How does a Refrigeration Cycle work? | What is Refrigeration?

Refrigeration has become a most vital part of commercial and domestic food management. The preservation of the food and some other products has become a most important factor for all households and commercial. For saving food, people are used refrigeration. The refrigeration prevents the food from spoiling by reducing its temperature than the surrounding temperature. It works on the refrigeration cycle. In this article, we are going to discuss refrigeration, working of refrigeration cycle and types.

What is a Refrigeration?

The process of maintaining and achieving a temperature lower than the atmospheric temperature to cool or preserve the food or other products is known as refrigeration. In other words, refrigeration is artificial cooling used in many household and industrial applications to preserve or cool the vine, fruits, or vegetables.

What is Refrigeration Cycle?

The refrigeration cycle is a thermodynamic cycle which uses to remove heat from a specific area you want to cool. The refrigeration cycle is also known as a heat pump cycle. This cycle is designed for refrigeration systems, air conditioning systems, and heat pumps.

The heat pump is a mechanical device used to transfer heat from the lower temperature reservoir to a high-temperature reservoir.

Refrigeration Cycle working

A refrigerator works on the refrigeration cycle. A refrigeration cycle works in the following way:

  1. Suction
  2. Compression
  3. Condensation
  4. Throttling
  5. Evaporation
PV diagram of Refrigeration cycle
PV diagram of Refrigeration Cycle
TS diagram of refrigeration cycle
TS diagram of Refrigeration Cycle

1) Suction Process:

First of all, the refrigerant is introduced into the compression chamber of the compressor. The refrigerant enters into the compression chamber as a vapor state.

2) Adiabatic Compression (1 to 2): 

The compressor has a piston that moves up and down inside the compression chamber. As the refrigerant enters the compression chamber, the inlet and outlet valve close, and the piston compresses the refrigerant.

Due to the compression process, the temperature of the vapor refrigerant increases from T1 to T2, and pressure increases from P1 to P2.  Line 1 to 2 of the above-given graph represents this process.

After the compression process, the compressed refrigerant enters into the condenser.

3) Condensation Process (2 to 3):

Line 2 to 3 represents the condensation process. As the compressed refrigerant enters into the condenser, the condenser condenses the compressed vapor refrigerant at constant pressure.

During the condensation process, the compressed refrigerant transfers its heat to the hot reservoir. Due to this heat transfer process, the vapor refrigerant converts into a liquid state. During this process, the enthalpy and volume of the refrigerant decrease. However, the pressure of the refrigerant remains the same during this whole process. After this process, the liquid refrigerant is transferred into the throttling valve for further process.

4) Throttling Process (3 to 4):

After the condensation process, the liquid refrigerant pushes into a throttling valve. As the refrigerant enters into this valve, it expands; due to that, the pressure and temperature of the liquid refrigerant reduce (As you can see in the above graph). However, the volume and enthalpy of the refrigerant increases.

After this process, the liquid refrigerant still remains in a liquid state; due to that, we need to pass it from the evaporator to convert liquid into a vapor state.

5) Evaporation Process (4 to 1):

Line 4 to 1 of the above-given PV diagram and TS diagram of the refrigeration cycle represent this process.

The evaporator is connected with a cold reservoir. As the low pressure and low-temperature liquid refrigerant enter the evaporator, the refrigerant absorbs heat from the cold reservoir and converts it into a vapor state. During this process, the volume and enthalpy of the refrigerant increase but its pressure and temperature remain constant.  

After this evaporation process, the vapor refrigerant again transfers to the compressor, and the whole cycle repeats.

Types of Refrigeration Cycles

The refrigeration cycle has the following major types:

  1. Stirling Cycle
  2. Reverse Carnot Cycle
  3. Vapour Compression Cycle
  4. Vapor Absorption Cycle
  5. Gas cycle

1) Vapour Compression Cycle

Maximum heat pumps, cooling systems, air conditioning system, and refrigeration use the vapor compression cycle. The vapour compression cycle uses two heat exchangers:

  1. One is a condenser with high temperature and emits heat at high temperatures.
  2. The other heat exchanger is an evaporator that absorbs heat at low temperatures.

The applications that work in both cooling and heating mode, a reversing valve is used to regulate the operation of these heat exchanges.

vapour compression cycle

As the vapour compression cycle starts working, the vapour refrigerant having low temperature and low pressure is introduced into the compressor.

The compressor increases the pressure and temperature and converts the vapor refrigerant into high pressure and high temperature superheated gas. This high-temperature superheated gas then flows into the condenser.

The condenser releases the heat of the gas into the atmosphere, condenses it, and transforms it into a liquid refrigerant.

After the condensation process, the liquid refrigerant enters the expansion valve. This expansion valve quickly lowers the pressure, which will cause a sudden drop in the temperature of the liquid refrigerant.

A cold mixture of liquid and low-pressure vapor then passes via the evaporator. The evaporator fully evaporates the mixture to absorb the heat from the environment and then returns to the compressor as a low temperature and low-pressure gas to recycle.

This type of refrigeration cycle uses in the vapor compression refrigeration systems, which are currently used for general freezing. The vapor compression cycle is used in all industrial applications, from small household refrigerators to large air conditioners.

2) Vapour Absorption Cycle

The working of the vapour absorption cycle is almost the same as the vapour compression cycle, but the absorption cycle increases the refrigerant’s vapour pressure. The absorption system uses a generator and an absorber instead of a compressor.

vapour absorption cycle

The absorbers dissolve the vapour refrigerant in the corresponding liquid (dilute solution), which turns the dilute solution into a concentrated solution. After this process, a pump uses to transfer the concentrated solution from the absorber to the generator.

As the concentrated solution enters the generator, the generator increases the pressure and temperature of the solution. After this process, the refrigerant vapor extracts from the concentrated solution.

Due to the removal of the refrigerant vapor, the concentrated solution again transforms in a dilute solution state, and a liquid pump pumps the refrigerant vapor back into the absorber.

The liquid pumps need to do some work, but they do a lot less work than compressors in a vapor compression cycle for a given amount of refrigerant. But, the generator of the absorption system needs a source of energy and consumes thermal energy.

Absorption refrigerators use the best suitable combination of absorbent and refrigerant. One of the perfect combinations is water (absorbent) and ammonia (refrigerant), as well as lithium bromide (absorbent) and water (refrigerant).

You can use renewable energies (such as solar energy, biomass, and waste-heat recovery) or fossil energy (such as natural gas, oil, coal, etc.) to power the absorption system.

Advantages of Vapour Absorption System
  1. It doesn’t need a compressor or any other reciprocating component.
  2. The vapour absorption refrigeration system has a long service life
  3. It is easy to operate.
  4. It has very low noise.
Disadvantages of Vapour Absorption System
  1. It has low COP
  2. This system has bulky size.
  3. The pump of this system has a very high cost.
  4. It needs high time to generate the refrigerating effect.

3) Gas cycle

A gas refrigeration cycle is a thermodynamic cycle that uses gas as a working medium, and this gas refrigerant doesn’t change its state even under the expansion and compression process. This cycle doesn’t have evaporation and condensation stages.

gas cycle

At certain extreme temperatures, the gas cycle has lower efficiency than the efficiency of the vapor compression cycle. This is because the vapour compression cycle works on the Rankine cycle while the gas cycle operates on the basis of the reverse Brayton cycle. Therefore, the working medium does not absorb or release heat at a constant temperature.

4) Stirling Cycle

Stirling heat engines can drive in the opposite direction. It uses mechanical energy to move the heat transfer in a reverse direction (i.e., heat pumps or coolers).

working of Stirling engine

You can create different layout configurations for this type of equipment. Some of these configurations require sliding or rotating seals, creating complex tradeoffs between refrigerant leaks and friction loss.

5) Reverse Carnot Cycle

This is a reversible cycle. The Carnot cycle has four processes (two isentropic and two isothermal) that can also work reversely. As the Carnot cycle starts working in the reverse direction, it is known as the reverse Carnot cycle.

Reversed Carnot cycle

The heat pumps or refrigerators that work in the reverse Carnot cycle are referred to as Carnot heat pumps or Carnot refrigerators.

A reverse heat engine uses an external source to move heat from the low-temperature body to the high-temperature body.

Components of Refrigeration

The refrigeration has the following major parts:

refrigeration system components

1) Compressor

The compressor is the most important part of the refrigeration cycle. It uses to increase the temperature and pressure of the gas. Before the compression process, the refrigerant has low pressure and temperature.

As the refrigerant introduces into the compressor, the compressor compresses the refrigerant and converts it into high pressure and high-temperature gas.

Different types of compressors are used in refrigerants. The most common types of compressors are given below:

  1. Rotary compressors
  2. Centrifugal compressors
  3. Scroll compressors
  4. Reciprocating compressors
2) Condenser

The condenser is a type of heat exchanger. As the compressed refrigerant enters the condenser, it removes heat from the compressed refrigerant and fully transforms it into saturated liquid refrigerant.

During this process, the temperature of the refrigerant reduces, but the pressure of the refrigerant remains high.

After the condensation process, the condensed refrigerant enters the expansion valve.

3) Expansion Valve

As the condensed or saturated liquid refrigerant enters the expansion valve, it expands. As the saturated liquid refrigerant expands, its pressure and temperature decrease.  During this process, the temperature of the refrigerant becomes equal to the surrounding temperature.

After the expansion process, the refrigerant transfers into the evaporator.

4) Evaporator

The evaporator uses to transform the liquid refrigerant into vapor refrigerant. The evaporator connects with the cold reservoir. As the liquid refrigerant enters the evaporator, it absorbs heat by the cold reservoir and the refrigerant transfers from the liquid state to the vapour state.

As the refrigerant transforms into a vapor state, it transfers to the compressors, and the whole cycle repeats.

Advantages and Disadvantages of Refrigeraion System 

Advantages of Air Refrigeration System

  • This refrigeration uses air as a refrigerant which is always available in the atmosphere.
  • The refrigerant (air) has no cost and is easily available.
  • This refrigeration has a very simple design and construction.
  • The air is non-corrosive, non-flammable, and non-toxic.
  • There is no fire hazard due to refrigerant leakage from the pipes.
  • This refrigerant can also be used cold air as a refrigerant.

Disadvantages of Refrigeration System

  1. This refrigeration system has a high operational cost.’
  2. The air refrigerant has lowO.P. than other types of refrigerants.
  3. The air refrigeration systems use more quantity of refrigerant than other refrigerants.
  4. This system has large and bulky parts.

Applications of Refrigeration System

  • Central air-conditioning
  • Surgical and medical aids
  • Freezing food product
  • Metal manufacturing
  • Chemical industries
  • Industrial air-conditioning
  • Food transportation
  • Ice making

Difference between heat pump and refrigeration cycle

Heat PumpRefrigerator
The heat pump transfers heat from the source (i.e., high-temperature area) to the sink (i.e., low-temperature area).The refrigerator transfers heat from the low-temperature area to the high-temperature area. The refrigerator is also known as a reverse heat pump.
The heat pump works on the heating cycle.The refrigerator works on the cooling cycle.
It uses to warm up a room or building.It uses to cool the room or a building.
The evaporator installs outside the room which is to be heated.The evaporator installs inside the room.
In the heat pump, the condenser installs in the room.In the refrigerator, the condenser installs outside the room.

FAQ Section

What are the four steps of refrigeration?

The refrigeration has the following four steps:

  1. Compression
  2. Expansion
  3. Condensation
  4. Evaporation

What are the four stages of refrigeration?

Refrigeration has the following four stages:

  1. Compression
  2. Expansion
  3. Condensation
  4. Evaporation

What is the refrigeration process?

The process of useless heat elimination from a specific area, point, or substance and transfer this heat to another area, point, substance, or atmosphere is known as a refrigeration process.

What are the types of refrigeration cycle?

The major common types of the refrigeration cycle are given below:

  1. Gas Cycle
  2. Vapour absorption cycle
  3. Vapour compression cycle

Who invented refrigeration?

n 1755, Scottish professor William Cullen invented the first artificial refrigeration. 

In a refrigeration cycle, the flow of refrigerant is controlled by?

An expansion or throttling valve uses to control the refrigerant flow.

What Are the Four Major Components of Refrigeration?

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

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