The presentation focuses on applications of drying, bound water, unbound water, Theory of drying, EMC, CMC, drying rate curve. It also includes the construction and working of dryers like tray dryer, drum dryer, fluidized bed dryer, vacuum dryer, freeze dryer etc.

1. DRYING
Mr. A. T. Sharma
Assist. Professor
Nanded Pharmacy College, Nanded

2. Drying
Definition: The removal of small amounts of
water or other liquid from a material by the
application of heat.
Applications:
o Preparation of bulk drugs
o Preservation of drug products
o Improved characteristics
o Improved handling

3. Theory of Drying
Water in a wet solid mass -
• Bound water: Minimum water held by the
material that exerts an equilibrium vapour
pressure less than the pure water at the same
temperature.
• Unbound water: The amount of water held by
the material that exerts an equilibrium vapour
pressure equal to that of pure water at the
same temperature.

5. Theory can be studied in two heads -
• Equilibrium relationships
• Rate relationships
Equilibrium Relationships
• Equilibrium Moisture Content
• The amount of water present in the solid which
exerts a vapour pressure equal to the vapour
pressure of the atmosphere surrounding it.
• Sorption and Desorption

7. • Measurement of EMC
• Applications of EMC
- Selection of experimental conditions to be
used for drying
- Drying should be stopped when moisture
content reaches to EMC
- Over drying can be avoided
• Factors affecting EMC
- Nature of material
- Nature of air

8. Free Moisture Content (FMC): The amount of
water that is free (easy) to evaporate from the
solid surface.
Free moisture content (FMC) = Total water
content – Equilibrium Moisture Content (EMC)

9. Rate Relationships
• A simple model which mimics the condition of a dryer.
• A wet slab of material with sufficient moisture content
placed in tray for drying
• Bottom and sides insulated
• Air of constant velocity, temperature, humidity and
pressure blown
• Superficial water diffuses through surrounding air and
carried away with air stream
• Periodically the slab is weighed
• The difference between in the weights of two successive
periods gives loss of moisture content, i.e. amount dried

10. Following calculations are done -
• Graph plotted as FMC on X-axis and drying rate
on Y-axis.
• Curve is called as Drying Rate Curve.
• Represents changes during drying

12. Tray Dryer
Principle:
• Hot air continuously circulated
• Forced convection heating
Construction:
• A rectangular chamber
• No. of trays placed one above the other
• A fan
• Electric heaters
• Trucks on wheels

14. Drum Dryer/Roller Dryer/Film Drum Dryer
Principle:
• A heated hollow metal drum rotates
• Dipped in solution
• A solution film on drum surface, dried to a layer
• Knife scrapping
Construction:
• A horizontally mounted hollow steel drum
• A feed pan
• A spreader
• A Doctor’s knife

15. Drum Dryer/Roller Dryer

16. Spray Dryer
Principle:
• Fluid atomized into fine droplets – thrown
radially into a moving stream of hot gas
• Temp. of droplets increased – fine droplets
dried as spherical droplets
• Process takes place within seconds before
droplets reach wall of dryer

18. Working:
• Atomization of
the liquid
-Pneumatic
-Pressure
nozzle
- Spinning disc
• Drying of the
liquid droplets
• Recovery of the
dried product

19. Fluidised Bed Dryer
Principle:
• Hot air (gas) at high pressure passed through
perforated bottom of a container containing
granules
• Granules lifted and suspended (Fluidisation)
• Hot gas surrounds individual granule and dries
it

20. Construction

21. Vacuum Dryer

22. Freeze Dryer

24. (Disclaimer: The images and diagrams in this presentation
have been downloaded from the google source. I am grateful
to all the publishers & the google.)
Thank You…!!!