The Experts below are selected from a list of 59586 Experts worldwide ranked by ideXlab platform
Detlef Lohse - One of the best experts on this subject based on the ideXlab platform.
-
Gravitational Effect in evaporating binary microdroplets
Physical Review Letters, 2019Co-Authors: Detlef Lohse, Christian Diddens, Herman Wijshoff, Michel VersluisAbstract:The flow in an evaporating glycerol-water binary submillimeter droplet with a Bond number $\mathrm{Bo}\ensuremath{\ll}1$ is studied both experimentally and numerically. First, we measure the flow fields near the substrate by microparticle image velocimetry for both sessile and pendant droplets during the evaporation process, which surprisingly show opposite radial flow directions---inward and outward, respectively. This observation clearly reveals that in spite of the small droplet size, Gravitational Effects play a crucial role in controlling the flow fields in the evaporating droplets. We theoretically analyze that this gravity-driven Effect is triggered by the lower volatility of glycerol which leads to a preferential evaporation of water then the local concentration difference of the two components leads to a density gradient that drives the convective flow. We show that the Archimedes number Ar is the nondimensional control parameter for the occurrence of the Gravitational Effects. We confirm our hypothesis by experimentally comparing two evaporating microdroplet systems, namely, a glycerol-water droplet and a 1,2-propanediol-water droplet. We obtain different Ar, larger or smaller than a unit by varying a series of droplet heights, which corresponds to cases with or without Gravitational Effects, respectively. Finally, we simulate the process numerically, finding good agreement with the experimental results and again confirming our interpretation.
-
Gravitational Effect on the formation of surface nanodroplets
Langmuir, 2015Co-Authors: Detlef Lohse, Xuehua ZhangAbstract:Nanoscale droplets at a solid–liquid interface are of high relevance for many fundamental phenomena and applied processes. The solvent exchange process is a simple approach to produce, e.g., oil nanodroplets over a large surface area on a substrate, by exchange oil-saturated ethanol by oil-saturated water, which has a lower oil solubility than ethanol. In this process, the size of the nanodroplets is closely related to the flow conditions. To achieve control of the droplet size, it is essential to fully understand the nucleation and growth of nanodroplets under different flow conditions. In this work, we investigate the Gravitational Effect on the droplet formation by the solvent exchange. We compared the droplet size as the substrate was placed on the upper or lower wall in a horizontal fluid channel or on the sides of a vertical channel with an upward or downward flow. We found significant difference in the droplet size for the three substrate positions in a wide channel with height h = 0.21 mm. The difference of droplet size was eliminated in a narrow channel with height h = 0.07 mm. The relevant dimensional control parameter for the occurrence of the Gravitational Effects is the Archimedes number Ar and these two heights correspond to Ar = 10 and Ar = 0.35, respectively. The Gravitational Effects lead to a nonsymmetric parabolic profile of the mixing front, with the velocity maximum being off-center and thus with different distances α(Ar)h and (1 – α(Ar))h to the lower and upper wall, respectively. The ratio of the total droplet volume on the lower and upper wall is theoretically found to be (α(Ar)/(1 – α(Ar)))3. This study thus improves our understanding of the mechanism of the solvent exchange process, providing guidelines for tailoring the volume of surface nanodroplets.
Bernardus J Geurts - One of the best experts on this subject based on the ideXlab platform.
-
metal 3d printed wick structures for heat pipe application capillary performance analysis
Applied Thermal Engineering, 2018Co-Authors: Davoud Jafari, Wessel W Wits, Bernardus J GeurtsAbstract:Abstract This paper examines the so-called capillary performance of a freeform porous structure fabricated by advanced 3D metal printing technology. The fabricated structure is intended as wick for two-phase heat transfer devices, in which it contributes to the transport of a liquid working fluid through capillary forces. A stainless steel porous structure is additively manufactured and characterized in terms of its porosity (e), Effective pore radius (reff), liquid permeability (K) and capillary performance (K/reff). Forced liquid flow tests with deionized water as working fluid are conducted to determine the permeability. Capillary penetration experiments are performed by means of height-time (h-t) and weight-time (w-t) techniques with different fluids to characterize the capillary performance of the printed wicks. The experimentally determined values of permeability and pressure drop are compared with the well-known Darcy’s law and Forchheimer corrections. The Kozeny–Carman correlation is found to predict the experimental values of permeability at lower flow velocities (0.07 m/s corresponding to a Reynolds number of 0.95), while at higher velocities an under-prediction of the experimental data is observed. The Kozeny-like model taking into account inertial Effects is updated in terms of constant values that fit with the experimental data very well. The accuracy of the theoretical models for characterizing capillary rate-or-rise processes is also assessed. It is concluded that the capillary penetration of liquids in the 3D-printed wick follows the law: h(t) ∼ t1/3 at intermediate stage. Observation confirms that the Gravitational Effect played a significant role in the 3D-printed wick, introducing slower capillary rising. Compared to sintered powder, screen mesh and composite wicks selected from literature, the designed 3D-printed wick enhances the capillary performance. It is concluded that due to the large permeability and capillary performance (K/reff), heat pipes in conjunction with a 3D-printed wick can significantly augment their heat transfer.
Yu O Tsupko - One of the best experts on this subject based on the ideXlab platform.
-
Gravitational lensing in a non uniform plasma
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: G S Bisnovatyikogan, Yu O TsupkoAbstract:We develop a model of Gravitational lensing in a non-uniform plasma. When a gravitating body is surrounded by a plasma, the lensing angle depends on the frequency of the electromagnetic wave, due to dispersion properties of plasma, in presence of a plasma inhomogeneity, and of a gravity. The second Effect leads, even in a uniform plasma, to a difference of the Gravitational photon deflection angle from the vacuum case, and to its dependence on the photon frequency. We take into account both Effects, and derive the expression for the lensing angle in the case of a strongly nonuniform plasma in presence of the gravitation. Dependence of the lensing angle on the photon frequency in a homogeneous plasma resembles the properties of a refractive prism spectrometer, which strongest action is for very long radiowaves. We discuss the observational appearances of this Effect for the Gravitational lens with a Schwarzschild metric, surrounded by a uniform plasma. We obtain formulae for the lensing angle and the magnification factors in this case and discuss a possibility of observation of this Effect by the planned VLBI space project Radioastron. We also consider models with a nonuniform plasma distribution. For different Gravitational lens models we compare the corrections to the vacuum lensing due to the Gravitational Effect in plasma, and due to the plasma inhomogeneity. We have shown that the Gravitational Effect could be detected in the case of a hot gas in the Gravitational field of a galaxy cluster.
-
Gravitational lensing in a non uniform plasma
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: G S Bisnovatyikogan, Yu O TsupkoAbstract:We develop a model of Gravitational lensing in a non-uniform plasma. When a gravitating body is surrounded by a plasma, the lensing angle depends on the frequency of the electromagnetic wave, due to the dispersion properties of the plasma, in the presence of a plasma inhomogeneity, and of gravity. The second Effect leads, even in a uniform plasma, to a difference of the Gravitational photon deflection angle from the vacuum case, and to its dependence on the photon frequency. We take into account both Effects, and derive the expression for the lensing angle in the case of a strongly non-uniform plasma in the presence of gravitation. The dependence of the lensing angle on the photon frequency in a homogeneous plasma resembles the properties of a refractive prism spectrometer, the strongest action of which is for very long radio waves. We discuss the observational appearance of this Effect for the Gravitational lens with a Schwarzschild metric, surrounded by a uniform plasma. We obtain formulae for the lensing angle and the magnification factors in this case and discuss the possibility of observation of this Effect by the planned very long baseline interferometry space project RadioAstron. We also consider models with a non-uniform plasma distribution. For different Gravitational lens models we compare the corrections to the vacuum lensing due to the Gravitational Effect in the plasma, and due to the plasma inhomogeneity. We show that the Gravitational Effect could be detected in the case of a hot gas in the Gravitational field of a galaxy cluster.
Christian Diddens - One of the best experts on this subject based on the ideXlab platform.
-
Gravitational Effect in evaporating binary microdroplets
Physical Review Letters, 2019Co-Authors: Detlef Lohse, Christian Diddens, Herman Wijshoff, Michel VersluisAbstract:The flow in an evaporating glycerol-water binary submillimeter droplet with a Bond number $\mathrm{Bo}\ensuremath{\ll}1$ is studied both experimentally and numerically. First, we measure the flow fields near the substrate by microparticle image velocimetry for both sessile and pendant droplets during the evaporation process, which surprisingly show opposite radial flow directions---inward and outward, respectively. This observation clearly reveals that in spite of the small droplet size, Gravitational Effects play a crucial role in controlling the flow fields in the evaporating droplets. We theoretically analyze that this gravity-driven Effect is triggered by the lower volatility of glycerol which leads to a preferential evaporation of water then the local concentration difference of the two components leads to a density gradient that drives the convective flow. We show that the Archimedes number Ar is the nondimensional control parameter for the occurrence of the Gravitational Effects. We confirm our hypothesis by experimentally comparing two evaporating microdroplet systems, namely, a glycerol-water droplet and a 1,2-propanediol-water droplet. We obtain different Ar, larger or smaller than a unit by varying a series of droplet heights, which corresponds to cases with or without Gravitational Effects, respectively. Finally, we simulate the process numerically, finding good agreement with the experimental results and again confirming our interpretation.
Seunghwa Ryu - One of the best experts on this subject based on the ideXlab platform.
-
Gravitational Effect on the advancing and receding angles of a two dimensional cassie baxter droplet on a textured surface
Langmuir, 2020Co-Authors: Donggyu Kim, Minsoo Jeong, Keonwook Kang, Seunghwa RyuAbstract:Advancing and receding angles are physical quantities frequently measured to characterize the wetting properties of a rough surface. Thermodynamically, the advancing and receding angles are often interpreted as the maximum and minimum contact angles that can be formed by a droplet without losing its stability. Despite intensive research on wetting of rough surfaces, the Gravitational Effect on these angles has been overlooked because most studies have considered droplets smaller than the capillary length. In this study, however, by combining theoretical and numerical modeling, we show that the shape of a droplet smaller than the capillary length can be substantially modified by gravity under advancing and receding conditions. First, based on the Laplace pressure equation, we predict the shape of a two-dimensional Cassie-Baxter droplet on a textured surface with gravity at each pinning point. Then, the stability of the droplet is tested by examining the interference between the liquid surface and neighboring pillars and analyzing the free energy change upon depinning. Interestingly, it turns out that the apparent contact angles under advancing and receding conditions are not affected by gravity, while the overall shape of a droplet and the position of the pinning point are affected by gravity. In addition, the advancing and receding of the droplet with continuously increasing or decreasing volume are analyzed, and it is shown that the Gravitational Effect plays a key role in the movement of the droplet tip. Also, the Gravitational Effect on the degree of the stability of the droplet upon the external Effect such as vibration is discussed. Finally, the theoretical predictions were validated against line tension-based front tracking modeling (LTM) that seamlessly captures the attachment and detachment between the liquid surface and the solid substrate. Our findings provide a deeper understanding on the advancing and receding phenomena of a droplet and essential insight into designing devices that utilize the wettability of rough surfaces.
-
Gravitational Effect on the advancing and receding angle of a 2d cassie baxter droplet on a textured surface
arXiv: Soft Condensed Matter, 2019Co-Authors: Donggyu Kim, Keonwook Kang, Seunghwa RyuAbstract:Advancing and receding angles are physical quantities frequently measured to characterize the wetting properties of a rough surface. Thermodynamically, the advancing and receding angles are often interpreted as the maximum and minimum contact angles that can be formed by a droplet without losing its stability. Despite intensive research on wetting of rough surfaces, the Gravitational Effect on these angles has been overlooked because most studies have considered droplets smaller than the capillary length. In this study, however, by combining theoretical and numerical modeling, we show that the shape of a droplet smaller than the capillary length can be substantially modified by gravity under advancing and receding conditions. First, based on the Laplace pressure equation, we predict the shape of a two-dimensional Cassie-Baxter droplet on a textured surface with gravity at each pinning point. Then the stability of the droplet is tested by examining the interference between the liquid surface and neighboring pillars as well as analyzing the free energy change upon depinning. Interestingly, it turns out that the apparent contact angles under advancing and receding conditions are not affected by gravity, while the overall shape of a droplet and the position of the pinning point is affected by gravity. In addition, the advancing and receding of the droplet with continuously increasing or decreasing volume is analyzed, and it is showed that the Gravitational Effect plays a key role on the movement of the droplet tip. Finally, the theoretical predictions were validated against line-tension based front tracking modeling that seamlessly captures the attachment and detachment between the liquid surface and the solid substrate.
