Truong V. Vu

Breakup modes of a laminar hollow water jet

Graphical Abstract

Numerical Investigations of Drop Solidification by a Front-Tracking Method

We present a front-tracking/finite difference method for simulation of drop solidification, where the melt is confined by its own surface tension. The problem includes temporal evolution of three interfaces, i.e. solid–liquid, solid–air, and liquid–air, that are explicitly tracked under the assumption of axisymmetry. The solid–liquid interface is propagated with a normal velocity that is calculated from the normal temperature gradient across the front and the latent heat. The liquid–air front is advected by the velocity interpolated from nearest bulk fluid flow velocities. Method validation is carried out by comparing computational results with exact solutions for two-dimensional Stefan problems, and with related experiments. We then use the method to investigate a drop solidifying on a cold plate in which there exists volume expansion due to density difference between the solid and liquid phases. Effects of the tri-junction in terms of growth angles on the solidification process are also investigated. Computational results show that a decrease in the density ratio of solid to liquid or an increase in the growth angle results in an increase in the height of the solidified drop. In addition, reducing the gravitational effect also increases the drop height after solidification.Copyright

Numerical Simulation of Formation and Breakup of a Compound Jet by the Front–Tracking/Finite Difference Method

The formation and breakup of an axisymmetric immiscible, viscous, laminar compound jet flowing vertically downward into and breaking up in another immiscible liquid is studied numerically. We use a front-tracking/finite difference method to track the unsteady motion and the breakup of the compound jet interfaces, which are governed by the incompressible Navier-Stokes equations for Newtonian fluids. We consider the formation and breakup of a three-fluid compound jet in which the inner fluid density is greater than the shell’s fluid density, and compare with the case when the inner fluid density is less than the shell’s fluid density. The effects of interfacial tensions in terms of Weber number are investigated. An increase in Weber number leads to an increase in the breakup length of the compound jet and a decrease in the size of compound drops.Copyright

Formation of a Hollow Jet and its Breakup in Ambient Air

An experiment investigation on the formation and breakup of a hollow jet issuing from a coaxial nozzle into ambient air has been carried out. The hollow jet consists of an outer jet of water that encloses an inner jet of argon gas. By varying the flow rate ratio of the inner jet to the outer jet, three different breakup patterns of hollow water jets are identified using two types of nozzles: (I) satellite formation, (II) single-core hollow drop formation, and (III) multi-core hollow drop formation. These patterns are mapped in a space of Weber number versus flow rate ratio, We – Q. Experimental results in pattern (II) show that increasing the flow rate ratio results in increasing the formation frequency, slightly increasing outer diameters of the hollow drops, and decreasing their wall thickness.Copyright