Refrigeration Evaporators: Types, Performance, and Maintenance

Evaporator: The Cooling Component

The evaporator is the facility that produces the cooling effect. It's a heat exchanger where heat from the chamber transfers to the refrigerant, causing it to boil. The material must be a good heat conductor for efficient heat transfer. It doesn't necessarily have to be installed inside the enclosure being cooled.

Types of Evaporators

Flooded Evaporator

• The refrigerant is primarily in a liquid state.
• High-performance due to constant temperature difference between fluid and cooling medium.
• Typically uses float level regulators for expansion.

Finned Tube Evaporator

• Smaller size achieved due to increased surface area from fins.
• Fins come in various shapes (circular, square, etc.).
• Attached to the tube mechanically.
• Air circuits can be natural or forced:
  • Natural: Air circulates due to density differences, creating convection currents. Mounted on ceilings or walls.
  • Forced: Air circulation is driven by fans, allowing for closer fin spacing and staggered tube arrangement.

Evaporator Configurations

Direct Expansion

The evaporator cools the chamber directly, either installed inside or in an annex with air ducts for even distribution.

Indirect Expansion

Uses a secondary circuit to maintain temperature, suitable for chambers distant from the compressor.

Frigorific vs. Refrigerant

Frigorific Genome: Cooling coil in the primary circuit (evaporator) uses latent heat for cooling.

Frigorific Fero: Cooling coil in the secondary circuit uses sensible heat for cooling.

Defrosting

Defrosting eliminates frost that forms on the evaporator when humid air passes over the cooling coil, causing water droplets to freeze.

Influence of Pressure and Oil

Evaporator performance is directly related to suction pressure:

• Increased suction pressure raises fluid temperature, reducing the temperature difference and decreasing performance.
• Decreased suction pressure lowers fluid temperature, increasing the temperature difference and improving performance.

Fan-Coil Maintenance

• Clean filters regularly to maintain airflow and coil efficiency.
• Ensure proper condensate drainage.
• Lubricate fan motor bearings if needed.
• Check electrical consumption.