The working principle of the evaporator is based on the physical law of phase change absorbing heat. It follows the four steps of the entire refrigeration cycle:
Step 1: Pressure reduction
The high-pressure and normal-temperature liquid refrigerant from the condenser flows through the capillary tube (or expansion valve) for throttling, resulting in a sudden drop in pressure and changing into low-pressure and low-temperature liquid (containing a small amount of gas), preparing for evaporation.
Step 2: Evaporation and heat absorption
These low-temperature and low-pressure liquid refrigerants enter the coil of the evaporator. Due to the very low pressure, the boiling point of the refrigerant becomes extremely low (much lower than the internal temperature of the refrigerator). Therefore, it quickly absorbs the heat from the air flowing over the surface of the evaporator, boils and evaporates into low-pressure and low-temperature gaseous refrigerant.
This “liquid → gas” phase change process absorbs a large amount of heat (latent heat of vaporization), which is the fundamental reason for refrigeration.
Step 3: Continued heat absorption
The gaseous refrigerant continues to flow forward in the evaporator pipes and further absorbs heat, causing a slight increase in temperature (overheating), ensuring that the liquid refrigerant completely evaporates and avoiding liquid impact on the compressor.
Step 4: Return
Finally, the low-pressure and low-temperature gaseous refrigerant at the end of the evaporator is drawn back by the compressor and enters the next cycle.
The entire process can be summarized as a simple formula: Refrigerant evaporation (phase change) → Absorbing a large amount of heat → The internal temperature of the refrigerator drops.
The difference between direct-cooling and air-cooling refrigerator evaporators
Characteristics: Direct-cooling refrigerator Air-cooling refrigerator
Evaporator location: Visible directly (on the inner wall of the freezer) Hidden (behind the back panel or between the layers)
Heat exchange method: Natural convection: Air contacts the cold wall and naturally sinks Forced convection: Air is blown through the finned evaporator by a fan
Frosting situation: Manual defrosting (frost accumulates on the visible inner wall) Automatic defrosting (frost is periodically removed by a heater, and the water is drained)
Temperature uniformity: Poor, with temperature differences Better, the fan makes the cold air circulation more uniform
Post time: Aug-27-2025