Hydrodynamics of a drying multicomponent liquid droplet (original) (raw)
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Hydrodynamic Pattern in Drying Saline Droplet with Suspended Nanoparticles
Journal of Bionic Engineering
Evaporation of multicomponent droplets has gained much attention nowadays because of their complex flow fields and various deposition patterns. Here we observe strong flows in evaporating sodium chloride saline droplets with suspended alumina oxide nanoparticles. The evolution of flow pattern was studied by tracking the trajectories of particles and the velocity field was investigated with Particle Image Velocimetry analysis. The non-uniform evaporation rate along the droplet surface leads to a concentration gradient which induces the convection flow. During the evaporation process before crystallization happens, evolution of the flow can be divided into two regimes. In Regime I, a centrosymmetric convection recirculation is formed gradually. In Regime II, the convection recirculation migrates to the droplet edge and evolves into several small vortexes. At the late evaporation stage, crystallization could induce strong convection flows. It is shown that the flow tends to become more chaotic with a lower salt concentration.
Formation of texture in residue of a drying drop of a multicomponent fluid
Doklady Physics, 2010
The increase in the number of works devoted to investigation of transport of a substance and formation of texture in residues of multicomponent fluids that dry on a substrate, which has been observed in recent decades, is caused by the fundamental character of interrelated problems of macromechanics and micro mechanics, as well as by a variety of technical applica tions. In the process of drying, a series of hydrody namic and physicochemical processes changing the thermodynamic and phase state of the medium occur in the solution drop. The texture of dry residue of the drop depends on the fluid composition and drying conditions. The possibility to form dry residues of the drops of solutions of mineral or organic substances is used in nanotechnologies and microtechnologies [1], to specify the texture of profiled surfaces , and in production of chemically and biologically active sub stances . The analysis of the texture of facies of bio logical fluids is considered as the foundation of new integrated methods of medical diagnostics .
Internal flow patterns of an evaporating multicomponent droplet on a flat surface
Evaporation processes of droplets with different ethanol/water compositions on a hydrophobic heated surface were investigated utilizing particle image velocimetry (PIV). It is found that the process of an evaporating two-component droplet can be divided into downward vortex stage, transition stage and upward vortex stage sequentially, while a pure water droplet only has upward vortices stage. The three stages were analyzed utilizing experimental results and dimensionless parameters, such as thermal Marangoni number (Ma T) and Solutal Marangoni number (Ma S). For downward vortex and transition stages, solutal and thermal Marangoni effects were dominating. The occurrence of transition stage indicated buoyancy effect becomes comparable to Marangoni effect as ethanol continuously evaporated, and the occurrence of upward vortex stage indicated most of ethanol gasified and buoyancy effect dominated. The influence of initial composition and heating power on the downward vortices and transition stages has also been investigated. With low input power, droplets with high ethanol concentration have shorter evaporation time in above two stages. On the contrary, however, droplets with high ethanol concentration have longer evaporation time in above two stages with high input power.
Advances in Condensed Matter Physics
This review is devoted to the simple process of drying a multicomponent droplet of a complex fluid which may contain salt or other inclusions. These processes provide a fascinating subject for study. The explanation of the rich variety of patterns formed is not only an academic challenge but also a problem of practical importance, as applications are growing in medical diagnosis and improvement of coating/printing technology. The fundamental scientific problem is the study of the mechanism of micro- and nanoparticle self-organization in open systems. The specific fundamental problems to be solved, related to this system, are the investigation of the mass transfer processes, the formation and evolution of phase fronts, and the identification of mechanisms of pattern formation. The drops of liquid containing dissolved substances and suspended particles are assumed to be drying on a horizontal solid insoluble smooth substrate. The chemical composition and macroscopic properties of the ...
Deposition pattern and tracer particle motion of evaporating multi-component sessile droplets
Journal of colloid and interface science, 2017
The understanding of near-wall motion, evaporation behavior and dry pattern of sessile nanofluid droplets is fundamental to a wide range of applications such as painting, spray drying, thin film coating, fuel injection and inkjet printing. However, a deep insight into the heat transfer, fluid flow, near-wall particle velocity and their effects on the resulting dry patterns is still much needed to take the full advantage of these nano-sized particles in the droplet. This work investigates the effect of direct absorptive silicon/silver (Si/Ag) hybrid nanofluids via two experiments. The first experiment identifies the motion of tracer particles near the triple line of a sessile nanofluid droplet on a super-hydrophilic substrate under ambient conditions by the multilayer nanoparticle image velocimetry (MnPIV) technique. The second experiment reveals the effect of light-sensitive Si/Ag composite nanoparticles on the droplet evaporation rate and subsequent drying patterns under different ...
Morphological transformations during drying of surfactant-nanofluid droplets
Journal of Industrial and Engineering Chemistry
The effect of surfactants with different chain length on the drying dynamics of nanosized dispersion droplets and on the final morphology of the grains formed after water evaporation is investigated experimentally. An acoustic levitator was used to examine the drying dynamics of single droplets and SEM imaging was used to characterise the morphology of the final dried grains. Results show that the drying of drops with high molecular weight surfactants leads to more irregular grains and that the grain morphology is related to surface tension driven instability of the evaporating droplets which may lead to formation of hollow dried grains.
2015
Ring-stains are seen when droplets of liquid containing particles are left to dry on a surface: a pinned contact line leads to outward radial flow, which is enhanced by the diverging evaporative flux at the contact line. As a result, suspended particles in the drops are transported to the edge of the droplet, and deposited in a circular stain. In the first section of this study, we investigated how the width and height of ring in water droplets containing suspensions of polystyrene microparticles with diameters ≤0.5μm vary with experimentally controlled parameters, including particle size, contact angle, concentration, evaporation rate and orientation of the droplets. Our studies found, for the first time, that the drying rate plays an important role in determining the shape of the final deposit which may contribute to a better understanding of a coffee ring effect. At low drying rates, nearly all the particles are deposited in the ring and the width and height of the ring follow a ...
Some physics inside drying droplets
Resonance, 2014
Netherlands. His research interests include micronanofluidics and nanoscale electrochemistry. Spreading of a droplet placed on a solid surface (sessile droplet) depends on the wetting properties of the liquid on that surface. Droplets are of great scientific interest because studying their formation and dynamics is important in many technologies such as in microfluidics [1, 2]. Evaporation of droplets is another interesting aspect that has caught much scientific attention. An example of an evaporating droplet is a coffee droplet spilled on a table. After evaporation the coffee droplet leaves a ring-like stain called a coffee ring or coffee stain [3]. This phenomenon, known as the 'coffee ring effect', occurs not only with coffee droplets but also with all droplets containing non-volatile solutes. There are a number of interesting physical processes going on within the droplets during evaporation to form the 'coffee stains'. In this article, we will see what they are.