Piston-cylinder work producing expansion device in a transcritical carbon dioxide cycle. Part I: experimental investigation

Abstract Carbon dioxide is receiving strong consideration as an alternative refrigerant substituting hydroclorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs) due to its zero ozone depletion potential and negligible global warming potential. The system performance of CO2 systems, however, is typically poor compared to the current conventional air conditioning systems using HCFC or CFC. One of the most effective ways to achieve parity with CFC and HCFC systems is to replace the expansion valve with an expansion device that minimizes entropy creation and allows for energy recovery during the expansion process. A piston-cylinder type work output expansion device was designed, constructed and tested as part of the study reported here. The first-cut prototype device is based on a highly modified small four-cycle, two-piston engine that is commercially available. The work-producing expander replaced the expansion valve in an experimental transcritical CO2 cycle and increased the system performance by up to 10% as characterized by COP. The prototype device was not meant to be a final product, but provided valuable insight and experimental results to validate a detailed simulation model of the device. The model and corresponding theoretical analysis are presented in a companion part II paper.