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
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.
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
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
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
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
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