Govt. Exams
Entrance Exams
Sherwood number Sh = k_c·L/D_AB represents the ratio of convective mass transfer to diffusive mass transfer, analogous to Nusselt number in heat transfer.
Schmidt number Sc = ν/D_AB = (μ/ρ)/D_AB, representing the ratio of kinematic viscosity to mass diffusivity, analogous to Prandtl number in heat transfer.
In equimolar counter-diffusion, the molar fluxes of the two components are equal in magnitude but opposite in direction, hence N_A = -N_B.
The distribution coefficient K_D = C_solvent/C_aqueous at equilibrium, determining the driving force for extraction and the selectivity of the separation process.
For a spherical particle in creeping flow with negligible convection, the Sherwood number approaches the purely diffusive limit of Sh = 2, independent of Reynolds and Schmidt numbers.
Schmidt number Sc = ν/D_AB where ν is kinematic viscosity and D_AB is mass diffusivity. It represents the relative importance of momentum and mass transport.
The mass transfer coefficient k_c is defined as molar flux per unit concentration difference, having dimensions of velocity (Length/Time), commonly expressed in cm/s or m/s.
Mass transfer coefficient (k) has dimensions of velocity: m/s. It represents the driving force (concentration difference) per unit area per unit time.
Fick's second law: ∂C/∂t = D(∂²C/∂x²), where ∂C/∂t represents the temporal change in concentration.
Diffusion is the movement of species due to concentration gradient (molecular level), while convection is the bulk movement of fluid carrying dissolved or suspended species.
