Fundamentals of Refrigeration

Fundamentals of Refrigeration

"Refrigeration is the science of producing & maintaining temperature below that of surrounding atmosphere."

Or

Refrigeration is a process that removes heat from a space, substance, or system to lower and/or maintain its temperature below the ambient temperature.

In simple refrigeration means the cooling or removal of heat from a system. Refrigeration is artificial (human-made) cooling.Energy in the form of heat is removed from a low-temperature reservoir and transferred to a high-temperature reservoir. The work of energy transfer is traditionally driven by mechanical means, but can also be driven by heat, magnetism, electricity, laser, or other means.

The equipment employed to maintain the system at a low temperature is termed as Refrigerating System & the system which is kept at lower temperature is called Refrigerated System.

The Refrigeration is generally produced by following three ways:

1. By Melting of Solid

2. By sublimation of a Solid

3. By Evaporation of a Liquid

Elements of Refrigeration System

All refrigeration system consists four basic units as given below.

1. A low temperature thermal Sink to which heat will flow from the space to be cooled.

2. Means of extracting energy from the sink, raising the temperature level of this energy, & deliver it to a heat receiver.

3. A receiver to which heat will be transferred from the high  temperature high pressure refrigerant.

4. Means of reducing pressure & temperature of refrigerant as it return from the receiver to the sink. 

Refrigeration System

The various refrigeration system may be enumerated as below:-

1. Ice Refrigeration

2. Air Refrigeration system (ARS)

3. Vapour Compression Refrigeration System (VCRS)

4. Vapour Absorption Refrigeration System (VARS)

5. Special Refrigeration System

  (a) Absorption Refrigeration System

  (b) Cascade Refrigeration System

  (c) Mixed Refrigeration System

  (d) Vortex Tube Refrigeration System

  (e) Thermoelectric Refrigeration System

  (f) Steam Jet Refrigeration System

Co-efficient of Performance (C.O.P)

The coefficient of performance, COP, of a refrigerator is defined as the heat removed from the cold reservoir Qcold, (i.e. inside a refrigerator) divided by the work W done to remove the heat (i.e. the work done by the compressor).

As can be seen, the better (more efficient) the refrigerator is when more heat Qcold can be removed from the inside of the refrigerator for a given amount of work. Since the first law of thermodynamics must be valid also in this case (Qcold + W = Qhot), we can rewrite the above equation:

For an ideal refrigerator (without losses and irreversibilities) can be derived that:

These formulas are applied also for an air conditioner, which works very much like a refrigerator.

Standard Rating of Refrigeration Machine

A ton of refrigeration (TR), also called a refrigeration ton (RT), is a unit of power used to describe the heat-extraction capacity of refrigeration and air conditioning equipment. 

"1 ton of refrigeration capacity is the amount of heat required to be removed in 24 hours, from 1 ton of water at 0 deg C in order to change its phase to ice."

OR

1 TOR indicates the amount of heat that needs to be extracted from 1 tonne of water at zero degree centigrade to convert it to 1 tonne of ice at zero degree centigrade in 1 day.

1 ton refrigeration = 200 Btu/min = 3.517 kJ/s = 3.517 kW = 4.713 HP= 210 KJ/min

Application of Refrigeration

1. Ice Making

2. Transportation of foods above & below freezing

3. Industrial air conditioning

4. Comfort air conditioning'

5. Chemical & related industries

6. Medical & surgical aids

7. Oil Refining & Synthetics rubber manufacturing

8. Manufacturing & treatment of metals

9. Freezing food products

10. Building construction