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Chapter: Mechanical and Electrical - Thermal Engineering - Refrigeration and Air Conditioning

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Classification of Refrigeration System

Types of Refrigeration • Vapour Compression Refrigeration (VCR): uses mechanical energy • Vapour Absorption Re frigeration (VAR): uses thermal energy

CLASSIFICATION OF REFRIGERATION SYSTEM

Types of Refrigeration

 

         Vapour Compression Refrigeration (VCR): uses mechanical energy

 

         Vapour Absorption Re frigeration (VAR): uses thermal energy

 

Vapour Compression Refrigeration

 

         Highly compressed flu ids 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

 

•   Lot of heat can be rem oved (lot of thermal energy to change liquid to vapour)

 

•   Heat transfer rate re mains high (temperature of working fluid mu ch lower than

 

what is being cooled)

Vapour Compression Refrig eration Cycle


Evaporator

 

Low pressure liquid re frigerant in evaporator absorbs heat and changes to a gas

 

Compressor

 

The superheated vapo ur enters the compressor where its pressure is raised

 

Condenser

 

The high pressure sup erheated gas is cooled in several stages in the co ndenser

 

Expansion

 

Liquid passes through expansion device, which reduces its pressure an d controls the flow into the evaporator

 

Type of refrigerant

 

         Refrigerant determine d by the required cooling temperature

 

         Chlorinated fluorocarb ons (CFCs) or freons: R-11, R-12, R-21, R-22 and R-502

 

Choice of compressor, design of condenser, evaporator determined by

 

         Refrigerant

 

         Required cooling

 

         Load

 

         Ease of maintenance

 

         Physical space requirements

 

         Availability of utilities (water, power)

 

 

Vapour Absorption  Refrigeration

 


Evaporator



Absorber

 


High pressure generator


Condenser


Evaporative Cooling

 

         Air in contact with water to cool it close to ‘wet bulb temperature’

 

         Advantage: efficient cooling at low cost

 

         Disadvantage: air is ri ch in moisture

 

COMPARISON BETWEEN VAPOR COMPRESSION AND A BSORPTION SYSTEM


 


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