Heat Transfer and Bubble Detachment in Subcooled Pool Boiling From a Microheater Array Under the Effect of a Nonuniform Electric Field

2007 ◽  
Author(s):  
Zan Liu ◽  
Cila Herman ◽  
Jungho Kim
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Pool Boiling ◽  
Nonuniform Electric Field ◽  
Working Fluid ◽  
Dielectric Fluid ◽  
Bubble Behavior ◽  
Bubble Detachment ◽  
Earth Gravity ◽  
The Individual

The effects of a nonuniform electric field on vapor bubble detachment and heat transfer rate were studied in pool boiling at different subcooled conditions for various wall temperatures. Dielectric fluid (FC-72) was used as the working fluid at 1 atm at earth gravity with two extreme gas concentration levels. An array of 3×3 independently controlled microheaters each 0.7×0.7 mm2 in size were maintained at constant temperature using electronic feedback loops, enabling the heat transfer from each heater to be determined. An electric field was applied between the horizontal upward facing microheater array, which was grounded, and a spherical, off-axis top electrode. Boiling heat transfer results with and without the electric field are presented in this study. Without the electric field, a single large “primary” bubble was observed to form due to the coalescence of the individual “satellite” bubbles which nucleated directly from each single heater array. Before its detachment, a dry spot formed underneath this primary bubble resulted in a reduction in heat transfer. With the electric field applied, three or more small “secondary” bubbles that nucleated and grew more rapidly and detached more frequently were observed. Due to the nonuniformity of the electric field, bubbles moved away from the top electrode (into the weaker region of the electric field) during their development. Higher overall heat transfer rates were measured from the heater array. In addition, the bubble behavior showed agreement with our previous investigation of injecting air bubbles into a stagnant, isothermal liquid through orifices.

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.

Pool Boiling Enhancement by Electrohydrodynamic Force and Diamond Coated Surfaces

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Ichiro Kano
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Cutting Tools ◽  
Diamond Particle ◽  
Working Fluid ◽  
Microstructured Surface ◽  
Microstructured Surfaces ◽  
Coated Surfaces

Boiling heat transfer enhancement via compound effect of the electrohydrodynamic (EHD) effect and microstructured surfaces 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. Microstructured surfaces, which are mainly used for cutting tools, were developed with diamond particles using electrodeposition technique. Four different particle diameters were prepared: 5, 10, 15, and a mixture of 5 and 1.5 μm. The critical heat flux (CHF) for diamond particle surfaces showed 27–30 W/cm2 which was 26–40% increase for comparing with a noncoated surface (21.5 W/cm2). Upon application of a −5 kV/mm electric field to the microstructured surface (a mixture of 5 and 1.5 μm particles), a CHF of 70.2 W/cm2 at a superheat of 21.7 K was obtained. The previous theoretical equation of pool boiling predicted the CHF with electric field and without the electrode within 10%. Also, the CHF enhanced by the diamond coated surfaces was correlated well with the contact angle.

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.

Visualization of Vertical Bubble Coalescence and Detachment Under the Influence of a Nonuniform Electric Field

2006 ◽  
Author(s):  
Z. Liu ◽  
C. Herman ◽  
D. Mewes
Keyword(s):  
Electric Field ◽  
Nonuniform Electric Field ◽  
Bubble Coalescence ◽  
Behavior Patterns ◽  
Air Bubbles ◽  
Bubble Behavior ◽  
Single Experiment ◽  
Flow Rates ◽  
Lower Volume ◽  
Detachment Time

The effect of a nonuniform electric field on the formation, coalescence and detachment of air bubbles injected into a stagnant, isothermal liquid through an orifice is studied to identify characteristic bubble behavior patterns. The results of the experimental visualization suggest significant differences in bubble shape and size caused by the electric field. The electric field was applied between a flat, circular and horizontal ground electrode and a spherical, off-axis top electrode. During formation the bubble was tilted towards or away from the upper electrode under the influence of the electric field. The direction of the tilt alternated (even in a single experiment), however, in the majority of the cases the bubble trajectory tilted towards the top electrode. The detachment frequency increased under the influence of the electric field, which indicates decreased bubble volume for lower volume flow rates. The effect of the electric field on vertical bubble coalescence was analyzed and quantified in terms of the detachment time.

Heat transfer from a wire to hexane in a nonuniform electric field

1991 ◽  
Vol 69 (2) ◽  
pp. 606-609 ◽  
Author(s):  
Tuula Ryde ◽  
Sigurds Arajs ◽  
Richard J. Nunge
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Nonuniform Electric Field

The Effect of Nanoscale Surface Modification on Boiling Heat Transfer and Critical Heat Flux

2010 ◽  
Author(s):  
Moo Hwan Kim
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Nuclear Power ◽  
Power Plants ◽  
Flow Boiling ◽  
Heated Surface ◽  
Pool Boiling ◽  
Working Fluid ◽  
Wetting Ability ◽  
Modified Surface

Recently, there were lots of researches about enormous CHF enhancement with the nanofluid in pool boiling and flow boiling. It is supposed the deposition of nanoparticles on the heated surface is one of main reasons. In a real application, nanofluid has a lot of problems to be used as the working fluid because of sedimentation and aggregation. The artificial surfaces on silicon and metal were developed to have the similar effect with nanoparticles deposited on the surface. The modified surface showed the enormous ability to increase CHF in pool boiling. Furthermore, under flow boiling, it had also good results to increase CHF. In these studies, we concluded that wetting ability of surface; e.g. wettability and liquid spreading ability (hydrophilic property of surface) was a key parameter to increase CHF under both pool and flow boiling. In addition, using wettability difference of surface; e.g. hydrophilic and hydrophobic, we conducted some tests of BHT (boiling heat transfer) enhancement using the oxide silicon which have micro-sized hydrophobic islands on hydrophilic surface. By using both of these techniques, we propose an optimized surface to increase both CHF and BHT. Also, the fuel surface of nuclear power plants is modified to have same effect and the results shows a good enhancement of CHF, too.

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