A study on cavitating flows with contaminant gas dissolved in the liquid

Many hydraulic devices experiencing cavitation are influenced by the presence of dissolved and non-condensable gases. When the pressure of a pure liquid locally drops below its vapor pressure, a phase change occurs, generating vapor bubbles within the fluid. However, any liquid can contain some dissolved gas as well as a small amount of non-condensable gas that does not dissolve in the liquid. This paper presents a model that separately accounts for cavitation caused by the phase change of the liquid into vapor (referred to as "true cavitation") and void formation resulting from the release of dissolved gases ("pseudo cavitation"). The work focuses on the development, implementation, and testing of a novel model addressing the release and absorption of dissolved gases. An Eulerian single-fluid formula- tion is used for the two-phase flow, incorporating multiple species transport equations for both the liquid and gas phases. The dissolution/release mass transfer term is derived from Epstein-Plesset theory for bubble growth by mass diffusion. A bubble number density transport equation is solved to evaluate the local bubble density and then predict the local bubble diameter. From this information, the rate of dissolved gas mass transfer is calculated, and the pseudo cavitation source term is determined. True cavitation is consistently modeled using a bubble dynamics model, as a separate and competing con- tribution. To demonstrate and validate the model’s performance, the CFD model is applied to cavitating nozzles, considering water as working liquid, with various dissolved gases, particularly CO2, which is of interest for carbon capture technologies.