Papers by Andrea Prosperetti
Angewandte Chemie, Nov 9, 2010
Physical Review E, Jun 20, 2013
The effect of particles falling under gravity in a weakly turbulent Rayleigh-Bénard gas flow is s... more The effect of particles falling under gravity in a weakly turbulent Rayleigh-Bénard gas flow is studied numerically. The particle Stokes number is varied between 0.01 and 1 and their temperature is held fixed at the temperature of the cold plate, of the hot plate, or the mean between these values. Mechanical, thermal, and combined mechanical and thermal couplings between the particles and the fluid are studied separately. It is shown that the mechanical coupling plays a greater and greater role in the increase of the Nusselt number with increasing particle size. A rather unexpected result is an unusual kind of reverse one-way coupling, in the sense that the fluid is found to be strongly influenced by the particles, while the particles themselves appear to be little affected by the fluid, despite the relative smallness of the Stokes numbers. It is shown that this result derives from the very strong constraint on the fluid behavior imposed by the vanishing of the mean fluid vertical velocity over the cross sections of the cell demanded by continuity.
Physical Review Letters, Feb 10, 2016
When a liquid droplet impacts a hot solid surface, enough vapor may be generated under it as to p... more When a liquid droplet impacts a hot solid surface, enough vapor may be generated under it as to prevent its contact with the solid. The minimum solid temperature for this so-called Leidenfrost effect to occur is termed the Leidenfrost temperature, or the dynamic Leidenfrost temperature when the droplet velocity is non-negligible. We observe the wetting/drying and the levitation dynamics of the droplet impacting on an (isothermal) smooth sapphire surface using high speed total internal reflection imaging, which enables us to observe the droplet base up to about 100 nm above the substrate surface. By this method we are able to reveal the processes responsible for the transitional regime between the fully wetting and the fully levitated droplet as the solid temperature increases, thus shedding light on the characteristic time-and length-scales setting the dynamic Leidenfrost temperature for droplet impact on an isothermal substrate.
APS Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2019
It is known that, in a linear shear flow, fluid inertia causes a particle to spin more slowly tha... more It is known that, in a linear shear flow, fluid inertia causes a particle to spin more slowly than the surrounding fluid. The present experiments performed with a sphere with fixed centre, but free to rotate in a fluid undergoing solid-body rotation around a horizontal axis indicate that the spin rate of the sphere can be larger than that of the flow when the sphere is sufficiently far from the axis. Numerical simulations at Reynolds number 5≤Re≤200 confirm this observation. To gain a better understanding of the phenomenon, the rotating flow is decomposed into two shear flows along orthogonal directions. It is found numerically that the cross-stream shear has a much stronger effect on the particle spin rate than the streamwise shear. The region of low stress at the back of the sphere is affected by the shear component of the incident flow. While for the streamwise case the shift is minor, it is significant for cross-stream shear. The results are interpreted on the basis of the effect of the shear flow components on the quasi-toroidal vortex attached in the sphere's near wake. The contributions of streamwise and cross-stream shear to the particle spin can be linearly superposed forRe=20 and 50.
Bulletin of the American Physical Society, Nov 20, 2006
For a linear shear flow it is known that a particle rotates slower than the surrounding flow when... more For a linear shear flow it is known that a particle rotates slower than the surrounding flow when inertial effects are included. Experiments performed for a sphere fixed (but free to rotate) in a flow in solid body rotation indicate that the rotation rate of a sphere can be faster than the rotation rate of the flow. Numerical simulations at moderate Re confirm this observation. To gain understanding of the phenomenon the effects of stream-wise and cross-stream shear on the rotation rate of a fixed sphere in a flow are numerically investigated. Moreover, the change of the flow due to the sphere is recorded. The results indicate that for moderate Re the two types of shear have completely different effects on the particle rotation rate. Moreover, the cross-stream effects appear to be dominant to the stream-wise effects. When the two types of shears are combined to create a strain field, the particle starts to rotate, although the undisturbed flow is non-rotational.
Journal of the Acoustical Society of America, Oct 25, 2002
Gas bubbles having a radius between 10 μm and 100 μm and rising freely in water when being subjec... more Gas bubbles having a radius between 10 μm and 100 μm and rising freely in water when being subjected to a shock front exhibit a liquid jetting phenomenon. The jet points in the direction of the propagating shock wave. A linear relationship between the jet length and the bubble radius is found and a lower bound of the averaged velocity of the liquid jet can be estimated to be between 50 m/s and 300 m/s increasing linearly for larger bubbles. In a later stage the jet breaks up and releases micron sized bubbles. In the course of shock wave mediated cell permeabilization this observation suggests a microinjection mechanism responsible for cell transfection when minute gas bubbles are present and exposed together with cells to shock waves.
Journal of Fluid Mechanics, Sep 6, 2021
A rapidly growing bubble close to a free surface induces jetting: a central jet protruding outwar... more A rapidly growing bubble close to a free surface induces jetting: a central jet protruding outwards and a crown surrounding it at later stages. While the formation mechanism of the central jet is known and documented, that of the crown remains unsettled. We perform axisymmetric simulations of the problem using the free software program BASILISK, where a finite-volume compressible solver has been implemented, which uses a geometric volume-of-fluid (VoF) method for the tracking of the interface. We show that the mechanism of crown formation is a combination of a pressure distortion over the curved interface, inducing flow focusing, and of a flow reversal, caused by the second expansion of the toroidal bubble that drives the crown. The work culminates in a parametric study with the Weber number, the Reynolds number, the pressure ratio and the dimensionless bubble distance to the free surface as control parameters. Their effects on both the central jet and the crown are explored. For high Weber numbers, we observe the formation of weaker 'secondary crowns', highly correlated with the third oscillation cycle of the bubble.
Journal of Physical Chemistry C, Aug 17, 2018
We study the formation of a nanobubble around a heated nanoparticle in a bulk liquid by using mol... more We study the formation of a nanobubble around a heated nanoparticle in a bulk liquid by using molecular dynamics simulations. The nanoparticle is kept at a temperature above the critical temperature of the surrounding liquid, leading to the formation of a vapor nanobubble attached to it. First, we study the role of both the temperature of the bulk liquid far away from the nanoparticle surface and the temperature of the nanoparticle itself on the formation of a stable vapor nanobubble. We determine the exact conditions under which it can be formed and compare this with the conditions that follow from a macroscopic heat balance argument. Next, we demonstrate the role of dissolved gas on the conditions required for nucleation of a nanobubble and on its growth dynamics. We find that beyond a certain threshold concentration, the dissolved gas dramatically facilitates vapor bubble nucleation due to the formation of gaseous weak spots in the surrounding liquid.
Physical review, May 22, 2003
It is known from experiment that the light emission from a sonoluminescing bubble can be increase... more It is known from experiment that the light emission from a sonoluminescing bubble can be increased by using more than one driving frequency. In this paper, a systematic method to determine the optimal conditions of pressure amplitude and relative phase for this effect is described. As a specific application, a two-frequency system-26.5 kHz and 53 kHz-is considered. It is found that the maximum temperatures achievable can be appreciably increased with respect to single-frequency drive, still maintaining spherical stability, provided the dissolved inert gas concentration is kept extremely low in order to maintain diffusive stability.
Journal of Physics: Condensed Matter, Dec 13, 2002
ABSTRACT
Proceedings of the National Academy of Sciences of the United States of America, Nov 21, 2016
Journal of Fluid Mechanics, Dec 17, 2009
A freely rotating sphere in a solid-body rotating flow is experimentally investigated. When the s... more A freely rotating sphere in a solid-body rotating flow is experimentally investigated. When the sphere is buoyant, it reaches an equilibrium position from which drag and lift coefficients are determined over a wide range of particle Reynolds numbers (2 6 Re 6 1060). The wake behind the sphere is visualized and appears to deflect strongly when the sphere is close to the cylinder axis. The spin rate of the sphere is recorded. In fluids with low viscosity, spin rates more than twice as large as the angular velocity of the cylinder can be observed. By comparing numerical results for a fixed but freely spinning sphere with a fixed non-spinning sphere for Re 6 200, the effect of the sphere spin on the lift coefficient is determined. The experimentally and numerically determined lift and drag coefficients and particle spin rates all show excellent agreement for Re 6 200. The combination of the experimental and numerical results allows for a parameterization of the lift and drag coefficients of a freely rotating sphere as function of the Reynolds number, the particle spin and the location of the particle with respect to the cylinder axis. Although the effect of the flow rotation on the particle spin is different in shear flow and solid-body rotating flow, the effect of spin on lift is found to be comparable for both types of flow.
Journal of the Acoustical Society of America, Apr 1, 1993
Journal of Physical Chemistry C, Feb 17, 2020
The understanding of the shrinkage dynamics of plasmonic bubbles formed around metallic nanoparti... more The understanding of the shrinkage dynamics of plasmonic bubbles formed around metallic nanoparticles immersed in liquid and irradiated by a resonant light source is crucial for the usage of these bubbles in numerous applications. In this paper, we experimentally show and theoretically explain that a plasmonic bubble during its shrinkage undergoes two different phases: first, a rapid partial bubble shrinkage governed by vapor condensation and, second, a slow diffusion-controlled bubble dissolution. The history of the bubble formation plays an important role in the shrinkage dynamics during the first phase as it determines the gas−vapor ratio in the bubble composition. Higher laser powers lead to more vaporous bubbles, while longer pulses and higher dissolved air concentrations lead to more gaseous bubbles. The dynamics of the second phase barely depends on the history of bubble formation, that is, laser power and pulse duration, but strongly on the dissolved air concentration, which defines the concentration gradient at the bubble interface. Finally, for the bubble dissolution in the second phase, with decreasing dissolved air concentration, we observe a gradual transition from a R(t) ∝ (t 0 − t) 1/3 scaling law to a R(t) ∝ (t 0 − t) 1/2 scaling law where t 0 is the lifetime of the bubble and theoretically explain this transition.
Journal of the Acoustical Society of America, Nov 1, 2011
The chemical production of radicals inside acoustically driven bubbles is determined by the local... more The chemical production of radicals inside acoustically driven bubbles is determined by the local temperature inside the bubbles. Therefore, modeling of chemical reaction rates in bubbles requires an accurate evaluation of the temperature field and the heat exchange with the liquid. The aim of the present work is to compare a detailed partial differential equation model in which the temperature field is spatially resolved with an ordinary differential equation model in which the bubble contents are assumed to have a uniform average temperature and the heat exchanges are modeled by means of a boundary layer approximation. The two models show good agreement in the range of pressure amplitudes in which the bubble is spherically stable. V
Physical Review Letters, Mar 24, 2021
Marangoni instabilities can emerge when a liquid interface is subjected to a concentration or tem... more Marangoni instabilities can emerge when a liquid interface is subjected to a concentration or temperature gradient. It is generally believed that for these instabilities bulk effects like buoyancy are negligible as compared to interfacial forces, especially on small scales. Consequently, the effect of a stable stratification on the Marangoni instability has hitherto been ignored. Here we report, for an immiscible drop immersed in a stably stratified ethanol-water mixture, a new type of oscillatory solutal Marangoni instability which is triggered once the stratification has reached a critical value. We experimentally explore the parameter space spanned by the stratification strength and the drop size and theoretically explain the observed crossover from levitating to bouncing by balancing the advection and diffusion around the drop. Finally, the effect of the stable stratification on the Marangoni instability is surprisingly amplified in confined geometries, leading to an earlier onset.
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Papers by Andrea Prosperetti