Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be considered "dried", the final product must be solid, in the form of a continuous sheet (e.g., paper), long pieces (e.g., wood), particles (e.g., cereal grains or corn flakes) or powder (e.g., sand, salt, washing powder, milk powder). A source of heat and an agent to remove the vapor produced by the process are often involved.mass transfersolventevaporationsolidsemi-solidliquidheat Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be considered "dried", the final product must be solid, in the form of a continuous sheet (e.g., paper), long pieces (e.g., wood), particles (e.g., cereal grains or corn flakes) or powder (e.g., sand, salt, washing powder, milk powder). A source of heat and an agent to remove the vapor produced by the process are often involved.mass transfersolventevaporationsolidsemi-solidliquidheat

To understand it …. We have to know some terminology…..

This can be discuss in two heading: 1. Equilibrium relationships 2. Rate relationships

Air of const. temp. and humidity  equilibrium reached  vapor pres. Of solid equal to surrounding atmosphere  No change in moisture content of solid.

Drying rate is plotted against the time or against FMC. If drying rate in Y axis and FMC in X axis than the curve is known as drying rate curve…. To study it we have to know some mathematical terminology and formula……

Loss of weight of Sample after drying LOD= X 100 % Total weight of wet sample

TypesExampleAdvantagesDisadvantages Static bedTray dryer Moving bedDrum dryer Fluidised bedFBD Pneumatic dryerSpray dryer

Advantages and Disadvantages of TRAY Dryer

DIELECTRIC OR MICROWAVE DRYING : DIELECTRIC OR MICROWAVE DRYING It is the method of drying in which electromagnetic radiation (radio frequency from MHz or microwave frequency at 915 or 2450 MHz) is applied to material dried. If polar solvent molecules are present, the electromagnetic field induce orientation of the dipoles in molecules

DIELECTRIC OR MICROWAVE DRYING : ( continue) Theory: The rate of heating is proportional to the dielectric constant of materials placed in the field. Water has dielectric constant 80 and the granule around 10, then water will be heated more rapidly than other components in granule.

 Pharmaceutical Engineering: Principle and Practices by C.V.S. Subrahmanyam; J. Thimma Setty; Sarasija Suresh; V. Kusum Devi.