Refrigeration and

Air-ConditioningLecture-1

Mechanical Engg. Department

Geeta Engineering College

Naultha Panipat

CONTENT Introduction Heat Engine RefrigeratorHeat PumpUnit of RefrigerationVapour Compression Refrigeration SystemDifference between Vapour and Air Refrigeration SystemCooling TowerEvaporative Condenser

Refrigeration: It is a process of reducing and maintaining the temperature of a body below the general temperature of its surrounding.

Heat Engine: The heat supplied to the engine is converted into useful work. If Q2 is the heat supplied to the engine and Q1 is the heat rejected from the engine, then the net work done by the engine is given by

WE =Q2 – Q1

Refrigerator: It is a device which is used to maintain the temperature of a body lower than the atmospheric temperature.

This is done by extracting the heat Q1 from the cold body and delivering it to a hot body. In doing so, work WR is required to be done on the system. Its C.O.P. is given by:

Heat Pump: It is a device which is used to maintain the temperature of any space or body above the atmospheric temperature.

This is done by delivering the heat Q2 to the hot body and extracting it from a low temperature body. In doing so, work WP is required to be done on the system.

The cycle of operation of both refrigerator and heat pump are same the only difference is the desired effect.

Its C.O.P. is given by:

Unit of Refrigeration:

The practical unit of refrigeration is ‘Tonne of refrigeration’ (TR).

A tonne of refrigeration is defined as the rate of heat extraction which is equal to the rate of heat supplied for uniform melting of one tonne (1000Kg) of ice at 00C in 24 hours.

Since the latent heat of ice is 335 KJ/Kg, therefore one tonne of refrigeration

1TR= 1000 x 335 KJ in 24 Hours

In actual practice one tonne of refrigeration is taken as equivalent to 210 KJ/min or 3.5 KW.

Vapour Compression Refrigeration System:

The main parts of the vapour compression refrigeration system are:

1. Compressor

2. Condenser

3. Expansion valve

4. Evaporator

1. Compressor: The low pressure and temperature vapour refrigerant from evaporator is drawn into the compressor through the inlet valve, where it is compressed to a high pressure and temperature.

Then this high pressure and temperature vapour is discharged into the condenser.

Diagram and T-S and P-V Plot

Vapour compression refrigeration system

2. Condenser: The condenser consists of coils of pipe in which the high pressure and temperature vapour refrigerant is cooled and condensed. The refrigerant, while passing through the condenser, gives up its latent heat to the surrounding condensing medium which is normally air or water.

3. Expansion valve: The function of the expansion valve is to allow the liquid refrigerant under high pressure and temperature to pass at a controlled rate after reducing its pressure and temperature.

4. Evaporator: An evaporator consists of coils of pipe in which the liquid-vapour refrigerant at low pressure and temperature is evaporated. In evaporating the liquid vapour refrigerant absorbs its latent heat of vaporisation from the medium which is to be cooled.

Difference between Vapour Refrigeration System and Air Refrigeration system:

The components of both the refrigeration systems are shown

Air refrigeration system

Vapour compression refrigeration system

Advantages of Vapour compression refrigeration system over Air refrigeration system

Smaller size for a given refrigerating capacity

Higher coeff. of performance

Lower power requirements for a given capacity

It can be used over large range of temp.

Thank You