Modeling of bubble detachment in reduced gravity under the influence of electric fields and experimental verification

Herman, Čila; Iacona, Estelle

doi:10.1007/s00231-003-0488-y

Cited by 24 publications

(9 citation statements)

References 15 publications

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“…In the approximately uniform field generated by a plane electrode above a plane wall, Herman and Iacona [39] observed the predicted elongation of the bubbles in the direction of the field. In the non-uniform field created by a small spherical electrode placed off-axis from the orifice, which might simulate the distortion of the field by detached bubbles in boiling, bubbles were elongated and tilted [37,38].…”

Section: Studies Of a Single Bubble In An Electric Fieldmentioning

confidence: 94%

“…This work has been summarized in a recent paper by Iacona et al [37] and extended to the coalescence of bubbles from adjacent nozzles by Liu et al [38]. Herman and Iacona [39] Chaddock model requires as input an experimental "contact angle" remote from the wall, beyond the region of necking, so it is an artefact of the local flow field and not a material property. Cho et al [42] computed the equilibrium shape of a gas bubble of specified volume, attached to a wall in combined uniform electrical and gravitational fields in a perfect dielectric liquid without bulk free charges.…”

Section: Studies Of a Single Bubble In An Electric Fieldmentioning

confidence: 99%

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A study of nucleate boiling and critical heat flux with EHD enhancement

et al. 2007

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Abstract. The paper describes results from an experimental and theoretical study of the effect of an electric field on nucleate boiling and the critical heat flux (CHF) in pool boiling of R123 at atmospheric pressure on a horizontal wall with a smooth surface.Two designs of electrode (parallel rods and wire mesh) were used.The experimental data exhibit some differences from the data obtained by other researchers in similar experiments on a wall with a different surface finish and with a slightly different design of wire mesh electrode. The hydrodynamic model for EHD enhancement of CHF cannot reconcile the differences.A theoretical model has been developed for the growth of a single vapour bubble on a superheated wall in an electric field, leading to a numerical simulation based on the level-set method. The model includes matching of sub-models for the micro-and macroregions, conduction in the wall, distortion of the electric field by the bubble, the temperature dependence of electrical properties and free-charge generation. In the present form of the model, some of these effects are realised in an approximate form. The capability to investigate dry-spot formation and wall temperature changes that might lead to CHF has been demonstrated.

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Section: Studies Of a Single Bubble In An Electric Fieldmentioning

confidence: 94%

Section: Studies Of a Single Bubble In An Electric Fieldmentioning

confidence: 99%

A study of nucleate boiling and critical heat flux with EHD enhancement

et al. 2007

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“…This difference with respect to the results of Pamperin and Rath [4] was attributed to geometric considerations that lead to significant variations in the bubble-detachment mechanics. Finally, the effect of electric fields on bubble detachment was also studied by Herman et al [14,15] and Di Marco et al [16]. For example, the latter investigation showed that the application of electric fields (0-18 kV) was effective in promoting bubble detachment, showing that electric fields of 10 kV generated bubbles of the same size as in normal gravity.…”

mentioning

confidence: 88%

Generation of a Monodisperse Microbubble Jet in Microgravity

et al. 2008

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A new method to create a jet of a virtually monodisperse microbubble suspension of prescribed bubble size into a quiescent cavity is proposed. The method is insensitive to gravity and is based on the creation of a slug flow at a T junction in a capillary tube before injection. We develop a theoretical analysis that establishes the validity and efficiency of the method, as controlled by the crossflow Weber number, and yields a simple explicit prediction for the bubble size in terms of the injection parameters. The method operates efficiently for small Weber numbers, yet it generates small bubbles of very uniform size. The reduced size dispersion is also explained within the theoretical model. The method of bubble formation, injection, and spreading by the resulting turbulent jet is validated experimentally in 4.7 s of free fall in the drop tower at the University of Bremen. Experiments demonstrate the physical principle behind the method of bubble formation and allow us to explore the dynamics of the resulting bubble jet after injection of the slug flow into a quiescent cavity in microgravity conditions as an efficient method of bubble spreading and transport. Detailed measurements of average local velocities show that bubbles are essentially passive with respect to the carrier mean flow, and the inherent turbulence of the flow is crucial for optimal spreading of the bubble distribution and reduction of bubble coalescence. The shape of the bubble jet is studied as a function of the Reynolds number. Finally, the degree of coalescence is also characterized and found to be remarkably small.

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“…Then, Cole and Rohsenow [6] modified the correlation developed by Cole [5] by replacing the wall superheat with a critical temperature. Herman and Lacona [7] carried out both experimental and theoretical researches on bubble detachment in reduced gravity under the influence of electric fields. A simple model for predicting bubble volume and shape at detachment was proposed in their paper.…”

Section: Introductionmentioning

confidence: 99%

Bubble departure size in flow boiling

et al. 2014

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HHeight from the beginning of heated portion of rod (m) JaJacob number k w Dimensionless bubble contact diameter L Perimeter of heated rod (m) n Constant p Pressure (Pa) q w Heat flux (kW/m 2 ) r Bubble radius (m or mm) Re b Bubble Reynolds number t Time (s) T Temperature (°C) U b Bubble velocity (m/s) U(x) Liquid velocity profile near wall (m/s) V b Bubble volume (m 3 ) u l Mean velocity of two phase (m/s) u* Friction velocity (m/s) X Vapor quality Greek symbols α Advancing contact angle β Receding contact angle δ Liquid film thickness (m or mm) η Thermal diffusivity (m 2 /s) θ Inclination angle ν Kinematic viscosity (m 2 /s) ρ Density (kg/m 3 ) σ Surface tension coefficient (N/m) τ Deviatoric stress tensor (N/m) Subscripts in Inlet l Liquid sat Saturation v Vapor w Wall (heated surface) Abstract Flow boiling experiments were conducted in a vertical annular channel to study bubble departure characteristics. Deionized water was used as the working fluid, and the tests were performed at atmospheric pressure. Bubble departure diameters were obtained from the images which were captured by a high-speed digital camera. The relationship between bubble contact diameter and departure diameter was discussed. A new model base on force balance analysis, taking bubble contact diameter into account for predicting bubble departure diameter is proposed in this study. A good agreement between predicted and measured results is achieved. List of symbols A Area (m 2 ) b Constant c Constant c pl Specific heat at constant pressure [J/(kg °C)] d w Bubble contact diameter (m or mm) D Equivalent diameter or bubble diameter (m or mm) D d Bubble departure diameter (m or mm) F Force (N) g Gravitational acceleration (9.81 m/s 2 ) G Mass flux [kg/(m 2 s)] h fg Latent heat (J/kg)

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Modeling of bubble detachment in reduced gravity under the influence of electric fields and experimental verification

Cited by 24 publications

References 15 publications

A study of nucleate boiling and critical heat flux with EHD enhancement

A study of nucleate boiling and critical heat flux with EHD enhancement

Generation of a Monodisperse Microbubble Jet in Microgravity

Bubble departure size in flow boiling

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