A refrigerated dryer is a type of compressed air dryer that removes moisture from compressed air by cooling it down to a temperature where the water vapor in the air condenses and can be removed. The principle of a refrigerated dryer is based on the fact that cooler air can hold less moisture than warm air.

In a refrigerated dryer, the compressed air is passed through a heat exchanger where it is cooled down to a temperature between 35°F and 50°F (1.7°C to 10°C) using a refrigerant. The moisture in the air then condenses into liquid form, which is drained out of the system. The cooled and dried air is then reheated before it is delivered to the point of use.

The refrigeration system of the dryer typically includes a compressor, a condenser, an evaporator, and an expansion valve. The compressor compresses the refrigerant gas, which is then cooled in the condenser and sent through the expansion valve to lower its pressure. This causes the refrigerant to expand and cool down further, which is used to cool down the compressed air in the heat exchanger.

Overall, the principle of a refrigerated dryer involves cooling down compressed air to a temperature where the moisture in the air condenses, and then separating the moisture from the air before delivering it to the point of use.