169 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
Controlled cavity collapse: scaling laws of drop formation
The formation of transient cavities at liquid interfaces occurs in an immense variety of natural processes, among which the bursting of surface bubbles and the impact of a drop on a liquid pool are salient. The collapse of a surface liquid cavity is a well documented natural process that leads to the ejection of a thin and fast jet. Droplets generated through this process can be one order of magnitude smaller than the cavity's aperture, and they are consequently of interest in drop on demand inkjet applications. In this work, the controlled formation and collapse of a liquid cavity is analyzed, and the conditions for minimizing the resulting size and number of ejected drops are determined. The experimental and numerical models are simple and consist of a liquid reservoir, a nozzle plate with the discharge orifice, and a moving piston actuated by single half-sine-shaped pull-mode pulses. The size of the jetted droplet is described by a physical model resulting in a scaling law that is numerically and experimentally validated
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
Production and characterization of carbamazepine nanocrystals by electrospraying for continuous pharmaceutical manufacturing
In this paper, an electrospray technique followed by annealing at high temperatures was developed to produce nanocrystals of carbamazepine (CBZ), a poorly water-soluble drug, for continuous pharmaceutical manufacturing process. Electrospraying solutions of CBZ in methanol obeys the expected scaling law of current, which is I ∼ Q[superscript 1/2] (I, electrical current; Q, flow rate), for liquids with sufficiently high conductivity and viscosity. Lower flow rates during electrospraying were preferred to produce smaller diameters of monodisperse, dense CBZ nanoparticles. CBZ nanoparticles were predominantly amorphous immediately after electrospraying. Crystallization of CBZ nanoparticles was accelerated by annealing at high temperatures. CBZ nanocrystals with the most stable polymorph, form III, were obtained by annealing at 90°C, which is above the transition temperature, 78°C, for the enantiotropic CBZ form III and form I. The solubility and dissolution rates of CBZ nanocrystals increased significantly as compared with those of CBZ bulk particles. Therefore, electrospray technology has the potential to produce pharmaceutical dosage forms with enhanced bioavailability and can readily be integrated in a continuous pharmaceutical manufacturing process.Novartis-MIT Center for Continuous Manufacturin
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