15 research outputs found
The scaling of exploding liquid jets under intense X-ray pulses
A general scaling of the evolution of an exploding liquid jet under an ultra
short and intense X-ray pulse from a X-ray free electron laser (XFEL) is
proposed. A general formulation of the conservation of energy for blasts in
vacuum partially against a deformable object leads to a compact expression that
governs the evolution of the gap produced by the explosion. The theoretical
analysis contemplates two asymptotic stages for small and large times from the
initiation of the blast. A complete dimensional analysis of the problem and an
optimal collapse of experimental data reveal that the universal approximate
analytical solution proposed is in remarkable agreement with experiments
Scaling laws of top jet drop size and speed from bubble bursting including gravity and inviscid limit
Jet droplets from bubble bursting are determined by a limited parametrical
space: the liquid properties (surface tension, viscosity, and density), mother
bubble size and acceleration of gravity. Thus, the two resulting parameters
from dimensional analysis (usually, the Ohnesorge and Bond numbers, Oh and Bo)
completely define this phenomenon when both the trapped gas in the bubble and
the environment gas have negligible density. A detailed physical description of
the ejection process to model both the ejected droplet radius and its initial
launch speed is provided, leading to a scaling law including both Oh and Bo.
Two critical values of Oh determine two limiting situations: one (Oh=0.038)
is the critical value for which the ejected droplet size is minimum and the
ejection speed maximum, and the other (Oh=0.0045) is a new critical value
which signals when viscous effects vanish. Gravity effects (Bo) are
consistently introduced from energy conservation principles. The proposed
scaling laws produce a remarkable collapse of published experimental
measurements collected for both the ejected droplet radius and ejection speed.Comment: 14 pages, three figures, published in 2018 in Physical Review Fluid
Unconditional jetting
Capillary jetting of a fluid dispersed into another immiscible phase is
usually limited by a critical Capillary number, a function of the Reynolds
number and the fluid properties ratios. Critical conditions are set when the
minimum spreading velocity of small perturbations along the jet
(marginal stability velocity) is zero. Here we identify and describe
parametrical regions of high technological relevance, where and the
jet flow is always supercritical independently of the dispersed liquid flow
rate: within these relatively broad regions, the jet does not undergo the usual
dripping-jetting transition, so that either the jet can be made arbitrarily
thin (yielding droplets of any imaginably small size), or the issued flow rate
can be made arbitrarily small. In this work, we provide illustrative analytical
studies of asymptotic cases for both negligible and dominant inertia forces. In
this latter case, requiring a non-zero jet surface velocity, axisymmetric
perturbation waves ``surf'' downstream for all given wave numbers while the
liquid bulk can remain static. In the former case (implying small Reynolds
flow) we found that the jet profile small slope is limited by a critical value;
different published experiments support our predictions.Comment: Submitted first (24-August-2008) to Physics of Fluids, withdrawn from
that journal on 6-April-2008, and submitted to Physical Review E the same da
A revision on Rayleigh capillary jet breakup
The average Rayleigh capillary breakup length of a cylindrical Newtonian
viscous liquid jet moving with homogeneous velocity (negligible
external forces) must be determined by the selection of normal modes with
time-independent amplitude and wavelength (invariant modes, IMs). Both positive
and negative group velocity IMs exist in ample ranges of the parameter domain
(Weber and Ohnesorge numbers), which explains (i) the average breakup length
independence on ambient conditions (long-term resonance), and (ii) its
proportionality to the inverse of the spatial growth rate of the dominant
positive group velocity IM. Published experimental results since Grace (1965,
PhD Thesis) confirm our proposal.Comment: 9 pages, 7 figure
On the physics of transient ejection from bubble bursting
The transient ejection due to a bubble bursting at the interface of a liquid
with a gas environment is here described using a dynamical scaling analysis
along the process. We show here that the ejection of a liquid microjet requires
the backfire of a vortex ring inside the liquid to preserve physical symmetry,
which involves a non-trivial scaling. We present the first single uniformly
valid expression for the size and speed of ejected droplets for the whole range
of the Ohnesorge and Bond numbers where droplet ejection occurs. The evolution
of the flow variables, the apparent singularity for a critical Ohnesorge
number, and the dispersion of data around this point are explained. Our model
generalizes or displaces other recently proposed ones, impacting for instance
the statistical description of sea spray.Comment: 10 pages, 3 figure
A new device for the generation of microbubbles
In this paper we present a new method for the production of bubble-liquid suspensions (from now
on BLS) composed of micron-sized bubbles and with gas to liquid volume ratios larger than unity.
We show that the BLS gas fraction ÊŽ=Qg and Q1 , being Qg and Q1 the flow rates of gas and liquid,
respectively, is controlled by a dimensionless parameter which accounts for the ratio of the gas
pressure inside the device to the liquid viscous pressure drop from the orifices where the liquid is
injected to the exit, where the BLS is obtained. This parameter permits the correct scaling of the
BLS gas volume fraction of all the experiments presented
The ocean fine spray
A major fraction of the atmospheric aerosols come from the ocean spray
originated by the bursting of bubbles from breaking waves. A theoretical
framework that incorporates the latest knowledge on film and jet droplets from
bubble bursting is proposed. Assuming that their relics constitute the ultimate
origin of primary and secondary sea aerosols through a diversity of
physicochemical routes, the model can be reduced to a single controlling
parameter to predict the global probability density distribution (pdf) of the
ocean spray. The bursting and collapse of small bubbles on the sea surface from
about 10 to 100 microns produces an extreme energy focusing and the ejection of
a rapid liquid spout whose size reaches the free molecular regime of the
gaseous environment. In these rarefied conditions, simulations show that this
spout yields a jet of sub-micrometer and nanometric scale droplets whose number
and speed can be far beyond any previous estimation, overcoming by orders of
magnitude alternative mechanisms recently proposed. The one-parameter model
fits remarkably well published experimental measurements along five orders of
magnitude of spray size, from about 5 nm to about 0.5 mm. According to this
proposal, the majority of aerosols determining the life on our planet would
have their extremely elusive birth in the uterus-like nano-shape of small
bursting bubbles on the ocean surface at the very latest instants of collapse.Comment: 12 pages, 13 figure