The Experts below are selected from a list of 178686 Experts worldwide ranked by ideXlab platform
Xurui Zhang - One of the best experts on this subject based on the ideXlab platform.
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inward flow of intervening liquid films driven by the marangoni effect during bubble solid collisions in ethyl alcohol nacl aqueous solutions
Langmuir, 2021Co-Authors: Xurui Zhang, Rogerio Manica, Qingxia LiuAbstract:The drainage dynamics of confined thin liquid films between an air bubble and a freshly cleaved mica surface were investigated in ethyl alcohol aqueous solutions. Focus was given to the holding stage, in which an unexpected increase in the thickness of a few hundred nanometers at the center of the film was captured by interferometry in ethyl alcohol-500 mM NaCl aqueous solutions. Such an increase in film thickness occurred when the ethyl alcohol concentration exceeded the critical value at a bubble Approach Velocity of 100 μm/s. For a given ethyl alcohol concentration, the increase in thickness at the center of the film did not happen when the bubble Approach Velocity was decreased to 10 μm/s. Compared to the cases in ethyl alcohol-500 mM NaCl solutions, no increase in thickness at the center of the film was observed in ethyl alcohol-water solutions under the same ethyl alcohol concentration and bubble Approach Velocity. The phenomenon of the increasing thickness at the center of the film was attributed to the net inward flow in the film, resulting from competition between the inward Marangoni flow and the outward drainage flow that was hindered by the narrow channel at the barrier rim of the film under a high electrolyte concentration. The inward Marangoni flow was achieved by a concentration gradient of ethyl alcohol between the film and the bulk solution resulting from the mobile air-liquid interface in the initial Approaching period.
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Probing Boundary Conditions at Hydrophobic Solid–Water Interfaces by Dynamic Film Drainage Measurement
2018Co-Authors: Xurui Zhang, Rogerio Manica, Plamen Tchoukov, Yuechao Tang, Qingxia LiuAbstract:A newly developed dynamic force apparatus was used to determine hydrodynamic boundary conditions of a liquid on a hydrophobic silica surface. For a given Approach Velocity of bubble to solid surfaces in an electrolyte solution, a reduced dimple formation and faster film drainage were observed by increasing the hydrophobicity of silica surfaces, indicating a significant change in hydrodynamic boundary conditions of water molecules from an immobile to a mobile water–hydrophobic silica interface. By comparing the measured film profiles with the predictions from the Stokes–Reynolds–Young–Laplace model, the slippage boundary condition of water on the hydrophobic silica surface of surface nanoroughness was quantified. Increasing the surface hydrophobicity was found to increase the mobility of water in the thin liquid film, promoting faster drainage of the liquid. For a given hydrophobicity of solids, the mobility of water occurred only above a critical bubble Approach Velocity and increased with increasing bubble Approach Velocity. In contrast, similar experiments with hydrophobized mica surfaces showed no-slip boundary condition of water at the molecularly smooth hydrophobic surface. The results collectively suggest that the observed mobility of water with more than 100 nm in thickness on the studied hydrophobic silica surfaces was due to the nanoroughness of hydrophobic surfaces. Such finding sheds light on one possible way of reducing the friction of water on hydrophobic solid surfaces by creating nanostructured surface of nanoroughness
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effect of Approach Velocity on thin liquid film drainage between an air bubble and a flat solid surface
Journal of Physical Chemistry C, 2017Co-Authors: Xurui Zhang, Rogerio Manica, Plamen Tchoukov, Zhenghe XuAbstract:The dynamic drainage process of the liquid film trapped between an air bubble and a flat silica surface over a wide range of hydrodynamic conditions is studied by a newly developed instrument called integrated thin liquid film force apparatus (ITLFFA) under different salt concentrations. The ITLFFA allows the simultaneous measurement of interaction forces and spatiotemporal film thickness with accurate control of bubble Approach Velocity in a large range of Reynolds number from 0.005 to 135. Our study demonstrates that increasing the bubble Approach Velocity plays a significant role in the hydrodynamic pressure and fluid flow within the draining film promoting dimple formation and longer drainage time. The drainage time also depends on the competition between the electrical double-layer and van der Waals interactions, which are repulsive in our system, resulting in a flat equilibrium film at the end. The evolution of the draining film is analyzed using the Stokes–Reynolds–Young–Laplace (SRYL) model. Compa...
Ravi M Warkhedkar - One of the best experts on this subject based on the ideXlab platform.
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thermal performance of elliptical pin fin heat sink under combined natural and forced convection
Experimental Thermal and Fluid Science, 2013Co-Authors: P A Deshmukh, Ravi M WarkhedkarAbstract:Abstract In this paper, the effects of design parameters have been experimentally investigated for the air side thermal performance under mixed (combined natural and forced) convection of the fully shrouded elliptical pin fin heat sinks and the values of optimum design parameters are sought. A theoretical model is used to predict the influence of various geometrical, thermal and flow parameters on the thermal resistance of the heat sink. An experimental measurement technique is utilized to indirectly measure the overall heat transfer coefficient of the heat sink in mixed convection with assisting flow. The thermal performance characteristics are obtained for various parameters with inline and staggered layout of the pin fin heat sinks resulting in optimum heat sink void fraction ( α ), and pin fin aspect ratio ( ϒ ). The comparative thermal performances of circular and elliptical profiled pin fin heat sinks are presented. Based on experimental data for the range of fin, air flow and heat sink parameters, with aspect ratio, 5.1 ⩽ ϒ ⩽ 9.18; heat sink void fraction, 0.534 ⩽ α ⩽ 0.884; Approach Velocity, 0.1 ⩽ U ∞ ⩽ 0.5; longitudinal fin pitch, 18 ⩽ S L ⩽ 36 mm; transverse fin pitch, 9 ⩽ S T ⩽ 18 mm; elliptical pin fin axis ratio ∊ = 0.66 and mixed convection parameter, 1 ⩽ Gr d /Re d ⩽ 100; generalized empirical correlations are developed for elliptical pin fin heat sink.
Junjie Jiao - One of the best experts on this subject based on the ideXlab platform.
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influence of acoustic pressure and bubble sizes on the coalescence of two contacting bubbles in an acoustic field
Ultrasonics Sonochemistry, 2015Co-Authors: Junjie Jiao, Kyuichi Yasui, Sandra E Kentish, Muthupandian Ashokkumar, Richard Manasseh, Judy LeeAbstract:In this study, the coalescence time between two contacting sub-resonance size bubbles was measured experimentally under an acoustic pressure ranging from 10kPa to 120kPa, driven at a frequency of 22.4kHz. The coalescence time obtained under sonication was much longer compared to that calculated by the film drainage theory for a free bubble surface without surfactants. It was found that under the influence of an acoustic field, the coalescence time could be probabilistic in nature, exhibiting upper and lower limits of coalescence times which are prolonged when both the maximum surface Approach Velocity and secondary Bjerknes force increases. The size of the two contacting bubbles is also important. For a given acoustic pressure, bubbles having a larger average size and size difference were observed to exhibit longer coalescence times. This could be caused by the phase difference between the volume oscillations of the two bubbles, which in turn affects the minimum film thickness reached between the bubbles and the film drainage time. These results will have important implications for developing film drainage theory to account for the effect of bubble translational and volumetric oscillations, bubble surface fluctuations and microstreaming.
P A Deshmukh - One of the best experts on this subject based on the ideXlab platform.
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thermal performance of elliptical pin fin heat sink under combined natural and forced convection
Experimental Thermal and Fluid Science, 2013Co-Authors: P A Deshmukh, Ravi M WarkhedkarAbstract:Abstract In this paper, the effects of design parameters have been experimentally investigated for the air side thermal performance under mixed (combined natural and forced) convection of the fully shrouded elliptical pin fin heat sinks and the values of optimum design parameters are sought. A theoretical model is used to predict the influence of various geometrical, thermal and flow parameters on the thermal resistance of the heat sink. An experimental measurement technique is utilized to indirectly measure the overall heat transfer coefficient of the heat sink in mixed convection with assisting flow. The thermal performance characteristics are obtained for various parameters with inline and staggered layout of the pin fin heat sinks resulting in optimum heat sink void fraction ( α ), and pin fin aspect ratio ( ϒ ). The comparative thermal performances of circular and elliptical profiled pin fin heat sinks are presented. Based on experimental data for the range of fin, air flow and heat sink parameters, with aspect ratio, 5.1 ⩽ ϒ ⩽ 9.18; heat sink void fraction, 0.534 ⩽ α ⩽ 0.884; Approach Velocity, 0.1 ⩽ U ∞ ⩽ 0.5; longitudinal fin pitch, 18 ⩽ S L ⩽ 36 mm; transverse fin pitch, 9 ⩽ S T ⩽ 18 mm; elliptical pin fin axis ratio ∊ = 0.66 and mixed convection parameter, 1 ⩽ Gr d /Re d ⩽ 100; generalized empirical correlations are developed for elliptical pin fin heat sink.
Rogerio Manica - One of the best experts on this subject based on the ideXlab platform.
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inward flow of intervening liquid films driven by the marangoni effect during bubble solid collisions in ethyl alcohol nacl aqueous solutions
Langmuir, 2021Co-Authors: Xurui Zhang, Rogerio Manica, Qingxia LiuAbstract:The drainage dynamics of confined thin liquid films between an air bubble and a freshly cleaved mica surface were investigated in ethyl alcohol aqueous solutions. Focus was given to the holding stage, in which an unexpected increase in the thickness of a few hundred nanometers at the center of the film was captured by interferometry in ethyl alcohol-500 mM NaCl aqueous solutions. Such an increase in film thickness occurred when the ethyl alcohol concentration exceeded the critical value at a bubble Approach Velocity of 100 μm/s. For a given ethyl alcohol concentration, the increase in thickness at the center of the film did not happen when the bubble Approach Velocity was decreased to 10 μm/s. Compared to the cases in ethyl alcohol-500 mM NaCl solutions, no increase in thickness at the center of the film was observed in ethyl alcohol-water solutions under the same ethyl alcohol concentration and bubble Approach Velocity. The phenomenon of the increasing thickness at the center of the film was attributed to the net inward flow in the film, resulting from competition between the inward Marangoni flow and the outward drainage flow that was hindered by the narrow channel at the barrier rim of the film under a high electrolyte concentration. The inward Marangoni flow was achieved by a concentration gradient of ethyl alcohol between the film and the bulk solution resulting from the mobile air-liquid interface in the initial Approaching period.
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Probing Boundary Conditions at Hydrophobic Solid–Water Interfaces by Dynamic Film Drainage Measurement
2018Co-Authors: Xurui Zhang, Rogerio Manica, Plamen Tchoukov, Yuechao Tang, Qingxia LiuAbstract:A newly developed dynamic force apparatus was used to determine hydrodynamic boundary conditions of a liquid on a hydrophobic silica surface. For a given Approach Velocity of bubble to solid surfaces in an electrolyte solution, a reduced dimple formation and faster film drainage were observed by increasing the hydrophobicity of silica surfaces, indicating a significant change in hydrodynamic boundary conditions of water molecules from an immobile to a mobile water–hydrophobic silica interface. By comparing the measured film profiles with the predictions from the Stokes–Reynolds–Young–Laplace model, the slippage boundary condition of water on the hydrophobic silica surface of surface nanoroughness was quantified. Increasing the surface hydrophobicity was found to increase the mobility of water in the thin liquid film, promoting faster drainage of the liquid. For a given hydrophobicity of solids, the mobility of water occurred only above a critical bubble Approach Velocity and increased with increasing bubble Approach Velocity. In contrast, similar experiments with hydrophobized mica surfaces showed no-slip boundary condition of water at the molecularly smooth hydrophobic surface. The results collectively suggest that the observed mobility of water with more than 100 nm in thickness on the studied hydrophobic silica surfaces was due to the nanoroughness of hydrophobic surfaces. Such finding sheds light on one possible way of reducing the friction of water on hydrophobic solid surfaces by creating nanostructured surface of nanoroughness
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effect of Approach Velocity on thin liquid film drainage between an air bubble and a flat solid surface
Journal of Physical Chemistry C, 2017Co-Authors: Xurui Zhang, Rogerio Manica, Plamen Tchoukov, Zhenghe XuAbstract:The dynamic drainage process of the liquid film trapped between an air bubble and a flat silica surface over a wide range of hydrodynamic conditions is studied by a newly developed instrument called integrated thin liquid film force apparatus (ITLFFA) under different salt concentrations. The ITLFFA allows the simultaneous measurement of interaction forces and spatiotemporal film thickness with accurate control of bubble Approach Velocity in a large range of Reynolds number from 0.005 to 135. Our study demonstrates that increasing the bubble Approach Velocity plays a significant role in the hydrodynamic pressure and fluid flow within the draining film promoting dimple formation and longer drainage time. The drainage time also depends on the competition between the electrical double-layer and van der Waals interactions, which are repulsive in our system, resulting in a flat equilibrium film at the end. The evolution of the draining film is analyzed using the Stokes–Reynolds–Young–Laplace (SRYL) model. Compa...