The diffusive mass transfer coefficient and the convective mass transfer coefficient are terms used in the field of mass transfer to describe different mechanisms of mass transfer.
Diffusive Mass Transfer Coefficient: This coefficient, often denoted as "k" or "D," quantifies the rate at which mass is transported through diffusion across a concentration gradient. Diffusion occurs due to the random movement of molecules, and the diffusive mass transfer coefficient represents the efficiency of this molecular diffusion process. It is influenced by factors such as the diffusivity of the species being transferred, the concentration gradient, and the properties of the medium in which diffusion takes place (e.g., temperature, viscosity).
Convective Mass Transfer Coefficient: This coefficient, often denoted as "h," represents the rate at which mass is transferred by convection, which involves the bulk movement of a fluid. Convection occurs when there is a fluid flow or mixing that carries the species of interest. The convective mass transfer coefficient accounts for the combined effects of fluid flow and molecular diffusion in the transfer process. It depends on various factors, including the flow velocity, fluid properties (e.g., density, viscosity), and the geometry of the system.
In summary, the diffusive mass transfer coefficient describes the rate of mass transfer through diffusion alone, while the convective mass transfer coefficient considers the contribution of both convection and diffusion to the overall mass transfer rate.