Effect of interline heat transfer on meniscus profile and capillary pressure

1978 ◽  
Author(s):  
P. WAYNER, JR.
Keyword(s):  
Heat Transfer ◽  
Capillary Pressure ◽  
Meniscus Profile

scholarly journals Characteristics of an Evaporating Thin Film in a Microchannel

2006 ◽  
Author(s):  
Hao Wang ◽  
Suresh V. Garimella ◽  
Jayathi Y. Murthy
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Capillary Pressure ◽  
Order Differential Equation ◽  
Initial Thickness ◽  
Thickness Profile ◽  
Wall Superheat ◽  
Evaporation Heat ◽  
Meniscus Profile

The thin-film region of an evaporating meniscus is investigated through an augmented Young-Laplace model and the kinetic theory-based expression for mass transport across a liquid-vapor interface. A fourth-order differential equation for the thickness profile is developed and the boundary conditions at the beginning of the thin-film region are discussed in detail. A perturbation on the initial thickness is employed to avoid the evaporation being totally suppressed all along the meniscus. The role of capillary pressure in controlling the meniscus profile and rate of liquid supply is detailed. The evaporation heat transfer coefficient is greatly suppressed at the beginning of the thin-film region due to disjoining pressure; in the intrinsic meniscus, evaporation is suppressed due to capillary pressure, especially for low wall superheat. The importance of the thin-film region in determining the overall heat transfer is shown to depend on the channel size and degree of superheat.

Evaporation From a Capillary Tube

1976 ◽  
Vol 98 (2) ◽  
pp. 178-181 ◽  
Author(s):  
G. Preiss ◽  
P. C. Wayner
Keyword(s):  
Heat Transfer ◽  
Evaporation Rate ◽  
Capillary Tube ◽  
Heat Transfer Characteristics ◽  
Glass Capillary ◽  
Transfer Characteristics ◽  
Wide Range ◽  
Glass Capillary Tube ◽  
Hydrostatic Head ◽  
Meniscus Profile

The heat transfer characteristics of an evaporating ethanol meniscus formed at the exit of a glass capillary tube were studied experimentally. The meniscus profile was photographed and was found to be a function of the evaporation rate and the initial hydrostatic head. The meniscus was found to be stable over a wide range of evaporation rates.

scholarly journals Optimization of Biporous Micropillar Array for Enhanced Heat Transfer Performance

2015 ◽  
Author(s):  
Mengyao Wei ◽  
Sivanand Somasundaram ◽  
Bin He ◽  
Qian Liang ◽  
Rishi Raj ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Aspect Ratio ◽  
Capillary Pressure ◽  
Heat Transfer Performance ◽  
Channel Width ◽  
Viscous Drag ◽  
Transfer Performance ◽  
Micro Channels ◽  
Pitch Ratio

Biporous evaporator wicks for heat pipe and vapor chambers can perform superiorly by reducing the viscous drag with larger pores or channels and simultaneously generate higher capillary pressure with smaller pores radius. Unlike conventional sintered metal biporous wicks, cylindrical silicon micropillar based evaporator with microchannels, possess the following advantages: mature and easily controllable fabrication process, possibility of direct integration with semiconductor devices and no risk of thermal expansion mismatch. In this work, we investigated a biporous wick for the evaporator design, which consists of micro pillar arrays interspersed within micro channels. This design was systematically studied by constructing a mathematical model, by coupling Brinkman’s equation with mass and energy conservation equations, to predict the biporous wicks’ heat transfer performance. In order to find the best combination of geometric factors that give the highest heat flux at a certain superheat value, optimization in Matlab was done. The effect of diameter to pitch ratio, aspect ratio, channel width and contact angle on wick’s permeability, capillary pressure and evaporative heat flux were also investigated. Conclusion was drawn that a higher diameter to pitch ratio of 0.57, reasonable aspect ratio of 1.75∼3.22, island to channel width ratio of around 1.96 are preferred in this kind of biporous wick’s design. Biporous wick show potential to dissipate heat flux of 515.7 W/cm2 at superheat of 40 °C, which is 134 % higher compared to monoporous wick.

An Evaporating Ethanol Meniscus—Part I: Experimental Studies

1979 ◽  
Vol 101 (1) ◽  
pp. 55-58 ◽  
Author(s):  
F. J. Renk ◽  
P. C. Wayner
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Capillary Flow ◽  
Experimental Studies ◽  
Resistance Thermometers ◽  
Flow Heat ◽  
Meniscus Profile

The profile of an evaporating ethanol meniscus was measured as a function of the evaporative heat flux using interferometry. A measure of the evaporative heat flux was obtained using vapor deposited resistance thermometers. The meniscus profile was found to be stable and a function of the heat flux for the heat flux range of 0 – 1.36w/m of interline. These results were used in an analysis of capillary flow heat transfer in Part II.

Modifying the Heat Transfer and Capillary Pressure of Loop Heat Pipe Wicks with Carbon Nanotubes

2011 ◽  
Vol 115 (19) ◽  
pp. 9312-9319 ◽  
Author(s):  
E. Terrado ◽  
R. Molina ◽  
E. Natividad ◽  
M. Castro ◽  
P. Erra ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Carbon Nanotubes ◽  
Heat Pipe ◽  
Capillary Pressure ◽  
Loop Heat Pipe

scholarly journals Analysis of the Wicking and Thin-Film Evaporation Characteristics of Microstructures

2009 ◽  
Vol 131 (10) ◽  
Author(s):  
Ram Ranjan ◽  
Jayathi Y. Murthy ◽  
Suresh V. Garimella
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Contact Angle ◽  
Free Surface ◽  
Capillary Pressure ◽  
Liquid Level ◽  
Performance Parameters ◽  
Liquid Meniscus ◽  
Thin Film Evaporation ◽  
Film Evaporation

The topology and geometry of microstructures play a crucial role in determining their heat transfer performance in passive cooling devices such as heat pipes. It is therefore important to characterize microstructures based on their wicking performance, the thermal conduction resistance of the liquid filling the microstructure, and the thin-film characteristics of the liquid meniscus. In the present study, the free-surface shapes of the static liquid meniscus in common microstructures are modeled using SURFACE EVOLVER for zero Bond number. Four well-defined topologies, viz., surfaces with parallel rectangular ribs, horizontal parallel cylinders, vertically aligned cylinders, and spheres (the latter two in both square and hexagonal packing arrangements), are considered. Nondimensional capillary pressure, average distance of the liquid free-surface from solid walls (a measure of the conduction resistance of the liquid), total exposed area, and thin-film area are computed. These performance parameters are presented as functions of the nondimensional geometrical parameters characterizing the microstructures, the volume of the liquid filling the structure, and the contact angle between the liquid and solid. Based on these performance parameters, hexagonally-packed spheres on a surface are identified to be the most efficient microstructure geometry for wicking and thin-film evaporation. The solid-liquid contact angle and the nondimensional liquid volume that yield the best performance are also identified. The optimum liquid level in the wick pore that yields the highest capillary pressure and heat transfer is obtained by analyzing the variation in capillary pressure and heat transfer with liquid level and using an effective thermal resistance model for the wick.

An Evaporating Ethanol Meniscus—Part II: Analytical Studies

1979 ◽  
Vol 101 (1) ◽  
pp. 59-62 ◽  
Author(s):  
F. J. Renk ◽  
P. C. Wayner
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Fluid Flow ◽  
Heat Sink ◽  
Capillary Flow ◽  
Local Heat ◽  
Heat Fluxes ◽  
Flow Heat ◽  
Very High ◽  
Meniscus Profile

A model of capillary flow heat transfer is used to analyze the data obtained in Part I. The results indicate that fluid flow resulting from a change in the meniscus profile replenishes the liquid evaporated in a stationary evaporating meniscus. Local evaporative heat fluxes can be very high near the interline region of a finite contact angle meniscus. Therefore, a small stationary evaporating meniscus can be used as a very effective local heat sink.

Numerical Study of an Evaporating Meniscus on a Moving Heated Surface

2006 ◽  
Vol 128 (12) ◽  
pp. 1285-1292 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Heated Surface ◽  
Transient Heat Conduction ◽  
Two Dimensions ◽  
Interface Motion ◽  
Wall Velocity ◽  
Moving Wall ◽  
Wall Superheat ◽  
Meniscus Profile

The present study is performed to numerically analyze an evaporating meniscus bounded between the advancing and receding interfaces on a moving heated surface. The numerical scheme developed for analyzing interface motion during bubble growth in pool boiling has been applied. A column of liquid is placed between a nozzle outlet and a moving wall, and calculations are done in two dimensions with a fixed distance between the nozzle and the wall. The results show that the wall velocity creates a circulation near the meniscus base, resulting in transient heat conduction. The local wall heat transfer is found to vary significantly along the meniscus base, the highest being near the advancing contact line. The heat transfer coefficient is found to depend on the advancing contact angle and wall velocity but is independent of the wall superheat. Reasonable agreement is observed when the meniscus profile and heat transfer results obtained from the numerical simulation are compared to the experimental data.

Influence of Parallel and Trapezoidal Wick Structures to the Heat Transfer Capability of MHPs

2017 ◽  
Vol 868 ◽  
pp. 33-38
Author(s):  
Yi Luo ◽  
Zhi Xin Li ◽  
Zi Cheng Yu ◽  
Xiao Dong Wang
Keyword(s):  
Heat Transfer ◽  
Capillary Pressure ◽  
Equilibrium Temperature ◽  
Input Power ◽  
Small Dimension ◽  
Working Fluid ◽  
Transfer Capability ◽  
Calculation Results ◽  
Heat Transfer Capability ◽  
Micro Structures

Heat transfer capability of micro heat pipe (MHP) is relied on the thermal resistance of material, the specific phase change latent heat of working fluid, and the pattern of micro structures which is served as wick. In this paper, parallel and trapezoidal micro Cu structures were designed and fabricated by UV-LIGA. The capillary pressure and the effective coefficient of heat transfer conductivity of the micro grooves were calculated and results showed that trapezoidal grooves with small dimension in evaporator and large dimension in condenser (forward trapezoidal) have the best performance, because this structure can generate larger capillary force of working fluid and enhance the heat transfer. Two MHPs based on the calculations were fabricated and tested, results demonstrated that forward trapezoidal groove had the lowest equilibrium temperature while the inversed trapezoidal groove had the highest equilibrium temperature, approved the numerical calculation results. When the input power was 10W, the equilibrium temperature of forward trapezoidal, parallel and backward trapezoidal grooved MHP was 67.2 oC, 73.4°C and 89.1 oC, respectively. The forward trapezoidal grooves enlarge the capillary pressure and benefit the heat transfer of MHP.

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