BITS Pilani Dubai Campus

Refrigeration Cycles

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TWO CATEGORIES OF THERMAL PLANTS[DEVICES]

WORK PRODUCING WORK CONSUMING

HEAT ENGINE HEAT PUMPS ( I.C ENGINE, REFRIGERATORS, GAS TURBINE COMPRESSORS

STEAM TURBINE) PUMPS

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DEFINITION

• REFRIGERATION is the cooling of air/liquids, thus providing

lower temperatures to preserve food, cool beverages, make ice and for

many other applications.

• AIR CONDITIONING :SIMULTANIUS CONTROL OF

TEMPERATURE, HUMIDITY, CLEANLINESS AND AIR MOTION.

REFRIGERATOR & HEAT PUMPS Generally heat flows in the direction of

decreasing temperature

i.e from higher temperature regions to low temperature ones.

This heat transfer process occurs in nature without requiring any devices.

The reverse process, however, cannot occur by itself.

The transfer of heat from a low temperature region to a high temperature one requires special devices called Refrigerators/Heat pumps

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REFRIGERATION- PRODUCTION OF COOL CONFINEMENT WITH RESPECT TO

SURROUNDINGS.

ARTIFICIAL WITHDRAWAL OF HEAT, PRODUCING A TEMPERATURE LOWER

THAN THAT WHICH WOULD EXIST.

SCIENCE OF PROVIDING & MAINTAINING TEMPERATURES BELOW THAT OF

SURROUNDINGS.

REFRIGERATION MACHINERY WHICH DOES HEATING IS CALLED A HEAT PUMP.

REFRIGERATION- PUMPING OF HEAT OUT OF THE SYSTEMS

HEAT PUMP – PUMPING OF HEAT FROM THE SURROUNDINGS INTO THE SYSTEMS

DEFINITION

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DIFFERENCE BETWEEN REFRGERATION & HEAT PUMP

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HEAT ENGINE

Q?

QL

PUMP

BOILER

TURBINE

CONDENSER

WORK

SYSTEM BOUNDARY

A HEAT ENGINE INVOLVING STEADY-STATE, STEADY FLOW PROCESSES.

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HEAT ENGINE

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HEAT PUMP & REFRIGERATOR

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REVERSED CARNOT CYCLE

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Most of the commercial refrigeration is produced by the

evaporation of a liquid called refrigerant.

Mechanical refrigeration depends upon the evaporation of liquid

refrigerant and its circuit

And its circuits includes the equipments naming evaporator,

compressor, condenser and expansion valve.

It is used for preservation of food, manufacture of ice, solid

carbon dioxide and control of air temperature and humidity in the

air-conditioning system.

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Important refrigeration applications :

1. Ice making

2. Transportation of foods above and below freezing

3. Industrial air-conditioning

4. Comfort air-conditioning

5. Chemical and related industries

6. Medical and surgical aids

7. Processing food products and beverages

8. Oil refining and synthetic rubber manufacturing

9. Manufacturing and treatment of metals

10. Freezing food products

11. Miscellaneous applications :

(i) Extremely low temperatures

(ii) Plumbing

(iii) Building construction etc.

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REFRIGERATION SYSTEMS

The various refrigeration systems may be enumerated as

below :

1. Ice refrigeration

2. Air refrigeration system

3. Vapour compression réfrigération system

4. Vapour absorption refrigeration system

• The rating of a refrigeration machine is obtained by refrigerating effect

or the amount of heat extracted in a given time from a body or space.

• One tonne of refrigeration is defined as the refrigerating effect (amount

of heat extracted ) produced by melting 1 tonne of ice from and at 00C in

24 hours.

• We know that latent heat of fusion of ice = 336 kJ/kg.

• Refrigerating effect of this heat in terms of tonne in 24 hours is rated as

• tonne of refrigeration

1T.R = 336x 1000/ 24 = 14000kJ/hr.

= 210kJ/min. = 3.85 kJ/se

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COEFFICIENT OF PERFORMANCE

• Performance of the refrigerator is

determined by using co- efficient of

performance which is defined as

• the ratio of heat absorbed by the

refrigerant while passing through the

evaporator to the work input required

to compress the refrigerant in the

compressor ;

• in short it is the ratio between heat

extracted and work done

input required

output desired COPR

LHinnet QQW ,

LH

LR

Q– Q

Q COP

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VAPOUR COMPRESSION REFRIGERATION SYSTEM

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P-H CHART

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