The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Ping Cheng - One of the best experts on this subject based on the ideXlab platform.
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Mesoscale simulation of Marangoni Convection about a vapor bubble in a liquid with temperature gradients under microgravity conditions
International Communications in Heat and Mass Transfer, 2016Co-Authors: Chaoyang Zhang, Ping ChengAbstract:Abstract Marangoni Convection around a 2-D vapor bubble in a liquid, subjected to an imposed negative temperature gradient in the vertical direction under microgravity conditions, is simulated with a newly developed lattice Boltzmann liquid/vapor phase-change method. It is shown that a floating bubble, initially at the center of a confined space, moves gradually toward the hot wall under zero gravity condition because of Marangoni Convection. With the increase of the Marangoni number, Marangoni Convection along the liquid–vapor interface appears to be more and more significant. Under microgravity conditions, a sessile bubble attached on a hot bottom wall facing upward at low superheats, the high velocity region on the liquid/vapor interface moves from the triple-contact line region upward as the wettability of the solid surface changes from hydrophobic to hydrophilic. It is shown that the average Nusselt number of such a sessile vapor bubble under microgravity conditions is larger or smaller than those under zero gravity condition, depending on whether the Marangoni Convection is in a direction parallel to or opposite to the direction of the gravity.
Bu-xuan Wang - One of the best experts on this subject based on the ideXlab platform.
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Numerical investigation on Marangoni Convection of binary fluids in a closed microcavity
Applied Thermal Engineering, 2015Co-Authors: Zhenchen Zheng, Leping Zhou, Yongping Yang, Pei-xue Jiang, Bu-xuan WangAbstract:Abstract Phase change can dramatically alter the interfacial temperature, resulting in surface tension gradients and consequently causing Marangoni Convection. The numerical investigation on Marangoni Convection of binary fluids in a closed microcavity is accomplished in this paper by using the volume of fluid (VOF) model with source terms added by user defined functions (UDF) due to mass transfer, with detailed velocity and temperature fields. For simple fluid, surface tension decreases with increasing temperature, resulting in thermal Marangoni Convection that can drive the liquid leave from hot regions and leading to film dryout. For binary fluids, however, the Marangoni Convection could also be caused by concentration gradients, resulting in greatly promoted backflow of the fluid. In particular, for self-rewetting fluids which have unique surface tension characteristics that increase with increasing temperature above a critical value, the Marangoni flow can drive the liquid flow towards hot regions, avoiding film dryout. The influence of non-condensable gas is also considered by providing detailed velocity fields near the contact region and it proves that non-condensable gas can negatively affect the heat and mass transfer.
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similarity simulation for Marangoni Convection around a vapor bubble during nucleation and growth
International Journal of Heat and Mass Transfer, 2001Co-Authors: David M Christopher, Bu-xuan WangAbstract:Abstract Marangoni Convection occurs around vapor bubbles during nucleation and growth due to the temperature variation along the surface. The surface tension variation resulting from the temperature gradient along the surface causes Marangoni Convection. Marangoni Convection is of importance in crystal growth melts and may influence other processes with liquid–vapor interfaces, in addition to boiling. The influence of Marangoni induced Convection is more obvious under microgravity but also occurs in earth gravity. This paper presents a similarity solution for Marangoni induced flow both for the velocity profile and the temperature profile, assuming developing boundary-layer flow along a surface with various imposed temperature profiles. The surface velocity, the total flow rate and the heat transfer characteristics are given for various temperature profiles and various Prandtl numbers. Since the predicted boundary layer thickness would be much less than the diameter of vapor bubbles during nucleate boiling, the bubble surface curvature effects can be neglected and this analysis can be used as a first estimate of the effect of Marangoni flow around a vapor bubble.
Takao Kashiwagi - One of the best experts on this subject based on the ideXlab platform.
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heat transfer enhancement by Marangoni Convection in the nh3 h2o absorption process
International Journal of Refrigeration-revue Internationale Du Froid, 2002Co-Authors: Yong Tae Kang, Takao KashiwagiAbstract:Abstract The objectives of this paper are to quantify the effect of Marangini Convection on the absorption performance for the ammonia–water absorption process, and to visualize Marangoni Convection that is induced by adding a heat transfer additive, n -octanol. A real-time single-wavelength holographic interferometer is used for the visualization using a He–Ne gas laser. The interface temperature is always the highest due to the absorption heat release near the interface. It was found that the thermal boundary layer (TBL) increased faster than the diffusion boundary layer (DBL), and the DBL thickness increased by adding the heat transfer additive. At 5 s after absorption started, the DBL thickness for 5 mass% NH 3 without and with the heat transfer additive was 3.0 and 4.5 mm, respectively. Marangoni Convection was observed near the interface only in the cases with heat transfer additive. The Marangoni Convection was very strong just after the absorption started and it weakened as time elapsed. It was concluded that the absorption performance could be improved by increasing the absorption driving potential ( x vb − x vi ) and by increasing the heat transfer additive concentration. The absorption heat transfer was enhanced as high as 3.0–4.6 times by adding the heat transfer additive that generated Marangoni Convection.
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Heat transfer enhancement by Marangoni Convection in the NH3–H2O absorption process
International Journal of Refrigeration, 2002Co-Authors: Yong Tae Kang, Takao KashiwagiAbstract:Abstract The objectives of this paper are to quantify the effect of Marangini Convection on the absorption performance for the ammonia–water absorption process, and to visualize Marangoni Convection that is induced by adding a heat transfer additive, n -octanol. A real-time single-wavelength holographic interferometer is used for the visualization using a He–Ne gas laser. The interface temperature is always the highest due to the absorption heat release near the interface. It was found that the thermal boundary layer (TBL) increased faster than the diffusion boundary layer (DBL), and the DBL thickness increased by adding the heat transfer additive. At 5 s after absorption started, the DBL thickness for 5 mass% NH 3 without and with the heat transfer additive was 3.0 and 4.5 mm, respectively. Marangoni Convection was observed near the interface only in the cases with heat transfer additive. The Marangoni Convection was very strong just after the absorption started and it weakened as time elapsed. It was concluded that the absorption performance could be improved by increasing the absorption driving potential ( x vb − x vi ) and by increasing the heat transfer additive concentration. The absorption heat transfer was enhanced as high as 3.0–4.6 times by adding the heat transfer additive that generated Marangoni Convection.
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visualization and model development of Marangoni Convection in nh3 h2o system
International Journal of Refrigeration-revue Internationale Du Froid, 1999Co-Authors: Yong Tae Kang, Atsushi Akisawa, Takao KashiwagiAbstract:Abstract The objectives of this paper are to obtain experimental data of surface tension and interfacial tension, and to develop a new model of Marangoni Convection for the best selection of heat transfer additive in ammonia–water absorption systems. The basic mechanism of Marangoni Convection in absorption systems was reviewed from the viewpoints of the surface tension and the interfacial tension gradients. Marangoni Convection was successfully visualized using a shadow graphic method. The solubility limits of the additives in ammonia–water solution ranged from 500 to 3000 ppm depending on the heat transfer additives. These values are much higher than those in LiBr–H2O solution in which the solubility ranged from 70 to 400 ppm. The temperature gradient of the surface tension should not be a criterion for Marangoni Convection inducement in NH3–H2O system. The concentration and temperature gradients of the interfacial tension should not be a criterion for Marangoni Convection inducement in NH3–H2O system. The magnitude of the interfacial tension did not affect the occurrence of Marangoni Convection either. It was found that addition of the heat transfer additive beyond the solubility limit assisted Marangoni Convection occurrence, but should not be a criterion for Marangoni Convection inducement. It was proposed that the radical-out model should be a criterion for Marangoni Convection inducement within the solubility limit in NH3–H2O system.
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Visualization and model development of Marangoni Convection in NH3–H2O system
International Journal of Refrigeration, 1999Co-Authors: Yong Tae Kang, Atsushi Akisawa, Takao KashiwagiAbstract:Abstract The objectives of this paper are to obtain experimental data of surface tension and interfacial tension, and to develop a new model of Marangoni Convection for the best selection of heat transfer additive in ammonia–water absorption systems. The basic mechanism of Marangoni Convection in absorption systems was reviewed from the viewpoints of the surface tension and the interfacial tension gradients. Marangoni Convection was successfully visualized using a shadow graphic method. The solubility limits of the additives in ammonia–water solution ranged from 500 to 3000 ppm depending on the heat transfer additives. These values are much higher than those in LiBr–H2O solution in which the solubility ranged from 70 to 400 ppm. The temperature gradient of the surface tension should not be a criterion for Marangoni Convection inducement in NH3–H2O system. The concentration and temperature gradients of the interfacial tension should not be a criterion for Marangoni Convection inducement in NH3–H2O system. The magnitude of the interfacial tension did not affect the occurrence of Marangoni Convection either. It was found that addition of the heat transfer additive beyond the solubility limit assisted Marangoni Convection occurrence, but should not be a criterion for Marangoni Convection inducement. It was proposed that the radical-out model should be a criterion for Marangoni Convection inducement within the solubility limit in NH3–H2O system.
Chaoyang Zhang - One of the best experts on this subject based on the ideXlab platform.
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Mesoscale simulation of Marangoni Convection about a vapor bubble in a liquid with temperature gradients under microgravity conditions
International Communications in Heat and Mass Transfer, 2016Co-Authors: Chaoyang Zhang, Ping ChengAbstract:Abstract Marangoni Convection around a 2-D vapor bubble in a liquid, subjected to an imposed negative temperature gradient in the vertical direction under microgravity conditions, is simulated with a newly developed lattice Boltzmann liquid/vapor phase-change method. It is shown that a floating bubble, initially at the center of a confined space, moves gradually toward the hot wall under zero gravity condition because of Marangoni Convection. With the increase of the Marangoni number, Marangoni Convection along the liquid–vapor interface appears to be more and more significant. Under microgravity conditions, a sessile bubble attached on a hot bottom wall facing upward at low superheats, the high velocity region on the liquid/vapor interface moves from the triple-contact line region upward as the wettability of the solid surface changes from hydrophobic to hydrophilic. It is shown that the average Nusselt number of such a sessile vapor bubble under microgravity conditions is larger or smaller than those under zero gravity condition, depending on whether the Marangoni Convection is in a direction parallel to or opposite to the direction of the gravity.
Mikhail Khenner - One of the best experts on this subject based on the ideXlab platform.
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Marangoni Convection in a thin film on a vertically oscillating plate.
Physical review. E Statistical nonlinear and soft matter physics, 2015Co-Authors: S. Shklyaev, A. A. Alabuzhev, Mikhail KhennerAbstract:Thermocapillary (Marangoni) Convection in a thin film on a plate oscillating with a frequency ranging from ultralow to high is considered. By adjusting the vibration amplitude, the impact of the vibration is kept non-negligible. Using the long-wave approximation framework, the amplitude equations are derived for each frequency interval, and linear and weakly nonlinear stability analyses are performed, supplemented by computations where necessary. In the case of a high vibration frequency, the surface tension effectively increases due to vibration, but the film still ruptures. When the frequency is ultralow, the vibration provides gravity modulation, and the surface deformation emerges subcritically, grows fast, and then decays, all during less than half of the vibration period. In the intermediate regime, the vibration either results in a short-wavelength instability or it does not affect the Marangoni Convection.
