Optical and Infrared Study of the Effect of a High Electric Field on the Pool Boiling Behavior of a Sub-Cooled Dielectric Liquid

2017 ◽  
Author(s):  
Sathiyanathan Sargunanathan ◽  
Abhishek Basavanna ◽  
Navdeep S. Dhillon ◽  
Seyed Reza Mahmoudi
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Applied Electric Field ◽  
Boiling Heat Transfer ◽  
Imaging Techniques ◽  
Pool Boiling ◽  
Bubble Nucleation ◽  
Dielectric Liquid ◽  
Dielectric Fluid ◽  
Nucleation Behavior

The formation and departure of bubbles on hot surfaces is of fundamental significance in many engineering applications including in boiling heat transfer. Both the bubble growth behavior and the boiling heat transfer performance parameters are affected by different variables and conditions, an interesting one of which is the electric field. Understanding its effect is of considerable significance, as it has been observed experimentally that the application of an electric field can lead to a significant enhancement in the boiling critical heat flux of a dielectric fluid. Although the exact physical mechanism behind this effect is not well understood, we hypothesize that it could be correlated to the effect of the electric field on individual evaporating bubbles and their altered interactions with the boiling surface. In this study, we employ optical and infrared imaging techniques to experimentally illustrate the effect of an applied electric field on the behavior of bubbles in sub-cooled pool boiling of a dielectric liquid (HFE-7100). Results indicate that bubble nucleation behavior, bubble geometry, and the bubble three-phase contact line dynamics are all simultaneously affected by the electric field. To help explain the experimental results, we further implement a CFD numerical model of an individual vapor bubble in the presence of an applied electric field.

Experimental Verification of Analytical Prediction of Pool Boiling CHF Incorporating the Effects of EHD and Contact Angle

2015 ◽  
Author(s):  
Ichiro Kano ◽  
Takahiro Sato ◽  
Naoki Okamoto
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Electric Field ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Contact Angles ◽  
Dielectric Liquid ◽  
Working Fluid ◽  
Analytical Prediction ◽  
Compound Effect

Boiling heat transfer enhancement via compound effect of Electro-Hydro-Dynamic (EHD) and contact angle has been experimentally and analytically investigated. A fluorinated dielectric liquid (Asahi Glass Co. Ltd, AE-3000) was selected as the working fluid. Pool boiling heat transfer in the saturated liquid was measured at atmospheric pressure. In order to change the contact angle between the boiling surface and the dielectric liquid, the different materials Cu, Cr, NiB, Sn, and mixture of 5 and 1.5 micro meter diamond particles were electrically deposited on a boiling surface. The critical heat flux (CHF) for different contact angles showed 20.5 ∼ 26.9 W/cm2 which was −7 ∼ 25 % of that for a non-coated Cu surface (21.5 W/cm2). Upon application of a −5 kV/mm electric field to the micro structured surface (the mixture of 5 and 1.5 micro meter particles), a CHF of 99 W/cm2 at a superheat of 33.5 K was obtained. The previous theoretical equation of pool boiling predicted the CHF with the electric field and without the electrode.

Nucleate Pool Boiling Heat Transfer Measurement and Flow Visualization for Ammonia-Water Mixture

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
A. Sathyabhama ◽  
T. P. Ashok Babu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Mass Fraction ◽  
Pool Boiling ◽  
Bubble Nucleation ◽  
Water Mixture ◽  
Nucleate Pool Boiling ◽  
Ammonia Water

Visualization of bubble nucleation during nucleate pool boiling outside a vertical cylindrical heated surface was done for ammonia-water binary mixture in order to obtain a descriptive behavior of the boiling, which was directly compared with the measured heat transfer coefficient data at low pressure of 4–8 bar and at low mass fraction of 0 < x < 0.3 and at different heat flux. Still images taken with high speed camera are used to demonstrate the decrease in boiling heat transfer coefficient with increase in ammonia mass fraction. Jensen and Memmel model has better agreement with experimental bubble diameter. Further work is required to obtain quantitative information about bubble nucleation parameters. It is found that both Calus and Rice and Stephan–Koorner correlation can predict the experimental heat transfer coefficient values with a maximum deviation of ± 20%.

scholarly journals Hydrophilic and Hydrophobic Nanostructured Copper Surfaces for Efficient Pool Boiling Heat Transfer with Water, Water/Butanol Mixtures and Novec 649

Nanomaterials ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 3216
Author(s):  
Matic Može ◽  
Viktor Vajc ◽  
Matevž Zupančič ◽  
Iztok Golobič
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Dissipation ◽  
Pool Boiling ◽  
Chemical Oxidation ◽  
Dielectric Fluid ◽  
Surface Stability ◽  
Copper Surfaces ◽  
Functionalized Surfaces ◽  
Fluorinated Silane

Increasing heat dissipation requirements of small and miniature devices demands advanced cooling methods, such as application of immersion cooling via boiling heat transfer. In this study, functionalized copper surfaces for enhanced heat transfer are developed and evaluated. Samples are functionalized using a chemical oxidation treatment with subsequent hydrophobization of selected surfaces with a fluorinated silane. Pool boiling tests with water, water/1-butanol mixture with self-rewetting properties and a novel dielectric fluid with low GWP (Novec™ 649) are conducted to evaluate the boiling performance of individual surfaces. The results show that hydrophobized functionalized surfaces covered by microcavities with diameters between 40 nm and 2 µm exhibit increased heat transfer coefficient (HTC; enhancements up to 120%) and critical heat flux (CHF; enhancements up to 64%) values in comparison with the untreated reference surface, complemented by favorable fabrication repeatability. Positive surface stability is observed in contact with water, while both the self-rewetting fluids and Novec™ 649 gradually degrade the boiling performance and in some cases also the surface itself. The use of water/1-butanol mixtures in particular results in surface chemistry and morphology changes, as observed using SEM imaging and Raman spectroscopy. This seems to be neglected in the available literature and should be focused on in further studies.

Correlation of Subatmospheric Pressure, Saturated, Pool Boiling of Water on a Structured-Porous Surface

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Sean J. Penley ◽  
R. A. Wirtz
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Bubble Nucleation ◽  
Distilled Water ◽  
Heat Transfer Correlation ◽  
Subatmospheric Pressure ◽  
Strong Function ◽  
Nucleation Sites ◽  
Boiling Heat Transfer Coefficient

Saturated pool-boiling experiments at 1 atm and subatmospheric pressure assess the utility of fine-filament screen-laminate enhanced surfaces as effective bubble nucleation sites. Experiments were conducted on vertically oriented, multilayer laminates in saturated distilled water at pressures of 0.2–1.0 atm. The performance of 12 different copper-filament surfaces, having pore hydraulic diameters ranging from 14 μm to 172 μm, is documented. Experimental results show that boiling performance is a strong function of screen-laminate geometry. In the present work, enhancement of up to 27 times that of an unenhanced surface was obtained at a superheat of 8 K and a pressure of 0.2 atm. Dimensional analysis and multiparameter regression are used to develop a heat transfer correlation that relates the boiling heat transfer coefficient to the lamination geometry.

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