Study of critical flow for supercritical CO₂ seal

Supercritical CO₂ (S-CO₂) has the potential to be used as the working fluid in a power cycle since S-CO₂ shows a density value high as its liquid phase while the viscosity value remains closer to its gaseous phase. Thus, it requires much less work to compress due to its low compressibility as well as relatively small flow resistance. However, the S-CO₂ leakage flow from turbo-machinery via seal becomes one of the important issues since not only it influences the cycle efficiency due to parasitic loss but also it is important for evaluating the system safety under various operating conditions. In this paper, the gap effect, which is studied by changing the diameter of an orifice, cavity length effect, and the number of tooth effect in a simulated labyrinth seal geometry nozzle are presented. Experimental results under various conditions including not only single phase flow but also two phase flow conditions are presented.