This document discusses various aspects of drying, including definitions, principles, measurement techniques, and classifications. Drying involves the removal of water or liquid from a solid-liquid mixture to form a dry solid, and differs from evaporation which concentrates solutions. Drying is important for preservation, size reduction, improving product properties, and reducing costs. Drying rates can be constant, falling, or in multiple falling periods. Moisture distributes unevenly in materials in different states. Dryers are classified based on solid handling methods (static, moving, fluidized), heat transfer methods (convection, conduction, etc.), and operating principles. Common dryer types include shelf, tunnel, rotary, fluidized bed, vacuum

1. DRYING
Dr. Ibtihal O. Alkarim

2. Definition
Dr. Ibtihal O. Alkarim
 Vaporization and removal of water and/or other
liquid from a solution, suspension or other
solid-liquid mixture to form a dry solid.

3. DON’T CONFUSED DRYING WITH
EVAPORIZATION
 EVAPORIZATION is
more often applied to
the concentration of
solution.
 But drying associated
with the removal of
relatively small
quantities of liquid to
give a dry product. Dr. Ibtihal O. Alkarim

4. IMPORTANCE
Dr. Ibtihal O. Alkarim
1. Preservation
2. Preliminary to size reduction
3. Improve Properties of final product
4. eliminate moisture which may lead to corrosion and
decrease the product or drug stability.
5. good properties of a material, e.g. flow-ability,
compressibility.
6. reduce the cost of transportation of large volume materials
(liquids)
7. material easy or more suitable for handling.

5. Theory of Drying
Dr. Ibtihal O. Alkarim
HEAT
TRANSFER
MASS
TRANSFER
DRYING

6. Dr. Ibtihal O. Alkarim
 Rate of evaporization dw/dϕ = q/λ
 Rate of diffusion dw/dϕ = KA(Hs-Hg)
 dw/dϕ = q/λ= KA(Hs-Hg)
 dw/dϕ = (qc+qr+qk)/λ= KA(Hs-Hg)

7. GENERAL PRINCIPLES
Dr. Ibtihal O. Alkarim
Genera
l terms
Saturated
humidity
Absolute
humidity
Relative
humidity
Dew point
Moisture
content

8. GENERAL PRINCIPLES
Dr. Ibtihal O. Alkarim
 ABSOLUTE HUMIDITY: weight of water vapor per
unit weight of dry air.
 SATURATION HUMIDITY: is the absolute
humidity at which the partial pressure of water
vapor in the air is equal to the vapor pressure of
free water at the same temperature.
 RELATIVE HUMIDITY: expresses the degree of
saturation

9. PRINCIPLES…
Dr. Ibtihal O. Alkarim
 MOISTURE CONTENT: usually determined by
measuring the los of weight of a sample when
heated in an oven
 DEW POINT: is temperature to which a given
mixture of air and water vapor must be cooled
to became saturated.

10. HUMIDITY MEASUREMENT
Dr. Ibtihal O. Alkarim
Gravimetric
method
Sling
pyschrometer
Dew point
Electric
hygrometer
Mechanical
hygrometer

11. GRAVIMETRIC METHOD
 Moisture absorbing
material such as
Phosphorus
Pentoxide
 Known amount of air
Dr. Ibtihal O. Alkarim

12. SLING PYSCHROMETER
Dr. Ibtihal O. Alkarim

13. Dr. Ibtihal O. Alkarim

14. DEW POINT
 Temperature at
which moisture
begins to form on a
polished surface in
contact with air.
Dr. Ibtihal O. Alkarim

15. MECHANICAL HYGROMETER
 Moisture-sensitive
element
Dr. Ibtihal O. Alkarim

16. ELECTRICAL HYGROMETER
 measurement
resistance in
moisture-absorbing
material.
Dr. Ibtihal O. Alkarim

17. Equilibrium moisture content
(E.M.C)
 Exposure to air at a
definite temperature
and humidity will
cause a material to
lose or gain moisture
until an E.M.C is
attained.
 Starch /Talc
 OVERDRYING!!!!! Dr. Ibtihal O. Alkarim

18. RATE OF DRYING
Dr. Ibtihal O. Alkarim

19. Dr. Ibtihal O. Alkarim
 A-B initial adjustment
 B-C constant rate period
 C-D first falling rate period
 D-E second falling rate period

20. DISRIBUTION OF MOISTURE
Dr. Ibtihal O. Alkarim

21. DISRIBUTION OF MOISTURE
Dr. Ibtihal O. Alkarim
1- Capillary state
Removal of water at one surface causes a
general flow through the bed.

22. DISRIBUTION OF MOISTURE….
Dr. Ibtihal O. Alkarim
2- Funicular state
Movement of water still possible BUT restricted
by friction
 Film around the particle is lost.
 In LENS-LIKE RING

23. DISRIBUTION OF MOISTURE…
Dr. Ibtihal O. Alkarim
3- Pendular state
Air movement is possible.
Migration of water only take place by
evaporation

24. CLASSIFICATION OF DRYERS
Dr. Ibtihal O. Alkarim

25. Nature of material
Absence or presence of agitation
BASED ON THE METHOD OF SOLID
HANDELING
Dr. Ibtihal O. Alkarim

26. Dr. Ibtihal O. Alkarim
STATIC MOVING FLUID PNEUMATIC

27. Static bed dryer
Dr. Ibtihal O. Alkarim
 No movement
 Only fraction exposed directly
 thichness

28. Moving bed dryer
Dr. Ibtihal O. Alkarim
 Gravity or mechanical agitation
 More rapid mass and heat transfer

29. Fluid bed dryer
Dr. Ibtihal O. Alkarim
 Suspended in upward moving gas stream

30. Pneumatic bed dryer
Dr. Ibtihal O. Alkarim
 Entrain and conveyed in high velocity gas
stream
 Very rapid mass and heat transfer
 Shortening drying time

31. Dr. Ibtihal O. Alkarim

32. Demonstrate major differences in dryer
design, operation, and energy
requirement
BASED ON METHOD OF HEAT
TRANSFER
Dr. Ibtihal O. Alkarim

33. Dr. Ibtihal O. Alkarim
CONVENCTION
COMPARTMENTAL
TUNNEL
ROTARY
FLUIDIZED
CONDUCTION
VACUUM
FREEZ

34. Shelf dryer
 Arrays
 Air gaps
 Heater and fan
 Very common
 versatility
Dr. Ibtihal O. Alkarim

35. Tunnel dryer
 Same as shelf dryer
but in a tunnel
shape
Dr. Ibtihal O. Alkarim

36. Tunnel dryer
Dr. Ibtihal O. Alkarim

37. Rotary dryer
 Individual drying
 Large scale
 Continuous drying
 Air rate,
temperature, mean
time
Dr. Ibtihal O. Alkarim

38. Dr. Ibtihal O. Alkarim

39. Fluid-bed dryer
Dr. Ibtihal O. Alkarim

40. Fluid-bed dryer
 Advantages:
1. Efficient heat and
mass transfer
2. Individual drying
3. Uniform drying
4. Produce free flowing
product
5. Short drying time
 Disadvantages:
1. May cause attrition
2. Loss of fine
3. Generation of
charges
Dr. Ibtihal O. Alkarim

41. Vacuum dryer
 Stout construction
 Work under
pressure 0.3-0.06
bar at which water
boils at 25-35C.
 Unstable material.
Dr. Ibtihal O. Alkarim

42. Dr. Ibtihal O. Alkarim

43. Freeze dryer
Dr. Ibtihal O. Alkarim