scholarly journals The Influence of Surfactants, Dynamic and Thermal Factors on Liquid Convection after a Droplet Fall on Another Drop

2020 ◽  
Vol 10 (12) ◽  
pp. 4414
Author(s):  
Sergey Y. Misyura ◽  
Vladimir S. Morozov ◽  
Oleg A. Gobyzov
Keyword(s):  
Thermocapillary Convection ◽  
Sessile Drop ◽  
Vortex Breakdown ◽  
Water Drop ◽  
Mass Transfer Rate ◽  
Practical Importance ◽  
Dynamic Factor ◽  
Velocity Jump ◽  
Thermocapillary Forces ◽  
Curvilinear Trajectory

The regularities of the processes and characteristics of convection in a sessile drop on a hot wall after the second drop fall are investigated experimentally. The movement of a particle on a drop surface under the action of capillary force and liquid convection is considered. The particle motion is realized by a complex curvilinear trajectory. The fall of droplet with and without surfactant additives is considered. Estimates of the influence of the thermal factor (thermocapillary forces) and the dynamic factor (inertia forces) on convection are given. The scientific novelty of the work is the investigation of the simultaneous influence of several factors that is carried out for the first time. It is shown that in the presence of a temperature jump for the time of about 0.01–0.1 s thermocapillary convection leads to a 7–8 times increase in the mass transfer rate in drop. The relative influence of inertial forces is found to be no more than 5%. The fall of drops with surfactant additives (water + surfactant) reduces the velocity jump inside the sessile drop 2–4 times, compared with the water drop without surfactant. Thermocapillary convection leads to the formation of a stable vortex in the drop. The dynamic factor and surfactant additive lead to the vortex breakdown into many small vortices, which results in the suppression of convection. The obtained results are of great scientific and practical importance for heat transfer enhancement and for the control of heating and evaporation rates.

scholarly journals Nonlinear Stability Of Free Thin Films: Thermocapillary And Van-Der-Waals Effects

2014 ◽  
Vol 44 (4) ◽  
pp. 83-96
Author(s):  
S. Tabakova ◽  
S. Radev
Keyword(s):  
Heat Transfer ◽  
Thin Films ◽  
Thermocapillary Convection ◽  
Van Der Waals ◽  
Linear Analysis ◽  
Film Rupture ◽  
Mobile Interfaces ◽  
Surrounding Environment ◽  
Thermocapillary Forces ◽  
The Stability

Abstract In the present work the dynamics of a non-isothermal thin viscous film, with fully mobile interfaces, is studied in the case when the inertial, viscous, capillary, van der Waals and thermocapillary forces are important. The film is laterally bounded by a frame, whose temperature is higher than the environmental one. The stability of the static film shapes is examined numerically by a linear and non-linear analysis. The results show that the film rupture is mostly governed by the dynamics, but it could be delayed or enhanced by the thermocapillary convection and the heat transfer with the surrounding environment.

scholarly journals Deep spontaneous penetration of a water droplet into hot granular materials

2020 ◽  
Author(s):  
Fangye Lin ◽  
Wei Wang ◽  
Stephane Dorbolo ◽  
Jun Zou
Keyword(s):  
Granular Material ◽  
Granular Materials ◽  
Water Drop ◽  
Practical Importance ◽  
Side View ◽  
Granular Bed ◽  
Granular Packing ◽  
Leidenfrost Effect ◽  
Leidenfrost Temperature ◽  
Hele Shaw Cell

Abstract The contact between droplets and granular materials is of practical importance for many processes, such as spraying cooling (to cool down the soil) and the wet dusting (to collect the grains). While the phenomenon is commonly known in nature and industry, our knowledge of the interaction between the water drop and hot grains is still very limited. Here, we experimentally investigated the drop behaviours released on a heated granular bed. Surprisingly, we found that the drops start digging the granular material as deep as 15 times the diameter of the droplet. Hot particles are absorbed into the drop and vaporise the liquid. The vapour production is so intense that the vapour is able to blow away the particles underneath the drop. The drop can then move downwards under the action of the gravity. In order to inspect this digging behaviour, two kinds of setups were designed: a 3D granular packing inside a cylinder and a quasi-2D packing inside a Hele-Shaw cell. The first allows the observation of the droplet with the heated material, while the second provides the direct observation from the side view to uncover the drop behaviour in the deep bed. One proposes a mechanism based on the Leidenfrost effect considering a rough surface that models the surface of the granular material. This model allows to explain why the droplet can dig on a range of temperatures between the boiling temperature of the cooling liquid and the Leidenfrost temperature relative to the granular material. In this range of temperatures, the cooling of the granular material is then rather efficient since the droplets vaporise deeply in the heart of the material.

Wetting of Water Drops on a PMMA Substrate in Viscous Medium

2018 ◽  
Author(s):  
Kumari Trinavee ◽  
Naga Siva Kumar Gunda ◽  
Sushanta K. Mitra
Keyword(s):  
Sessile Drop ◽  
Water Drop ◽  
Surrounding Medium ◽  
Water System ◽  
Viscous Medium ◽  
Liquid System ◽  
Pmma Substrate ◽  
Wide Range ◽  
Liquid Systems ◽  
Water Drops

There is a significant surge in the development of water repellant (superhydrophobic), oil repellent (superoleophobic) surfaces. Though these surfaces are well studied for air medium (inviscid), still there is a lack of fundamental understanding of wetting behavior in presence of surrounding viscous medium. In the present work, we investigate the wetting behaviour of water drops on a PMMA substrate surrounded by viscous oil medium for a wide range of viscosity ratio. The sessile drop is generated at the needle tip (J-needle for denser oil) close to the PMMA substrate to initiate the spreading of a water drop on the substrate. Experimentally measured contact angle at static equilibrium can well interpret the wetting behaviour of water drop on PMMA substrate placed in oil (surrounding medium). It is also observed that the theoretical values of water (drop)-oil and oil (drop)-water system satisfy the Young’s equation of two liquid system, but certain percentage errors are observed when compared to experimental results. These differences are interpreted in terms of interfacial energies of the two-liquid systems. In addition, ‘complementary hysteresis’ model recently put forward by Ozkan et al. [Surf. Topogr.: Metrol. Prop.2017,5,024002] is modified to study the wetting characteristics. Finally, based on the comparison of experimental and theoretical values, a short perspective is provided on the potential of a stable thin lubricant film under the droplet that changes the wetting characteristics of the substrate.

Dynamics of a sessile drop in forced vibration

2007 ◽  
Vol 587 ◽  
pp. 395-423 ◽  
Author(s):  
BOJAN VUKASINOVIC ◽  
MARC K. SMITH ◽  
ARI GLEZER
Keyword(s):  
Sessile Drop ◽  
Water Drop ◽  
Wave Pattern ◽  
Critical Value ◽  
Temporal Complexity ◽  
Low Viscosity ◽  
Lattice Mode ◽  
Individual Wave ◽  
Spatio Temporal ◽  
Azimuthal Waves

The interfacial dynamics of a sessile water drop was investigated experimentally. The low-viscosity drop was forced by an underlying diaphragm driven vertically by a piezoelectric actuator. This high-frequency forcing produced very low diaphragm displacements, even at high acceleration amplitudes. As the driving amplitude was increased from zero, the drop exhibited several transitions to states of increasing spatio-temporal complexity. The first state of the forced drop consisted of harmonic axisymmetric standing waves that were present for even the smallest diaphragm motion. Wave modes up to 14 were observed an compared to theoretical results. As the forcing amplitude increased above a critical value, a parametrically driven instability occurred that resulted in the appearance of subharmonic azimuthal waves along the contact line. The critical accelerations and the resulting wavenumbers of the azimuthal waves were documented. For larger values of the forcing amplitude, the subharmonic azimuthal waves coupled with the harmonic axisymmetric waves to produce a striking new lattice-like wave pattern. With a further increase in the forcing amplitude, the lattice mode disappeared and the interface evolved into a highly disordered state, dominated by subharmonic wave motion. The characteristics of the lattice and pre-ejection modes were documented with phase-locked measurements and spectral analysis. Finally, as the forcing amplitude increased above another critical value, the interface broke up via droplet ejection from individual wave crests.

scholarly journals Water stable aggregates of Japanese Andisol as affected by hydrophobicity and drying temperature

2014 ◽  
Vol 62 (2) ◽  
pp. 97-100 ◽  
Author(s):  
D.A.L. Leelamanie ◽  
Jutaro Karube
Keyword(s):  
Contact Angle ◽  
Sessile Drop ◽  
Water Drop ◽  
Aggregate Stability ◽  
Water Repellency ◽  
Water Stability ◽  
Drying Temperature ◽  
Hydrophobic Materials ◽  
Soil Hydrophobicity ◽  
Penetration Time

Abstract Hydrophobicity is a property of soils that reduces their affinity for water, which may help impeding the pressure build-up within aggregates, and reducing aggregate disruption. The purpose of this study was to examine the relation of soil hydrophobicity and drying temperature to water stability of aggregates while preventing the floating of dry aggregates using unhydrophobized and hydrophobized surface Andisol. Soil was hydrophobized using stearic acid into different hydrophobicities. Hydrophobicity was determined using sessile drop contact angle and water drop penetration time (WDPT). Water stability of aggregates (%WSA) was determined using artificially prepared model aggregates. The %WSA increased as the contact angle and WDPT increased. Contact angle and WDPT, which provided maximum %WSA showing less than 1 s of floating, was around 100° and 5 s, respectively. Although the %WSA gradually increased with increasing contact angle and WDPT above this level, high levels of hydrophobicity initiated aggregate floating, which would cause undesirable effects of water repellency. Heating at 50°C for 5 h d-1 significantly affected %WSA and hydrophobicity in hydrophobized samples, but did not in unhydrophobized samples. The results indicate that the contact angle and wetting rate (WDPT) are closely related with the water stability of aggregates. The results further confirm that high levels of hydrophobicities induce aggregate floating, and the drying temperature has differential effects on hydrophobicity and aggregate stability depending on the hydrophobic materials present in the soil.

scholarly journals Density and surface tension of molten cast irons

2021 ◽  
pp. 40-40
Author(s):  
P. Fima ◽  
N. Sobczak
Keyword(s):  
Surface Tension ◽  
Sessile Drop ◽  
Chemical Interaction ◽  
Practical Importance ◽  
Substrate Material ◽  
Cast Irons ◽  
Polycrystalline Alumina ◽  
Compacted Graphite ◽  
Graphite Cast Iron ◽  
Contact Heating

Computer-aided development of liquid-assisted metallurgical processes requires reliable basic data for the molten materials, including thermophysical properties such as density, surface tension and viscosity. Cast irons belong to the group of Fe-C alloys of practical importance due to their good technological and utility properties, yet experimental thermophysical data of cast irons in the literature are scarce. In this study, the density and surface tension of three compacted graphite cast iron alloys were measured by the sessile drop method in contact heating mode in the temperature range of 1473 - 1723 K with polycrystalline alumina as a substrate. The drop profile images were recorded both during heating and subsequent cooling regimes. At 1473 K, the density values of the studied compacted graphite irons are between 6.66 and 6.69 g?cm-3, whereas surface tension values are between 1130 and 1510 mN?m-1. The density decreases with increasing temperature, while surface tension dependence on temperature is less obvious. The obtained results are compared to the available literature data and analyzed taking into account chemical interaction of liquid cast irons with the substrate material.

scholarly journals Some Features of the Ultrasonic Liquid Extraction of Metal Ions

Molecules ◽  
2019 ◽  
Vol 24 (19) ◽  
pp. 3549 ◽  
Author(s):  
O.M. Gradov ◽  
Yu.A. Zakhodyaeva ◽  
I.V. Zinov’eva ◽  
A.A. Voshkin
Keyword(s):  
Metal Ions ◽  
Sound Pressure ◽  
Treatment Time ◽  
Theoretical Calculations ◽  
Mass Transfer Rate ◽  
Practical Importance ◽  
Experimental Studies ◽  
Immiscible Liquid ◽  
Water Soluble ◽  
Spherical Drop

The non-linear equation of the radial oscillations of a liquid ball in an immiscible liquid under the exposure of time-varying sound pressure was obtained. The behavioral features of a liquid spherical drop placed in such a media were analyzed in the presence of ultrasound irradiations. The slowing-down effect of the extracted metal ions under its exposure has been studied for the first time, using theoretical and experimental approaches. This phenomenon mechanism was revealed, and analytical equations for the mass transfer rate as a function of the sound pressure oscillations amplitude and the substrate ultrasonic treatment time are presented. Experimental studies of Fe3+ ions extracted from chloride and nitrate solutions in systems based on water-soluble polymers were carried out, and a convincing coincidence with the results of theoretical calculations was established. The conditions for achieving the desired extraction efficiency when applying the ultrasonic stimulating effect are specified. The derived result opens the complementary possibility in operations, with the separateness of extraction processes, that which has the essential practical importance.

Role of Thermocapillary Convection in Rupture of a Falling Liquid Film Heated From Below

2010 ◽  
Author(s):  
Elizaveta Gatapova ◽  
Dmitry Zaitsev ◽  
Oleg Kabov
Keyword(s):  
Liquid Film ◽  
Thermocapillary Convection ◽  
Physical Mechanism ◽  
Dominant Role ◽  
Falling Liquid Film ◽  
Fiber Optical ◽  
Dry Patch ◽  
Critical Film Thickness ◽  
Thermocapillary Forces

The present work is aimed to describe and explain the physical mechanism of the rupture of a liquid film of moderate thickness falling down a heated substrate. Our investigations are based on the experimental data obtained using IR thermography, fiber optical technique as well as theoretical estimation of critical values. We show that thermocapillary convection may be responsible for critical film thickness. By investigating the instability of thermocapillary cells we demonstrate that thermocapillary forces play a dominant role in the first and the second stages of the dry patch formation process.

Practical Importance of Spatial Resolution and Analytical Sensitivity in AEM X-ray Microanalysis

1990 ◽  
Vol 48 (2) ◽  
pp. 432-433
Author(s):  
J. Zhang ◽  
D.B. Williams ◽  
J.I. Goldstein
Keyword(s):  
Spatial Resolution ◽  
Practical Importance ◽  
Beam Current ◽  
Specimen Thickness ◽  
Analytical Sensitivity ◽  
Related Factors ◽  
X Ray ◽  
Probe Size ◽  
Excitation Volume ◽  
Two Parameters

Analytical sensitivity and spatial resolution are important and closely related factors in x-ray microanalysis using the AEM. Analytical sensitivity is the ability to distinguish, for a given element under given conditions, between two concentrations that are nearly equal. The analytical sensitivity is directly related to the number of x-ray counts collected and, therefore, to the probe current, specimen thickness and counting time. The spatial resolution in AEM analysis is determined by the probe size and beam broadening in the specimen. A finer probe and a thinner specimen give a higher spatial resolution. However, the resulting lower beam current and smaller X-ray excitation volume degrade analytical sensitivity. A compromise must be made between high spatial resolution and an acceptable analytical sensitivity. In this paper, we show the necessity of evaluating these two parameters in order to determine the low temperature Fe-Ni phase diagram.A Phillips EM400T AEM with an EDAX/TN2000 EDS/MCA system and a VG HB501 FEG STEM with a LINK AN10 EDS/MCA system were used.

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