Spray Cooling Using Multiple Nozzles: Visualization and Wall Heat Transfer Measurements

Volume 3 ◽  
2004 ◽  
Author(s):  
Bohumil Horacek ◽  
Jungho Kim ◽  
Kenneth T. Kiger
Keyword(s):  
Heat Transfer ◽  
Contact Line ◽  
Heated Surface ◽  
Spray Cooling ◽  
Line Length ◽  
Strongly Correlated ◽  
Phase Contact ◽  
Three Phase ◽  
Phase Change Heat Transfer ◽  
Total Internal Reflectance

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.

Direct Numerical Simulation of the Microscale Fluid Flow and Heat Transfer in the Three-Phase Contact Line Region During Evaporation

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Stefan Batzdorf ◽  
Tatiana Gambaryan-Roisman ◽  
Peter Stephan
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Contact Line ◽  
Thin Liquid Film ◽  
Contact Angles ◽  
Length Scale ◽  
Phase Contact ◽  
Flow And Heat Transfer ◽  
Three Phase

The heat and mass transfer close to the apparent three-phase contact line is of tremendous importance in many evaporation processes. Despite the extremely small dimensions of this region referred to as the microregion compared to the macroscopic length scale of a boiling process, a considerable fraction of heat can be transferred in this region. Due to its small characteristic length scale, physical phenomena are relevant in the microregion, which are completely negligible on the macroscopic scale, including the action of adhesion forces and the interfacial heat resistance. In the past, models have been developed taking these effects into account. However, so far these models are based on the assumption of one-dimensional (1D) heat conduction, and the flow within the thin liquid film forming the microregion near the apparent three-phase contact line is modeled utilizing the lubrication approximation. Hence, the application of existing models is restricted to small apparent contact angles. Moreover, the effects of surface structures or roughness are not included in these lubrication models. To overcome these limitations, a direct numerical simulation (DNS) of the liquid flow and heat transfer within the microregion is presented in this paper. The DNS is employed for validation of the existing lubrication model and for investigation of the influence of surface nanostructures on the apparent contact angle and in particular on the heat transfer within the microregion.

Effect of Surface Roughness on the Behavior of Bubbles Growing and Departing From a Heated Surface

2017 ◽  
Author(s):  
Navdeep S. Dhillon
Keyword(s):  
Surface Roughness ◽  
Contact Line ◽  
Bubble Growth ◽  
High Speed ◽  
Heated Surface ◽  
Scaling Analysis ◽  
Phase Contact ◽  
Bubble Behavior ◽  
Three Phase ◽  
Effect Of Surface

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.

The effect of three-phase contact line speed on local evaporative heat transfer: Experimental and numerical investigations

2012 ◽  
Vol 55 (7-8) ◽  
pp. 1896-1904 ◽  
Author(s):  
Christian Kunkelmann ◽  
Khalid Ibrahem ◽  
Nils Schweizer ◽  
Stefan Herbert ◽  
Peter Stephan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Contact Line ◽  
Phase Contact ◽  
Numerical Investigations ◽  
Line Speed ◽  
Three Phase ◽  
Evaporative Heat Transfer

Test of the stability of a three-phase contact line with negative line tension

1999 ◽  
Vol 96 (9) ◽  
pp. 1335-1339 ◽  
Author(s):  
ALAN E. VAN GIESSEN, DIRK JAN BUKMAN, B.
Keyword(s):  
Contact Line ◽  
Line Tension ◽  
Phase Contact ◽  
Three Phase ◽  
The Stability

Numerical Simulation of Heat Transfer Mechanisms in Spray Cooling

2010 ◽  
Author(s):  
Eelco Gehring ◽  
Mario F. Trujillo
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Spray Cooling ◽  
Impingement Zone ◽  
Ongoing Work ◽  
Efficient Suppression ◽  
A Cell ◽  
Cooling Behavior ◽  
Free Surface Capturing ◽  
The Impact

A primary mechanism of heat transfer in spray cooling is the impingement of numerous droplets onto a heated surface. This mechanism is isolated in the present and ongoing work by numerically simulating the impact of a single train of FC-72 droplets employing an implicit free surface capturing methodology. The droplet frequency and velocity ranges from 2000–4000 Hz, and 0.5–2 m/s, respectively, with a fixed drop size of 239 μm. This gives a corresponding Weber and Reynolds range of 10–170 and 330–1300, respectively. Results show that the impingement zone is largely free of phase change effects due to the efficient suppression of the local temperature field well below the saturated value. Due in part to the relatively high value of the Prandtl number and the compression of the boundary layer from the impingement flow, a cell size on the order of 1 μm is necessary to adequately capture the heat transfer dynamics. It is shown that the cooling behavior increases in relation to increasing frequency and impact velocity, but is most sensitive to velocity. In fact, for sufficiently low velocities the calculations show that the momentum imparted on the film is insufficient to maintain a near stationary liquid crown. The consequence is a noticeable penalty on the cooling behavior.

Faster Nucleation of Ice and Carbon Dioxide Hydrates at the Three-Phase Contact Line

2021 ◽  
Author(s):  
Aritra Kar ◽  
Awan Bhati ◽  
Palash V. Acharya ◽  
Ashish Mhadeshwar ◽  
Roger Bonnecaze ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Contact Line ◽  
Phase Contact ◽  
Three Phase
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