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 N2 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 N2 or Ar, but decrease at higher temperature with addition of the residual gas, or at a concentration of 4%.