Mass transfer

Mass transfer is the movement of chemical species between locations or phases, driven by differences in chemical potential and shaped by diffusion, fluid motion, and interfacial resistance.

Fick's laws of diffusion: Equations relating diffusive flux to concentration gradients and their change over time. They quantify molecular transport when concentration gradients drive species through a medium.
Chemical potential: A thermodynamic quantity that measures how a system's free energy changes when a component is added. Differences in chemical potential provide the general thermodynamic driving force for species movement.
Absorption (chemistry): Transfer of a component from a gas mixture into a liquid phase. Gas absorption relies on transport across a gas–liquid interface and into the liquid.
Heat transfer: The movement of thermal energy through conduction, convection, or radiation. It shares transport mathematics with species movement but transports energy rather than chemical components.
Advection: Transport of a substance by the bulk motion of a fluid. Bulk flow carries species alongside molecular diffusion in moving fluids.
Concentration gradient: The spatial rate and direction of change in a substance's concentration. It is the common approximation for the driving force in diffusion models.
Distillation: A separation process that uses vaporization and condensation to enrich components according to volatility. Vapor–liquid mass transfer helps determine separation efficiency and required equipment.
Momentum transfer: The transport of momentum within or between fluid regions, associated with fluid motion and stress. It is another transport process, but its transported quantity is momentum rather than species.
Mass-transfer coefficient: A parameter relating a species flux to a driving-force difference across a defined region or interface. It packages complex flow and diffusion effects into a usable rate relation.
Conservation of mass: The physical principle that mass is neither created nor destroyed in ordinary chemical and physical processes. Species balances account for accumulation, transport, generation, and consumption.

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