Mechanical Basics

What is Refrigeration Cycle?

A Refrigeration Cycle is a Thermodynamic Cycle i.e. a sequence of process that begins and ends with same state. It is a process through, which we used to produce Cooling. The Refrigerator Cycle is used in Refrigerating Machine and Gas Refrigerator. The most considerably used Refrigeration Cycle Process is predicted on evaporation of liquid, the Joules-Thomson effect or expansion of working fluid.

Refrigeration is the branch of knowledge, which deals with process of reducing and maintaining the temperature of space or material below the temperature of girding, which is maintained at lower temperature by withdrawing the heat from cold body and expelling to hot body is known as Refrigerate Space. The machine that maintain the space at lower temperature than girding is known as Refrigerator and the process is called as Refrigeration.

Refrigeration Cycle

Theoretically, the Thermodynamic Cycle consists of non-dissipative and frictionless processes. So, the thermodynamic cycle operates in forward direction to produce the Mechanical Energy/Power from Heat Energy, or it can also be operated in reverse direction to produce the Heat Energy from Mechanical Energy. The reversed cycle is primarily used for the cooling effect, which produces during a portion of the cycle and so is called as Refrigeration Cycle.

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Looking at history of Refrigeration Cycle; In 1834, American innovator Jacob Perkins, erected the world’s first working Refrigeration System using a closed cycle. His prototype system worked, but it didn’t succeed commercially. Until 1929, Refrigeration System caused several fatal accidents like poisonous gas blurted, etc.

Therefore, in 1930, many researches were initiated to develop a danger-free system of refrigeration; leading to discovery of Freon, which became the standard device for almost all Domestic Refrigerators.

Parts of Refrigeration Cycle

The Refrigeration Cycle consists of mainly 4 components/parts and they are as follow

Refrigeration Cycle Components

1. Compressor
2. Condenser
3. Expansion valve
4. Evaporator

Note: We can read about these Refrigeration Cycle Components in the upcoming Types of Refrigeration Cycle.

Necessity of Refrigeration

We, the people, with normal health and peculiar habits prefer to take tasteful diet in order to satisfy the tongue. But, our fascination for particular goods calls for conservation of perishable goods even during those periods, during which, they are not naturally available.

As an example, in India, the mangoes are gathered during summer season, but the demand for the same persists throughout the times. Hence, an artificial terrain has to be created (most suitable for the commodity), under which, minimum spoilage will occur.

Therefore, artificial refrigerant becomes necessary for the following application, which is developed using the Refrigeration Cycle.

  • Preservation of vegetables and fruits (refrigeration slows down the deterioration process)
  • Preservation of milk products like butter, cheese, ghee etc. (refrigeration increases the life of these items), etc.
  • Preservation of medicines.

Refrigerating Effect

Refrigerating effect is the amount of heat absorbed by the refrigerant during its travel to evaporator. In addition to latent heat of vaporization, refrigerating effect may include sensible heat absorbed in the process of superheating carried out in the evaporator. In other words, refrigerating effect is the rate of heat absorption from the substance or space to be cooled.

Refrigerating Effect or Refrigeration achieved is measured and expressed in Ton Of Refrigeration, i.e. TOR.

Co-Efficient of Performance [COP]

Co-Efficient of Performance (COP) of Refrigerant Unit or Refrigeration or Refrigeration Cycle is that the quantitative relation of warmth absorbed to the quantity of labor equipped.

Co-Efficient Of Performance

Here, the refrigerant impact is that the quantity of warmth far from the substance or house to be cooled. this is often conjointly referred to as refrigeration capability or extraction capability or evaporation capability of the system or desired impact.

This refrigeration capability is expressed in ‘Tons of Refrigeration’ (TOR). The Work done is that the energy equipped to Mechanical Device. It’s co-jointly referred to as mechanical device power. It is usually expressed in kilowatt.

The value of COP is usually quite taken as One. Normally, COP of Vapour compression cooling running on Vapour Compression Cycle (V.C.C.) ranges between Three to Four. To calculate theoretical COP of cooling, the in-operation refrigeration cycle of plant is planned on P-H Diagram, such as suction pressure and also the discharge pressure of the cooling and consequently, theoretical COP is calculated.

Now, allow us to thought of that, the cooling is started and run to get refrigeration impact. Throughout this running condition, heat absorbed by refrigerant and work equipped to mechanical device in variety of consumed electricity square measure calculated. Then mistreatment on top of formula, COP is decided. This determined price of COP throughout running condition of cooling, it is termed as Actual COP of Cooling.

However, it is found that, throughout running condition, performance of cooling is greatly influenced by many factors like in operation variables, elements load performance, style of system parts, maintenances of the system, operating conditions, etc.

Therefore, actual COP determined throughout running condition but theoretically, COP calculated by considering ideal conditions only. In short, Actual COP is usually less than but not equal to Theretical COP.

Unit of Refrigeration

Refrigeration achieved is measured in terms of Refrigerating Effect obtained. Refrigerating effect is the rate of heat absorption from the substance or space to be cooled. Refrigerating effect or Unit Of Refrigeration is measured in Tons of Refrigeration (TOR).

Therefore, refrigeration capacity is expressed in terms of TOR, i.e. ‘Tonnage of Refrigeration’ or ‘Tons of Refrigeration’

1 TOR is defined as the quantity of heat required to be removed from 1 ton of water at 0֯C to form 1 ton of ice at 0֯C within 24 hours.

Whereas; 1 Ton = 1 x 10 3 kg

Latent heat of fusion of ice is defined as the amount of heat to be removed from water at 0֯C to convert it into ice at 0֯C.

Since the heat removed at constant temperature, the type of heat removed is latent heat to convert water into ice.

For 1 kg, latent heat of fusion of ice is taken as hfg=335 KJ/kg

By definition, 1 TOR is the quantity of heat to be removed from 1 ton of water during 24 hours. Therefore, 

Ton of Refrigeration Formula

For practical calculations, the value of 1 TOR is taken as 210 KJ/min or 30517 KW.

Applications of Refrigeration Cycle and Refrigeration

The applications of Refrigeration or Refrigeration Cycle may be divided into four categories:

Refrigeration Cycle For Domestic purpose

  • Refrigeration Cycle is concerned primarily with household refrigerators and home freezers. These units are usually smaller in size and are used for preservation of perishable commodities (for short duration) like vegetables, fruits, milk products, poultry products, etc. and also for chilling of drinks and drinking water.
  • Storage of medicines, ice, blood, etc.

Refrigeration Cycle For Commercial purpose

Commercial refrigeration is concerned with cold storage, retail stores, restaurants, hotels, etc. for storing, displaying, processing, and dispensing of perishable commodities of types.

Refrigeration Cycle for Industrial purpose

a) Refrigeration is used in many industries to have economical and good quality products.

b) For example

  • Painting industry
  • Chemical industry
  • Pharmaceutical industry
  • Textile and rubber industry
  • Oil refineries
  • Separation and liquidification of gases
  • Processing of photographic material
  • Treatment of air for blast furnace.
  • Ice plant.
  • Printing and Packing Industries.

Refrigeration Cycle Human comfort

a) Refrigeration Cycle for Comfort Air Conditioning

  • It is an air conditioning system having purpose of conditioning the air for human comfort
  • Installation of comfort air conditioning are found in homes, schools, hotel, retail stores, factories, automobiles, buses, trains, planes, and ships.
  • Comfort air conditioning also finds wide applications in hospitals, restaurants, theaters, offices, public building, etc.

b) Refrigeration Cycle for Industrial Air Conditioning

It is an air conditioning system having purpose of conditioning the air for carrying out industrial processes and for several other industrial applications. For example:

  • For control of moisture content in the air,
  • To govern the rate of chemical reaction
  • For precision manufacturing of articles or products,
  • To provide clean, filtered air for trouble-free operation and production of goods.

Refrigeration Cycle in Marine and Transportation Refrigeration

  • Marine refrigeration includes refrigeration for fishing boats, vessels, transporting perishable cargo, large ships, etc.
  • Transportation refrigeration includes refrigeration applied to trucks, railways, aircrafts, etc.

Conclusion        

We have undertaken the detail and complete study of Refrigeration Cycle, necessity of refrigeration, unit of refrigeration, concept of COP in Refrigeration Cycle. So, from refrigeration point of view, the machine that runs on Refrigeration Cycle is referred as Refrigerator and external work refers the power supplied to compressor of refrigeration system. Overall, the refrigeration effect or cooling is done at Evaporation Unit or Evaporator as it absorbs the heat from space and cools down the space.

Frequently Asked Questions:

State the Law of Refrigeration?

Ans. The Law of refrigeration refers to Clausius Statement’s Second Law of Thermodynamics, which states that “It is impossible for a machine to transfer heat from a body at low temperature to a body at high temperature without supply of external work”. It means that heat cannot flow itself from cold body to hot body against the temperature gradient without supply of external work.

What is the way to increase the COP of Refrigerator or Refrigeration Cycle?

Ans. The COP is the magnitude relation of cooling, which results given by the refrigerant to the work done by mechanical device. To boost COP of Refrigeration Cycle, it is needed to decrease the mechanical device work. Therefore, decrease in condensation pressure and temperature can increase the cooling. 

Why we find the COP and not Efficiency for Refrigeration Cycle?

Ans. The COP and Efficiency are the units that specified to find the output quantity and quality. If the specified output should be in type of work, we have to calculate Efficiency; if the specified output is heat, we have to calculate COP. In refrigeration, the required output is often in type of heat. Therefore, the output is calculated in COP. Whereas, in different cases like engine, the specified output is work. So, we have a tendency to calculate Efficiency.

What does the Coefficient of Performance tells us in Refrigeration Cycle?

Ans. The COP is a performance rating that tells us how effective a setup or cooling is at transferring heat with respect to the power it consumes. Remember, white goods move heat from coldness and pump heat to extreme temperature. This uphill movement of warmth from coldness space into extreme temperature space called as Work done. So, the Coefficient of Performance tells us how much work is done after removing the losses and power utilized by devices.

What are Refrigeration Controls?

Ans Refrigeration controls ensure that every element of a cooling process coordination with one another. These elements embrace the thermostat, condenser, mechanical device, and evaporator, that have to be compelled to operate.

Why cannot water be used as a Refrigerant?

Ans. Using the water as a refrigerant would not be a really economical selection that is why it is not in use. Truly, once an excitation is getting used the water, current is acting as a refrigerant because it circulates through the building and returns to the evaporator to displace the warmth it’s picked up at every location.

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