Lesson 7.6: Refrigeration & Air Conditioning (Vapor Compression, Psychrometrics)

Refrigeration and Air Conditioning are essential topics in thermal engineering. GATE and PSU exams often test vapor compression cycles, psychrometric properties, and system analysis.

🔹 1. Introduction

• Definition:

  • Refrigeration: Process of removing heat from a space or substance to maintain temperature below surroundings.

  • Air Conditioning: Control of temperature, humidity, and air quality in an enclosed space.

• Applications: Domestic refrigerators, cold storage, AC systems, industrial cooling

• Key Concepts: Coefficient of performance (COP), refrigeration effect, psychrometrics, vapor compression cycle

🔹 2. Vapor Compression Refrigeration Cycle (VCR)

• Components: Compressor, Condenser, Expansion Valve, Evaporator

• Process:

  1. Compression: Low-pressure vapor compressed to high-pressure vapor (work input)

  2. Condensation: High-pressure vapor rejected to surroundings (heat Q_out)

  3. Expansion: Throttling through expansion valve (pressure drop, temperature drop)

  4. Evaporation: Absorbs heat from refrigerated space (heat Q_in)

• COP (Coefficient of Performance):

COPref=QinWinputCOP_\text{ref} = \frac{Q_\text{in}}{W_\text{input}}COPref​=Winput​Qin​​

• Applications: Domestic and industrial refrigerators, AC systems

🔹 3. Psychrometrics

• Definition: Study of air properties and moisture content

• Key Properties:

  1. Dry bulb temperature (DBT)

  2. Wet bulb temperature (WBT)

  3. Relative Humidity (RH)

  4. Dew Point

  5. Specific Humidity / Humidity Ratio

• Processes:

  1. Heating & Cooling of air

  2. Humidification & Dehumidification

  3. Mixing of air streams

• Psychrometric Chart: Graphical representation of air properties used in AC system design

🔹 4. Solved Examples (PYQ Style)

1. Calculate COP of vapor compression cycle given pressures and temperatures

2. Determine refrigeration effect for given mass flow of refrigerant

3. Find relative humidity and dew point using psychrometric chart

4. Analyze cooling load for air conditioning system

🔹 5. Practice Exercises

1. Draw and analyze PV and TS diagrams of VCR cycle

2. Calculate work input and heat rejection in a refrigeration system

3. Solve psychrometric problems for humidification and dehumidification

4. Compute COP and efficiency of AC systems

5. Determine air properties for given DBT and WBT

🔹 6. Summary

• Refrigeration: Removing heat to maintain low temperature

• Air Conditioning: Control of temperature, humidity, and air quality

• Vapor Compression Cycle: Most widely used refrigeration cycle

• Psychrometrics: Study of air properties for AC system design

• Exam Tip: Draw PV/TS diagrams and use psychrometric charts for accurate solutions