Dr Xueliang Zhu
About
My research project
Breakup dynamics of flashing jet throughout accidental release of superheated liquidsSuperheated liquids such as liquefied petroleum gas (LPG), liquefied natural gas (LNG), liquid chlorine, liquid ammonia, and liquid hydrogen are widely used in modern industries and daily lives. Structural failure of an industrial superheated liquid tank or pipe usually results in flashing jets consisting of a mixture of massive droplets and vapor due to the violent phase transition. By the violent and drastic phase change, the consequent jet, which is normally called flashing jet, evaporates rapidly and is split into massive droplets. As the current measurement tools such as high-speed photography and laser diagnosis technology develop rapidly, the breakup of flashing jets has been proved to be the joint effort of thermodynamic and mechanical effects. However, they failed to demonstrate the relationship between the mentioned two effects. My PhD research especially priorities the breakup regimes and characteristics of the consequent flashing jet and focuses on the relationship between thermodynamic and mechanical effects. The research will be performed using the improved and self-designed experimental platform as well as some simple CFD methods. My primary aim is to reveal the form regimes of droplets and vapor in flashing jets, deepen the understanding of the vapor-liquid two-phase phenomenon and provide some basic knowledge for the prevention, control and response of such accidents.
Supervisors
Superheated liquids such as liquefied petroleum gas (LPG), liquefied natural gas (LNG), liquid chlorine, liquid ammonia, and liquid hydrogen are widely used in modern industries and daily lives. Structural failure of an industrial superheated liquid tank or pipe usually results in flashing jets consisting of a mixture of massive droplets and vapor due to the violent phase transition. By the violent and drastic phase change, the consequent jet, which is normally called flashing jet, evaporates rapidly and is split into massive droplets. As the current measurement tools such as high-speed photography and laser diagnosis technology develop rapidly, the breakup of flashing jets has been proved to be the joint effort of thermodynamic and mechanical effects. However, they failed to demonstrate the relationship between the mentioned two effects. My PhD research especially priorities the breakup regimes and characteristics of the consequent flashing jet and focuses on the relationship between thermodynamic and mechanical effects. The research will be performed using the improved and self-designed experimental platform as well as some simple CFD methods. My primary aim is to reveal the form regimes of droplets and vapor in flashing jets, deepen the understanding of the vapor-liquid two-phase phenomenon and provide some basic knowledge for the prevention, control and response of such accidents.
Publications
Accidental releases of superheated liquids, such as liquefied petroleum or natural gases, are featured by depressurization across the outlet leading to liquid flashing within the upstream container and the downstream jet. In this work, dynamic behaviors of in-tank liquid with phase change throughout depressurized releases and the influence on the primary breakup of flashing jet were studied with an experimental 20 L tank. In-tank parameters (pressure, temperature, and liquid mass) and downstream jet morphology were characterized. A new nondimensional number (ηp), the ratio between the superheat levels of the saturated states corresponding to liquid temperature and pressure, was developed to describe the liquid's thermodynamic state under both release and ambient conditions. A thermodynamics-determined release rate model was established to characterize flow behaviors at the exit. Results showed a strong correlation between the initial ηp0 and key process parameters I (depressurization and release rates): I = aηp0b, where a and b are constants for a particular I. A ηp0-based criterion was derived to characterize in-tank release dynamics and thermodynamics: ηp0
•Breakup regime of superheated liquid jet under depressurized release is examined.•Both thermal nonequilibrium and mechanical forces are involved as driving effects.•The coupling regime of the two driving effects during depressurization is explored.•Non-flashing, partially flashing, and fully flashing breakup modes are identified.•The interaction of the two driving effects is quantified by dimensionless analysis. Superheated liquid jets disintegrate into numerous droplets when released into the ambient with lower saturated pressure, driven by thermal nonequilibrium induced flashing and the accompanying mechanical forces. Such a phenomenon facilitates fuel atomization in energy utilization while posing a serious threat during accidental releases. In this work, the breakup and droplet formation of superheated liquid jets under depressurized releases were investigated with an experimental 20 L tank. A high-speed camera was utilized to characterize breakup behaviors. The interaction between thermodynamic and mechanical effects during depressurization was discussed based on linear stability analysis and bubble dynamics. Furthermore, the quantitative relationship between the two driving effects under different conditions was established using dimensionless and multiple regression analyses. Results show that the thermodynamic effect increases with the decreased mechanical effect during depressurization because of the increased energy of bubble burst, regardless of the external or internal flashing regime. Non-flashing, partially flashing, and fully flashing breakup modes are identified. The dimensionless and multiple regression analyses show that in addition to thermodynamic (Ja, ρv/ρl, Rp, and ηp) and mechanical (Wev and Oh) effects, the inhibition induced by the cooling effect (Pr and Ec) should not be overlooked. The quantitative expression among them agrees well with experimental data with R2=0.976.
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 (RpJa) and mechanical (WevOh) 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 (fA), droplet diameter (dSMD), and droplet velocity (ud), and their relationship with jet breakup were revealed. Results show that non-flashing (NFB), partially flashing (PFB), and fully flashing (FFB) breakups coincide with RpJa(WevOh)1/7