VAPOUR ABSORPTION REFRIGERATION SYSTEMS

Submitted to :

Mr. Sumit Sharma

Presented By :

Akshay Mistri, Rahul Kumar

Tarun Sharma, Zubin Rizwan

Section : 6MAE3Y

CONTENTS• Introduction

• Simple Vapour Absorption System

• Practical Vapour Absorption System

• C.O.P of Ideal 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

• References

INTRODUCTION

• 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 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

COEFFICIENT OF PERFORMANCE OF IDEAL ABSORPTION SYSTEM

C.O.P OF IDEAL ABSORPTION SYSTEM (CONTINUED)

Various energy transfers in VARS

C.O.P OF IDEAL ABSORPTION SYSTEM (CONTINUED)

= C.O.P of Carnot refrigerator working b/w temperature limits & .

= C.O.P of Carnot engine working b/w temperature limits & .

Thus C.O.P of ideal absorption system,

= [ ] x [ ]

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.

• 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.

DOMESTIC ELECTROLUX REFRIGERATOR

• Developed from an invention by “Carl Munters” & “Baltzer Von Platen”.

• Also known as “Three-fluid absorption system” and “Munter’s Platen System”.

• Three fluids used are ammonia, hydrogen and water.

Domestic Electrolux Refrigerator

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 evaporates into gas at low temperature in evaporator.

• mixture enters absorber where is absorbed in water, returns back.

• Strong sol. in goes to generator, where it is heated and vapours then go to water separator.

• Water separates in separator, weak sol. Sent back to absorber and vapour move to condenser. After condensation in condenser liq. moves to evaporator.

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.

ROLE OF HYDROGEN

• Helps in maintaining uniform total pressure throughout the system.

• Permits the refrigerant to evaporate at low temperature in evaporator, corresponding to its partial pressure.

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.)

REFERENCES

• Er. R.K. Rajput.Vapour Absorption Refrigeration Systems. Feb 03, 2014, “A textbook of Refrigeration & Air-conditioning-2013”.

• Prof. M. Ramgopal. Various energy transfers in VARS (image). Feb 02, 2014, from http://nptel.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Ref

• Prof. R. C. Arora. Domestic Electrolux Refrigerator (image). Feb 02, 2014, from http://nptel.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Ref%20and%20Air%20Cond/pdf