Suppression of Thermocapillary Effect in Evaporating Thin Film of Micro Heat Pipes

This paper presents a theoretical study on the flow mechanism of different types of working fluids incorporated with Marangoni effect in a microelectronics cooling device. It is known that surface tension gradient effect or thermocapillary effect can be induced by temperature gradient which leads to the thermocapillary flow. By adding a small quantity of alcohol into the pure working fluid, the characteristics of surface tension can be altered without changing other thermo physical properties of the working fluid. A theoretical model is employed to focus on the suppression of thermocapillary effect in evaporating thin liquid film. The study reveals the fluid flow mechanism of a working fluid can be altered with thermocapillary effect. Thermal performance of microelectronics cooling devices can also be enhanced by utilizing aqueous solution as the working fluid.

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

International Journal of Numerical Methods for Heat &amp Fluid Flow ◽

10.1108/hff-05-2020-0266 ◽

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.

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Thermal analysis of heat pipe using self rewetting fluids

Thermal Science ◽

10.2298/tsci101102020s ◽

2011 ◽

Vol 15 (3) ◽

pp. 879-888 ◽

Cited By ~ 7

Author(s):

Rathinasamy Senthilkumar ◽

Subaiah Vaidyanathan ◽

Sivaramanb Balasubramanian

Keyword(s):

Surface Tension ◽

Heat Pipe ◽

Heat Transport ◽

Pure Water ◽

Heat Pipes ◽

The Self ◽

Working Fluid ◽

Surface Tension Gradient ◽

Condenser Section ◽

Maximum Heat

This paper discuses the use of self rewetting fluids in the heat pipe. In conventional heat pipes, the working fluid used has a negative surface-tension gradient with temperature. It is an unfavourable one and it decreases the heat transport between the evaporator section and the condenser section. Self rewetting fluids are dilute aqueous alcoholic solutions which have the number of carbon atoms more than four. Unlike other common liquids, self-rewetting fluids have the property that the surface tension increases with temperature up to a certain limit. The experiments are conducted to improve the heat-transport capability and thermal efficiency of capillary assisted heat pipes with the self rewetting fluids like aqueous solutions of n-Butanol and n-Pentanol and its performance is compared with that of pure water. The n-Butanol and n-Pentanol are added to the pure water at a concentration of 0.001moles/lit to prepare the self rewetting fluids. The heat pipes are made up of copper container with a two-layered stainless steel wick consisting of mesh wrapped screen. The experimental results show that the maximum heat transport of the heat pipe is enhanced and the thermal resistances are considerably decreased than the traditional heat pipes filled with water. The fluids used exhibit an anomalous increase in the surface tension with increasing temperature.

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Dynamics of Thin Film Under a Volatile Solvent Source Driven by a Constant Pressure Gradient Flow

Fluids ◽

10.3390/fluids4040198 ◽

2019 ◽

Vol 4 (4) ◽

pp. 198

Author(s):

Mohammad Irshad Khodabocus ◽

Mathieu Sellier ◽

Volker Nock

Keyword(s):

Thin Film ◽

Surface Tension ◽

Free Surface ◽

Evolution Equation ◽

Constant Pressure ◽

Thin Liquid Film ◽

Gradient Flow ◽

Surface Tension Gradient ◽

Nonlinear Parabolic ◽

Induced Flow

The evolution of a thin liquid film subject to a volatile solvent source and an air-blow effect which modifies locally the surface tension and leads to Marangoni-induced flow is shown to be governed by a degenerate fourth order nonlinear parabolic h-evolution equation of the type given by ∂ t h = − div x M 1 h ∂ x 3 h + M 2 h ∂ x h + M 3 h , where the mobility terms M 1 h and M 2 h result from the presence of the source and M 3 h results from the air-blow effect. Various authors assume M 2 h ≈ 0 and exclude the air-blow effect into M 3 h . In this paper, the authors show that such assumption is not necessarily correct, and the inclusion of such effect does disturb the dynamics of the thin film. These emphasize the importance of the full definition t → · grad γ = grad x γ + ∂ x h grad y γ of the surface tension gradient at the free surface in contrast to the truncated expression t → · grad γ ≈ grad x γ employed by those authors and the effect of the air-blow flowing over the surface.

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Numerical Analysis on the Dropwise Condensation of a Binary Vapor Mixture

10.1115/imece2001/htd-24130 ◽

2001 ◽

Author(s):

Hirokuni Akiyama ◽

Takao Nagasaki ◽

Yutaka Ito

Keyword(s):

Numerical Simulation ◽

Liquid Film ◽

Thin Liquid Film ◽

Marangoni Effect ◽

Ethanol Vapor ◽

Surface Tension Gradient ◽

Two Dimensional ◽

Vapor Mixture ◽

Horizontal Wall ◽

Phase Equilibrium Condition

Abstract A numerical simulation was performed on the condensation of water and ethanol vapor mixture on a horizontal wall in a plane two-dimensional field. The analysis solves unsteady flow and heat-and-mass transfer both for liquid and vapor with the phase equilibrium condition at the interface, using FDM and boundary-fitted coordinates to track the deformation of interface. The calculation was started from a very thin smooth liquid film, and it was found that instability occurs when the film thickness reaches a certain value resulting in the formation of relatively small droplets. With the growth of the droplets, they coalesce into larger ones. Between the droplets an extremely thin liquid film exists, and the surface tension gradient sustains the droplets. With the increase of the wall subcooling the maximum droplet becomes large due to the increase of the Marangoni effect.

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Theoretical Model of Droplets Motions on Solid Surface With Radial Wettable and Evaporation Rate Gradients

Volume 8A: Heat Transfer and Thermal Engineering ◽

10.1115/imece2018-87890 ◽

2018 ◽

Author(s):

Yanjie Yang ◽

Zan Wu ◽

Xiaoqian Chen ◽

Bengt Sundén ◽

Yiyong Huang

Keyword(s):

Surface Tension ◽

Theoretical Model ◽

Solid Surface ◽

Radial Direction ◽

Evaporation Rate ◽

Marangoni Effect ◽

Droplet Radius ◽

Surface Tension Gradient ◽

Capillary Length ◽

Liquid Vapor

Wettability gradient in radial direction and evaporation rate gradient can cause droplet motion on a solid surface. Here a theoretical model is proposed. Besides, an equation of droplet velocity is derived on a solid surface. We consider the wettability and evaporation rate gradients are mainly caused by the chemical composition and surface roughness, only along the radial direction. Surface tension at the liquid-vapor interface is constant as it is assumed that the temperature does not change during the whole process. Thus, Marangoni effect induced by the liquid-vapor surface tension gradient is neglected. Besides, as droplet size is set as less than the capillary length (l=γ/ρg), the gravity effect is ignored as well. The velocity at the droplet center on a gradient surface along the radial direction is half of that along the x-direction. With the simulation of water droplet, the center velocity decreases with time and the droplet radius increases at the beginning part and then decreases.

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Study on the Instability of Two-Phase Flow in the Heat-Absorbing Tube of Trough Solar Collector

International Journal of Photoenergy ◽

10.1155/2017/6547203 ◽

2017 ◽

Vol 2017 ◽

pp. 1-8

Author(s):

Ying Zhang ◽

Peiyao Liu ◽

Peisheng Li ◽

Yue Chen ◽

Yanni Pan

Keyword(s):

Surface Tension ◽

Temperature Gradient ◽

Velocity Gradient ◽

Marangoni Effect ◽

Surface Tension Gradient ◽

Promoting Effect ◽

Two Phase ◽

Buoyancy Convection ◽

Interface Wave ◽

Rayleigh Benard

The Marangoni effect and Rayleigh-Benard effect in the two-phase region of solar trough heat-absorbing tube are simulated by FTM (front tracking method). Considering the Marangoni effect alone, although surface tension gradient and surface tension affect the interface wave, the two effects have different characteristics. The surface tension gradient caused by the temperature gradient is one of the factors that swing the interface. The amplitude attenuation of the interface wave decreases with the increase of the Marangoni number (Ma). In general, the surface tension gradient enhances the convection opposite to the temperature gradient. Under the gravity field, the Rayleigh-Benard effect influences the development of the vortex structure in the flow field, which in turn affects the velocity gradient near the interface to influence the evolution of the interface fluctuation. In a small Rayleigh number (Ra), the buoyancy convection reduces the velocity gradient, thus suppressing the evolution of the interfacial wave. In the range of Ra < 4.0E4, the larger the Ra, the stronger the inhibitory effect. However, when the Ra number is large (Ra > 4.0E4), the situation is just the opposite. The larger the Ra is, the stronger the promoting effect is.

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A new hydrodynamic interpretation of liquid metal droplet motion induced by electrocapillary phenomenon

Soft Matter ◽

10.1039/d1sm00873k ◽

2021 ◽

Author(s):

Jiao Ye ◽

Si-Cong Tan ◽

Lei Wang ◽

Jing Liu

Keyword(s):

Surface Tension ◽

Liquid Metal ◽

Electric Potential ◽

Potential Gradient ◽

Marangoni Effect ◽

Metal Droplet ◽

Surface Tension Gradient ◽

Droplet Motion ◽

Liquid Metal Droplet

The Marangoni effect, induced by the surface tension gradient resulting from the gradient of temperature, concentration, or electric potential gradient along the surface, is commonly utilized to manipulate a droplet....

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On the Role of Marangoni Effects on the Critical Heat Flux for Pool Boiling of Binary Mixtures

Journal of Heat Transfer ◽

10.1115/1.2824021 ◽

1996 ◽

Vol 118 (1) ◽

pp. 103-109 ◽

Cited By ~ 52

Author(s):

W. R. McGillis ◽

V. P. Carey

Keyword(s):

Surface Tension ◽

Heat Flux ◽

Binary Mixtures ◽

Critical Heat Flux ◽

Full Range ◽

Pool Boiling ◽

Marangoni Effect ◽

Restoring Force ◽

Marangoni Effects

The Marangoni effect on the critical heat flux (CHF) condition in pool boiling of binary mixtures has been identified and its effect has been quantitatively estimated with a modified model derived from hydrodynamics. The physical process of CHF in binary mixtures, and models used to describe it, are examined in the light of recent experimental evidence, accurate mixture properties, and phase equilibrium revealing a correlation to surface tension gradients and volatility. A correlation is developed from a heuristic model including the additional liquid restoring force caused by surface tension gradients. The CHF condition was determined experimentally for saturated methanol/water, 2-propanol/water, and ethylene glycol/water mixtures, over the full range of concentrations, and compared to the model. The evidence in this study demonstrates that in a mixture with large differences in surface tension, there is an additional hydrodynamic restoring force affecting the CHF condition.

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