Career Point Cares

R.A.C. Assignment Topic: V.C. Cycle

Submitted To, Submitted By,Mr. Aditya Mishra Sir Chinmay Sharma(K10881)

B.tech (Mechanical)sem./year:- 6th/ 3rd

Career Point Cares

COP of Vapour Compression CycleDefinition of Refrigeration:

Refrigeration is the process of Producing lower temperature as compared to surrounding. To maintain lower temperature continuously, heat must be extracted continuously. Hence

Refrigeration system must operate in a cycle.

Career Point Cares

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.

Career Point Cares

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

cycle.

Career Point Cares

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.

Career Point Cares

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

Career Point Cares

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)

Career Point Cares

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

Career Point Cares

• Effects:-Reduction in Refrigeration effectsIncrease in work inputDecrease in COPDecrease in volumetric efficiency due to increase in pressure

ratio.

Career Point Cares

RE= h1-h4

Win=h2-h1

COP= RE/Win

• Case 2:- Increase in condenser pressure

Career Point Cares

• Effects:-Reduction in Refrigeration effectsIncrease in work inputDecrease in COPDecrease in volumetric efficiency due to increase in pressure

ratio.

Career Point Cares

RE= h1-h4

Win=COP= RE/Win

• Case 3:- Superheating

Career Point Cares

• Effects:-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.

Career Point Cares