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Artykuły w czasopismach na temat "Electrohydrodynamic (EHD) instability"
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Feng, Y., i J. Seyed-Yagoobi. "Linear Instability Analysis of a Horizontal Two-Phase Flow in the Presence of Electrohydrodynamic Extraction Force". Journal of Heat Transfer 124, nr 1 (19.04.2001): 102–10. http://dx.doi.org/10.1115/1.1414132.
Pełny tekst źródłaStreszczenie:
The flow regimes associated with a horizontal internal two-phase (liquid-vapor) flow in the presence and absence of the electric field are investigated with the linear stability analysis. The momentum interchange due to the entrainment between the two phases is included in the analysis. The presence of the electric field promotes instability by providing the electrohydrodynamic (EHD) extraction force. Qualitative stability maps for the annular two-phase flow are provided with and without the electric field presence. Onset of the instability is compared with the experimental data and it is shown that the transition between the EHD-enhanced and EHD-suppressed convective boiling heat transfer is located near the annular-to-mist transition region.
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Almasi, Fatemeh, Manuel Hopp-Hirschler, Abdellah Hadjadj, Ulrich Nieken i Mostafa Safdari Shadloo. "Coupled Electrohydrodynamic and Thermocapillary Instability of Multi-Phase Flows Using an Incompressible Smoothed Particle Hydrodynamics Method". Energies 15, nr 7 (1.04.2022): 2576. http://dx.doi.org/10.3390/en15072576.
Pełny tekst źródłaStreszczenie:
This paper concerns the study of coupled effects of electrohydrodynamic (EHD) and thermocapillary (TC) on the dynamic behaviour of a single liquid droplet. An incompressible Smoothed Particle Hydrodynamic (ISPH) multiphase model is used to simulate EHD-TC driven flows. The complex hydrodynamic interactions are modeled using the continuum surface force (CSF) method, in which the gradient of the interfacial tension and the Marangoni forces are calculated with an approximated error or 0.014% in the calculation of Marangoni force compared to the analytical solutions which is a significant improvement in comparison with previous SPH simulation studies, under the assumption that the thermocapillarity generates sufficiently large stress to allow droplet migration, while the electrohydrodynamic phenomena influences the droplet morphology depending on the electrical and thermal ratios of the droplet and the ambient fluid. This study shows that, when applying a vertical electric field and thermal gradient, the droplet starts to stretch horizontally towards a break-up condition at a high rate of electrical permitivity. The combined effect of thermal gradient and electric field tends to push further the droplet towards the break-up regime. When the thermal gradient and the electric field vector are orthogonal, results show that the droplet deformation would take place more slowly and the Marangoni forces cause the droplet to migrate, while the stretching in the direction of the electric field is not seen to be as strong as in the first case.
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Li, Fang, Bo-Fu Wang, Zhen-Hua Wan, Jian Wu i Mengqi Zhang. "Absolute and convective instabilities in electrohydrodynamic flow subjected to a Poiseuille flow: a linear analysis". Journal of Fluid Mechanics 862 (16.01.2019): 816–44. http://dx.doi.org/10.1017/jfm.2018.958.
Pełny tekst źródłaStreszczenie:
We present a study of absolute and convective instabilities in electrohydrodynamic flow subjected to a Poiseuille flow (EHD-Poiseuille). The electric field is imposed on two infinite flat plates filled with a non-conducting dielectric fluid with unipolar ion injection. Mathematically, the dispersion relation of the linearised problem is studied based on the asymptotic response of an impulse disturbance imposed on the base EHD-Poiseuille flow. Transverse, longitudinal and oblique rolls are investigated to identify the saddle point satisfying the pinching condition in the corresponding complex wavenumber space. It is found that when the ratio of Coulomb force to viscous force increases, the transverse rolls can transit from convective instability to absolute instability. The ratio of hydrodynamic mobility to electric mobility, which exerts negligible effect on the linear stability criterion when the cross-flow is small, has significant influence on the convective–absolute instability transition, especially when the ratio is small. As we change the value of the mobility ratio, a saddle point shift phenomenon occurs in the case of transverse rolls. The unstable longitudinal rolls are convectively unstable as long as there is a cross-flow, a result which is deduced from a one-mode Galerkin approximation. Longitudinal rolls have a larger growth rate than transverse rolls except for a small cross-flow. Finally, regarding the oblique rolls, a numerical search for the saddle point simultaneously in the complex streamwise and transverse wavenumber spaces always yields an absolute transverse wavenumber of zero, implying that oblique rolls give way to transverse rolls when the flow is unstable.
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Dutta, Satarupa, Abir Ghosh, Partho Sarathi Gooh Pattader i Dipankar Bandyopadhyay. "Electric field mediated von Kármán vortices in stratified microflows: transition from linear instabilities to coherent mixing". Journal of Fluid Mechanics 865 (18.02.2019): 169–211. http://dx.doi.org/10.1017/jfm.2018.1023.
Pełny tekst źródłaStreszczenie:
Application of an electric field across the pressure-driven stratified flow of a pair of miscible fluids inside a microchannel manifests interesting electrohydrodynamic (EHD) instabilities. Experiments uncover distinctive instability regimes with an increase in electric field Rayleigh number ($Ra^{\unicode[STIX]{x1D713}}$) – a linear-onset regime, a time-periodic nonlinear regime analogous to the von Kármán vortex street in the downstream and a regime with coherent flow patterns. The experiments also reveal that such linear and nonlinear instabilities can be stimulated non-invasively in a microchannel to mix or de-mix fluids simply by turning the electric field on or off, indicating the suitability of the process for on-demand micromixing. The characteristics of these instabilities have been theoretically investigated with the help of an Orr–Sommerfeld framework, which discloses the possibility of five distinctive finite-wavenumber modes for the instability. The EHD stresses originating due to the application of electric field stimulate a pair of shorter-wavelength electric field modes beyond a critical value of $Ra^{\unicode[STIX]{x1D713}}$. Increase in the levels of charge injection and EHD stresses lower the critical $Ra^{\unicode[STIX]{x1D713}}$ of these modes. The relatively longer-wavelength viscous mode is found to appear when the viscosity stratification between the fluid layers is high. Beyond a threshold Schmidt number ($Sc$), a diffusive mode is also found to appear near the mixed interfacial region. A thinner interface between the fluids at a higher $Sc$ helps this mode to behave as the interfacial mode of immiscible fluids. Contrast of ionic mobility in the fluids leads to the appearance of the K-mode of instability at much shorter wavelengths. The reported phenomena can be of significance in the domains of microscale mixing, pumping, heat exchange, mass transfer and reaction engineering.
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Moatimid, Galal M., i Mohamed A. Hassan. "The Instability of an Electrohydrodynamic Viscous Liquid Micro-Cylinder Buried in a Porous Medium: Effect of Thermosolutal Marangoni Convection". Mathematical Problems in Engineering 2013 (2013): 1–14. http://dx.doi.org/10.1155/2013/416562.
Pełny tekst źródłaStreszczenie:
The electrohydrodynamic (EHD) thermosolutal Marangoni convection of viscous liquid, in the presence of an axial electric field through a micro cylindrical porous flow, is considered. It is assumed that the surface tension varies linearly with both temperature and concentration. The instability of the interface is investigated for the free surface of the fluid. The expression of the free surface function is derived taking into account the independence of the surface tension of the heat and mass transfer. The transcendental dispersion relation is obtained considering the dependence of the surface tension on the heat and mass transfer. Numerical estimations for the roots of the transcendental dispersion relation are obtained indicating the relation between the disturbance growth rate and the variation of the wave number. It is found that increasing both the temperature and concentration at the axial microcylinder has a destabilizing effect on the interface, according to the reduction of the surface tension. The existence of the porous structure restricts the flow and hence has a stabilizing effect. Also, the axial electric field has a stabilizing effect. Some of previous analytical and experimental results are recovered upon appropriate data choices.
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He, Xuerao, Pedro A. Vázquez i Mengqi Zhang. "Numerical analyses of wire-plate electrohydrodynamic flows". Journal of Fluid Mechanics 966 (27.06.2023). http://dx.doi.org/10.1017/jfm.2023.419.
Pełny tekst źródłaStreszczenie:
We present numerical analyses of two-dimensional electrohydrodynamic (EHD) flows of a dielectric liquid between a wire electrode and two plate electrodes with a Poiseuille flow, using direct numerical simulation and global stability analysis. Both conduction and injection mechanisms for charge generation are considered. In this work we focused on the intensity of the cross-flow and studied the EHD flows without a cross-flow, with a weak cross-flow and with a strong cross-flow. (1) In the case without a cross-flow, we investigated its nonlinear flow structures and linear dynamics. We found that the flow in the conduction regime is steady, whereas the flow in the injection regime is oscillatory, which can be explained by a global stability analysis. (2) The EHD flow with a weak cross-flow is closely related to the flow phenomena in an electrostatic precipitator (ESP). Our analyses indicate that increasing the cross-flow intensity or the electric Reynolds number leads to a less stable flow. Based on these results, we infer that one should adopt a relatively low voltage and weak cross-flow in the wire-plate EHD flow to avoid flow instability, which may hold practical implications for ESP. (3) The case of strong cross-flow is examined to study the EHD effect on the wake flow. By comparing the conventional cylindrical wake with the EHD wake in linear and nonlinear regimes, we found that the EHD effect brings forward the vortex shedding in wake flows. Besides, the EHD effect reduces the drag coefficient when the cross-flow is weak, but increases it when it is strong.
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Kano, Ichiro. "Effect of Electric Field Distribution Generated in a Microspace on Pool Boiling Heat Transfer". Journal of Heat Transfer 136, nr 10 (15.07.2014). http://dx.doi.org/10.1115/1.4027881.
Pełny tekst źródłaStreszczenie:
This study describes the effect of an electric field on nucleate boiling and critical heat flux (CHF) in pool boiling. A dielectric liquid of AE-3000 was used as the working fluid. A heating surface was polished to a surface roughness of 0.05 μm. A microsized electrode, in which slits were provided, was designed to generate a nonuniform electric field and produce electrohydrodynamic (EHD) effects with the application of high dc voltages. The obtained results confirmed CHF enhancement as the EHD effects increased CHF to 86.2 W/cm2 with a voltage of −3000 V, which was four times greater than pool boiling in the absence of the electrode. The usual traveling wave on the bubble interface, induced by the Kelvin–Helmholtz instability, was modified by adding the EHD effects. The traveling wave model exhibits the essential features of the phenomenon and shows good agreement with the experimental data.
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Kano, Ichiro, Yuta Higuchi i Tadashi Chika. "Development of Boiling Type Cooling System Using Electrohydrodynamics Effect". Journal of Heat Transfer 135, nr 9 (26.07.2013). http://dx.doi.org/10.1115/1.4024390.
Pełny tekst źródłaStreszczenie:
This paper describes results from an experimental study of the effect of an electric field on nucleate boiling and the critical heat flux (CHF) in pool boiling at atmospheric pressure. A dielectric liquid of HFE-7100 (3 M Co.) was used as working fluid. A heating surface was polished with the surface roughness (Ra) of 0.05 μm. A microsized electrode, in which the slits were provided, was designed in order to generate non uniform high electric fields and to produce electrohydrodynamic (EHD) effects with the application of high voltages. The obtained results confirmed the enhancement of CHF since the EHD effects increased the CHF to 47 W/cm2 at the voltage of −1500 V, which was three times as much as CHF for the free convection boiling. From the observations of the behavior of bubbles over the electrode and of the boiling surface condition, the instability between the liquid and the vapor increased the heat flux, the heat transfer coefficient (HTC), and the CHF. The usual traveling wave on the bubble interface induced by the Kelvin-Helmholtz instability was modified by adding the EHD effects. The ratio of critical heat flux increase with and without the electric field was sufficiently predicted by the frequency ratio of liquid–vapor surface at the gap between the boiling surface and the electrode.
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Wang, Zhentao, Qian Kong, Bin Li, Jiameng Tian, Kai Yu i Junfeng Wang. "Electrohydrodynamic instability and disintegration of low viscous liquid jet". Physics of Fluids, 7.11.2022. http://dx.doi.org/10.1063/5.0130381.
Pełny tekst źródłaStreszczenie:
The simple-jet mode can be developed from dripping, dripping faucet (transition), and jetting when subjected to a sufficient strong electric field caused by needle-plated electrode. In present work, the instability and disintegration of an electrified jet of anhydrous ethanol in the electrohydrodynamic (EHD) simple-jet mode are visualized by high-speed camera. A systematic analysis and description on the evolution of the breakup morphology of the charged jet in the simple-jet mode was carried out. In dripping mode at low Weber number, the unstable simple-jet occurs, while the stable simple-jet mode happens as Weber number higher than critical value. In dripping faucet and jetting regime, the simple-jet mode can easily take place, and jet undergoes typical breakup modes including varicose, whipping, whipping assisted bifurcation and ramified instabilities as electric potential increasing. The growth rate of the maximum perturbation of the zero-, first- and second-order surface waves determines the type of the instabilities. The operating window of the simple-jet mode is presented to indicate that the simple-jet mode only operates in the suitable range of Weber number and electric Bond number. The spray characteristics including envelope angle, droplet size and the stable length of the electrified jet have been explored to demonstrate the uniform drops could be generated in the simple-jet regime. The evolution from the cone-jet to the simple-jet mode is also observed when a special hemispherical nozzle is used. For an almost stable electric potential, the cone-jet can gradually transform into the simple-jet with an increase in liquid flowrate.
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Kano, Ichiro, i Naoki Okamoto. "Experimental Verification of a Prediction Model for Pool Boiling Enhanced by the Electrohydrodynamic Effect and Surface Wettability". Journal of Heat Transfer 139, nr 8 (11.04.2017). http://dx.doi.org/10.1115/1.4036040.
Pełny tekst źródłaStreszczenie:
Enhancing of boiling heat transfer by combining the electrohydrodynamic (EHD) effect and surface wettability has been shown to remove the high heat fluxes from electrical devices such as laser diodes, light emitting diodes, and central processing units. However, this phenomenon is not well understood. Our previous studies on the critical heat flux (CHF) of pool boiling have shown that CHF greatly increases with the application of an electric field and that the wall temperature can be decreased to a level with the safe operation of the electrical devices by using a low contact angle with the boiling surface. To verify the earlier prediction model, CHF enhancement by changing the contact angle with the boiling surface and by the application of an electric field was investigated. A fluorinated dielectric liquid (Asahi Glass Co. Ltd, Tokyo, Japan, AE-3000) was selected as the working fluid. To allow the contact angle between the boiling surface and the dielectric liquid to be changed, several different materials (Cu, Cr, NiB, Sn) and a surface coated with a mixture of 1.5 and 5 μm diamond particles were used as boiling surfaces. The CHFs at different contact angles were 20.5–26.9 W/cm2, corresponding to 95–125% of that for a polished Cu surface (21.5 W/cm2). Upon application of a −5 kV/mm electric field to the microstructured surface (the mixture of 1.5 μm and 5 μm diamond particles), a CHF of 99 W/cm2 at a superheat of 33.5 K was obtained. Based on this experimental evidence, we normalized the CHF and contact angle using our previously developed hydrodynamic instability model and semi-empirical model derived from the interfacial area density close to the boiling surface. This procedure allowed us to develop a general model that predicted CHF well, including the CHF for the de-ionized (DI) water.
Rozprawy doktorskie na temat "Electrohydrodynamic (EHD) instability"
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Rath, Pranaya Kishore. "Experimental Investigation of Electrons In and Above Liquid Helium". Thesis, 2022. https://etd.iisc.ac.in/handle/2005/5838.
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Electrons on the surface of liquid helium form a nearly ideal 2-dimensional electron system (2DES). An electron density up to 2 × 10^9 cm-2, known as the critical electron density, can be achieved on the liquid helium surface, above which an electro-hydrodynamic (EHD) instability sets in, which results in the formation of MEBs. Due to this limitation in maximum possible density, only the classical liquid and solid phases of the 2DES can be accessed in this system.
But at the same time, on the surface of thin liquid helium film and with the multi-electron bubbles (MEBs), it may be possible to achieve high electron density than that of the critical electron density. This can allow the observation of quantum melting, i.e., the phase transition between the quantum solid to the liquid phase of the 2DES. Although extensive theoretical and experimental studies have already been done, the quantum melting transition has not been
achieved experimentally on these systems yet. In this thesis, we have used multiple new experimental approaches to obtain electron densities higher than what has been achieved before and to study the MEBs effectively.
First, we studied the temporal dynamics of the EHD instability and the effect of the applied electric field and charge density on the instability. The unstable wave vectors were determined experimentally, and their temporal growth was studied carefully. The determined unstable wave vectors were found to be a good match with the theoretically expected values obtained from the dispersion relation. At the same time, the analysis of the growth rate of unstable
vectors were found to be limited by the kinematic viscosity of the liquid helium.
Next, we investigated the lifetime of MEBs trapped on a dielectric surface and compared the result with previous results on free bubbles in bulk liquid helium. The reduced lifetime of trapped bubbles suggested an impact of convective heat flow around the bubbles on their lifetimes. Then we performed an experimental investigation that confirmed the effect of
convective heat flow direction inside the experimental cell on the lifetime of such trapped MEBs. Determination of the electronic phase inside an MEB is one of the biggest challenges of the time. Unfortunately, there is no direct way or technique for such investigation. We discussed how the MEB surface fluctuation with an external oscillating electric field could be observed, which may allow a possible way of studying the phase of the 2DES. We studied the surface fluctuations of electrically excited MEBs and observed different normal mechanical modes of the bubble wall. Then we extended our discussion on why liquid helium-4 is not a suitable medium to study the MEBs at low temperatures (below λ), where interesting phenomena occur, and how liquid helium-3, based on its physical property, can be a suitable replacement for this purpose. We generated MEBs inside liquid helium for the first time. The generated MEBs at 1.1 K were found to be stable with long lifetimes. This result opens the possibility of studying the MEBs at much lower temperatures where quantum properties dominate over classical for the 2DES.
Finally, we discussed the problem associated with achieving high electron density on the thin helium film and how integrating an NEA material as a substrate can help us overcome the problem. We fabricated NEA materials, i.e., cBN pellet, and optimized the rf sputtering deposition of cBN film. We performed a preliminary pick-up measurement on the charged thin helium with these materials as substrates, which showed some positive indications that need to
be confirmed with further advanced experimental investigations.INSPIRE, DST India
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Thenkarai, Narayanan Venkat raman. "Numerical modeling of microfluidic two-phase electrohydrodynamic instability". 2010. http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.000052156.
Pełny tekst źródłaStreszczenia konferencji na temat "Electrohydrodynamic (EHD) instability"
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Reddy, Varun, i Jeffrey D. Zahn. "Two Phase Electrohydrodynamic Instability Micromixing". W ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-80493.
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This work characterizes two phase electrohydrodynamic (EHD) instability micromixing of two immiscible organic and aqueous fluid phases. EHD mixing of the two phase microflow is promoted by creating an unstable flow profile by electrically inducing motion of the phase boundary. The aqueous phase is assumed to be infinitely conducting due to dissolved salt ions, while the organic phase is assumed to be non-conducting. As electrodes are biased, charges accumulate at the aqueous/organic interface. At a critical voltage the interface becomes unstable so that the aqueous and organic layers will mix. This is modeled for both inviscid and viscous flows using linear stability analysis considering the interfacial kinematic and stress conditions which predicts the stability criteria with a range of unstable wavenumbers which may be excited The mixing of an unstable “sausaging” and “kink” modes are visualized using epifluorescent microscopy of the dyed organic phase. The characteristic unstable wavenumbers predicted using linear stability theory are determined from the power spectrum of the captured images and compared to the analytical model. Onset of instability is seen at 40 volts RMS at a frequency of 250 kHz. This voltage corresponds to an electric field of Eo = 8 × 105 V/m across the organic phase. The instability becomes progressively more dynamic as the field strength is increased. The system recovers after the field is removed. At low field strengths the theoretical field and fastest growth wavenumbers for mixing compares favorably with the initially applied field whereas at higher field strengths the theoretical field is much larger than the initially applied field. This is attributed to the larger level of mixing and the ability of the instability to grow beyond the linear range while the electric field increases as the mixing process occurs due to entrainment of highly conductive fluid decreasing the effective dielectric spacing.
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Narayanan, Venkat R. T., Jianbo Li, Jeffrey D. Zahn i Hao Lin. "Numerical Modeling of Microfluidic Two-Phase Electrohydrodynamic Instability". W ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-67757.
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Organic-aqueous liquid (phenol) extraction is one of many standard techniques to efficiently purify DNA directly from cells. Effective dispersion of one fluid phase in the other increases the surface area over which biological component partitioning may occur, and hence enhances DNA extraction efficiency. Electrohydrodynamic (EHD) instability can be harnessed to achieve this goal and has been experimentally demonstrated by one of the co-authors (JDZ). In this work, analysis and simulation are combined to study two-phase EHD instability. In the problem configuration, the organic (phenol) phase flows into the microchannel in parallel with and sandwiched between two aqueous streams, creating a three-layer planar geometry; the two liquid phases are immiscible. An electric field is applied to induce instability and to break the organic stream into droplets. The Taylor-Melcher leaky-dielectric model is employed to investigate this phenomenon. A linear analysis is carried out with a Chebyshev pseudo-spectral method, whereas a fully nonlinear numerical simulation is implemented using a finite volume, immersed boundary method (IBM). The results from both models compare favorably with each other. The linear analysis reveals basic instability characteristics such as kink and sausage modes. On the other hand, the nonlinear simulation predicts surface deformation in the strongly nonlinear regime pertinent to droplet formation. These numerical tools will be used to investigate the effects of the applied electric field, geometry, and convective flow rate on mixing and dispersion. The eventual objective is to maximize surface area of the organic phase under given experimental conditions for optimized DNA extraction.
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Kano, Ichiro, i Kyohei Sato. "Effect of Electric Field Distribution Generated in a Micro Space on Pool Boiling Heat Transfer". W ASME 2013 11th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/icnmm2013-73118.
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This paper describes results from an experimental study of the effect of an electric field on nucleate boiling and the critical heat flux (CHF) in pool boiling. A dielectric liquid of AE-3000 (AGC Co. Ltd) was used as working fluid. A heating surface was polished with the surface roughness (Ra) of 0.05 μm. A micro sized electrode, in which the slits were provided, was designed in order to generate non uniform electric field and to produce electrohydrodynamic (EHD) effects with the application of high dc voltages. The obtained results confirmed the enhancement of CHF since the EHD effects increased the CHF to 82 W/cm2 at the voltage of −3000 V, which was four times greater than CHF for the pool boiling. The usual traveling wave on the bubble interface induced by the Kelvin-Helmholtz instability was modified by adding the EHD effects.
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Yajima, Takeshi, Akira Yabe i Hiroshi Maki. "Theoretical Model of Electric Field Effects on the Enhancement of Critical Heat Flux". W ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-60080.
Pełny tekst źródłaStreszczenie:
Critical heat flux enhancement by the electrohydrodynamic (EHD) effect has been analyzed quantitatively based on the increased frequency of liquid-vapor interface oscillations around the edge of the bubble. The majority of heat transfer occurs when the liquid film thickness becomes less than 50 μ m, which only occurs once per period. The main mechanism of heat flux enhancement induced by the EHD effect would be a result of an increase in surface tension due to the effect of electric lines of force. By representing the terms of the forces for a change in curvature and the surface tension resulting from the electric lines of force, the equation of the liquid-vapor instability was obtained and analyzed. Experimentally it has been shown that as the applied voltage increased, the periodic time interval of the thickness change was shortened. This effect reduces the potential for dryout of the liquid film by making the minimum thickness time period shorter. By measuring the pressure oscillation on the boiling surface, the change of the thin liquid film thickness and the dynamic shape of bubbles, the relationship among the pressure, the liquid film thickness and the bubble shape was clarified. Consequently, this model successfully explains the relationship between the applied voltage and the enhancement of the critical heat flux.
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Cândido, Sílvio, i José C. Páscoa. "Numerical Analysis on the Stability Conditions of an Electrohydrodynamic Jet". W ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-24101.
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Abstract The Taylor cone jet is a well-known electrohydrodynamic flow (EHD), usually produced by applying an external electric field to a capillary liquid. The generation of this kind of flow involves a multi-phase and a multi-physics process and its stability has a specific operation window. This operating window is intrinsically dependent on the flow rate and magnitude of the applied electric voltage. In case high voltages are applied to the jet it can atomize and produce an electrospray. Our work presents a numerical study of the process of atomization of a Taylor cone jet using computational fluid dynamics (CFD). The study intents to assess the limit conditions of operation and the applied voltage needed to stabilize an electrospray. The numerical model was implemented within OpenFOAM, where the multi-phase hydrodynamics equations are solved using a volume-of-fluid (VOF) approach. This method is coupled with the Maxwell equations governing an electrostatic field, in order to incorporate the electric body forces into the incompressible Navier-Stokes equations. The leaky-dielectric model is used and, therefore, the interface between the two phases is subject to the hydrodynamic surface tension and electric stress (Maxwell stress). This allows a leakage of charge though the phase due to ohmic conduction. Thus, the permittivity and conductivity of the phases are taken into consideration. A two-fluid system with relevant electric properties can be categorized as, dielectric-dielectric, dielectric-conducting, and conducting-conducting considering the electrical conductivity and permittivities of the participating phases. Due to the usage of the leaky-dielectric model, it is possible to simulate any of this physical situations. By increasing the applied voltage reaches a value where the cone instability is verified, allowing a discussion on this effect. It is demonstrated that to adequately model the process of atomization a fine grid refinement is needed. The validation of the numerical model is made by comparing against diverse experimental data, for the case of a stable jet. The diameter and velocity of the droplet and the electric current of the jet are the main variables that are compared with previous results. The tests were performed with Heptane. The cone and the jet are strongly affected by the flow rate. The dimensionless diameter, as a function of the dimensionless flow rate, agrees with the scaling laws. The model predicts accurate results over a wide range of flow rates with an accuracy of around 10%. The results are obtained using structured meshes.
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Morales, Mercedes C., i Jeffrey D. Zahn. "Development of a Diffusion Limited Microfluidic Module for DNA Purification via Phenol Extraction". W ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-68086.
Pełny tekst źródłaStreszczenie:
Purification of Deoxyribonucleic acid (DNA) by organic-aqueous liquid extraction, also called phenol extraction, is a standard technique commonly utilized in biology laboratories. In order to minimize interaction energies, membrane components and proteins naturally partition to the organic (phenol) phase while the DNA stays in the aqueous phase, where it can be easily removed. In recent years, microfluidics has become a driving force toward more efficient and autonomous platforms for fluid based diagnostics, chemical reaction chambers, separation and preparation of biological materials. In this work, fabrication, and performance of a long microfluidic device for DNA extraction are presented. The devices were fabricated using soft lithography to transfer lithographically defined features into a PDMS structure via replica molding. Stratified-flow experiments using a rhodamine dye conjugated bovine serum albumin protein (BSA) in an aqueous phase were conducted to demonstrate the ability to remove proteins from the aqueous phase into the phenol phase. Additionally, the study of BSA partitioning and DNA isolation in a two-phase system under stratified flow condition were presented, separately and conjunctly. Finally, protein partitioning and DNA recovery obtained with this device could be compared with other types of mixing and extraction such as mixing by droplet formation and electrohydrodynamic (EHD) instability.
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Kano, Ichiro, Yuta Higuchi i Tadashi Chika. "Development of Boiling Type Cooling System Using Electrostatic and Electroconvection Force". W ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/mnhmt2012-75038.
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The paper describes results from an experimental study of the effect of an electric field on nucleate boiling and the critical heat flux (CHF) in pool boiling at atmospheric pressure with polished smooth boiling surface. A micro scaled electrode with slits for bubbles to come out was designed in order to create non uniform high electric field strength and to produce electrohydrodynamics (EHD) convection with the application of dc voltage. The application of high electric field strongly enhanced the heat flux and the heat transfer coefficient. From observations of the behavior of bubbles over the electrode and the boiling surface condition, the instability between the liquid and the vapor increased the heat flux, the heat transfer coefficient and the CHF.