MAJOR ASSIGNMENT VAPOUR COMPRESSION REFRIGERATION CYCLE

SUBMITTED TO- MR. ADITYA MISHRA

ASS.PROF.OF ME DEPT.

SUBMITTED BY-SAMANT SINGHUID –K11019B.TECH 3RD YEARBRANCH-MECHANICAL

Table of Content • Refrigeration• Refrigerant• Vapour compression cycle• Effect • Cop• Merit • Demerit• Advantage• Application • References

Introduction • It is a heat operated system.• It is quite similar to Vapour Compression systems. Condensation and

evaporation takes place at two different pressure levels to achieve refrigeration.• The main motive is to raise the temperature of the refrigerant from evaporator

pressure to condenser pressure.• Here refrigerant is dissolved in inert liquid in absorber and pumped to

condenser.• After raising pressure of refrigerant it is separated from solution by heating.• After condensation in condenser, refrigerant is throttled by expansion valve and

then it evaporates in evaporator providing the refrigeration effect.

Refrigeration

• Refrigeration is the process of producing of lower temperature compare to the surrounding temperature to maintain the lower temperature.

• For example : vapour compression cycle, vapour absorption cycle, gas refrigeration cycle.

Refrigerant

• Refrigerant are the substance which are used for producing lower temperature .for example ammonia,water,air,R-12,R-22,R-134.

Refrigeration effect: It is the amount of heat which is to be extracted from the storage space in order to maintain lower temperature is called desire effect of refrigeration system.

Vapour compression Refrigeration System:There are four component in Vapour compression cycle.

1. Compressor:- Compresses the refrigerant to high pressure and temperature from low pressure and temperature.

2. Condenser:- The latent heat of refrigerant is removed by circulating water or atmospheric air.

3. Expansion Valve:- In the throttle valve where the pressure is reduced at a controlled rate.

4. Evaporator:- A liquid-Vapour mixture refrigerant then enters the evaporator at low pressure where the latent heat of evaporation is converted into vapour and the cycle repeats.

Fig:- The P-h diagram is another convenient diagram often used to illustrate the refrigeration

cycle.

Determination of COP:

Assumptions made for drawing T-S and P-h Diagram:1. The refrigerant leaving the evaporator is dry and saturated.2. The compression of vapour in the evaporator is isentropic.3. There is no sub cooling of the refrigerant in the condenser.4. There is no pressure losses in the system.

Conditions of vapour at the end of compression:There are three different conditions at which the refrigerant from the compressor.a. Vapour is dry and saturated.b. Vapour is wet condition.c. Vapour is superheated condition.

COP Of V.C. CycleApply Steady flow energy equation ( Neglect K.E & P.E changes)1. Compressor: Q1-2 + C1

2/2 + Z 1 + h1 = W1-2 + C22/2 + Z 2+ h2

W1-2 = - ( h2 – h1)2. Condenser:Q2-3 + C2

2/2 + Z 2 + h2 = W2-3 + C32/2 + Z 3+ h3

Q2-3 = - (h2 - h3)3. Throttle Valve:Q3-4 + C3

2/2 + Z 3 + h3 = W3-4 + C42/2 + Z 4+ h4

h3 = h4 (Isenthalpic process)

4. Evaporator:Q4-1 + C4

2/2 + Z 4 + h4 = W4-1 + C12/2 + Z 1+ h1

Q4-1 + h4 = h1

Q4-1 = h1 – h4

Co-efficient of Performance: It is the ratio of net refrigerating effect to the work required to produce that effect.

Co-efficient of performance = Refrigerating effect/ Work input = ( h1 – h4 ) / (h2 – h1)

Effects of variation of properties on the performance of Vapour compression cycle:

Case 1:- Decrease in Evaporator:

RE= h1-h4

Win=h2-h1

COP= RE/Win

EffectReduction in Refrigeration effectsIncrease in work inputDecrease in COPDecrease in volumetric efficiency due to increase in pressure

ratio.

RE= h1-h4

Win=h2-h1

COP= RE/Win

• Case 2:- Increase in condenser pressure

Effect Reduction in Refrigeration effectsIncrease in work inputDecrease in COPDecrease in volumetric efficiency due to increase in pressure

ratio.

RE= h1-h4

Win=COP= RE/Win

• Case 3:- Superheating

Effect Increase in Refrigeration effectIncrease in work input due to temperature at the inlet to

compressor increase.COP may increase or decrease depending on the refrigerant. In

case of R- 12 superheating result in increase in COP where as in case of NH3 superheating results in decrease in COP.

MERIT

• Cop is high.• Size of evaporator is small.• Evaporator temperature adjustment is small.• Easily available .• It is used for small places like shops.

Demerit

• Initial cost is high.• Inflammability• Leakage• Toxicity

Advantages

• Lot of heat can be removed (lot of thermal energy to change liquid to vapors).

• heat transfer rate become high(temperature of working fluid much lower than what is being cooled).

Application • 1. Ice making.

• 2. Transportation of food items above and below freezing.

• 2. Industrial Air – Conditioning.

• 4. Comfort Air – Conditioning.

• 5. Chemical and related industries.

• 6. Medical and Surgical instruments.

• 7. Processing food products and beverages.

• 8. Oil Refining.

• 9. Synthetic Rubber Manufacturing.

• 10. Manufacture and treatment of metals.

• 11. Freezing food products.

• 12. Manufacturing Solid Carbon Dioxide.

• 13. Production of extremely low temperatures (Cryogenics)

• 14. Plumbing.

• 15. Building Construction.

References

• Er. R.K. Rajput.Vapour compression Refrigeration Systems. Feb 03, 2014, “A textbook of Refrigeration & Air-conditioning-2013”.

• Prof. M. Ramgopal. Various energy transfers in VARS (image). Feb 02, 2014, from http://nptel.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/

• Prof. R. C. Arora. Domestic Electrolux Refrigerator (image). Feb 02, 2014, from http://nptel.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Ref%20and%20Air%20Cond/pdf.