The impact of viscoplastic drops on a heated surface in the Leidenfrost regime

Soft Matter ◽  
2016 ◽  
Vol 12 (36) ◽  
pp. 7624-7631 ◽  
Author(s):  
Simeng Chen ◽  
Volfango Bertola
Keyword(s):  
High Speed ◽  
Heated Surface ◽  
High Speed Imaging ◽  
The Impact

The impact morphology of viscoplastic drops on a heated surface in the Leidenfrost regime is investigated experimentally by high-speed imaging.

Time-dependent measurements of length and area of the contact line in contact-boiling regime

2021 ◽  
Vol 926 ◽  
Author(s):  
Mohammad Khavari ◽  
Tuan Tran
Keyword(s):  
Contact Line ◽  
Contact Area ◽  
High Speed ◽  
Liquid Droplet ◽  
Heated Surface ◽  
Bubble Nucleation ◽  
High Speed Imaging ◽  
Wide Range ◽  
Length And Area ◽  
The Impact

During the impact of a liquid droplet on a sufficiently heated surface, bubble nucleation reduces the contact area between the liquid and the solid surface. Using high-speed imaging combined with total internal reflection, we measure and report how the contact area decreases with time for a wide range of surface temperatures and impact velocities. We also reveal how formation of the observed fingering patterns contributes to a substantial increase in the total length of the contact line surrounding the contact area.

scholarly journals Dilute polymer solution drops impacting on heated surfaces: New impact morphologies and impact regime maps

2017 ◽  
Author(s):  
Volfango Bertola ◽  
Chetan Lakhanpal
Keyword(s):  
Polymer Solution ◽  
High Speed ◽  
Heated Surface ◽  
Polymer Concentration ◽  
Dilute Polymer Solution ◽  
High Speed Imaging ◽  
Satellite Droplet ◽  
Molecular Weights ◽  
Temperature Impact ◽  
The Impact

The impact morphology of dilute polymer solution drops on a heated surface is studied experimentally by meansof high-speed imaging, with respect to the following parameters: surface temperature; impact Weber number; polymer concentration; polymer molecular weight. In addition to impact morphologies observed in Newtonian drops (deposition, rebound, secondary atomisation and breakup/splashing), three new impact regimes have been identified: (i) a single satellite droplet ejected in the direction of bouncing but tethered to the main drop by a thin liquid filament; (ii) a splashing-like behaviour (semi-splashing), where the rim instability  generates  satellite droplets tethered to the lamella by thin liquid filaments; (iii) a spray-like behaviour (semi-spray), where a fine secondary atomisation generated upon impact is quickly absorbed back into the drop globule. Experiments were carried out using drops of aqueous polyethylene oxide (PEO) solutions, with mass concentrations of 100 ppm, 200 ppm and 400 ppm, and PEO molecular weights of 2 MDa, 4MDa, and 8MDa. The impact morphology on a polished aluminium surface with temperatures ranging between 160°C and 400°C was investigated for impact Weber numbers between 20 and 170, taking side view images of impacting drops at a rate of 1,000 frames persecond.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4905

scholarly journals Air mediates the impact of a compliant hemisphere on a rigid smooth surface

Soft Matter ◽  
2021 ◽  
Author(s):  
Siqi Zheng ◽  
Sam Dillavou ◽  
John M. Kolinski
Keyword(s):  
Elastic Body ◽  
Elastic Properties ◽  
Impact Velocity ◽  
Solid Surface ◽  
High Speed ◽  
Smooth Surface ◽  
High Speed Imaging ◽  
The Impact ◽  
Rigid Smooth

When a soft elastic body impacts upon a smooth solid surface, the intervening air fails to drain, deforming the impactor. High-speed imaging with the VFT reveal rich dynamics and sensitivity to the impactor's elastic properties and the impact velocity.

scholarly journals When does a granular material behave like a continuum fluid?

2012 ◽  
Vol 704 ◽  
pp. 1-4 ◽  
Author(s):  
John R. de Bruyn
Keyword(s):  
Granular Material ◽  
Temporal Resolution ◽  
High Speed ◽  
High Impact ◽  
High Temporal Resolution ◽  
Granular Bed ◽  
Fluid Limit ◽  
High Speed Imaging ◽  
Impact Energies ◽  
The Impact

AbstractA flowing granular material can behave like a collection of individual interacting grains or like a continuum fluid, depending in large part on the energy imparted to the grains. As yet, however, we have no general understanding of how or under what conditions the fluid limit is reached. Marston, Li & Thoroddsen (J. Fluid Mech., this issue, vol. 704, 2012, pp. 5–36) use high-speed imaging to investigate the ejection of grains from a granular bed due to the impact of a spherical projectile. Their high temporal resolution allows them to study the very fast processes that take place immediately following the impact. They demonstrate that for very fine grains and high impact energies, the dynamics of the ejecta is both qualitatively and quantitatively similar to what is seen in analogous experiments with fluid targets.

scholarly journals Bubble Dynamics in a Narrow Gap Flow under the Influence of Pressure Gradient and Shear Flow

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 208
Author(s):  
Peter Reinke ◽  
Jan Ahlrichs ◽  
Tom Beckmann ◽  
Marcus Schmidt
Keyword(s):  
Shear Flow ◽  
Pressure Gradient ◽  
High Speed ◽  
Bubble Dynamics ◽  
Three Dimensional ◽  
High Speed Imaging ◽  
Two Phase ◽  
Bubble Generation ◽  
Gap Flow ◽  
The Impact

The volume-of-flow method combined with the Rayleigh–Plesset equation is well established for the computation of cavitation, i.e., the generation and transportation of vapor bubbles inside a liquid flow resulting in cloud, sheet or streamline cavitation. There are, however, limitations, if this method is applied to a restricted flow between two adjacent walls and the bubbles’ size is of the same magnitude as that of the clearance between the walls. This work presents experimental and numerical results of the bubble generation and its transportation in a Couette-type flow under the influence of shear and a strong pressure gradient which are typical for journal bearings or hydraulic seals. Under the impact of variations of the film thickness, the VoF method produces reliable results if bubble diameters are less than half the clearance between the walls. For larger bubbles, the wall contact becomes significant and the bubbles adopt an elliptical shape forced by the shear flow and under the influence of a strong pressure gradient. Moreover, transient changes in the pressure result in transient cavitation, which is captured by high-speed imaging providing material to evaluate transient, three-dimensional computations of a two-phase flow.

scholarly journals COMPARATIVE ANALYSIS OF GOLF CLUBHEAD MOTION AT IMPACT

2020 ◽  
pp. 437
Author(s):  
Simon Kraśna ◽  
Milan Čoh ◽  
Ivan Prebil ◽  
Krzysztof Mackala
Keyword(s):  
High Speed ◽  
Imaging System ◽  
Narrow Range ◽  
Golf Swing ◽  
Body Type ◽  
Additional Insight ◽  
High Speed Imaging ◽  
Circular Arc ◽  
Impact Phase ◽  
The Impact

The purpose of the study was to investigate clubhead kinematics during the impact phase of a golf swing. Three highly skilled golfers of a distinguished body type were instructed to perform driver, 6-iron and pitching wedge trials. A high-speed imaging system was used to capture the clubhead motion near the impact. Conventional golf swing parameters were analysed for comparison. Additionally, a circular arc was fitted to the clubhead path, and the moving trihedron was introduced as a reference frame for observing the clubhead rotation. Despite differences in their body type, golfers achieved comparable clubhead speed, while the radius of the fitted circular arc was in a narrow range. The moving trihedron, together with conventional parameters of the golf swing, enabled additional insight to the clubhead motion and clubface orientation. Individual swing characteristics, which result in the clubhead motion prior to impact, could clearly be observed, enabling improvement of the golfer’s swing technique.

Springboard Droplet Bouncing on Flexible Superhydrophobic Substrates

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Patricia B. Weisensee ◽  
Junjiao Tian ◽  
Nenad Miljkovic ◽  
William P. King
Keyword(s):  
Natural Frequency ◽  
Contact Time ◽  
High Speed ◽  
Flexible Substrate ◽  
Superhydrophobic Surfaces ◽  
High Speed Imaging ◽  
Impact Speed ◽  
Lift Off ◽  
The Impact ◽  
Maximum Spreading

Droplet impact on rigid, superhydrophobic surfaces follows the well-known spreading, recoil, and lift-off behavior at lower impact speeds (a), and splashing at higher impact speeds (b). The contact time tc of these bouncing droplets is independent of the impact speed, and difficult to control. Using high speed imaging (9500 fps) of water droplets impacting superhydrophobic substrates with stiffness 0.5 to 7630 N/m (rigid), we were able to show that substrate flexibility can reduce contact times. Upon impact on a flexible substrate, the droplet excites the substrate to oscillate at the membrane or cantilever natural frequency (d). The oscillation accelerates the droplet upwards, initiating early droplet lift-off at the edges of the droplet close to the point of maximum spreading (c). Droplets fully lift off before fully recoiling, i.e. in a pancake shape. We call this phenomenon the springboard effect. Contact times are reduced by up to 50% compared to rigid substrates.

Altering Bubble Dynamics via Vapor Extraction

2014 ◽  
Author(s):  
Randall G. Fox ◽  
Corey D. Juarez ◽  
Deborah V. Pence ◽  
James A. Liburdy
Keyword(s):  
High Speed ◽  
Bubble Dynamics ◽  
Heated Surface ◽  
Bubble Diameter ◽  
Nucleation Site ◽  
Vapor Extraction ◽  
High Speed Imaging ◽  
Conduction Model ◽  
Gap Height ◽  
Surface Bubble

Bubble dynamics in the presence of a porous confining surface through which vapor is extracted was experimentally investigated. Using a pulsed laser operating at 3500 pulses per second (pps), bubbles were generated at a single, 30 μm diameter nucleation site in a silicon disk. A time-averaged heat flux of 80 W/cm2 and a constant pressure differential of 35 kPa across a porous surface were maintained. The surface, a supported porous Teflon® membrane, has a nominal porosity of 55% and pore diameter of 0.45μm. Steady-state heating was achieved as determined from a one-dimensional conduction model yielding a dimensionless surface temperature fluctuations of less than 0.01%. Bubble diameter and frequency were determined using high-speed imaging for ten gap heights ranging between 0.52 mm and 3.99 mm, where the gap height is defined as the distance between the heated surface and the confining surface. Bubble dynamics of freely departing, coalescing, and rupturing bubbles are considered. Results are compared to diameters and frequencies achieved in unconfined (i.e. pool boiling) conditions. Isolated bubble dynamics depend on gap height and can be grouped into three ranges: greater than, equal to, and less than the bubble diameters for unconfined conditions, which for the present conditions is 1.53 mm. This paper is a work in progress.

scholarly journals Mechanisms of Atomization from Rotary Dental Instruments and Its Mitigation

2020 ◽  
pp. 002203452097964
Author(s):  
A. Sergis ◽  
W.G. Wade ◽  
J.E. Gallagher ◽  
A.P. Morrell ◽  
S. Patel ◽  
...  
Keyword(s):  
High Speed ◽  
Light Sheet ◽  
Care Providers ◽  
High Speed Imaging ◽  
Current Crisis ◽  
Worst Case ◽  
Tooth Contact ◽  
Dental Instruments ◽  
Dental Procedures ◽  
The Impact

Since the onset of coronavirus disease 2019, the potential risk of dental procedural generated spray emissions (including aerosols and splatters), for severe acute respiratory syndrome coronavirus 2 transmission, has challenged care providers and policy makers alike. New studies have described the production and dissemination of sprays during simulated dental procedures, but findings lack generalizability beyond their measurements setting. This study aims to describe the fundamental mechanisms associated with spray production from rotary dental instrumentation with particular focus on what are currently considered high-risk components—namely, the production of small droplets that may remain suspended in the room environment for extended periods and the dispersal of high-velocity droplets resulting in formites at distant surfaces. Procedural sprays were parametrically studied with variables including rotation speed, burr-to-tooth contact, and coolant premisting modified and visualized using high-speed imaging and broadband or monochromatic laser light–sheet illumination. Droplet velocities were estimated and probability density maps for all laser illuminated sprays generated. The impact of varying the coolant parameters on heating during instrumentation was considered. Complex structured sprays were produced by water-cooled rotary instruments, which, in the worst case of an air turbine, included droplet projection speeds in excess of 12 m/s and the formation of millions of small droplets that may remain suspended. Elimination of premisting (mixing of coolant water and air prior to burr contact) resulted in a significant reduction in small droplets, but radial atomization may still occur and is modified by burr-to-tooth contact. Spatial probability distribution mapping identified a threshold for rotation speeds for radial atomization between 80,000 and 100,000 rpm. In this operatory mode, cutting efficiency is reduced but sufficient coolant effectiveness appears to be maintained. Multiple mechanisms for atomization of fluids from rotatory instrumentation exist, but parameters can be controlled to modify key spray characteristics during the current crisis.

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