Paper No 217 – Development of a Near-isothermal Compressor for Transcritical Carbon Dioxide Cycle – 14th IEA Heat Pump Conference, Chicago, USA
This study demonstrates the feasibility of a near-isothermal compressor for the transcritical CO2 compression cycle. A copper tube-based compression chamber was designed, built, and installed in the open-loop liquid piston compression system. The oil compressed the CO2 in the chamber from 40°C, 4,000 kPa to 10,000 kPa by an external gear pump. A 59% isothermal compression efficiency was measured at 900 RPM motor speed. To increase the efficiency, we tried the following two options: (1) lower the operation speed and (2) enhance the heat transfer rate. Evaporative cooling was applied by installing a mist generator in front of the chamber to improve the outer heat transfer performance. According to the experimental results, simply slowing down the operation to 270 RPM increases the efficiency to 80%, and combining evaporative cooling and slower operation delivers 93.8% of isothermal efficiency. Under this enhancement, the compression power can be 30% less than the isentropic compression. Several suggestions have been proposed to improve the current prototype's performance.