An Improved Model for Predicting Affected Region of Flashing Jet

Abstract

When a water piping system operating under high temperatures and pressures is damaged and water is expelled into the atmosphere, a phenomenon known as depressurization boiling or flashing occurs. This flashing jet poses a risk to human safety and can damage safety equipment through impingement. Consequently, evaluating the region affected by the flashing jet impinging on the surrounding equipment and people is necessary. In this study, we conducted experiments to verify the affected region of the jet involving both saturated and subcooled water under low-pressure conditions at the jet inlet, up to 2 MPaA, and extended our investigation to high-pressure conditions up to 7 MPaA using computational fluid dynamics (CFD). The findings revealed that the mass flux predictions, according to the homogeneous equilibrium model (HEM) outlined in the American National Standards Institute (ANSI) standard, align with both experimental and CFD analysis results. However, the evaluations of both the asymptotic plane width and distance—parameters delineating the jet's affected region—were found to be underestimated in the ANSI standard compared with the experimental and CFD analysis results. To address this difference from real phenomena, we developed an improved model that incorporates mass flux and enthalpy as variables. This improved model more accurately predict the asymptotic plane width and distance than the ANSI standard. Utilizing this improved model enables precise prediction of the flashing jet's affected region, spanning conditions from saturated to subcooled water across various pipe diameters.