Massatransfer

Mass transfer, often written as two words or with a hyphen (mass-transfer), is the net movement of mass from regions of higher to lower chemical potential or concentration, driven by gradients in concentration, temperature, pressure, or electrical potential. It encompasses diffusion, convection, and migration, and occurs within and between phases such as gas–liquid, liquid–liquid, or solid–gas interfaces. In engineering and physics, mass transfer is treated as a transport process distinct from chemical reaction and energy transfer. The one-word form Massatransfer is uncommon in scholarly literature.

Molecular diffusion is described by Fick's laws, with the diffusive flux J_A = -D ∇C_A and the time evolution ∂C_A/∂t = D ∇^2 C_A. Convection transports mass by bulk flow, usually characterized by mass transfer coefficients and boundary layers. Migration refers to movement under external fields, such as electric fields or gravity. In multi-phase systems, mass transfer across interfaces is described using interfacial resistances and boundary-layer concepts, e.g., two-film theory, yielding an overall flux that depends on the driving force (concentration difference) and the resistances on each side of the interface.

Key dimensionless groups include the Sherwood number, the Péclet number, and the Schmidt number; these are used to correlate mass transfer coefficients in duct flows, packed beds, and membranes. Mass transfer processes underpin many operations, including distillation, absorption, stripping, drying, crystallization, membrane separations, and environmental remediation, as well as fuel cells and biological transport in tissues.

Experimental and numerical methods—such as experimental determination of mass transfer coefficients, boundary-layer theory, and computational fluid dynamics—are used to analyze and optimize systems involving mass transfer.