Objectives Applications and factors influencing evaporation Differences between evaporation and other heat process Principles, construction ,working, uses, merits and demerits of : -Steam jacketed kettle -Horizontal tube evaporator -Climbing film evaporator -Forced circulation evaporator -Multiple effect evaporator -Economy of multiple effect evaporator

1. EVAPORATION
By
Yogeshwary Bhongade
M.Pharm
Assistant Professor
Gondia college of Pharmacy, Gondia

2. Objectives
Applications and factors influencing evaporation
Differences between evaporation and other heat
process
Principles, construction ,working, uses, merits and
demerits of :
-Steam jacketed kettle
-Horizontal tube evaporator
-Climbing film evaporator
-Forced circulation evaporator
-Multiple effect evaporator
-Economy of multiple effect evaporator
CONTENTS

3. Evaporation means simply vaporization from the
surface of a liquid.
Vaporization of a liquid below its boiling point is
called evaporation.
Thus, no boiling occurs and the rate of
vaporization depends on the diffusion of vapour
through the boundary layers above the liquid.
Evaporation is the opposite of condensation.
INTROUCTION

4. The removal of liquid from a solution by boiling
the solution in a suitable vessel and withdrawing
the vapour, leaving a concentrated liquid residue.
or
Evaporation is the process by which molecules
undergo the a spontaneous transition from the
liquid phase to the gas phase.
DEFINITION

5. When heat applied in solution the motion of
molecules increase and molecules present in the
surface overcome the surface tension of the liquid
and it evaporates because surface molecules have less
cohesive force than others.
MECHANISM

6. There are seven factors to affect evaporation.
1. Temperature
2. Temperature & Time of Evaporation
3. Temperature & Moisture content
4. Type of product required
5. Effect of concentration
6. Surface area
7. Vapour pressure of liquid to be evaporated
Factors affecting the Evaporation

7. Temperature
Rate of evaporation is directly proportional to the
temperature of liquid.
Evaporation can be accelerated by increasing
temperature but can cause decomposition of the
heat sensitive drugs.
Eg. Glycosides & Alkaloids are decomposed at
temperature below 100 oC
Harmones, Vitamins, Enzyme and Antibiotics
being more heat- sensitive need special treatment
to avoid decomposition
eg.Malt extract is concentrated by evaporation
under their reduced pressure to avoid loss of

8. Exposure to a relatively high temperature for a
short period of time may be less harmful to
active principles of drug than a lower
temperature with a exposure of longer period.
On the basis of this fact liquid is exposed to high
temperature for short period of time in film
evaporation.
Temperature & Time of Evaporation

9. In presence of moisture some drug constituents
decompose readily if hated at high temperature.
this is due to hydrolysis of active constituents.
Temperature & Moisture content

10. On evaporation of the liquid, the concentrated
liquids, semisolid or solid are formed.
Selection of method and equipment's depends on
types of product required.
Type of product required

11. During evaporation the upper layer of liquid
under evaporation has tendency to form film and
formation of precipitate in the product which
result into lowering down of the rate of
evaporation.
Efficient stirring is required in order to prevent
degradation of the product at the bottom due to
excessive heat and it will also prevent deposition of
solids.
Effect of concentration

12. Rate of evaporation is directly proportional to the
surface area of evaporator in which the liquid is
evaporated.
Larger the surface area of the evaporator, shorter
is the time required for the evaporation.
Surface area

13. Rate of vapour pressure is directly proportional to
the vapour pressure of the evaporating liquid.
The liquid has maximum vapour pressure at it's
boiling point.
As such the rate of evaporation can be increased
by rising the temperature of the evaporating
liquid.
The rate of evaporation of liquid is the maximum
at its boiling point.
Vapour pressure of liquid to be evaporated

14. The equipment used in the process of evaporation
are called evaporators.
the evaporators are divided into three groups.
1. Natural circulation evaporators
2. fed circulation evaporators
3. film evaporators.
EVAPORATORS

15. Steam jacketed kettle
 Evaporating pan consists of a
hemispherical pan made from copper
or stainless steel and surrounded by
steam jacket.
 The hemispherical shape provides a
large surface area for evaporation.
 The evaporators are mounted in such
a way that they can be tilted to
remove the product.
 The evaporating pans are heated by
steam which passes through a steam
jacket.

16. Advantages
 simplest equipment for liquid evaporation
Economical
Easy to clean, use and maintain

17. Disadvantages
Decomposition of product
Limited heating surface
Not suitable for thermolabile material
No provision to recollect costly organic solvents
Discomfort to the worker due to saturation of
atmospheric pressure.

18. Horizontal tube evaporator
In this type of evaporator, several parallel 8 feet
long tubes are joined together in series.
Each tube is enclosed in the opposite direction to
the feed liquid in the inner tube.
 The liquid passes through the tubes, gets
evaporated as it moves along the tube and
finally passes to a separator.
 The concentrated liquid is collected at the
bottom while the vapour is led off to the
atmosphere or used for some heating purpose.

19. Horizontal tube evaporator
 The horizontal-tube evaporator is
a development of the open pan, in
which the pan is closed in,
generally in a vertical cylinder.
 The heating tubes are arranged in
a horizontal bundle immersed in
the liquid at the bottom of the
cylinder.
 Liquid circulation is rather poor in
this type of evaporator.

20. Advantages
It's relatively low cost per unit of heating surface.
Very simple operation.
Easy renewal of heating surface
It's ability to cary large volume
Small space required for shipment

21. Disadvantages
Not easy to clean

22. Application
Horizontal tube evaporators used in evaporation
of sugar syrup, tank water, beef extract,
phosphoric acid, zinc chloride

23. Climbing film evaporators
 Vertical evaporator: long tubes also known
as climbing film evaporators
 Long tube evaporators a large number of
vertical tubes about 7 meters in length and
50 mm in diameter are enclosed in an outer
jacket to which steam is supplied.
 The pre-heated feed liquid is admitted at
the base.
 Here it boils and the vapour formed take
the liquid up the tube at a velocity of about
6-7 meters/second.
 The liquid takes only a few seconds to
travels the length of the tube, so the
evaporator is very suitable for heat-sensitive
substances

24. Advantages
 large area of heat transfer
 Most suitable foe thermolabile material
High evaporation rate
No elevation of boiling point
suitable for foam producing material.

25. Expensive
Difficult to clean and maintained
Difficult to maintain proper feed rate
Disadvantages

26.  In this types of evaporators, some mechanical
device is fitted to circulate the contents heating in
it. e.g. an evaporating pan in which the material is
agitated by a stirring rod or by mechanical
propeller.
The liquid is circulated by means of a pump and as
it is under pressure in the tubes the boiling point is
raised and no boiling takes places.
As the liquid leaves the tubes and enters the body
of the evaporator, there is a drop in pressure and
vapour gets removed from the supper heated
liquid.
Forced circulation evaporator

27. Forced circulation evaporator

28. Advantages
Forced-circulation evaporators are the most versatile of
all evaporators. This is because they do not depend on a
natural thermosyphon effect that limits the heat-
transfer coefficient.
High heat-transfer coefficients can be achieved for
problem liquors, and hence required surface area is
kept to a minimum.
The economics are especially favorable for applications
that require the more expensive alloys such as stainless
steels, high-nickel alloys, etc. Also since material is
pumped around the unit, fouling can be controlled well.
Operation is not limited by the liquid/vapor ratio, and
turn down can be as low as 5% of capacity.

29. Advantages
 Forced-circulation evaporators offer the highest
operational flexibility, since heat transfer, vapor-
liquid separation and crystallization can take place
in separate components by locating pumps outside of
the evaporator or by using propellers as in propeller
calandria units.
 Forced circulation leads to high tube side velocities
(6-18 ft/ s), and hence higher heat-transfer
coefficients and smaller heating surfaces.
 Positive circulation renders this unit relatively
insensitive to variations in physical properties or
loads, making it suitable for crystallizing solutions or
slurries.

30. Rapid liquid movement improve heat transfer.
Useful for evaporation of viscus liquid
Rapid evaporation rate
Advantages

31. Disadvantages
These evaporators are usually less economical
than other types, due to operating and
maintenance costs for the pumps.
Corrosion-erosion can occur, due to high
circulation velocities. Also, plugging of tubes
where liquor enters can be a problem in salting
services where the salt deposits detach and
accumulate at the bottom.

32. Uses
These devices are ideal for crystallizing, and for
concentrating thermally degradable materials and
viscous solutions

33. Two evaporators are connected together with a piping
arrangement so that the vapour from the calandria of
first effect (which is heated by steam) is used to heat the
calandria of the second effect.
 This means that the calandria of the second effect is
used as condenser for the first effect, so that latent heat
of vaporization is used to evaporate more quantity of the
liquid instead of its going as waste.
The vapour from the second effect then taken to a
condenser and converted into liquid.
Multiple Effects Evaporation

35. Advantages
Suitable for large scale & for continuous
operation.
 Highly economical when compared to single
effect.
 Multiple effects, or stages, are now used to
minimize the energy input required to evaporate
or boil off undesirable water content.
The total evaporation achieved in these systems is
approximately the number of effects times the
energy input to the first effect.

36. Disadvantages
Large floor space required
High head-room requirements.
Higher pressure drop through the tubes than in a
falling film evaporator.
Hydro static head at the bottom of the tubes may
increase product temperature and cause
temperature-sensitivity problems

37. Evaporation under reduced pressure should be done
with care because there is danger of overheating of the
liquid
Evaporation under reduced pressure is also known as
vacuum evaporation.
Vacuum evaporation is the process of causing the
pressure in a liquid filled container to be reduced below
the vapour pressure of the liquid, causing the liquid to
evaporate at a lower temperature than normal.
in case of food and other product vacuum evaporation
facilitate storage of food and other products for prolong
period of time.
Evaporation Under Reduced Pressure

38. Vacuum evaporation was also used when boiling or
heating a substances at normal temperature would
chemically change the consistency of the product.
Vacuum evaporation was used whenever possible
because of saving of time, heat and labour.

39. Prevent damage to the heat sensitive material
Higher temperature gradients without need for
extensive temperature
Advantages

40. Single-Effect Vacuum Evaporator
A single effect evaporator is utilized using water as feed
and condensed water and liquid water as product.
This evaporator may be run with and without a vacuum
at different steam pressures.
Running the evaporator under a vacuum proved to be
more efficient with respect to steam usage for
evaporation.
Single-effect evaporator is discussing briefly in above
heading of Calandria-type evaporator.
In this type of evaporator the vapor from boiling liquid
is condensed and discarded.

42. Triple-effect Vacuum Evaporator
This equipment adopts the principle of multitubular
circulation out-heating working principle to keep the
short heating time of materials, rapid evaporation
speed, large concentration ratio, so that to keep the
raw-effect of materials effectively.
Energy will be well saved 70% than single-effect
evaporator. Materials are evaporated & concentrated
under sealed state which is clean and comfortable.
Besides, it is equipped with special foam-removing
device to prevent the material running phenomenon.
 All the parts touched with materials are made of
stainless steel and be polished.

43. The equipment has the properties of good
corrosion-proof, easy of cleaning in accordance
with requirements of Pharmacy, Food Hygiene.
It can be matched with PC control system and be
easy of operation and stable effects.

46. Evaporation vs Vaporization

47. Evaporation Vs Drying

48. Sublimation Vs Evaporation

49. Evaporation Vs Boiling

50. Evaporation Vs Distillation

51. Evaporation Vs Condensation