Evaporation.pptx

Evaporation
Submitted By-
Rajat Uppal (16110040)
Sunil Kumar (16110049)

INDEX
 What is Evaporation?
 Types of Evaporation.
 Factors affecting evaporation.
 Types of Evaporators:-
• Climbing film
• Falling Film
• Forced Circulation
• Natural Circulation

Evaporation means simply vaporization
from the surface of a liquid below its
boiling point.
Thus, no boiling occurs and the rate of
vaporization depends on the diffusion of
vapour through the boundary layers
above the liquid.
EVAPORATION

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

 Concentration –
With inc in conc-->Crystal formation  Clogging of tubes
 Foaming – Foam causes heavy entrainment by accompanying
vapors.
 Temperature Sensitivity- High Temp Damage (Food)
 Scale- Some soln deposits scales on heating reducing overall
coff. Of evaporation.
 Material of Construction – Soln can react with the material of
evaporator.
FACTORS AFFECTING THE EVAPORATION

Other properties to be considered are-:
Specific Heat
Heat of Concentration
Toxicity
Radioactivity
Explosion hazards
OTHER FACTORS

• Equipments which are used for evaporation
are called Evaporators.
Types of Evaporator:
1. Natural circulation evaporator
2. Forced circulation evaporator.
3. Film evaporators(Climbing film & Falling
film)
EVAPORATORS

• Working principle:
• The movement of the liquid results from
convection currents set up by the heating
process.
• Convection currents: The process in which
heat moves through a gas or liquid as the
hotter parts rises and the cooler part sinks.
NATURAL CIRCULATION EVAPORATORS

1) They are simple, easy and cheap to
construct.
2) They are easy to use and clean.
3) Stirring of the evaporating liquids
can be done easily.
ADVANTAGES

1)The whole of the liquid is heated all the time
which may lead to decomposition of the
components.
2)On the evaporating surface foam is rapidly
formed which decreases evaporation. Solids
may be deposited at the bottom which make
the stirring necessary.
3)This pan can only be used for evaporating
aqueous and thermostable liquid extracts.
4)They can not be used for evaporating extracts
containing organic solvents like alcohol etc.
DISADVANTAGES

 Construction:
• The evaporator consists of a short tube calendria and
a large cylindrical vessel (body of the evaporator) for
separation of vapor and liquid takes place.
• The liquor inlet is provided at the side of the
cylindrical vessel.
• A pump is fitted in between the calendria and the
body of the evaporator.
• A tangential inlet for liquid under high pressure is
placed at neck of the body of the evaporator.
• The vapor outlet is placed at the top of the body and
it may be passed through a condenser to collect the
condensed liquid.
FORCED CIRCULATION EVAPORATORS

1)These have an great advantage over natural
circulation evaporators in that the rapid liquid
movement improves heat transfer, especially
with viscous liquids or materials that deposit
solids or foam readily.
2)The equipment is suitable for operation under
reduced pressure due to the capacity of the
process to overcome the effect of greater
viscosity of liquids.
3)These evaporators possess rapid evaporation
rate.
ADVANTAGES

• Corrosion-erosion can occur, due to high
circulation velocities.
• Salt deposits detach and accumulate at
the bottom.
DISADVANTAGES

Film evaporators spread the material as a film
over the heated surface, and the vapor
escapes the film.
Types:-
Climbing Film evaporators
Falling Film evaporators
FILM EVAPORATORS

• Working
• At the upper end, the mixture of vapor and concentrated liquor
enters a separator, the vapor passes to a condenser, and the
concentrated liquid to a receiver.
• Cold or pre heated liquor is introduced into the tube.
• Heat is transferred to the liquor from the walls and boiling
begins.
• Ultimately sufficient vapor has been formed for the smaller
bubbles to unite to a large bubble,filling the width of the tube.
• As more vapor is formed, the slug of liquid is blown up the tube,
the tube is filled with vapor, while the liquid continues to
vaporize rapidly, the vapor escaping up the tube and, because of
friction between the vapor and liquid, the film also is dragged up
the tube upto a distance of 5 to 6 metres.
CLIMBING FILM EVAPORATORS

Working principle
• The liquor to be evaporated is introduced at
the top of the evaporator tubes and the liquor
comes down due to gravity.
• The concentrate and vapor leaves the bottom.
They are separated in a chamber where the
concentrate is taken out through product
outlet and vapor from vapor outlet.
FALLING FILM EVAPORATORS

 Advantages:
• Because of obtaining good heat transfer the method
being especially useful with liquids that are too
viscous to be processed in units in which the film is
formed naturally.
 Disadvantages:
• A major disadvantage of falling film evaporators is
the potential instability of the falling film
• Expense to manufacture and install the instrument is
high.
• Difficult to clean and maintain.
ADVANTAGES & DISADVANTAGES

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