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UNIT - III

Chapter – 5

Thermal Engineering 2:

Thermal Systems Applications

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�Thermal Systems Applications �

Refrigeration system
Air conditioning system
Pumps
Blowers, and
Compressors

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Session – 1

Contents:

Introduction to refrigeration system
Parts of Refrigerator
Vapor Compression Refrigerator
Vapor Absorption Refrigerator
Comparison between Vapour Compression and Absorption systems
Properties of good refrigerant
Performance characteristics of a refrigeration system
Air Conditioning system

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��Refrigeration system��

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Refrigeration system

Introduction:

It is an art of Artificial cooling employed in,

Ice making
Cold storage
Preservation of the

perishables such as, 🡪 Milk

🡪 Vegetables / Food

🡪 Drinks

🡪 Medicines, etc.

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Refrigeration system

Definition:

Refrigeration is defined as a method of reducing the temperature of a system below that of the surroundings, and

🡪 maintain it at the lower temperature by continuously abstracting the heat from it.

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Refrigeration system

Parts of a Refrigerator:

Evaporator
Compressor or Pump
Condenser
Expansion device

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�Terminologies used in Refrigeration system�

Refrigerating effect:

It is the rate at which the heat is absorbed in a cycle from the space to be cooled.

Ton of Refrigeration:

It is defined as the quantity of heat absorbed in order to form 1 ton of ice in 24 hours, when the initial temperature of water is 0⁰ C.

Water at 0⁰ C 24 Hours 1 Ton of Ice

(Initial state) Heat absorption (Final state)

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�Terminologies used in Refrigeration system�

Coefficient of performance (COP):

Performance of a Refrigerator system is expressed by COP.

It is defined as the ratio of heat absorbed in a system to the work supplied.

COP = Heat absorbed

Work supplied

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Refrigeration system

Types of a Refrigeration systems:

Vapour Compression Refrigerator

Vapour Absorption Refrigerator

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�1. Vapour Compression Refrigerator�

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Domestic Refrigerator

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�1. Vapour Compression Refrigerator�

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1. Vapour Compression Refrigerator

Refrigerant:

Working fluid.

Ex: Ammonia, Freon, Methyl chloride, CO₂.

Circulated in the refrigeration system.

During evaporation,

Absorbs latent heat from the space.
Liquid becomes vapour.

During condensing,

Gives off heat to the surroundings.
Vapour becomes liquid.

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1. Vapour Compression Refrigerator

Evaporator:

Made of coiled metal tubes.
Placed in freezing compartment.
One end is connected to the suction end of the compressor.
Other end is connected to expansion (throttle) valve.

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1. Vapour Compression Refrigerator

Evaporator:

Liquid refrigerant at low pressure & low temperature,

🡪 enters the evaporator.

Absorbs heat from the contents in the freezing compartment.

Refrigerant evaporates & lowers the temperature of the space.

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1. Vapour Compression Refrigerator

Compressor:

A mechanical device.
Driven by an electric motor.

Used to circulate the Refrigerant, in the system.

Draws the low pressure vapours from evaporator.

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1. Vapour Compression Refrigerator

Compressor:

Compress them to high pressure & high temperature.

Sends dry refrigerant vapours at high pressure to condenser.

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1. Vapour Compression Refrigerator

Condenser:

High pressure & high temperature refrigerant vapour gives off latent heat to the atmosphere.

(Heat flows from high to low level).

Condenses in to liquid, due to heat rejection.(Temp. lowers).

High pressure condensed liquid refrigerant at room temp (approx) flows to the throttle valve.

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1. Vapour Compression Refrigerator

Expansion device (throttle valve):

High pressure liquid refrigerant, expands to low pressure & low temperature.

🡪 Causes the refrigerant to evaporate partly.

Refrigerant coming out of this valve, will be

🡪 Wet vapour with low temp. (around -10⁰ C).

Refrigerant then passes through the Evaporator. Cycle repeats.

Thermostat is used to maintain the required temp. in the Refrigerator.

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�1. Vapour Compression Refrigerator�

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�1. Vapour Compression Refrigerator�

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Condenser

Evaporator

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2. Vapor Absorption Refrigerator

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Evaporator

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Compressor

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Condenser

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Expansion Device

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Ammonia	In vapour absorption refrigerators.
Carbon-dioxide	In marine refrigerators.
Sulphur dioxide	In household refrigerators.
Methyl chloride	In small scale refrigeration and domestic refrigerators.
Freon-12	In domestic vapour compression refrigerators.
Freon-22	In Air-conditioners.

Refrigerants commonly used in practice

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Properties of a Good Refrigerant:

Thermodynamic Properties

Physical

Properties

Safe Working Properties

Other

Properties

Boiling Point.
Freezing Point
Evaporator and condenser Pressure.
Latent heat of evaporation.

Specific Volume.
Specific Heat.
Viscosity.

Toxicity.
Flammability.
Corrosiveness.
Chemical Stability.

COP.
Odour.
Leak.
Action with lubricating oil.

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�Thermodynamic Properties�

Boiling Point:

An ideal refrigerant must have “low boiling temperature” at atmospheric pressure.

Freezing Point:

Must have a very “low freezing point” because, the refrigerant should not freeze at low evaporator temperatures.

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�Thermodynamic Properties�

Evaporator & Condenser Pressure:

Pressures in both should be slightly above atm. Pressure, in order to avoid the leakage of atm. air and also to enable the detection of the leakage of the refrigerant.

Latent heat of Evaporation:

Latent heat of Evaporation must be very high, so that a minimum amount of refrigerant will accomplish the desired result.

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�Physical Properties�

Specific Volume:

It is the ratio of Volume of the fluid/Mass of the fluid, in m³/kg.
Specific volume of the refrigerant must be very low.
It will reduce the size of the compressor.

Viscosity:

Viscosity of a refrigerant at both the liquid & vapour states must be very low as it improves the heat transfer and reduces the pumping pressure.

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�Safe working Properties�

Toxicity:

Refrigerant must be non-toxic, because any leakage, increases suffocation & poisons the atmosphere.

Corrosiveness:

Refrigerant should be non-corrosive, to prevent the corrosion of the metallic parts of the Refrigerator.

Chemical stability:

Refrigerant must not decompose under operating conditions.

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�Other Properties�

COP

COP of a Refrigerant must be high, so that the energy spent in refrigeration will be less.

Odour

Refrigerant must be odourless, otherwise some food stuff such as meat, butter etc. loses their taste.

Leakage Tests

Refrigerant must be such that any leakage can be detected by simple tests.

Action with lubricating oil

Refrigerant must not react with the lubricating oil, used in lubricating the parts of compressor.

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Properties of a good Refrigerant

High latent heat of vaporization.
Low boiling and low freezing point.
Non-toxic and non-corrosiveness
Non-flammable and non-explosive.
High thermal conductivity
Easy to handle
Low specific volume of vapour.
High coefficient of performance

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Air-Conditioning

Major components:

Evaporator
Condenser
Compressor
Capillary tube

2 Fans – One for Evaporator & other for Condenser.

– Driven by a single motor.

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Air-Conditioning

Unit is generally mounted on window sill.
Evaporator unit is placed inside the room.
Condenser part projects outside.

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Air-Conditioning

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Air-Conditioning

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Air-Conditioning

Evaporator Fan:

Draws the air (relatively at higher temperature) continuously from the space in the room, through air filter.

Forces this air to pass over the Evaporator.

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Air-Conditioning

Evaporator:

Refrigerant absorbs the heat from air & evaporates.

Air gets cooled.

High temperature & low pressure refrigerant is drawn by the Compressor.

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Air-Conditioning

Compressor:

Evaporated refrigerant with high temperature is drawn by the suction end of the compressor.

Compresses the refrigerant and delivers to the Condenser with high pressure.

High temperature & high pressure refrigerant enters the Condenser.

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Air-Conditioning

Condenser Fan:

Draws atmospheric air from outside the room, and

Makes the air to flow over the Condenser.

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Air-Conditioning

Condenser:

High pressure and high temperature refrigerant vapour flows through this.

Gives off heat to atmospheric air.

Temperature of the refrigerant is lowered.

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Air-Conditioning

Capillary tube:

Cooled (low temperature), high pressure refrigerant from Condenser, passes through the capillary tube.
Undergoes expansion, lowering the pressure of the refrigerant.
Low pressure & low temperature refrigerant is made to flow through Evaporator.
Cycle repeats.

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