An Improved Heat Exchanger and An Oil Separator For CO2 Heat Pumps

"The U.S. military's Environmental Control Units (ECUs) predominantly operate with halogen-containing refrigerants (CFCs or HCFCs). Since many of these units are nearing the end of their useful lives, an opportunity exits to develop more efficient, costeffective, and easily supportable systems that use natural refrigerants such as CO2. While CO2 systems possess advantages over conventional systems, they also present technical challenges that need to be solved before their wide use in military andcommercial applications. Advanced Thermal and Environmental Concepts (ATEC), Inc. in collaboration with ThermaSys Inc. and the University of Maryland propose to develop highly effective oil free heat exchangers that will boost the Coefficient ofPerformance (COP) of CO2 systems. The proposed effort will consist of two tasks. The first task involves development of a novel, inexpensive, controllable (on-line/on-demand) oil separation unit for separation of oil from CO2. The second task willinvolve development of innovative micro channel heat exchangers using passive or active heat transfer enhancement techniques. The results of this research will enable the design of cost effective, oil-free heat exchangers that are lighter in weight andsmaller in size than the state-of-the-art heat exchangers. Development of high efficiency, oil-free micro channel heat exchangers can substantially boost the Coefficient of Performance (COP) of CO2 systems,