dryexpansion

Dry expansion is a method used in refrigeration and air conditioning where the evaporator is fed by a metering device that throttles the refrigerant to the evaporator, with the design intended to operate with little or no liquid flood inside the evaporator. In a dry-expansion system, the expansion device lowers the pressure of the liquid refrigerant so it enters the evaporator at its low evaporating pressure. As heat is absorbed, the refrigerant partially vaporizes inside the evaporator, and the outlet from the evaporator is kept at a controlled level of superheat to prevent liquid slugging back to the compressor.

How it works: The expansion device (which can be a thermostatic expansion valve, electronic expansion valve, or sometimes a fixed-size capillary tube in small systems) restricts flow so that only a portion of the refrigerant—the liquid that reaches the evaporator—evaporates there, while vapor continues to flow toward the compressor. The evaporator is designed to operate with a high fraction of dry vapor, and the system relies on maintaining adequate superheat at the evaporator outlet for safe compressor protection.

Advantages and limitations: Dry expansion systems can be simpler and cheaper for small or low-charge installations and reduce the risk of liquid slugging when properly tuned. However, they require accurate control of superheat and load-dependent metering; performance can decline at partial loads, and misadjustment can lead to reduced efficiency or compressor damage if liquid refrigerant enters the compressor.

Applications: Dry expansion has been used in various small to medium refrigeration and air-conditioning applications, particularly where simple metering and low cost are priorities. It is often contrasted with flooded-evaporator designs, which rely on liquid refrigerant flooding the evaporator to improve heat transfer.