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.

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.

Inverse-thermocapillary evaporation in a thin liquid film of self-rewetting fluid

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Elaine Lim ◽  
Tze Cheng Kueh ◽  
Yew Mun Hung
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Liquid Film ◽  
Temperature Region ◽  
Thin Liquid Film ◽  
Thermocapillary Flow ◽  
Working Fluid ◽  
Surface Tension Gradient ◽  
Thermocapillary Effect ◽  
Content Type

Purpose The present study aims to investigate the inverse-thermocapillary effect in an evaporating thin liquid film of self-rewetting fluid, which is a dilute aqueous solution (DAS) of long-chain alcohol. Design/methodology/approach A long-wave evolution model modified for self-rewetting fluids is used to study the inverse thermocapillary characteristics of an evaporating thin liquid film. The flow attributed to the inverse thermocapillary action is manifested through the streamline plots and the evaporative heat transfer characteristics are quantified and analyzed. Findings The thermocapillary flow induced by the negative surface tension gradient drives the liquid from a low-surface-tension (high temperature) region to a high-surface-tension (low temperature) region, retarding the liquid circulation and the evaporation strength. The positive surface tension gradients of self-rewetting fluids induce inverse-thermocapillary flow. The results of different working fluids, namely, water, heptanol and DAS of heptanol, are examined and compared. The thermocapillary characteristic of a working fluid is significantly affected by the sign of the surface tension gradient and the inverse effect is profound at a high excess temperature. The inverse thermocapillary effect significantly enhances evaporation rates. Originality/value The current investigation on the inverse thermocapillary effect in a self-rewetting evaporating thin film liquid has not been attempted previously. This study provides insights on the hydrodynamic and thermal characteristics of thermocapillary evaporation of self-rewetting liquid, which give rise to significant thermal enhancement of the microscale phase-change heat transfer devices.

Heat transfer at film condensation of moving vapor with nanoparticles over a flat surface

2015 ◽  
Vol 82 ◽  
pp. 316-324 ◽  
Author(s):  
Andriy A. Avramenko ◽  
Igor V. Shevchuk ◽  
Andrii I. Tyrinov ◽  
Dmitry G. Blinov
Keyword(s):  
Heat Transfer ◽  
Flat Surface ◽  
Film Condensation

Film Condensation in Horizontal Triangular Section Microchannels: A Theoretical Model

2004 ◽  
Author(s):  
Huasheng Wang ◽  
John W. Rose
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Shear Stress ◽  
Theoretical Model ◽  
Channel Wall ◽  
Horizontal Tube ◽  
Film Condensation ◽  
General Behaviour ◽  
Condensate Film ◽  
Local Mean

The paper presents a theoretical model to predict film condensation heat transfer from a vapor flowing in a horizontal tube with equilateral triangular section minichannels or microchannels. The model is based on fundamental analysis which assumes laminar condensate flow on the channel walls and takes account of surface tension, vapor shear stress and gravity. The case considered here is where the channel wall temperature is uniform and the vapor is saturated at inlet. Sample numerical results are given for the channel size (side of triangle) of 1.0 mm and for refrigerant R134a. The general behaviour of the condensate flow pattern (spanwise and streamwise profiles of the condensate film), as well as streamwise variation in quality and local mean (over section perimeter) heat-transfer coefficient, are qualitatively in accord with expectations on physical grounds.

Numerical Modeling of the Conjugate Heat Transfer Problem for Annular Laminar Film Condensation in Microchannels

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Stefano Nebuloni ◽  
John R. Thome
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Wall Temperature ◽  
Conjugate Heat Transfer ◽  
Channel Wall ◽  
Transfer Problem ◽  
Film Condensation ◽  
Laminar Film Condensation

This paper presents numerical simulations of annular laminar film condensation heat transfer in microchannels of different internal shapes. The model, which is based on a finite volume formulation of the Navier–Stokes and energy equations for the liquid phase only, importantly accounts for the effects of axial and peripheral wall conduction and nonuniform heat flux not included in other models so far in the literature. The contributions of the surface tension, axial shear stresses, and gravitational forces are included. This model has so far been validated versus various benchmark cases and versus experimental data available in literature, predicting microchannel heat transfer data with an average error of 20% or better. It is well known that the thinning of the condensate film induced by surface tension due to gravity forces and shape of the surface, also known as the “Gregorig” effect, has a strong consequence on the local heat transfer coefficient in condensation. Thus, the present model accounts for these effects on the heat transfer and pressure drop for a wide variety of geometrical shapes, sizes, wall materials, and working fluid properties. In this paper, the conjugate heat transfer problem arising from the coupling between the thin film fluid dynamics, the heat transfer in the condensing fluid, and the heat conduction in the channel wall has been studied. In particular, the work has focused on three external channel wall boundary conditions: a uniform wall temperature, a nonuniform wall heat flux, and single-phase convective cooling are presented. As the scale of the problem is reduced, i.e., when moving from mini- to microchannels, the results show that the axial conduction effects can become very important in the prediction of the wall temperature profile and the magnitude of the heat transfer coefficient and its distribution along the channel.

Numerical Modeling of the Conjugate Heat Transfer Problem for Annular Laminar Film Condensation in Microchannels

2009 ◽  
Author(s):  
Stefano Nebuloni ◽  
John R. Thome
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Heat Flux ◽  
Conjugate Heat Transfer ◽  
Channel Wall ◽  
Transfer Problem ◽  
Film Condensation ◽  
Laminar Film Condensation ◽  
Micro Channels ◽  
Uniform Wall

This paper presents numerical simulations of annular laminar film condensation heat transfer in micro-channels of different internal shapes. The model, which is based on a finite volume formulation of the Navier-Stokes and energy equations for the liquid phase only, importantly accounts for the effects of axial and peripheral wall conduction and non-uniform heat flux not included in other models so far in the literature. The contributions of the surface tension, axial shear stresses and gravitational forces are included. This model has so far been validated versus various benchmark cases and versus experimental data available in literature, predicting microchannel heat transfer data with an average error of 20% or better. It is well-known that the thinning of the condensate film induced by surface tension due to gravity forces and shape of the surface, also known as the ‘Grigorig’ effect, has a strong consequence on the local heat transfer coefficient in condensation. Thus, the present model accounts for these effects on the heat transfer and pressure drop for a wide variety of geometrical shapes, sizes, wall materials and working fluid properties. In this paper, the conjugate heat transfer problem arising from the coupling between the thin film fluid dynamics, the heat transfer in the condensing fluid and the heat conduction in the channel wall has been studied. In particular, the work has focused on three external channel wall boundary conditions: a uniform wall temperature, a non uniform wall heat flux and single-phase convective cooling is presented. As the scale of the problem is reduced, i.e. when moving from mini to micro channels, the results shows that the axial conduction effects can become very important in the prediction of the wall temperature profile and the magnitude of the heat transfer coefficient and its distribution along the channel.

Effects of Surface Tension on Film Condensation in a Porous Medium

1990 ◽  
Vol 112 (3) ◽  
pp. 751-757 ◽  
Author(s):  
A. Majumdar ◽  
C. L. Tien
Keyword(s):  
Boundary Layer ◽  
Surface Tension ◽  
Porous Medium ◽  
Film Condensation ◽  
Phase Zone ◽  
Two Phase ◽  
Liquid Zone ◽  
Darcy Velocity ◽  
Characteristic Boundary ◽  
Surface Tension Forces

In the process of film condensation in a porous medium, the thermodynamics of phase equilibria requires the existence of a two-phase zone lying between the liquid and the vapor regions. In the two-phase zone, solutions of the conservation equations indicate a boundary-layer profile for the capillary pressure. The liquid zone is analyzed using three models, which assume either slip or no slip at the wall and Darcy velocity or no shear at the interface with the two-phase zone. The results show that the condition of no slip at the wall must be satisfied in all cases except where the thickness of the liquid zone is much larger than the characteristic boundary layer in the porous medium. At the interface with the two-phase zone, the assumption of no shear is more realistic than that of an imposed Darcy velocity, in conjunction with no-slip condition at the wall. Comparisons with experiments suggest that the drag on the liquid film due to surface tension is significant for permeabilities lower than 10−7 m2. A dimensionless group, characterizing viscous flow due to surface tension forces, is introduced in this study.

Heat Transfer During Condensation Inside Small Channels: Applicability of General Correlation for Macrochannels

2010 ◽  
Author(s):  
Mirza Mohammed Shah
Keyword(s):  
Heat Transfer ◽  
Small Diameter ◽  
Practical Interest ◽  
Film Condensation ◽  
Mean Deviation ◽  
General Correlation ◽  
Rectangular Channels ◽  
Wide Range ◽  
Mini Channels ◽  
Small Channels

Prediction of heat transfer during film condensation in mini and microchannels is of much practical interest. No well-verified method for this purpose is available. The applicability of the author’s well-validated general correlation (Shah 2009) for condensation in tubes to small channels is investigated in this paper. A wide range of data for condensation in horizontal micro and mini channels were compared with it. This correlation was found to predict 500 data points from 15 studies on small diameter channels with a mean deviation of 15.9 percent. These data included single round and rectangular channels as well as multiport channels with round and rectangular ports with equivalent diameters from 0.49 to 5.3 mm, 8 fluids, reduced pressures from 0.048 to 0.52, and mass flux from 50 to 1400 kg/m2s. This indicates its applicability to minichannels. However, a large amount of data for diameters from 0.114 to 2.6 mm showed large deviations from this correlation. The discrepancy in the overlapping range of data could be due to difficulties in accurate measurements on small channels.

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.

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