VACUUM DRYING is a process in which drying is carried out at reduced pressures and lower relative humidity compared to ambient pressure, enabling faster drying which lowers the heat required for rapid drying. This is the mass transfer operation in which the moisture present in a substance, usually a wet solid, is removed by means of creating a vacuum.
Vacuum drying is based on the principle of creating a vacuum to decrease the chamber pressure below the vapor pressure of the water, causing it to boil. With the help of vacuum pumps, the pressure is reduced around the substance to be dried. This decreases the boiling point of water inside that product and thereby increases the rate of evaporation significantly. The result is a significantly increased drying rate of the product. As reduced pressure is maintained in vacuum drying system, the boiling point of water is 25-30 °C.
Vacuum Drying Consists of 3 Phases: Evacuation, Evaporation & Final Drying.