Composition of Refrigerated Air Dryers

The freeze-drying principle of refrigerated air dryers generally works below 0°C while the medium remains frozen. 

Only at the later stage for reducing residual moisture content will the medium temperature rise above 0°C, normally not exceeding 40°C.

Under vacuum conditions, after water vapor sublimates directly, the substance remains in the frozen ice frame and forms a spongy porous structure. 

Therefore, its volume barely changes after drying. Once purified water for injection is added before reuse, the substance dissolves rapidly.

1. Compressor

Most refrigeration compressors adopted by refrigerated air dryers are medium-and-high temperature hermetic reciprocating compressors. 

They feature compact structure, small size, light weight, low vibration, low noise and high energy efficiency ratio.

The motor and compressor body of the hermetic compressor are sealed inside a steel shell. The motor operates in gaseous refrigerant and enjoys favorable cooling conditions for longer service life. 

A specified volume of lubricating oil is stored at the bottom of the dryer shell to automatically lubricate all components during operation, and supplementary oil is generally unnecessary.

2. Heat Exchanger & Evaporator

The core function of the heat exchanger is to recover cold energy carried by compressed air cooled in the evaporator (waste cold for most users). 

Such cold energy cools high-temperature compressed air saturated with water vapor, lowering the thermal load of the refrigeration system and realizing energy saving.

The temperature of low-temperature compressed air rises inside the heat exchanger, preventing condensation on the outer wall of exhaust pipelines caused by excessively low temperature.
3. Condenser & Sub-cooler
The condenser in a refrigerated air dryer cools high-pressure superheated refrigerant vapor discharged from the refrigerant compressor into liquid refrigerant to sustain continuous refrigeration circulation.

Heat dissipated by the condenser includes heat absorbed by refrigerant inside the evaporator plus heat converted from compression work. Hence the condenser bears a larger load than the evaporator. 

Condensers for refrigerated air dryers fall into two categories: air-cooled condensers and water-cooled condensers.

4. Cyclone Separator (Gas-Water Separator)
The cyclone separator belongs to inertial separators and is widely applied for gas-solid separation.

Compressed air enters tangentially along the cylinder wall and creates rotary flow inside. Water droplets mixed in the gas rotate simultaneously and generate centrifugal force. 

Larger droplets with greater centrifugal force move toward the outer wall, gather after hitting the baffle wall and separate from the airflow.

5. Hot Gas Bypass Valve

Mass condensed water precipitates when compressed air is cooled inside the evaporator. The refrigerant evaporation temperature needs to be controlled to prevent faults. 

A simple and effective solution is installing a hot gas bypass valve between the condenser and evaporator. The pressure sensing tube of the valve is directly connected to evaporation pressure.

When evaporation pressure drops below the set threshold, the hot gas bypass valve opens automatically. 

High-temperature refrigerant vapor from the condenser flows directly into the evaporator to raise evaporation temperature and avoid ice blockage.

6. Automatic Drain Valve
Condensed water inside the refrigerated air dryer shall be drained timely to prevent increased moisture content in compressed air. Automatic drain valves are equipped for convenient water discharge.
When the water level in the drain cup fails to reach the designated height, compressed air pressure presses down the float ball to seal the drain outlet and avoid air leakage.
7. Filter Drier

During the operation of refrigeration equipment, impurities such as moisture, solid powder and dirt exist in refrigerant and refrigeration oil, 

which may cause blockage of throttling holes under severe conditions. Therefore, a filter drier must be installed upstream of the refrigerant liquid supply pipeline.

Trace moisture in refrigerant brings the greatest harm to the refrigeration system. Drying treatment of refrigerant, refrigeration oil, evaporator, condenser and connecting pipelines is extremely critical.