At the impact of a liquid droplet on smooth surface heated above liquid's boiling point, either immediately boils when it contacts (``contact boiling''), or without any contact forms Leidenfrost vapor layer towards hot and bounces back (``gentle film both ejects tiny droplets upward (``spraying boiling''). We experimentally determine conditions under which behaviors in each regime can be realized. show that dimensionless maximum spreading $\ensuremath{\gamma}$ impacting surfaces gentle...

The energy budget and dissipation mechanisms during droplet impact on solid surfaces are studied numerically theoretically. We find that for high velocities negligible surface friction at the (i.e. free-slip), about one half of initial kinetic is transformed into energy, independent parameters detailed loss mechanism(s). argue this seemingly universal rule related to deformation mode reminiscent pipe flow undergoing a sudden expansion, which head can be calculated by multiplying incoming...

3D printing of common metals is highly challenging because are generally solid at room conditions. Copper and gold pillars manufactured with a resolution below 5 μm height up to 2 mm, using laser-induced forward transfer create eject liquid metal droplets. The solidified drop's shape crucial for discussed as function the laser energy.

When a droplet impacts upon surface heated above the liquid's boiling point, either comes into contact with and boils immediately (contact boiling), or is supported by developing vapor layer bounces back (film boiling, Leidenfrost state). We study transition between these characteristic behaviors how it affected parameters such as impact velocity, temperature, controlled roughness (i.e., micro-structures fabricated on silicon surfaces). In film regime, we show that residence time of droplets...

At impact of a liquid drop on solid surface, an air bubble can be entrapped. Here, we show that two competing effects minimize the (relative) size this entrained bubble: for large velocity and droplets, inertia flattens bubble, whereas small capillary forces bubble. However, demonstrate experimentally, theoretically, numerically in between there is optimum, leading to maximal entrapment. For 1.8 mm diameter ethanol droplet, optimum achieved at 0.25 m/s. Our results have strong bearing...

Taylor-Couette flow -- the between two coaxial co- or counter-rotating cylinders is one of paradigmatic systems in physics fluids. The (dimensionless) control parameters are Reynolds numbers inner and outer cylinder, ratio cylinder radii, aspect ratio. response system torque required to retain constant angular velocities, which can be connected velocity transport through gap. While low number regime has been very well explored '80s '90s last century, fully turbulent major research activity...

Technologies including (3D-) (bio-)printing, diesel engines, laser-induced forward transfer, and spray cleaning require optimization therefore understanding of micrometer-sized droplets impacting at velocities beyond 10 m s⁻¹.

When a liquid droplet impacts hot solid surface, enough vapor may be generated under it to prevent its contact with the solid. The minimum temperature for this so-called Leidenfrost effect occur is termed temperature, or dynamic when velocity non-negligible. We observe wetting drying and levitation dynamics of impacting on an (isothermal) smooth sapphire surface using high-speed total internal reflection imaging, which enables us base up about 100 nm above substrate surface. By method we are...

We present an experimental study on the drag reduction by polymers in Taylor–Couette turbulence at Reynolds numbers ( $Re$ ) ranging from $4\times 10^3$ to $2.5\times 10^4$ . In this regime, Taylor vortex is and accounts for more than 50 % of total angular velocity flux. Polyacrylamide with two different average molecular weights are used. It found that rate increases polymer concentration approaches maximum (MDR) limit. At MDR, friction factor follows $-0.58$ scaling, i.e. $C_f \sim...

We analyze the reversals of large-scale flow in Rayleigh-B\'enard convection both through particle image velocimetry visualization and direct numerical simulations underlying Boussinesq equations a (quasi-) two-dimensional, rectangular geometry aspect ratio 1. For medium Prandtl number there is diagonal roll two smaller secondary rolls remaining corners diagonally opposing each other. These corner-flow play crucial role for wind reversal: They grow kinetic energy thus also size thanks to...

Tailoring the hydrodynamic boundary condition is essential for both applied and fundamental aspects of drag reduction. Hydrodynamic friction on superhydrophobic substrates providing gas–liquid interfaces can potentially be optimized by controlling interface geometry. Therefore, establishing stable optimal crucial but rather challenging. Here we present unique microfluidic devices that allow presence controllable microbubbles at microchannels. We experimentally numerically examine effect...

A drop impacting on a solid surface deforms before the liquid makes contact with surface. We directly measure time evolution of air layer profile under droplet using high-speed color interferometry, obtaining thickness and during wetting process. Based extracted profiles obtained at multiple times, we velocity exiting from gap between solid, account for mechanism bubble entrapment. The present work offers tool to accurately quantitatively study impact dynamics short scale impact.

Abstract We study drop impact on a deep pool of the same fluid, with an emphasis air layer trapped under droplets from its formation to rupture. The penetration velocity at very short time scale prior rupture is shown, using energy argument and experimental verification, be one-half velocity. then deduce dependence position liquid viscosity show that volume resulting bubbles can related both those impacting solid surfaces rigid spheres surfaces.

A drop of water that freezes from the outside-in presents an intriguing problem: expansion upon freezing is incompatible with self-confinement by a rigid ice shell. Using high-speed imaging we show this conundrum resolved through intermittent fracturing brittle shell and cavitation in enclosed liquid, culminating explosion partially frozen droplet. We propose basic model to elucidate interplay between steady build-up stresses their fast release. The reveals for millimetric droplets fragment...

Fluid turbulence is commonly associated with stronger drag, greater heat transfer, and more efficient mixing than in laminar flows. In many natural industrial settings, turbulent liquid flows contain suspensions of dispersed bubbles light particles. Recently, much attention has been devoted to understanding the behavior underlying physics such by use both experiments high-resolution direct numerical simulations. This review summarizes our present various phenomenological aspects bubbly...

Nanodroplets on a solid surface (i.e. nanodroplets) have practical implications for high-throughput chemical and biological analysis, lubrications, lab-on-chip devices, near-field imaging techniques. Oil nanodroplets can be produced solid-liquid interface in simple step of solvent exchange which good oil is displaced by poor solvent. In this work, we experimentally theoretically investigate the formation process under well-controlled flow conditions. We find that contact angle independent...

3D-Particle Tracking (3D-PTV) and Phase Sensitive Constant Temperature Anemometry in pseudo-turbulence--i.e., flow solely driven by rising bubbles-- were performed to investigate bubble clustering obtain the mean rise velocity, distributions of velocities, energy spectra at dilute gas concentrations ($\alpha \leq2.2$%). To characterize pair correlation function $G(r,\theta)$ was calculated. The deformable bubbles with equivalent diameter $d_b=4-5$ mm found cluster within a radial distance...

We analyze the global transport properties of turbulent Taylor-Couette flow in strongly regime for independently rotating outer and inner cylinders, reaching Reynolds numbers cylinders ${\mathrm{Re}}_{i}=2\ifmmode\times\else\texttimes\fi{}{10}^{6}$ ${\mathrm{Re}}_{o}=\ifmmode\pm\else\textpm\fi{}1.4\ifmmode\times\else\texttimes\fi{}{10}^{6}$, respectively. For all ${\mathrm{Re}}_{i}$, ${\mathrm{Re}}_{o}$, dimensionless torque $G$ scales as a function Taylor number Ta (which is proportional to...

We experimentally determine the phase diagram for impacting ethanol droplets on a smooth, sapphire surface in parameter space of Weber number $\mathit{We}$ versus temperature $T$ . observe two transitions, namely one towards splashing (disintegration droplet) with increasing , and Leidenfrost state (no contact between droplet plate due to lasting vapour film) Consequently, there are four regimes: no (deposition regime), (contact–splash neither nor (bounce finally contact, but (film–splash...

Combining a laser pulse with liquid in microcapillary tubes series of experiments, fluid-mechanics group at University Twente finds new way generating highly focused and ultrafast jets understands how to control the jet speed.

We investigate the statistical properties of kinetic $\unicode[STIX]{x1D700}_{u}$ and thermal $\unicode[STIX]{x1D700}_{\unicode[STIX]{x1D703}}$ energy dissipation rates in two-dimensional (2-D) turbulent Rayleigh–Bénard (RB) convection. Direct numerical simulations were carried out a box with unit aspect ratio Rayleigh number range $10^{6}\leqslant Ra\leqslant 10^{10}$ for Prandtl numbers $Pr=0.7$ 5.3. The probability density functions (PDFs) both are found to deviate significantly from...

The development of needle-free drug injection systems is great importance to global healthcare. However, in spite its potential and research history over many decades, these are not commonly used. One the main problems that existing methods use diffusive jets, which result scattered penetration severe deceleration causing frequent pain insufficient penetration. Another long-standing challenge accurate small volume injections. In this paper we employ a novel method injection, using...

Rough surfaces have been widely used as an efficient way to enhance the heat-transfer efficiency in turbulent thermal convection. In this paper, however, we show that roughness does not always mean a enhancement, but some cases it can also reduce overall heat transport through system. To reveal this, carry out numerical investigations of Rayleigh–Bénard convection over rough conducting plates. Our study includes two-dimensional (2D) simulations Rayleigh number range $10^{7}\leqslant...