Refrigerant Expansion Energy Recovery System

The objective of this proposal is to demonstrate the feasibility of a scroll expansion device for energy recovery in a trans-critical CO2 vapor compression cycle, using conditions typical of Army Environmental Control units (ECUs). Implementation of ascroll expander in a CO2 vapor compression system such as an ECU has the potential to improve system performance so that it is comparable to or even surpasses that of conventional fluorocarbon-based systems. Scroll designs are used extensively incompressors for air conditioners and heat pumps and have also been used for expansion devices. The pressures and flow rates expected in a CO2 ECU are well-suited to a scroll device. Preliminary calculations suggest that bearing loads are manageable, andthat the two scrolls can be manufactured to sufficient accuracy using conventional computer numerically controlled (CNC) milling techniques. Therefore, we would expect the device to maintain high volumetric and mechanical efficiencies, thus substantiallyimproving the overall ECU efficiency. The use of a scroll expander in a CO2 vapor compression system can substantially improve system efficiency, thus enhancing the potential for commercialization of CO2- based air conditioners and heat pumps in a widevariety of applications.