Drying – Pharmaceutical Engineering B. Pharm Third Semester PDF Notes


Contents of
this session

• Introduction to drying   

• Theory of drying

• Mechanism of drying process

• Rate of drying curve   

• Factors affecting drying

• Classification of dryers

• Tray dryer and Vacuum dryer

• Fluidized bed dryer

• Drum dryer

• Spray dryer

• Freeze dryer


At the end of this lecture student will be able to:

• Outline the industrial applications of drying

• Explain the differences between evaporation and drying

• Describe the stages of rate of drying

• Explain the process of drying

• Explain the stages of drying process

• Enlist types of dryers

• Discuss the construction and working process of tray dryer
and vacuum dryer

• Discuss the construction and working process of fluidized
bed dryer

• Explain the process operation of drum dryer

• Discuss the construction and working process of spray

• Explain the process operation of freeze dryer


• Drying is the process of complete removal of solvent from
the substance and the end product is a solid

• Thermal and non-thermal are the two methods of drying
process Mass and heat trasfer are the two process of drying

• Wet solid mass contains both bound and unbound water

• Equilibrium moisture content is the amount of water
present in the solid which exerts vapor pressure equal to atmosphere
surrounding it

• Rate of drying curve is obtained by plotting free moisture
content versus drying rate

• Different stages of drying include initial adjustment
period, constant rate period, first falling rate period and second falling rate

• Tray dryer is used for localized drying of substances

• Vacuum dryer is used for drying heat sensitive substances

• Fluidized bed dryer is used for generalized drying process

• Bag filters used in the F.B.D. prevents the escape of
finer particles from the equipment during drying process

• Drum dryers are used for drying solutions, slurries and

• Spray dryer utilizes generalized drying process

• It can be used for coating of polymer over the granules –
Spansule technology

• Freeze dryer utilizes triple point as the drying

• It can be used in the preparation of vaccines and blood

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