Miguel Perez-Saborid

ONE-DIMENSIONAL SIMULATION OF THE BREAKUP OF CAPILLARY JETS OF CONDUCTING LIQUIDS. APPLICATION TO E.H.D. SPRAYING

Nonlinear breakup of charged liquid jets is numerically analyzed in this work in the limit of a very small electrical Strouhal number Te/Tb≪1 (i.e. negligible charge relaxation effects, applicable to highly conducting liquids), where Te is the electric relaxation time of charges, and Tb is the breakup time in a Lagrangian framework following the liquid jet at its average axial velocity. The influence of the electrical Bond’s number and viscosity on (i) the capillary Rayleigh’s most probable breakup length, (ii) the breakup time, (iii) the volume of the satellite, and (iv) the charge of both main drop and satellite, are analyzed. The model is related to the microjet break-up phenomena in the electrospraying of liquids in steady cone-jet mode, and its range of applicability to those particular problems discussed. Previous experimental results [Mutoh et al., 1979, Convergence and disintegration of liquid jets induced by an electrostatic field. J. Appl. Phys. 50, 3174–3179; Clopeau and Prunet-Foch, 1989, Electrostatic spraying of liquids in cone-jet mode. J. Electrostatics 22, 135–159.] support our numerical finding that the influence of the electrical Bond’s number on Rayleigh’s length is small within the usual parametrical limits of stability of a steady Taylor cone-jet at atmospheric pressure.

Linear stability of co-flowing liquid-gas jets

A temporal, inviscid, linear stability analysis of a liquid jet and the co-flowing gas stream surrounding the jet has been performed. The basic liquid and gas velocity profiles have been computed self-consistently by solving numerically the appropriate set of coupled Navier–Stokes equations reduced using the slenderness approximation. The analysis in the case of a uniform liquid velocity profile recovers the classical Rayleigh and Weber non-viscous results as limiting cases for well-developed and very thin gas boundary layers respectively, but the consideration of realistic liquid velocity profiles brings to light new families of modes which are essential to explain atomization experiments at large enough Weber numbers, and which do not appear in the classical stability analyses of non-viscous parallel streams. In fact, in atomization experiments with Weber numbers around 20, we observe a change in the breakup pattern from axisymmetric to helicoidal modes which are predicted and explained by our theory as having an hydrodynamic origin related to the structure of the liquid-jet basic velocity profile. This work has been motivated by the recent discovery by Ganan-Calvo (1998) of a new atomization technique based on the acceleration to large velocities of coaxial liquid and gas jets by means of a favourable pressure gradient and which are of emerging interest in microfluidic applications (high-quality atomization, micro-fibre production, biomedical applications, etc.).

Aerodynamic effects in the break-up of liquid jets: on the first wind-induced break-up regime

We present both numerical and analytical results from a spatial stability analysis of the coupled gas–liquid hydrodynamic equations governing the first wind-induced (FWI) liquid-jet break-up regime. Our study shows that an accurate evaluation of the growth rate of instabilities developing in a liquid jet discharging into a still gaseous atmosphere requires gas viscosity to be included in the stability equations even for low

Monodisperse microbubbling: Absolute instabilities in coflowing gas–liquid jets

{\it We}_g

Vortex breakdown in compressible flows in pipes

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Downstream evolution of unconfined vortices: mechanical and thermal aspects

{\it We}_g{=}\rho_gU_l^2R_0/\sigma

Axisymmetric breakup of bubbles at high Reynolds numbers

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Whipping of electrified liquid jets

\rho_g, U_l, R_0

Acoustic characterization of monodisperse lipid-coated microbubbles: Relationship between size and shell viscoelastic properties

and

Nonparallel local spatial stability analysis of pipe entrance swirling flows

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