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What is Mass transfer ?
When a concentration gradient exists within a fluid consisting of two or more components, each component tends to migrate in such a direction as to reduce the concentration gradient. This process is known as mass transfer. Mass transfer operations depend on molecules diffusing or vaporizing from one distinct phase to another and are based upon difference in the physico-chemical properties of the molecules, such as vapour pressure or solubility.
1. what is Absorption : A gas mixture is absorbed by a liquid in which the solute is more or less soluble. The gas mixture consists mainly of an inert gas and the solute. The liquid is essentially immiscible in the gas phase. When a solute is transferred from the solvent liquid to the gas phase, the operation is known as desorption or stripping.
2. what is Adsorption?: Adsorption involves the transfer of mass from either a gas or a liquid to the surface of a solid. The fluid adheres to the solid surface instead of dissolving in the solid in the usual sense.
3. what is Extraction?: Extraction refers to an operation in which one or more components of a liquid or a solid phase are transferred to another liquid phase. Extraction utilizes the differences in the solubilities of the components. In liquid-liquid extraction or solvent extraction, a solute in a liquid solution is removed by contacting with another liquid solvent which is relatively immiscible with the solution. The liquid which is added to the solution to bring about the extraction is known as the solvent.
4. what is Distillation?: Distillation is an operation whereby the components of a liquid mixture containing miscible and volatile substance are separated by partial vaporization by virtue o of differences in vapour pressure. The concentration of the more volatile constituents of the liquid mixture is higher in the vapour than in the feed solution, While that of the less volatile components is higher in the liquid. Two principal method are used in distillation.
a. A vapour is produced by boiling the liquid mixture to be separated and all the vapour is either removed as such, or condensed as product.
b. A part of the vapour produced by boiling in the distillation still is condensed and returned as liquid to the still so as to be bright into intimate contact with the vapour on its way to the condenser. The part of the vapour returned as liquid to the still is known as reflux, and the operation is called rectification.
5. what is Humidification?: In humidification the vapour content in a gas stream can be increased by passing the gas over a liquid which then evaporates into the gas stream. In dehumidification, the vapour content in a gas stream can be reduced by condensation on a cold surface. Dehumidication involves the transfer of water vapour from the gas phase to the liquid phase.
6. what is Drying?: Drying, in General, means the removal of relatively small a mounts of water or other liquid from a solid or nearly solid material. Evaporation refers to the removal of relatively large amounts of the water from solutions.
7. what is Crystallization?: Crystallization is a process whereby solid particles are formed from a liquid solution. The solution is concentrated and usually cooled until the solute concentration become higher than its solubility at that temperature.
8. what is Membrane Separation?: This process involves the diffusion of a solute from a liquid or gas through a semi-permeable membrane to another fluid.
9. what is Foam Separation?: This is a process whereby surface-active compounds in a solution can be selectively concentrated and separated by accumulation at the interface between the liquid and gas. Depending on the type of substances to be separated, this process can be divided into two categories: foam fractionation and froth flotation
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