Breakup regime of flashing jet under thermal nonequilibrium and mechanical forces and its relationship with jet characteristics during depressurized releases of superheated liquid

Accidental superheated liquid emissions into the atmosphere yield two-phase releases. The resulting flashing jet, driven by thermal nonequilibrium and mechanical forces, breaks up into massive droplets, fostering beneficial conditions for fire, explosion, and toxic diffusion. In this work, a 20 L tank was built to examine two-phase flow behaviors during depressurized releases of superheated liquids via a high-speed camera and phase Doppler anemometry. Different breakup regimes of flashing jet and dimensionless groups that effectively represent thermodynamic (R_pJa) and mechanical (We_vOh) driving effects were determined. Based on the interaction between the two effects, quantitative criteria to distinguish different regimes were developed. The accompanying jet characteristics, including jet angle (θ), area fraction (f_A), droplet diameter (d_SMD), and droplet velocity (u_d), and their relationship with jet breakup were revealed. Results show that non-flashing (NFB), partially flashing (PFB), and fully flashing (FFB) breakups coincide with R_pJa(We_vOh)^1/7 < 41, 41 ≤R_pJa(We_vOh)^1/7 < 223, and 223 ≤R_pJa(We_vOh)^1/7, respectively. For small-sized nozzles (d≤3 mm), θ₂ and f_A2 increase within 41 ≤R_pJa(We_vOh)^1/7 < 558 and then keep stable. The difference for large-sized nozzles resides in 223 ≤R_pJa(We_vOh)^1/7 < 558 (early FFB regime), where θ₂ and f_A2 decrease slightly due to the enhanced droplet evaporation. In 41 ≤R_pJa(We_vOh)^1/7, d_SMD2 decreases and u_d2 increases, but at an extremely low rate within 558 ≤R_pJa(We_vOh)^1/7.