Vapor Compression Cycle: What, How, Types, Working, Applications and Various Facts:


In this article ”Vapor compression cycle ” is discuss and vapor compression cycle related facts are also summarize briefly. The vapor compression cycle is commonly used is the system of refrigeration.

In the system of refrigeration which follows the cycle of thermodynamic, is used in a wide range. The energy of heat is transforming from a cold reservoir and after that transfer into a hot reservoir. In a closed cycle fluids is used and go through compression, condensation, and expansion, evaporation process.

What is vapor compression cycle?

The Vapor compression cycle is used in automobile and refrigeration industry. Chilling the storage food items and meat in the warehouses, oil refineries, chemical processing plants many others it is widely used.

The Vapor compression cycle explain as a liquid refrigerant is uses which rotate circularly in the system and works as a medium. The liquid refrigerant absorb the heat from any particular space where cooling is needed and also can remove heat from any particular space where heating is needed for the system.

Vapor compression cycle
Image – Vapor Compression Cycle
Image Credit – Wikipedia Commons

The vapor compression cycle is done in a closed cycle. In the system of vapor compression cycle the fluid which is work as a medium is actually a vapor. In a very speedy mode the fluid is evaporate and changes itself alternatively between the liquid phase and vapor or condenses inside of refrigerating plant.

Vapor compression cycle diagram:

The Vapor compression cycle the liquid refrigerant changes its state of phase for two times. In first step liquid refrigerant change itself liquid to vapor and in next step change itself vapor to liquid.

The Vapor compression cycle diagram can be explain as help of two diagrams which is given below,

Pressure – Volume diagram

Image – Pressure – Volume diagram; Image Credit – Wikipedia

Temperature –Specific entropy diagram

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

Vapor compression cycle process and working principle:

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 – Vapor compression cycle process and working principle
Image Credit – Wikipedia Commons
  1. Compression
  2. Condensation
  3. Throttling
  4. Evaporation

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 T2. The total work done 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,

Output/Input = h1 – h4/h2 – h1

What is simple vapor compression cycle?

The simple vapor compression cycle air is used as a refrigerant and it is evaporate at very low temperature and low pressure. The mechanical energy is required to run the compressor of the system.

The simple vapor compression cycle can be explain as the heat engine which is works in reverse technically that can be known as Reverse Carnot engine. The simple vapor compression cycle transfer heat from lower temperature reservoir to higher temperature reservoir.

What is vapor compression cycle of a refrigeration system?

The vapor compression cycle of a refrigeration system is one of the most common used and popular refrigeration systems among the all refrigeration system. For both domestic and industrial purpose vapor compression cycle of a refrigeration system is used.

The vapor compression cycle of a refrigeration system is belong to the refrigeration cycle which is mainly general class type and in this system the refrigerant is undergoes phase chance , minimum during one process. The cycle is working in a closed system and refrigerant is moves in a circular motion.

In vapor compression cycle NH­3, R – 12, R- 11 refrigerant are uses. The vapor compression cycle of a refrigeration system consists of refrigerant compressor, liquid compressor, liquid receiver, evaporator and expansion valve which are known as refrigerant control valve.

Vapor absorption refrigeration cycle:

The vapor absorption refrigeration cycle can work easily where high power is not available. The main difference between vapor compression cycle and vapor absorption refrigeration cycle is compressor is replaced.

In the vapor absorption refrigeration cycle lowering the temperature of the system which is done in a closed system, refrigerant work as medium and removing unwanted heat from any particular space of the system and after removing transfer the heat where temperature is lower in the refrigeration system.

Read more about Saturated Suction Temperature : Need to know Critical Facts

In the vapor absorption refrigeration cycle generator, pressure reducing valve, expansion valve, condenser pump and absorber is used.  Ammonia is use in the system as a refrigerant and the mixture of ammonia, lithium bromide, water and water is used as an absorbent.

Ideal vapor compression cycle:

Ideal vapor compression refrigeration cycle system at first refrigerant enter into the compressor as a saturated vapor after that the refrigerant became cool to the liquid state of saturated inside the condenser. When the throttling process is happened in the evaporator vapour and pressure is absorb in the refrigerate space.

Simple vapor compression cycle:

Simple vapor compression cycle refrigeration cycle systems at first refrigerant enter into the compressor as a vapor at lower pressure. After that the refrigerant became superheated at higher pressure inside the condenser. When the throttling process is happened in the heat is release and enters to next process of the cycle.

Read more about Superheat Hvac : IT’S IMPORTANT CONCEPT AND 3 FAQs

Actual vapor compression cycle:

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

Read more about Superheat Refrigeration : Its All Important 4 notes

Vapor absorption cycle:

Vapor absorption cycle in the refrigeration system can be describe as refrigerant condensed in the condenser and evaporate at evaporator. In this all refrigeration system process are present such as compression, condensation and expansion evaporation. As a refrigerant lithium bromide, water or ammonia can be used.

Vapor absorption cycle applications:

Application of vapor absorption cycle in refrigeration system is given below,

Domestic refrigeration:

 In dwelling units food is storage in domestic refrigeration.

Cold storage and Food processing:

For processing, preserving and storage food items from its origin of source to the distribution point of the wholesale distributions.

Commercial refrigeration:

Displaying and holding fresh and frozen food items in retain outlet.

Medical refrigeration:

For keeping the medicine in right temperature medical refrigeration is used.

Electronic cooling:

For controlling temperature in large computers, CMOS circuit (Complementary metal–oxide–semiconductor)electronic cooling is used.

Vapor absorption cycle working principle:

The Vapor absorption cycle working principle is summarize in below,

  1. At beginning of the process vapour comes from evaporator and then go to absorber and vapour is absorbed in water.
  2. During the process of absorbing latent heat and heat of mixing is emitted.
  3. Cooling process is done by the absorber to keep the temperature lower in the system.
  4. Absorbing capacity is increases when the absorber is in lower temperature.
  5. Strong aqua mixture of ammonia and water is comes from the absorber and go to the top of the analyzer with the help of pump through aqua heat exchanger.
  6. By the generator the aqua falls mixture is sent to analyzer. In the generator higher temperature is present for this reason low boiling ammonia easily can be separate from the mixture.
  7. The heating process of the generator can be done with the help of solar energy, steam energy or electric energy. In this time ammonia vapour is raises by the analyzer.
  8. During this process wet vapour became dry vapour and sent to the condenser by rectifier.
  9. Water is separated. After separation water is again back to generator this known as Drip. Anhydrous ammonia vapour only goes to the condenser. Liquid ammonia go from condenser to evaporator through the valve of expansion for continue the cycle.
  10. When the aqua mixture is hot it became weaker and comes to evaporator of the system through the heat exchanger. The weak hot aqua again absorbs the vapour of ammonia and cycle stays in continue.
  11. Heat exchanger of the aqua heat the strong aqua mixture and pass to the generator in this process heat is reduced in the heating materials in the generator.

Vapor absorption cycle processes:

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 vapour stays at very low pressure and temperature.  The vapour 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 vapour enter to condenser. The vapour 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.

Difference between vapor compression and absorption cycle:

The vital difference between vapor compression and absorption cycle is Coefficient of performance vapor compression is high and for vapor absorption refrigeration cycle Coefficient of performance is low.

In below briefly the Difference between vapor compression and absorption cycle is given,

ParticularVapor compression cycle of a refrigeration systemVapour absorption refrigeration cycle of a refrigeration system
Coefficient of performance(COP)High, range is about 0.3Low, range is about 0.6
NoiseVery high operationQuiet operation
Wear and TearHigh, because moving parts are more present in the system of the compression.Low, because moving parts are less present in the system of the absorption.
BulkinessMore lessMore
Presence of shelterCannot situated in outside of the system without shelterCan be situated in outside of the system without shelter
Affected by loadsToo muchReduction of load no effect
Leakage possibilityMoreLess
Charging of refrigerantSimpleComplicated
Working of high grade energyHigh, electrical energy is needed to precede the operation.Low, electrical energy is not needed to precede the operation, by the help of Ignition combustion engine, process heat or kerosene lamp the vapour absorption refrigeration cycle of a refrigeration system can work.
Operating costHighLess
CapacityLess, upto 1000 tonsMore, above 1000 tons
Suitable refrigerantNH­_3, R – 12, R- 11Ammonia
Energy supplied as inputMechanicalHeat energy
Condition of refrigerantCompressedAbsorbed and heated.
Supply of energyLowHigh
Maintenance costHighLow
PressureHighLow
Work capacityLimitedLarge

Frequent Asked Question:-

Question: Write down the advantages of Vapor Compression refrigeration cycle.

Solution: The advantages of Vapor Compression refrigeration cycle is listed below,

  1. Coefficient of performance is too high.
  2. Size is not too big for this reason installation is easy.
  3. Running cost is low.
  4. Temperature can be easily handled by the help of regulating expansion valve.
  5. Evaporator size is not big.

Question: Write down the disadvantages of Vapor Compression refrigeration cycle.

Solution: The disadvantages of Vapor Compression refrigeration cycle is listed below,

  1. The refrigerants which are used they are toxic.
  2. Initial cost is high.
  3. Leakage is present.

Indrani Banerjee

Hi..I am Indrani Banerjee. I completed my bachelor's degree in mechanical engineering. I am an enthusiastic person and I am a person who is positive about every aspect of life. I like to read Books and listen to music. Let's connect through LinkedIn-https://www.linkedin.com/in/indrani-banerjee-2487b4214

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