Categorization of iso-pentane flashing spray based on morphology, thermodynamical and mechanical effects

Accidental release of superheated liquids is typically accompanied with hazardous flashing jets. Indeed, flashing jets undergo fragmentation into massive fine droplets, thus forming ideal circumstances for fires and explosion. To gain a deeper understanding of depressurized release, we studied the dynamics of iso-pentane at superheats of 40–80 °C and injection pressures of 0.6–3.0 MPa. The internal flow pattern and external spray morphology are visualized at quasi-steady stage using a high-speed camera. Results show that the flashing patterns can be classified into non-flashing, transitional flashing, and flare flashing arising from the interaction between thermodynamic and mechanical effects. The contribution of thermodynamic effect decreases as mechanical effect intensifies, due to the suppression of bubble nucleation and burst. We propose the index k, based on JaR_p = k(We_vOh)^−1/7, to identify different flashing regions, i.e., k below 211 for non-flashing, k between 212 and 425 for transitional flashing, and k above 425 for flare flashing. Besides, the microscopic characteristics involving droplet velocity and diameter distribution are investigated and a new correlation for drop size is proposed, which is dependent on factors such as nozzle aspect ratio, mechanical force, and thermodynamic force. These findings should help to define policies to decrease the risk associate with flashing jets.