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Mass transfer is the net movement of mass from one location (usually meaning stream, phase, fraction, or component) to another. Mass transfer occurs in many processes, such as absorption , evaporation , drying , precipitation , membrane filtration , and distillation .
Mass transfer in a system is governed by Fick's first law: 'Diffusion flux from higher concentration to lower concentration is proportional to the gradient of the concentration of the substance and the diffusivity of the substance in the medium.' Mass transfer can take place due to different driving forces. Some of them are: [12]
A McCabe–Thiele diagram for the distillation of a binary (two-component) feed is constructed using the vapor-liquid equilibrium (VLE) data—which is how vapor is concentrated when in contact with its liquid form—for the component with the lower boiling point. Figure 1: Typical McCabe–Thiele diagram for distillation of a binary feed
In the life sciences, mass flow, also known as mass transfer and bulk flow, is the movement of fluids down a pressure or temperature gradient. [1] As such, mass flow is a subject of study in both fluid dynamics and biology. Examples of mass flow include blood circulation and transport of water in vascular plant tissues. Mass flow is not to be ...
For instance, distillation in a plate column is analyzed by writing down the mass balances for each plate, wherein the known vapor-liquid equilibrium and efficiency, drip out and drip in comprise the total mass flows, with a sub-flow for each component. Combining a stack of these gives the system of equations for the whole column.
Membrane separation processes operate without heating and therefore use less energy than conventional thermal separation processes such as distillation, sublimation or crystallization. The separation process is purely physical and both fractions ( permeate and retentate ) can be obtained as useful products.
Dialysis is the process used to change the matrix of molecules in a sample by differentiating molecules by the classification of size. [6] [7] It relies on diffusion, which is the random, thermal movement of molecules in solution (Brownian motion) that leads to the net movement of molecules from an area of higher concentration to a lower concentration until equilibrium is reached.
Stripping works on the basis of mass transfer. The idea is to make the conditions favorable for the component, A, in the liquid phase to transfer to the vapor phase. This involves a gas–liquid interface that A must cross. The total amount of A that has moved across this boundary can be defined as the flux of A, N A.