Condensers, Expansion Valves, Evaporators & Controls in Refrigeration Systems
Refrigeration systems rely on several key components working together to achieve efficient cooling. Among these, the condenser, expansion valve, evaporator, and control devices play crucial roles. Let’s break down their functions, types, and importance in detail.
🌡️ Condensers
The condenser is the component where heat is removed from the refrigerant and transferred to the ambient medium (air or water).
- Purpose: Converts high-pressure/high-temperature vapor refrigerant into high-pressure/high-temperature liquid while rejecting heat.
- Heat Rejected: Equal to the heat absorbed during evaporation plus the heat added during compression.
Working Principle
- Hot vapor refrigerant from the compressor enters the condenser coils.
- As it passes through, the refrigerant rejects its latent heat to the surrounding medium (air or water).
- The refrigerant condenses into liquid form and is collected in a receiver, from where it is supplied to the expansion valve.
Types of Condensers
- Water-Cooled Condenser – Uses water as the cooling medium, common in large industrial systems.
- Air-Cooled Condenser – Uses ambient air, often with fans, suitable for domestic and commercial units.
- Evaporative Condenser – Combines air and water cooling, offering high efficiency in hot climates.
🔧 Expansion Valve
The expansion valve regulates the flow of liquid refrigerant into the evaporator.
- Function: Reduces refrigerant pressure and temperature, allowing controlled entry into the evaporator.
- Some refrigerant may evaporate during throttling, but the majority vaporizes inside the evaporator.
🌀 Evaporators
The evaporator is the cooling section of the system.
- Function: The refrigerant absorbs heat from the surroundings during evaporation, producing the cooling effect.
- Process:
- Low-pressure liquid refrigerant enters the evaporator coils.
- It absorbs its latent heat of vaporization from the medium being cooled.
- The refrigerant changes into low-pressure vapor and returns to the compressor.
Key Notes
- Evaporation is pressure-dependent; at higher altitudes, evaporation temperature changes due to atmospheric pressure differences.
- Evaporators are designed with coils of pipes to maximize heat transfer.
Advantages
- Smaller size for a given refrigerating capacity.
- Higher coefficient of performance (COP).
- Lower power requirements.
- Simple design and operation.
- Usable over a wide temperature range.
⚙️ Essential Controls in Refrigeration
For reliable and economical operation, refrigeration systems are equipped with control devices.
1. Starting Relay
- Provides the necessary torque to start the compressor motor.
- Disconnects the starting winding once the motor reaches operating speed.
- Works on the principle of electromagnetism.
2. Overload Protector
- Protects compressor motor windings from damage due to excessive current.
- Uses a bimetallic strip that bends when overheated, opening motor contacts.
- Responds to abnormal conditions like low/high voltage, high load, or abnormal suction/discharge pressures.
3. Thermostat
- Controls the temperature inside the refrigerator or freezer.
- A bulb filled with refrigerant senses temperature changes.
- Cut-out temperature → Motor stops when desired cooling is achieved.
- Cut-in temperature → Motor restarts when temperature rises.
- Reduces compressor running time, lowering operating costs and extending compressor life.
✅ Conclusion
The condenser, expansion valve, evaporator, and control devices form the backbone of refrigeration systems.
- The condenser rejects heat.
- The expansion valve regulates refrigerant flow.
- The evaporator absorbs heat to create cooling.
- The controls ensure safe, efficient, and economical operation.
By understanding these components, learners and professionals can grasp how refrigeration systems achieve efficient cooling and how each part contributes to overall performance.