Refrigeration Cycle Experiment: Procedure, COP Calculation, and P-H Diagram

Refrigeration Cycle Experiment: Procedure, COP Calculation, and P-H Diagram

The refrigeration cycle experiment on a vapour compression refrigeration unit allows engineering students to analyse the complete refrigeration cycle, compressor, condenser, expansion valve, and evaporator, measuring pressures, temperatures, and power consumption to determine the Coefficient of Performance (COP) and compare it with the ideal Carnot COP. This guide covers theory, apparatus, procedure, observation table, and P-H diagram construction for engineering laboratory use.

Theory: Vapour Compression Refrigeration Cycle

The standard vapour compression cycle operates on four processes:

• 1→2 Compression: Refrigerant vapour is compressed adiabatically, pressure and temperature rise
• 2→3 Condensation: High-pressure vapour condenses to liquid in the condenser, rejecting heat Q_H to surroundings
• 3→4 Expansion: Liquid refrigerant expands through a throttle valve, pressure and temperature drop
• 4→1 Evaporation: Low-pressure refrigerant evaporates in the evaporator, absorbing heat Q_L (the refrigeration effect)

Refrigeration effect: Q_L = m × (h₁ – h₄) kW

Compressor work: W = m × (h₂ – h₁) kW

Actual COP: COP = Q_L / W

Carnot COP (ideal): COP_Carnot = T_L / (T_H – T_L)

Apparatus Description

Scientico India’s Refrigeration Training Unit consists of:

• Hermetically sealed compressor (R-134a or R-22 refrigerant)
• Air-cooled or water-cooled condenser
• Thermostatic expansion valve (TEV) and sight glass
• Evaporator with calorimeter for refrigeration effect measurement
• High and low side pressure gauges (compound gauge)
• Thermocouple array at compressor inlet/outlet, condenser outlet, evaporator outlet
• Wattmeter for compressor power input
• P-H chart for refrigerant for plotting the cycle

Experimental Procedure

1. Start the refrigeration unit and allow system to reach steady state (10–15 minutes)
2. Record high-side pressure P₂ (condenser) and low-side pressure P₁ (evaporator)
3. Record temperatures: T₁ (compressor suction), T₂ (compressor discharge), T₃ (condenser outlet), T₄ (evaporator inlet)
4. Record compressor power input W from wattmeter (watts)
5. If calorimeter is fitted: measure water flow rate and temperature rise to calculate Q_L directly
6. Use refrigerant P-H chart to read enthalpy values h₁, h₂, h₃, h₄ at the measured pressures and temperatures
7. Calculate refrigeration effect Q_L, compressor work W, COP_actual, and COP_Carnot
8. Repeat at 2–3 different condenser temperatures (vary cooling water or load)

Observation Table

Parameter	Run 1	Run 2	Run 3
Low-side pressure P₁ (bar)
High-side pressure P₂ (bar)
Suction temp T₁ (°C)
Discharge temp T₂ (°C)
Condenser outlet T₃ (°C)
Evaporator inlet T₄ (°C)
Compressor power W (W)
h₁ (kJ/kg)
h₂ (kJ/kg)
h₃ = h₄ (kJ/kg)
Q_L (kW)
COP_actual
COP_Carnot

P-H Diagram Construction

1. Plot points 1 (h₁, P₁), 2 (h₂, P₂), 3 (h₃, P₂), 4 (h₄, P₁) on the refrigerant P-H chart
2. Connect: 1→2 (vertical compression line), 2→3 (horizontal condensation), 3→4 (vertical throttling), 4→1 (horizontal evaporation)
3. Identify the two-phase (wet) region and superheat region on the diagram
4. Compare actual cycle to ideal (no superheating, no subcooling) cycle

Viva Questions

• Why is the COP_actual always less than COP_Carnot?
• What is superheat in the refrigeration cycle and why is it desirable?
• How does increasing the condenser temperature affect COP?
• What is the function of the sight glass in a refrigeration system?
• Compare vapour compression and vapour absorption refrigeration systems

Get a Quote

Scientico India exports CE-certified Refrigeration Training Units to engineering colleges in UAE, Saudi Arabia, Kenya, Malaysia, Bangladesh, Philippines, and 60+ countries. Contact [email protected] for a proforma invoice within 24 hours.

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