Vacuum drying

Vacuum drying is the mass transfer operation in which the moisture present in a substance usually wet solid is removed by means of creating vacuum. In chemical process industries like food, pharmaceutical, agricultural, textile, paper & pulp etc. drying is an essential unit operation to remove the moisture from various substances to get a solid finished product .Vacuum drying is generally used for the drying of those substances which are hygroscopic and heat sensitive and is based on the principle of creating vacuum. With the help of vacuum the pressure is reduced around the substance to be dried and boiling point of water inside that product decreases and rate of evaporation of water increases significantly thus increasing drying rate. The pressure maintained in vacuum drying is generally 0.0296 –0.059 atm and the boiling point of water is 25-30 ◦C .The vacuum drying is a batch operation and at reduced pressures the relative humidity is also lower and that is why the drying occurs faster.