Rwfrigeration working principle

Working of VARS system
Submitted to :
Navneet Goyal
(Mech. Department, SLIET)
Presented By :
Sandeep Pathak
Reg. No-GWT/SL/14/1609
ROLL No.-1436155

Contents
 Basic concept and VCRS System
 Introduction of VARS
 Simple Vapour Absorption System
 Practical Vapour Absorption System
 Properties of Ideal Refrigerant and Absorbent
 Properties of Ideal Refrigerant-Absorbent combination
 Advantages of Absorption system over Compression system
 Domestic Electrolux Refrigerator
 Principle & Working of Domestic Electrolux refrigerator
 Advantages & Disadvantages of Domestic Electrolux Refrigerator
 Solar refrigeration system
 Magnetic refrigeration system

Refrigeration Basics
High Temperature
Reservoir
Low Temperature
Reservoir
R Work Input
Heat Absorbed
Heat Rejected
How does
it work?

Basics
 Refrigeration is the removal of heat from a material or space, so that it’s temperature is
lower than that of it’s surroundings.
 When refrigerant absorbs the unwanted heat, this raises the refrigerant’s temperature
(“Saturation Temperature”) so that it changes from a liquid to a gas — it evaporates. The
system then uses condensation to release the heat and change the refrigerant back into a
liquid. This is called “Latent Heat”.
 This cycle is based on the physical principle, that a liquid extracts heat from the surrounding
area as it expands (boils) into a gas.
 To accomplish this, the refrigerant is pumped through a closed looped pipe system.
 The closed looped pipe system stops the refrigerant from becoming contaminated and
controls its stream. The refrigerant will be both a vapor and a liquid in the loop.

“Saturation Temperature” – can be defined as the temperature of a liquid, vapor,
or a solid, where if any heat is added or removed, a change of state takes place.
 A change of state transfers a large amount of energy.
 At saturation temperature, materials are sensitive to additions or removal of heat.
 Water is an example of how saturation property of a material, can transfer a large amount of heat.
 Refrigerants use the same principles as ice. For any given pressure, refrigerants have a saturation
temperature.
 If the pressure is low, the saturation temperature is low. If pressure is high, saturation temperature is
high.
“Latent Heat”- The heat required to change a liquid to a gas (or the heat that must be
removed from a gas to condense it to a liquid), without any change in temperature.
 Heat is a form of energy that is transferred from one object to another object.
 Heat Is a form of energy transferred by a difference in temperature.
 Heat transfer can occur, when there is a temperature difference between two or more objects. Heat will
only flow from a warm object to a colder object.
 The heat transfer is greatest, when there is a large temperature difference between two objects.

6© UNEP 2006
• Vapour Compression Refrigeration (VCR):
uses mechanical energy
• Vapour Absorption Refrigeration (VAR): uses
thermal energy
• Magnetic Refrigeration: remove heat and
maintain low temperature
Refrigeration systems:

7© UNEP 2006
• Highly compressed fluids tend to get colder when
allowed to expand
• If pressure high enough
• Compressed air hotter than source of cooling
• Expanded gas cooler than desired cold temperature
Two advantages
• Lot of heat can be removed (lot of thermal energy to change
liquid to vapour
• Heat transfer rate remains high (temperature of working
fluid much lower than what is being cooled
VCRS SYSTEM

Condenser
Evaporator
High
Pressure
Side
Low
Pressure
Side
Compressor
Expansion
Device
1
2
3
4
Refrigeration cycle of vcrs

VARS SYSTEM
 It is a heat operated system.
 It is quite similar to Vapour Compression systems. Condensation and
evaporation takes place at two different pressure levels to achieve
refrigeration.
 The main motive is to raise the temperature of the refrigerant from evaporator
pressure to condenser pressure.
 Here refrigerant is dissolved in inert liquid in absorber and pumped to
condenser.
 After raising pressure of refrigerant it is separated from solution by heating.
 After condensation in condenser, refrigerant is throttled by expansion valve
and then it evaporates in evaporator providing the refrigeration effect.

Simple vapour absorption system
 Ammonia vapour from evaporator is
absorbed by water in absorber.
Condensation heat released is absorbed
by cooling water.
 After being pumped to generator, heat is
supplied which gives ammonia vapour.
Weak sol. sent back to absorber.
 High pressure vapour is condensed to high
pressure liquid ammonia in condenser.
 Liquid ammonia is throttled by expansion
valve, and then it evaporates absorbing
heat from evaporator.
Simple Vapour Absorption System

Practical vapour absorption system
Water vapours if reach condenser may block the
expansion valve. Therefore, analyser-rectifier is
used practically.
Analyser : Strong solution flows down the trays.
Due to high saturation temperature water
condenses down and 𝑁𝐻3 vapours escape
through.
Rectifier : A water cooled heat exchanger which
further condenses water vapour. (If any left)
Heat Exchanger : Used to cool weak solution
from generator. It also heats the strong solution
coming from pump, thereby reducing heat to be
supplied at generator, increasing economy.
Practical Vapour Absorption System

Properties of ideal refrigerant & absorbent
Properties of ideal refrigerant :
 It should boil b/w 2˚-10 ˚C and
condense at 40 ˚C or above.
(pressure around atmospheric)
 Large latent heat of vaporization.
 High critical temperature.
 Low specific heat.
 Stability in complete cycle.
Properties of ideal absorbent :
 Greater affinity for refrigerant.
 Heat released during absorption of
refrigerant should be minimum.
 High boiling point.
 Low specific heat.
 Chemical stability.

Properties of ideal refrigerant-absorbent combination
 Refrigerant should have high affinity for absorber at low temperatures &
less affinity at high temperatures.
 Mixture should have low specific heat and viscosity.
 It should be non-corrosive, non toxic, non flammable and non irritating.
 Large difference in normal boiling points of refrigerant and absorbent.
Commonly used combinations in air-
conditioning applications :
• Ammonia-water
• Lithium-bromide water

Advantages of absorption system over compression
system
 No moving part except pump-motor, which is comparatively smaller than
compressor system.
 Quiet in operation, low maintenance cost.
 Can work only with thermal energy as an input.
 Can be built for huge working capacities. (even for above 1000 TR)
 Can be operated at designed C.O.P’s or even at part loads by varying
generator temperature.
 Space and Auto. control requirements favour absorption system.

Principle & working of Electrolux refrigerator
Principle : If a liquid is exposed to an
inert atmosphere, it will evaporate
until atmosphere becomes saturated
with the liquid vapours. Evaporation
thus produces cooling effect.
Working :
 Liquid 𝑁𝐻3 evaporates into 𝐻2 gas
at low temperature in evaporator.
 𝑁𝐻3 + 𝐻2 mixture enters absorber
where 𝑁𝐻3 is absorbed in water,
𝐻2 returns back.
 Strong sol. 𝑁𝐻3 in 𝐻2 𝑂 goes to
generator, where it is heated and
vapours then go to water
Working cycle of Electrolux Refrigerator

Points worth noting (for
Electrolux ref.)
 Complete cycle is carried
out entirely by flow of
gravity of refrigerant.
 With this type of machine,
efficiency is not important
since the energy input is
very small.
 Due to low C.O.P, it cannot
be used for industrial
purposes.
 Helps in maintaining uniform total
pressure throughout the system.
 Permits the refrigerant to
evaporate at low temperature in
evaporator, corresponding to its
partial pressure.
ROLE OF HYDROGEN

Advantages
(Electrolux ref.)
 No pump/compressor
required.
 No mechanical troubles, low
maintenance.
 No lubrication required, no
wear-tear.
 Completely leak proof.
 Noiseless.
 Easy control, only by heat
input.
 More complicated in
construction and working.
 Low C.O.P.
 If spoiled once, cannot be
repaired and has to be
replaced fully.
DISADVANTAGES
(ELECTROLUX REF.)

Rwfrigeration working principle

• Utilisation of solar energy for cooling purpose
• In this system ,solar energy is coupled with
vapour absorption refrigeration system
• So,the power is supplied by solar energy
Magnetic Refrigeration
•Magnetic refrigeration is a cooling technology based on
the magneto caloric effect.
•It is used to attain temperature well below 1 Kelvin

Rwfrigeration working principle

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