of the species. This dimensionless quantity tells you whether momentum transport or mass transport dominates: a large Sc means momentum diffusion is faster than mass diffusion, while a small Sc means mass diffusion is relatively faster. The statement that the Schmidt number is the ratio of kinematic viscosity to diffusivity is correct. The other ratios described correspond to different concepts (for example, density to viscosity is not a diffusion ratio, velocity to viscosity is not dimensionless, and inertial to viscous forces is the Reynolds number).