Direct Expansion System | Cold Plate

Direct Expansion System

A direct expansion system enables the most compactly designed refrigerant system. A direct expansion system eliminates the use of a secondary coolant loop and uses the refrigerant to directly cool the desired payload via a cold plate. The cold plate can be customized to generate a very high heat flux, operating at temperatures well below ambient. In the cold plate of a direct expansion system, the refrigerant undergoes an isothermal phase change, which offers extremely tight temperature control across the cold plate.

A direct expansion system consists of the basic 4 components of a vapor compression refrigeration system: a compressor, a condenser, an expansion valve, and an evaporator. In a DX system, the evaporator absorbs heat directly from the payload. Because no secondary coolant is required, minimal parts are needed in the system. No fans are required to circulate the cool air and no pump is required to circulate the coolant. These additional components add complexity and inefficiency. A secondary coolant (air or liquid) dictates additional thermal resistance and they add heat to the system which reduces the net cooling capacity. The figure below demonstrates the details of a vapor compression refrigeration cycle for a direct expansion system.

Direct Expansion System schematic for high heat flux applications

Direct Expansion System Schematic

A Direct Expansion system using Aspen’s miniature compressor technology offers the most compact cooling solution. Aspen’s miniature systems can fully integrate into a final solution which is compact, quiet, reliable and affordable.  Direct expansion cold plates can be found in many applications.  For instance, active thermal management of industrial, medical and scientific lasers where the cold plate is mounted directly to the laser module.  The temperature can be controlled with high precision, +/- 0.4°C.  With Aspen Systems rotary compressor, extremely compact systems can be designed for high heat flux applications in electronics cooling, batteries, laboratory cold plates, etc.

Examples of direct expansion systems