AIR CONDITIONINGBuilding Services IIIFaculty: Khushboo Priya

BASIC REFRIGERATION PRINCIPLES

THERMODYNAMICS

Thermodynamics is a branch of natural science concerned with heat which is in motion.

FIRSTA definite amount of mechanical work is needed to produce a definitive amount of heat and vice versa. In other words, the ratio of work done and heat produced is always constant.

LAWS OF THERMODYNAMICS

SECONDAn isolated system, if not already in its state of thermodynamic equilibrium, spontaneously evolves towards it. “Heat cannot flow from a cold body to a hot body unless an external agency acts on it”“The thermal efficiency of a heat engine is always less than unity”

LAWS OF THERMODYNAMICS

HEAT

Heat is a form of energy which gives the sensation of warmth or hotness.A body becomes hotter when it gains heat energy and becomes colder when it gives out heat energy. Heat can be converted into other forms of energy and the other forms of energy can be converted into heat. The availability of heat energy to do a work depends on the difference in temperature levels and hence heat energy is always kinetic in nature.

TEMPERATURE

It is defined as the degree of hotness or coldness of a body.

When a substance receives heat the following effects are notices:

Change in colorChange in volumeChange in pressureChange in RadiationChange in electrical resistance

HEAT TRANSFER

LATENT HEAT

Latent Heat is the heat released or absorbed by a substance when it changes state, with no change in temperature.

LATENT HEAT OF FUSION

Latent Heat of Fusion is defined as the amount of heat required to convert a unit mass of the substance from solid to liquid form at its melting point without any rise in temperature.

LATENT HEAT OF VAPOURIZATION

Latent Heat of vaporization is defined as the amount of heat required to convert a unit mass of the substance from liquid into its vapor state at the same temperature.

SATURATION TEMPERATURE

A Liquid is said to be saturated when sufficient heat has been added to raise its temperature to boiling level at the existing pressure and any increase in temperature will start vaporization whereas decrease in temperature will result in reduction of sensible heat.Therefore the temperature at which the liquid reaches its maximum heat is called saturation temperature.

PRESSURE TEMPERATURE RELATIONSHIP FOR LIQUIDS

Water boils at 100 deg C. Increase in atmospheric pressure means subsequent increase in boiling point whereas a decrease in pressure leads to reduction in boiling point. Boiling Water may not be hot as water boils at very low pressure when heated under vacuum.

This phenomenon is true for all liquids especially refrigerants which are used to produce low temperature.

REFRIGERATION

Refrigeration is defined as the process of cooling and maintaining a temperature well below that of the surrounding atmospheric temperature.

A machine which makes use of the process of refrigeration to maintain low temperature is called a Refrigerator.

Application: In Chemical industry for separating and liquefying gases and liquids. Ice manufacturing units In cold storage For cooling water In controlling humidity during the manufacturing and treatment of steel In oil refineries to remove wax from oil.

• A Text book on Building Services, R.Udayakumar

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