Vapor Compression Refrigeration Cycle: What, Diagram, Efficiency, Working, Steps


In this article the “Vapor compression refrigeration cycle” topic and vapor compression refrigeration cycle related facts are going to summarize to briefly that a clear concept can we get from it effortlessly.

In vapor compression refrigeration cycle a refrigerant which is stays in fluid is used within a system which stays in as closed and proposed to going in four methods such as compression, then cooling with condensation, after that that expansion and lastly heating with evaporation.

What is vapor compression refrigeration cycle?

In the system of air conditioning the vapor compression refrigeration cycle is commonly used. The fluid which is works as medium in the vapor compression refrigeration cycle is states in vapor state.

Vapor compression refrigeration cycle can be explain in this way lowering the inside temperature of a closed system than the normal temperature and helps to reject the excess amount of heat from the area of the closed system and after doing this process finally transfer the excess amount of heat in environment.

Vapor compression refrigeration cycle
Image – A simple stylized diagram of a heat pumps’s Vapor compression refrigeration cycle
1. Condenser; 2. Expansion valve; 3. Evaporator; 4. Compressor ;
Image Credit – Wikipedia

The compression refrigeration cycle of vapor is used in many purposes like, for domestic purposes, commercial purposes, industrial services and automobile sectors.

In vapor compression cycle the refrigerants which are used commonly they are, NH­_3, R – 12, and R- 11. In the vapor compression cycle of a refrigeration system which components are used they are listed below,

  • Refrigerant compressor
  • Liquid compressor
  • Liquid receiver
  • Evaporator valve

Expansion valve These Evaporator valve and Expansion valve both are called as refrigerant control valve.

Vapor compression refrigeration cycle diagram:

The Vapor compression cycle contain liquid refrigerant which act as a medium of the vapor compression refrigeration cycle. The refrigerant changes state of phase during the process for two times.

A simple type of vapor compression refrigeration cycle diagram if we observe then can found main four components.

They are components are,

Compressor:-

The refrigerant when it is vapour state that time it carry lower temperature and lower pressure than the regular one and enters to the compressor of the vapor compression refrigeration cycle from the evaporator of the system. After enter to the evaporator the vapour became carry higher temperature as well as higher pressure. The refrigerant vapor of the system which carries higher temperature and higher pressure is entering to the condenser with the help of discharge valve.

Condenser:-

In the condenser when the refrigerant vapors of the system which carries higher temperature and higher pressure is enter that time the vapor of the refrigerant became condensed and cooled for the coils are present in the pipe inside the air conditioning system.

When the refrigerant is go through the condenser that time latent heat is emitted in the surrounding of the condensing medium which consider as water or air.

Read more about Hydrocyclone Separator

Receiver:-

The liquid refrigerant which is in condensed state of phase is stored in a container from the condenser. The container where liquid refrigerant is stores is known as receiver. After go through the condenser liquid refrigerant is comes to the evaporator by the evaporator valve.

Expansion valve:-

Another name for the expansion valve is throttle valve. The function of expansion valve is to give permission to liquid refrigerant go through with high temperature and high pressure where the liquid refrigerant could reduce its pressure and temperature.

Evaporator:-

In the evaporator of any cooling system contain pipes or coils where the liquid refrigerant has low temperature and low pressure. In evaporator liquid refrigerant is evaporated and transfer into vapor refrigerant where the temperature and pressure is both are stays in low.

In the beginning of the process the liquid refrigerant change its state of phase liquid to vapor and after that the liquid refrigerant change state of phase from vapor state to liquid.

Vapor compression refrigeration cycle T-S and P-V diagram:

For any cooling system the cycle process of vapor compression can be figure out with the help of Pressure – Volume diagram and Temperature –Specific entropy diagram.

Pressure – Volume diagram

Image – Pressure – Volume diagram; Image Credit – Wikipedia


Temperature –Specific entropy diagram

Image – Temperature –Specific entropy diagram;
Image Credit – Wikipedia

If we observe the Pressure – Volume diagram and Temperature –Specific entropy diagram then can figure out refrigerant vapor is entr to the compressor in dry saturation situation. After that the saturated and dry refrigerant vapor is enter to the compressor of the refrigeration system at the point 1 where the vapor refrigeration is compress in isentropically process. Now the vapor refrigerant is go from 1 point to 2 point at this particular time pressure is increases from pressure of evaporator to pressure of condenser.

Now at the point 2 saturated refrigerant vapor is enter to the condenser. In condenser heat is emitted at the fixed pressure. For emission of heat normally temperature of the system is decreases and at the same time change of phase is happened. Latent heat is rejected and reaches to liquid refrigerant at saturation temperature at the point of 3.

Then the liquid refrigerant is passes by the expansion valve. In this situation liquid refrigerant decreases its pressure and throttle upbringing the enthalpy constant.

How vapour compression refrigeration system works?

The Vapor compression cycle is a method which is most commonly used in various fields because its cost of charge is very low and the construction of the vapor compression cycle is quite easy to establish.

The cycle process of vapor compression in refrigeration system is working based on reverse Rankine cycle. The Vapor compression cycle process is proceeding in four steps. They are listed below,

Image – The cycle process of vapor compression in refrigeration system; Image Credit – Wikipedia

In this below section the four steps are discusses,

Compression (Reversible adiabatic compression):

 The refrigerant of vapor compression cycle at low temperature and pressure stretched from evaporator to compressor where the refrigerant is compressed isentropically. The pressure is rises from p1 to p2 and temperature is rises from T1 to T 2.  The total workdone per kg of refrigerant happened during isentropic compression can be express as,

w = h2 – h1

Where,

h1 = Amount of enthalpy of vapor compression cycle in temperature T1, at the step of suction of compressor

h2  = Amount of enthalpy of vapor compression cycle in temperature T2, at the step of discharge of compressor.

Condensation (Constant pressure heat rejection):

The refrigerant of vapor compression cycle is passes through from compressor to condenser at high temperature and pressure. At constant pressure and temperature the refrigerant is completely condensed. The refrigerant changes its state from vapor to liquid.

Throttling (Reversible adiabatic expansion):

At high temperature and high pressure the refrigerant of vapor compression cycle is expanded through the process of throttling. That time the expansion valve is stays in low temperature and pressure. A little amount of liquid refrigerant is evaporating by the help of expansion valve and a huge amount of liquid refrigerant is vaporised by the help of evaporator.

Evaporation (Constant pressure heat addition):

The refrigerant mixture of vapor and liquid is completely evaporated and changed itself into vapor refrigerant. During this evaporation process the refrigerant is absorb latent heat which state is cool. The amount of latent heat absorption by the refrigerant in vapor cycle is known as Refrigerating effect.

Performance of vapour compression cycle in the refrigeration system:

The vapour compression cycle in the refrigeration system is working at evaporator in the law of Steady Flow Energy Equation,

h4 + Qe = h1 + 0

Qe = h1 – h4

The vapour compression cycle in the refrigeration system is working at condenser in the law of Steady Flow Energy Equation,

h2 + Qc = h3 + 0

Qc = h3 – h2

The vapour compression cycle in the refrigeration system is working at expansion valve in the law of Steady Flow Energy Equation,

h3 + Q = h4 + W

We know, value of Q and W is 0

So, we can write,

h3 = h4

Performance of vapour compression cycle in the refrigeration system is,

Vapor compression refrigeration cycle steps:

Vapor absorption cycle process is done by four steps.

Compression process:

In first of the Vapor absorption cycle process compression process is done. In this process vapor stays at very low pressure and temperature.  The vapor is enters to the compressor when it is compressed subsequently and isentropically. After this both temperature and pressure are increases.

Condensation process:

After completing the process in compressor vapor enter to condenser. The vapor is condensed in the high pressure and goes to the receiver tank.

Expansion process:

After completing the process in condenser vapour enter to expansion valve from receiver tank. The throttling process is done in the low pressure and low temperature.

Vaporization process:

After completing the process in expansion valve vapour enter to evaporator. In the evaporator the vapour is extracts heat and circulating fluid in the surrounding environment and in lower pressure vapour is vaporized.

If without throttling expansion is takes place then the level of temperature will be drop in very low temperature and undergoes sensible heat, latent heat to particularly reach to stage of evaporation.

Increasing Vapor compression refrigeration cycle efficiency:

Increasing Vapor compression refrigeration cycle efficiency in a system is listed below,

  1. Optimize setting
  2. Size of the compressors to match loads as nearly as possible
  3. Install VFDs on screw compressor
  4. Install VFDs on motor of the compressor
  5. Use integrated automation system
  6. Use floating head pressure to maintain ideal temperature.

Actual vapor compression refrigeration cycle:

Actual vapor compression cycle refrigeration cycle is not same process as the theoretical vapor compression refrigeration cycle. In the actual vapor compression cycle loss and unavoidable vapor is present.  The refrigerant leaves the evaporator in the state of superheat.

Frequent Asked Questions:-

Question: – Mention the characteristics for good refrigerant.

Solution: – Refrigerant is actually a medium which carry heat during the process of the vapor compression refrigeration cycle. In the refrigeration system heat is absorb from a lower temperature system and after that heat is rejected so system can absorb higher temperature.

The characteristics for good refrigerant is listed below,

  1. Refrigerant should have high critical temperature
  2. Refrigerant should have low boiling point
  3. Non toxic
  4. Non flammable
  5. Non explosive
  6. High latent heat of vaporization
  7. Non corrosiveness for the metals uses in the system of vapor compression refrigeration cycle
  8. Low specific heat of liquidity refrigerant
  9. Low specific heat of vaporized refrigerant
  10. Easy to identified leaks by taking smell or suitable indicator
  11. Easy to liquefy at moderate temperature and pressure.
Image – Refrigerant; Image Credit – Wikipedia

Question: – Describe the major difference between Carnot cycle and Rankine cycle.

Solution: – The major difference between Carnot cycle and Rankine cycle is discuss below,

ParameterCarnot CycleRankine Cycle
DefinitionCarnot cycle in not a practical cycle it’s a theoretical cycle. The efficiency of the carnot cycle is highest between difference of two temperatureRankine cycle in not a theoretical cycle it’s a practical cycle.
Ideal forCarnot cycle appropriate for heat engine.Rankine cycle is appropriate for vapor compression refrigeration cycle.
EfficiencyEfficiency of carnot cycle is higher than the rankine cycle.Efficiency of rankine cycle is lower than the carnot cycle.
Heat rejectionIn Carnot cycle heat rejection is done when temperature stays at constant.In Rankine cycle heat rejection is done when pressure stays at constant.

Indrani Banerjee

Hi..I am Indrani Banerjee. I completed my bachelor's degree in mechanical engineering. I am a enthusiastic person and I am a person who is positive about every aspect of life. I like to read Books and listening to music.

Recent Posts