EFFECT OF RESIDUAL NON-CONDENSABLE GASES ON THE PERFORMANCE OF A CARBON DIOXIDE EVAPORATOR AND THE SYSTEM PERFORMANCE

Inert gases are conveniently used for leak detection. Relative to CO2, majority of the inert gases are non-condensable. It is of great significance to understand the effects of residual non-condensable gases on the performance of a refrigeration system. This paper investigates, both theoretically and experimentally, on the impact of residual non-condensable gases on the performance of a carbon dioxide (CO2) evaporator and the system performance. A theoretical analysis indicates that residual non-condensable gases can convert homogeneous nucleation into a heterogeneous nucleation process and accelerate phase change, thus, reducing superheat or incipient boiling temperature. To investigate the influence of residual non-condensable gases on the performance of an evaporator and the CO2 trans-critical refrigeration cycle system, experiments adding a small amount of N-2 and Ar into the system are carried out. Residual non-condensable gases have different effects on the parameters of refrigerant properties and nucleate boiling under different operating conditions. Experimental results indicate that at a lower inlet temperature within 1%, 2%, 3% of residual gases concentration, the heat transfer coefficient of evaporator and refrigeration coefficient of the system increase with the addition of N-2 or Ar, but decrease at higher temperature with addition of the residual gas, or at a concentration of 4%.