Design and Setup of the Micro-Turboexpander Transcritical CO2 System

The relative low COP of transcritical CO2 systems caused by the throttle valve limited the further development. The replacement of a throttle valve with a turboexpander, an ejector or a vortex tube is leading to the way for improving the COP of a transcritical CO2 system. In this paper, a transcritical carbon dioxide refrigeration cycle with different expansion devices was analyzed theoretically using the first and second laws of thermodynamics. A transcritical CO2 system with micro-turboexpander for refrigerating capacity of 15 kW was designed and set up. Two turboexpanders with 10.6 mm radial reaction turbine wheel and 10.1 mm rotor diameter were designed for the 15 kW transcritical CO2 refrigeration system, and the rotating speed is about 100 krpm. The proposed turboexpanders outlet states are CO2 two-phase flow and subcooled CO2 liquid flow, respectively. This study will lay a foundation for the application of turboexpanders in transcritical CO2 systems.