Numerical simulation of a liquid bridge in a coaxial gas flow

Abstract

The dynamical response of an isothermal liquid bridge to a coaxial gas stream is examined from axisymmetric numerical simulations of the Navier-Stokes equations. The simulation method is previously validated by calculating the temporal evolution of the first oscillation mode in both cylindrical and axisymmetric liquid bridges. The comparison with other theoretical approaches and experiments shows good agreement in most cases, although significant discrepancies are found between the simulation and the experimental values of the damping rate for hexadecane. The simulation of a liquid bridge in a coaxial gas stream shows that a recirculation cell always appears in the liquid driven by the gas viscous stress on the free surface. The recirculation cell speed depends quasilinearly on the gas velocity for the range of gas flow rates considered. If the gas stream and gravity have the same direction, then the speed of the recirculation cell increases considerably due to the free surface deformation of the liquid bridge at equilibrium. This effect does not occur when gravity has the opposite direction because viscous dissipation in the liquid increases in this case. If the gas stream and gravity point downward, the liquid bridge shrinks at the upper part and bulges at the lower owing to the accumulation of momentum there. The same occurs for zero gravity, but noncylindrical liquid bridges deform more than cylindrical shapes with the same slenderness. If one inverts the direction of the gravity force, the interface deformation caused by the gas stream is the opposite, and its magnitude is smaller. The magnitude of the free surface deformation depends almost linearly on the gas stream velocity for both zero and normal gravity conditions.

Hydrothermal waves in a liquid bridge subjected to a gas stream along the interface

“…As for the dynamic interface deformation, it was obtained in several numerical (Herrada et al. 2011) and experimental (Matsunaga et al. 2012; Yang et al.…”

“…The impact of a gas flow on the stability of statically deformed LBs was experimentally examined by Yano et al (2016) for Pr = 28, 67 when Re gas < 50, and it showed that the gas moving upward (downward) shifts the vertex position to the side of the smaller (larger) volume ratio. As for the dynamic interface deformation, it was obtained in several numerical (Herrada et al 2011) and experimental (Matsunaga et al 2012;Yang et al 2018) studies that the interface deformation does not exceed 10 μm in a millimetric LB when the velocity of gas is as large as 2 m s −1 . Recent results of linear stability analysis of a LB with high Prandtl number, Pr = 68, presented by Carrión, Herrada & Montanero (2020) showed that dynamic free surface deformation has very little effect on the stability of the flow.…”

Variety of flow patterns in a liquid bridge subjected to a gas stream

“…Certainly, the two-phase model is more consistent with experiments [32,33] and practical applications and exhibits richer dynamics [34][35][36] depending on the flow rates of the two phases, the choice of fluids (gas and liquid), the sizes of the fluid domains and the mutual orientation of the flows. More recent numerical efforts have been focused on investigating the role of gas moving along the interface with the purpose of controlling the Marangoni instability by shear and thermal stresses [37,38].…”

Investigation of Two-Phase Flow in a Hydrophobic Fuel-Cell Micro-Channel

“…The ability of the model in predicting the morphology, the critical liquid volume to form a plug, as well as the time of obstruction makes it useful for assessing and mitigating the potential for flooding/blockage by slug/plug flow in PEM fuel cells, but it should be noted that this analytic model is limited to quasi-equilibrium bridges. The model is not valid when viscous and inertial forces are important or when the bridge exhibits dynamic behaviour [72]. For instance, modeling of the nonlinear process leading to liquid bridge breakup when the critical volume is surpassed requires the solution of the Navier-Stokes equations [73].…”