Comparing Drum-Pump and Direct Expansion Refrigeration Systems

This article reviews drum-pump and direct expansion technologies to provide guidance for refrigeration system selection.

A basic refrigeration system includes an evaporator, condenser, expansion valve, and compressor that facilitate a series of thermodynamic processes. A refrigerant that flows through the system changes phases as it absorbs heat in the evaporator and releases heat in the condenser. Such refrigeration systems are extremely common, and are used in nearly every home kitchen refrigerator and air-conditioning unit.

This article focuses on direct expansion and drum-pump refrigeration processes for the cooling of large quantities of hot process gases in an industrial system in which the evaporator is located in the process unit, away from the refrigeration system.

A drum-pump process is a liquid refrigeration pumped process in which the drum and pump are integrated into a single skid-mounted module; the liquid and vapor refrigerant are separated in the recycle drum. A direct expansion process does not require a pump and the phase separation takes place in the evaporator. Both direct expansion and drum-pump processes use circulating evaporators, in which the refrigerant in its vapor phase flows to the compressor and the liquid is recirculated in the evaporator. Circulating evaporators have a higher heat-transfer coefficient in the exchanger shell side than commonly used dry expansion evaporators.

This article compares direct expansion and drum-pump refrigeration, describes some of the challenges of each technology, and uses a case study simulation to examine the optimal configuration and power consumption of each technology.