STEADY MICROSTRUCTURE OF A CONTACT LINE FOR A LIQUID ON A HEATED SURFACE OVERLAID WITH ITS PURE VAPOR: PARAMETRIC STUDY FOR A CLASSICAL MODEL

2009 ◽  
Vol 21 (3) ◽  
pp. 213-248 ◽  
Author(s):  
A. Ye. Rednikov ◽  
S. Rossomme ◽  
P. Colinet
Author(s):  
Isaac Perez-Raya ◽  
Satish G. Kandlikar

Effective heat transfer techniques benefit the development of nuclear and fossil fuel powered steam generators, high power electronic devices, and industrial refrigeration systems. Boiling dissipates large heat fluxes while keeping a low and a constant surface temperature. However, studies of the fluid behavior surrounding the bubble and the heat transfer near the contact-line are scare due to difficulties of flow visualization, chaotic conditions, and small length scales. The preset study shows the simulation of bubble growth over a heated surface from conception to departure. The computation of mass transfer with interfacial temperature gradients leads to proper bubble growth rates. Models to include the interface sharpness uncover the dynamic and thermal interaction between the interface and the fluid. Results indicate that the nucleation of a bubble (in water at 1 atm with 6.2 K wall superheat) has an influence region of 2Db (where Db is the departure bubble diameter). In addition, results reveal a thin thermal film near the interface that increases the heat transfer at the contact-line region. Numerical bubble growth rates compare well with experimental data on single bubble nucleation.


Author(s):  
Alyssa Recinella ◽  
Joseph Baldwin ◽  
Charles Krouse ◽  
Robert Walkowiak ◽  
Pruthvik Raghupathi ◽  
...  

Nucleate boiling is one of the most efficient methods to dissipate heat. However, the complex physics of heat transfer near the contact line is not well understood. Due to the difficulty in measuring and analyzing heat transfer around a bubble at high heat fluxes, novel approaches must be taken. This paper focuses on the design of an experimental setup used to simulate heat transfer at the contact line by studying an oscillating meniscus on a heated surface. A preliminary design of the experimental test setup is described in this paper. The experimental test setup will be composed of a liquid injection system with a needle, an oscillator, a heated surface, and a sensor to measure the meniscus volume. A feedback loop will be used to control the liquid injection system and prevent dry out or flooding during evaporation. Furthermore, a conic speaker will be used to induce oscillations at a range of 10–200 Hz. These oscillations simulate liquid displacement during bubble nucleation, growth, and bubble departure. Finally, a sensor that measures the volume of the liquid will be connected to the heated plate and the needle in order to measure the volume of the meniscus while oscillating. A fundamental understanding of the heat transfer in the contact line region is expected.


Volume 3 ◽  
2004 ◽  
Author(s):  
Bohumil Horacek ◽  
Jungho Kim ◽  
Kenneth T. Kiger

Time and space resolved heat transfer data on a nominally isothermal surface cooled by two spray nozzles was obtained using an array of individually controlled microheaters. Visualization and measurements of the liquid-solid contact area and three-phase contact line length were made using a total internal reflectance technique. The spacing between the nozzles and the heated surface was varied between 7 mm and 17 mm. Little interaction between the two sprays was observed for the tested conditions, with the heat flux produced by a single nozzle remaining comparable to that produced by two nozzles, provided the areas considered were limited to the regions impacted by the sprays. Variations in the heat transfer across the surface, however, increased significantly with decreasing spacing. The phase change heat transfer was strongly correlated with the length of the three-phase contact line.


2021 ◽  
Vol 926 ◽  
Author(s):  
Mohammad Khavari ◽  
Tuan Tran

During the impact of a liquid droplet on a sufficiently heated surface, bubble nucleation reduces the contact area between the liquid and the solid surface. Using high-speed imaging combined with total internal reflection, we measure and report how the contact area decreases with time for a wide range of surface temperatures and impact velocities. We also reveal how formation of the observed fingering patterns contributes to a substantial increase in the total length of the contact line surrounding the contact area.


Author(s):  
Navdeep S. Dhillon

The phenomenon of bubble growth on a heated surface is of fundamental importance in many scientific and engineering applications, including boiling heat transfer. Although the growth of a homogeneous bubble in a pool of hot liquid is well understood, bubbles growing on hot solid surfaces involve evaporation from a three-phase contact line and therefore exhibit several peculiar features. One of these is the effect of surface texture and wetting properties on the size and timing of bubbles that form and depart from a uniformly heated surface. Here, we present pool boiling experimental results elucidating this important phenomenon. Using high-speed optical imaging, we perform a comparative study of the process of growth and departure of bubbles on plain and rough surfaces and explore the different factors that dictate this behavior. Using scaling analysis, we analyze the primary forces acting on a growing bubble and show that the effect of surface roughness on bubble behavior can be explained in terms of the dependence of these forces on the rate of bubble growth and in-turn on the rate of thin-film evaporation from the three-phase contact line of the bubble.


Author(s):  
Vladimir S. Ajaev ◽  
M. Markos Gebresilassie

We develop a mathematical model for heat transfer and fluid flow near a contact line on a heated surface in the presence of thermocapillary flow and evaporation. The coupled heat transfer and flow problem is reduced to an equation for local thickness, which is then solved numerically. The steady-state results indicate that thermocapillary stresses act to reduce the rate of liquid flow towards the contact line and increase interfacial curvature there. We also discuss solutions than involve moving contact lines, applicable to studies of start-up and shut-down operations of heat pipes. The velocity of the contact line and the apparent contact angle are found as functions of the Marangoni number. Thermocapillary effect is shown to reduce contact line speed and increase the apparent contact angle. Finally, the local solution is incorporated into global solutions for curvature variations of an evaporating three-dimensional meniscus in a corner. This configuration is typically encountered in proposed designs of micro heat pipes. Interface curvature is found as a function of the axial coordinate for the case of linear axial temperature variation in the corner.


2017 ◽  
Vol 837 ◽  
pp. 115-128 ◽  
Author(s):  
M. Jalaal ◽  
C. Seyfert ◽  
B. Stoeber ◽  
N. J. Balmforth

Spreading and stationary droplets of a thermally responsive fluid on a heated surface are studied. The fluid undergoes a reversible gel formation at elevated temperature. The spatio-temporal pattern of gel formation within the droplet is examined using an experimental method based on spectral domain optical coherence tomography and time varying speckle patterns. Two stages of gel formation can be distinguished: first, a thin crust appears starting at the contact line. Second, a gel layer appears above the heated plate and then expands upward. We attribute the first stage of gel formation to solvent evaporation and heating through the air and the second to thermal conduction through the fluid from the base. Gel formation at the contact line is likely responsible for the arrest of spreading droplets, but was not detectable with our experimental protocol at the time of contact line arrest, suggesting that this arose over a microscopic length scale. Overall, substrate heating provides an effective way to control the final shape of droplets of thermo-responsive fluids.


1999 ◽  
Vol 96 (9) ◽  
pp. 1335-1339 ◽  
Author(s):  
ALAN E. VAN GIESSEN, DIRK JAN BUKMAN, B.

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