2. INTRODUCTION…
Process in which a liquid changes to the gaseous state at
the free surface, below the boiling point through the
transfer of heat energy.
Net loss of water from a liquid surface that results from a
phase change from a liquid to a vapour.
4. Practical definition…
Removal of solvent from the solution by boiling the liquor
in suitable vessel and withdrawing the vapour, leaving a
concentrated liquid residue in the vessel.
5. Relationship can be expesssed by
S = surface urea of the liquid exposed, m
p = atmospheric pressure. kPa
b = maximum vapour pressure at the temperature of air,kPa
b’ = pressure due to the vapour of the liquid, actually present in
the air. kPa
K = constant, m/s
8. 1. TEMPERATURE
higher the temperature greater the value of b
greater will be the evaporation.
9. VAPOUR PRESSURE
Directly proportional
Lower the p value, the greater the evaporation.
Lower the external pressure, the lower the boiling
point of the liquid greater will be the
evaporation.
11. MOISTURE CONTENT OF THE-FEED
Some drug constituents undergo hydrolysis readily in
presence of moister at high temperatures.
To prevent decomposition, the materialis exposed to
lower temperature initially, then exposed to higher
temperature for final concentration.
Prepration of dry extract of belladonna.
12. TIME OF EVAPORATION
Time of exposure is longer, greater will be the
evaporation.
Provided the constituents are thermostable
Film evaporators are used.
13. FILM AND DEPOSITS
Vegetable extracts are concentrated in steam pan, film
may be formed.
Film reduce evaporating surface.
Stirring is necessary.
14. Type of evaporators
1. Evaporaters with heating medium in jacket.
Steam jacketed kettle (evaporating pan)
2. Vapour heated evaporaters with tubular heating
surfaces.
15. Vapour heated
evaporaters with
tubular heating
surfaces
Evaporators with
tubes placed vertically
short tubes
long tubes
Evaporators with
tubes placed
horizondally
Horizontal tube
evaporator
17. USES
Suitable for concentrating aqueous and thermostable liquors,
eg: Liquorice extract.
ADVANTAGES
Constructed both for small scale and large scale operations.
Simple in construction and easy to operate, clean and maintain.
Low cost and maintenance.
Wide variety of materials can be used for construction such as
copper, stainless steel and aluminium.
Stirring of the contents and removal of the product is easy
18. DISADVANTAGES
Heat economy is less, hence cost per material production is more.
Not suitable for heat sensitive materials due to long time of
exposure.
The heating area decreases as the product gets more concentrated.
Boling point of the water cannot be reduced, since reduced pressure
cannot be created in open type evaporater.
22. USES
Manufacture of cascara extract, sugar, salt, caustic soda.
ADVANTAGES
Tubes increase the heating surface nearly 10 to 15 times
when compared to steam jacketed kettle.
Vigorous circulation enhances the rate of heat transfer.
A number of units can be joined to obtain more efficient
effect.
25. USES
Concentration of insulin, liver extracts and vitamins.
ADVANTAGES
Large area for heat transfer is provided employing long
and narrow tubes.
Time of contact between the liquor and the heating surface
is very short.
Tubes are not submerged.
Low hold up and small floor space.
26. DISADVANTAGES
If feed rate is high, the liquor may be concentrated
insuffciently.
Expensive
Large head space is required.
29. ADVANTAGES
Suitable for high viscous liquids
Liquid hold up is less and hold-up time is very small.
Highly acidic and corrosive feeds can be concentratred.
32. USES
Concentration of insulin and liver extracts.
Thermolabile subtances.
ADVANTAGES
Heat transfer coefficient is high due to rapid liquid
movement.
Suitable for high viscous preparations
