The Effect of Thermocapillary Flow on Heat Transfer in Dropwise Condensation

1970 ◽  
Vol 92 (1) ◽  
pp. 46-52 ◽  
Author(s):  
J. J. Lorenz ◽  
B. B. Mikic
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Marangoni Number ◽  
Liquid Drop ◽  
Practical Interest ◽  
Dropwise Condensation ◽  
Internal Circulation ◽  
Vapor Interface ◽  
Surface Tension Forces ◽  
Finite Difference Techniques

The effect of fluid flow induced by surface tension forces on heat transfer through a drop was considered. The model is a hemispherical liquid drop growing on a flat isothermal-surface. The solution was obtained by finite-difference techniques for different values of the Marangoni number (Nm) associated with surface tension forces and the Biot number (Bi) associated with heat transfer at the liquid-vapor interface. The ranges of parameters covered by this investigation include the regimes of most practical interest for water. The results show that the contribution of internal circulation in the drops to the increase of heat transfer in dropwise condensation is insignificant.

The Influence of Thermocapillary Flow on Heat Transfer in Film Condensation

1973 ◽  
Vol 95 (1) ◽  
pp. 21-24 ◽  
Author(s):  
J. D. Cary ◽  
B. B. Mikic
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Flat Surface ◽  
Practical Interest ◽  
Thermocapillary Flow ◽  
Film Condensation ◽  
Finite Difference Technique ◽  
Relative Measure ◽  
Circular Arcs ◽  
Surface Tension Forces

The influence of fluid flow—induced by surface-tension forces—on heat transfer through a condensate film broken by non-wetting strips was considered. The film was modeled as a two-dimensional layer on an isothermal, vertical flat surface; the layer has a flat midsection with circular arcs at the edges. The solution was obtained by a finite-difference technique for several values of the Marangoni number (Nm) which provides a relative measure of the surface-tension forces and of the Biot number (Bi) which provides a relative measure of the heat transfer at the liquid–vapor interface. The range of parameters covered by this work transcends the limits of most practical interest for water. The results show that internal thermocapillary circulation causes modest increases in heat transfer. It is concluded that thermocapillary flow might be an important factor in determining the geometry of channeled condensate films.

Condensate Drop Movement on Heat Transfer Surface With Bulk Temperature Gradient in Marangoni Dropwise Condensation

2010 ◽  
Author(s):  
Zhihao Chen ◽  
Yoshio Utaka
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Temperature Gradient ◽  
Heat Transfer Surface ◽  
Surface Tension Gradient ◽  
Bulk Temperature ◽  
Dropwise Condensation ◽  
Wide Range ◽  
Initial Drop ◽  
Temperature Side

When a bulk temperature gradient was applied to a horizontal condensing surface in Marangoni dropwise condensation, the spontaneous movement of condensate drops occurred. The characteristics of the condensate drop movement in a condensate system of water and ethanol binary vapor mixture were experimentally investigated for a wide range of bulk temperature gradients and for various mass fractions. Drops moved from the low-temperature side to the high-temperature side of the heat transfer surface. When the initial drop distance was adopted as a parameter for the Marangoni force acting on the condensate drop together with the surface tension gradient corresponding to the surface temperature of the condensing surface, the drop moving velocity correlated well as a function of both the surface tension gradient and the initial drop distance. In the range of larger initial drop distances, the condensate drop velocity increases as the initial drop distance is reduced and it subsequently decreases after the velocity reaches its maximum value under an almost constant bulk surface tension gradient.

Force Analysis of Bubble Dynamics in Flow Boiling Silicon Nanowire Microchannels

2016 ◽  
Author(s):  
Tamanna Alam ◽  
Wenming Li ◽  
Fanghao Yang ◽  
Ahmed Shehab Khan ◽  
Yan Tong ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Silicon Nanowire ◽  
Bubble Nucleation ◽  
Force Analysis ◽  
Vapor Interface ◽  
Liquid Vapor

In microchannel flow boiling, bubble nucleation, growth and flow regime development are highly influenced by channel cross-section and physical phenomena underlying this mechanism are far from being well-established. Relative effects of different forces acting on wall-liquid and liquid-vapor interface of a confined bubble play an important role in heat transfer performances. Therefore, fundamental investigations are necessary to develop enhanced microchannel heat transfer surfaces. Force analysis of vapor bubble dynamics in flow boiling Silicon Nanowire (SiNW) microchannels has been performed based on theoretical, experimental and visualization studies. The relative effects of different forces on flow regime, instability and heat transfer performances of flow boiling in Silicon Nanowire microchannels have been identified. Inertia, surface tension, shear, buoyancy, and evaporation momentum forces have significant importance at liquid-vapor interface as discussed earlier by several authors. However, no comparative study has been done for different surface properties till date. Detailed analyses of these forces including contact angle and bubble flow boiling characteristics have been conducted in this study. A comparative study between Silicon Nanowire and Plainwall microchannels has been performed based on force analysis in the flow boiling microchannels. In addition, force analysis during instantaneous bubble growth stage has been performed. Compared to Plainwall microchannels, enhanced surface rewetting and critical heat flux (CHF) are owing to higher surface tension force at liquid-vapor interface and Capillary dominance resulting from Silicon Nanowires. Whereas, low Weber number in Silicon Nanowire helps maintaining uniform and stable thin film and improves heat transfer performances. Moreover, force analysis during instantaneous bubble growth shows the dominance of surface tension at bubble nucleation and slug/transitional flow which resulted higher heat transfer contact area, lower thermal resistance and higher thin film evaporation. Whereas, inertia force is dominant at annular flow and it helps in bubble removal process and rewetting.

Prediction of Conjugate Heat Transfer in a Solid–Liquid System: Inclusion of Buoyancy and Surface Tension Forces in the Liquid Phase

1989 ◽  
Vol 111 (3) ◽  
pp. 690-698 ◽  
Author(s):  
J. R. Keller ◽  
T. L. Bergman
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Steady State ◽  
Conjugate Heat Transfer ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Fluid Motion ◽  
Numerical Predictions ◽  
Solid Liquid ◽  
Surface Tension Forces

Numerical predictions have been obtained for steady-state conjugate heat transfer in an open rectangular cavity. For the geometry considered, fluid motion is driven by augmenting buoyancy and surface tension forces. Predictions of the steady-state solid volume fraction and various solid thicknesses were obtained for a high Prandtl number fluid characterized by various Rayleigh and Marangoni (Ma) numbers. Due to numerical difficulties associated with large surface tension effects, a limited range of Ma was investigated (Ma≤250). The predictions show that surface tension induced flow can affect the solid geometry and, ultimately, freezing or melting rates. Specifically, the solid–liquid interface shape is altered, the steady-state solid volume fraction is decreased, and the solid thickness at the top surface is smaller, compared to the pure buoyancy-driven case. The dimensionless solid volume fraction and solid thicknesses are related to the governing dimensionless parameters of the problem. Finally, predictions are made for high Marangoni number flows (Ma>>250) to demonstrate the potential governing influence of surface tension effects in phase-change systems.

scholarly journals A numerical study of the Bénard cell

1971 ◽  
Vol 45 (4) ◽  
pp. 805-829 ◽  
Author(s):  
André Cabelli ◽  
G. de Vahl Davis
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Numerical Method ◽  
Liquid Surface ◽  
Numerical Study ◽  
Three Dimensional ◽  
Critical Value ◽  
Two Dimensional ◽  
Surface Tension Forces ◽  
Biot Numbers

When a layer of liquid is heated from below at a rate which exceeds a certain critical value, a two- or three-dimensional motion is generated. This motion arises from the action of buoyancy and surface tension forces, the latter being due to variations in the temperature of the liquid surface.The two-dimensional form of the flow has been studied by a numerical method. It consists of a series of rolls, rotating alternately clockwise and anticlockwise, which are shown to be symmetrical about the dividing streamlines. As well as a detailed description of the motion and temperature of the liquid, and of the effects on these characteristics of variations in the Rayleigh, Marangoni, Prandtl and Biot numbers, a study has been made of the conditions under which the motion first starts, the wavelength of the rolls and the rate of heat transfer across the liquid layer.

Transient Thermo-Diffuso-Capillary Convection Around a Bubble in a Surfactant Solution: A Numerical Investigation Using the Volume-of-Fluid Technique

2019 ◽  
Author(s):  
D. S. Kalaikadal ◽  
R. M. Manglik ◽  
M. A. Jog
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Heat Transfer Enhancement ◽  
Marangoni Number ◽  
Marangoni Convection ◽  
Surface Tension Gradient ◽  
Accurate Estimation ◽  
Interface Temperature ◽  
Transfer Enhancement ◽  
Capillary Flows

Abstract Marangoni Convection occurs when a surface tension gradient is established at a liquid-gas interface. The variation in surface tension could be driven by an interface temperature gradient, resulting in Thermocapillary Convection, or by an interface concentration gradient, giving rise to Diffuso-Capillary Convection, or a combination of both. Such flows are found to be of interest in microgravity (and otherwise), as they are known to significantly contribute to heat and mass transfer enhancement at the interface. This paper deals with the computational study of bubble induced thermo-diffuso capillary convection in the presence of surfactants and a stratified thermal field. Bubble induced thermo-capillary convection in a pure liquid has been substantially studied and the effects of various parameters like liquid properties, wettability, bubble size, channel depth, and temperature gradients on the strength of thermo-capillary currents and the associated heat transfer enhancement at the bubble interface are well established. In this study the physico-chemical properties of an aqueous solution of Sodium-Dodecyl-Sulphate (SDS), a surfactant, were used to introduce the effects of surfactant concentration-induced surface-tension gradients in addition to the temperature induced gradients. Unlike in purely thermo-capillary flows, where the interface sees a near-constant surface-tension gradient from base to apex, the presence of surfactant molecules at the interface results in gradients that vary significantly along the interface with maximum gradients at the bubble base and the apex, resulting in a pair opposing vortices anchored to the bubble interface. The presence of the opposing vortices, results in weaker capillary-flows at higher thermal Marangoni numbers. This is in contrast with purely thermal Marangoni convection, where a larger Marangoni number yields a stronger capillary flow. It was also observed that while the Marangoni number may provide an accurate estimation of heat-transfer enhancement under steady-state conditions, it may not be possible in the case of a transiently developing Marangoni-flow. The heat transfer enhancement is maximum near the time of bubble introduction and then diminishes to a lower, stable value. Also, the capillary flows and the associated heat transfer is found to significantly vary with the wetting behavior at the liquid-solid-vapor interface, even for the same set of Marangoni numbers.

Heater Size and Orientation Effect on Pool Boiling of FC-72

2010 ◽  
Author(s):  
Rishi Raj ◽  
Jungho Kim ◽  
John McQuillen ◽  
William Sheredy ◽  
Wendell Booth ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Pool Boiling ◽  
Threshold Value ◽  
Orientation Effect ◽  
Relative Importance ◽  
Capillary Length ◽  
Low Gravity ◽  
Size Dependent ◽  
Surface Tension Forces

A recent study on pool boiling for upward facing square heaters reported two pool boiling regimes depending on the relative importance of buoyancy and surface tension forces. At higher gravity levels and/or with larger heaters when the ratio of heater size Lh (length of a side for a square heater) to capillary length Lc was greater than 2.1, boiling was buoyancy dominated and the heat transfer results were heater size independent. Boiling was surface tension dominated and heat transfer results were heater size dependent when Lh/Lc<2.1 (small heaters and/or low gravity conditions). This paper studies the effects of orientation on the balance between buoyancy and surface tension forces. The threshold value of Lh/Lc for transition between pool boiling regimes was found to be 1.8 for heaters oriented at 45°, 90°, and 135°.

scholarly journals Instabilities in a drop-strip system: a simplified model

2012 ◽  
Vol 468 (2141) ◽  
pp. 1304-1324 ◽  
Author(s):  
Marco Rivetti ◽  
Sébastien Neukirch
Keyword(s):  
Experimental Data ◽  
Surface Tension ◽  
Energy Barrier ◽  
Applied Load ◽  
Liquid Drop ◽  
Elastic Beam ◽  
Simplified Model ◽  
Elastic Strip ◽  
System A ◽  
Surface Tension Forces

We study the deformation of an elastic strip by a liquid drop. At small enough scales, capillarity is the dominant fluid effect and surface tension forces may be sufficient to fold the beam, resulting in the wrapping of the drop by the beam. However, wrapping of the drop can be inhibited by the weight of the beam, which creates an energy barrier. The barrier can be overcome by input of kinetic energy in the form of impact of the drop. We introduce a semi-analytical model to study equilibria and their stability in three drop-beam systems: evaporation of a drop wetting and bending an elastic beam; impact of a drop on an elastic beam; lifting of a heavy elastic beam by a drop and we show the model reproduces experimental data. In relevant cases, we use the concept of suddenly applied load to discuss dynamic instabilities.

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