scholarly journals Single-bubble EHD behavior into water two-phase flow under electric-field stress and gravitational acceleration using PFM

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Maryam Aliakbary Mianmahale ◽  
Arjomand Mehrabani-Zeinabad ◽  
Masoud Habibi Zare ◽  
Mahdi Ghadiri
Keyword(s):  
Heat Flux ◽  
Electric Field ◽  
Contact Angles ◽  
Temperature Fields ◽  
Single Bubble ◽  
Phase Field Method ◽  
Time Interval ◽  
Gravitational Acceleration ◽  
Two Phase ◽  
Field Stress

AbstractIn this study, single-bubble electro-hydrodynamic effects on the two-phase laminar flow of water under electric field stress are investigated using numerical modeling. A 2D axisymmetric model is also developed to study the growth and departure of a single bubble. The phase-field method is applied to track the interphase between liquid and gas. The growth of the attached vapor bubble nucleus to a superheat at 7.0 °C and 8.5 °C are evaluated with 50° and 90° contact angles. The results show that the enhancement of the contact angle changes the velocity and temperature fields around the bubble. It is observed that the growing size and base of the bubble is increased with increasing the wall superheat, but the bubble departure diameter and time are decreased. The electric field results in raising the number of detached bubbles from the superheat at a certain time interval but decreasing the bubbles departure size. Additionally, the formation of stretched bubbles enhances the rate of heat flux and there is a non-linear relationship between the applied voltage and heat flux.

scholarly journals Dynamics Behaviors of Droplet on Hydrophobic Surfaces Driven by Electric Field

Micromachines ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 778 ◽  
Author(s):  
Jie Liu ◽  
Sheng Liu
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Substrate Surface ◽  
Contact Angles ◽  
Droplet Microfluidics ◽  
Phase Field Method ◽  
Sessile Droplet ◽  
Hydrophobic Surfaces ◽  
Droplet Motion ◽  
Plate Electrode

Droplet microfluidic technology achieves precise manipulation of droplet behaviors by designing and controlling the flow and interaction of various incompatible fluids. The electric field provides a non-contact, pollution-free, designable and promising method for droplet microfluidics. Since the droplet behaviors in many industrial and biological applications occur on the contact surface and the properties of droplets and the surrounding environment are not consistent, it is essential to understand fundamentally the sessile droplet motion and deformation under various conditions. This paper reports a technique using the pin-plate electrode to generate non-uniform dielectrophoresis (DEP) force to control sessile droplets on hydrophobic surfaces. The electrohydrodynamics phenomena of the droplet motion and deformation are simulated using the phase-field method. It is found that the droplet moves along the substrate surface to the direction of higher electric field strength, and is accompanied with a certain offset displacement. In addition, the effect of pin electric potentials, surface contact angles and droplet volumes on the droplet motion and deformation are also studied and compared. The results show that higher potentials, more hydrophobic surfaces and larger droplet volumes exhibit greater droplet horizontal displacement and offset displacement. But for the droplet vertical displacement, it is found that during the first revert process, the release of the surface tension can make the droplet with low potentials, small contact angles or small droplet volumes span from negative to positive. These results will be helpful for future operations encountered in sessile droplets under non-uniform electric fields towards the droplet microfluidics applications.

Two-Phase Flow of Dusty Casson Fluid with Cattaneo-Christov Heat Flux and Heat Source Past a Cone, Wedge and Plate

2018 ◽  
Vol 387 ◽  
pp. 625-639 ◽  
Author(s):  
B. Mahanthesh ◽  
Oluwole Daniel Makinde ◽  
Bijjanal Jayanna Gireesha ◽  
Koneri L. Krupalakshmi ◽  
Isaac Lare Animasaun
Keyword(s):  
Heat Flux ◽  
Differential Equations ◽  
Heat Source ◽  
Regression Line ◽  
Casson Fluid ◽  
Temperature Fields ◽  
Dust Particles ◽  
Integration Scheme ◽  
Physical Parameters ◽  
Two Phase

This article addresses the boundary layer flow and heat transfer in Casson fluid submerged with dust particles over three different geometries (vertical cone, wedge and plate). The aspects of Cattaneo-Christov heat flux and exponential space-based heat source (ESHS) are also accounted. At first, the partial differential equations are transformed into a set of ordinary differential equations via appropriate similarity transformations. Resulting equations are solved via shooting method coupled with the Runge-Kutta-Fehlberg-45 integration scheme. The consequences of dimensionless parameters on velocity and temperature fields of both fluid and dust particles phase are analyzed. The rate of increment/decrement in the skin friction as well as the Nusselt number for various values of physical parameters are also estimated via slope of linear regression line using data points.

scholarly journals Critical heat flux enhancement in microgravity conditions coupling microstructured surfaces and electrostatic field

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Alekos Ioannis Garivalis ◽  
Giacomo Manfredini ◽  
Giacomo Saccone ◽  
Paolo Di Marco ◽  
Artyom Kossolapov ◽  
...  
Keyword(s):  
Heat Flux ◽  
Electric Field ◽  
Critical Heat Flux ◽  
Electric Fields ◽  
Parabolic Flight ◽  
Dielectric Fluid ◽  
Two Phase ◽  
Microstructured Surfaces ◽  
Microgravity Conditions ◽  
Plain Surface

AbstractWe run pool boiling experiments with a dielectric fluid (FC-72) on Earth and on board an ESA parabolic flight aircraft able to cancel the effects of gravity, testing both highly wetting microstructured surfaces and plain surfaces and applying an external electric field that creates gravity-mimicking body forces. Our results reveal that microstructured surfaces, known to enhance the critical heat flux on Earth, are also useful in microgravity. An enhancement of the microgravity critical heat flux on a plain surface can also be obtained using the electric field. However, the best boiling performance is achieved when these techniques are used together. The effects created by microstructured surfaces and electric fields are synergistic. They enhance the critical heat flux in microgravity conditions up to 257 kW/m2, which is even higher than the value measured on Earth on a plain surface (i.e., 168 kW/m2). These results demonstrate the potential of this synergistic approach toward very compact and efficient two-phase heat transfer systems for microgravity applications.

Surface Wettability Effects in Heat and Fluid Flow

2006 ◽  
Author(s):  
Yasuyuki Takata
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Two Phase Flow ◽  
Contact Angles ◽  
Bubble Nucleation ◽  
Surface Wettability ◽  
Water Repellent ◽  
Phase Flow ◽  
Two Phase ◽  
Wide Range

Effects of surface wettability on liquid-vapor phase change phenomena and single- and two-phase flow in tube have been studied in wide range of contact angles using superhy drophilic (SH) and super-water-repellent (SWR) surfaces. Heat transfer in falling film evaporation on a TiO2-coated SH surface is tremendously enhanced due to very thin stable film. In pool bioling, critical heat flux (CHF) and minimum heat flux (MHF) increase with the decrease in contact angle. Wetting limit temperature of water drop on heated surface increases with the decrease in contact angle. In pool boiling on SWR surface, bubble nucleation and film boiling occur in extremely small superheating. Drag reduction was observed in water flow in tube with SWR coating in laminar flow region, and on the other hand, in two-phase flow pressure drop for the SH wall is smaller than that for the SWR wall.

scholarly journals A Photographic Study of Boiling in an Accelerating System

1965 ◽  
Vol 87 (3) ◽  
pp. 374-380 ◽  
Author(s):  
W. A. Beckman ◽  
H. Merte
Keyword(s):  
Heat Flux ◽  
Growth Rates ◽  
Bubble Growth ◽  
High Speed ◽  
Pool Boiling ◽  
Motion Pictures ◽  
Heating Surface ◽  
Contact Angles ◽  
Gravitational Acceleration ◽  
Centrifugal Acceleration

Pool boiling of distilled and degassed water in an accelerating system was studied by means of high speed motion pictures, up to 20,000 frames per sec. The acceleration was produced by the centrifuge principle with the heating surface oriented normal to the vectorial sum of the centrifugal acceleration and the gravitational acceleration. The range of experimental variables include: heat flux between 16,000 and 72,000 Btu/hr-ft2, acceleration between one and 100 times standard gravitational acceleration, and subcooling of 2 and 10 deg F. From the photographs, data are presented on bubble growth rates, departure sizes, frequency of formation, and departure contact angles.

scholarly journals Control temperature fluctuations in two-phase CuO-water nanofluid by transfiguration of the enclosures

2020 ◽  
pp. 334-334
Author(s):  
Hadi Pourziaei Araban ◽  
Javad Alinejad ◽  
Ganji Domiri
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Wall Temperature ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Temperature Fields ◽  
Two Phase ◽  
Flux Boundary Condition

The innovation of this paper is to simulate two-phase nanofluid natural convection inside the transformable enclosure to control the heat transfer rate under different heat flux. Heat transfer of a two-phase CuO-water nanofluid in an enclosure under different heat flux has many industrial applications including energy storage systems, thermal control of electronic devices and cooling of radioactive waste containers. The Lattice Boltzmann Method based on the D2Q9 method has been utilized for modeling velocity and temperature fields. Streamlines, isotherms and nanoparticle volume fraction, have been investigated for control the heat transfer rate for several cases. The purpose of this feasibility study is to achieve uniform temperature profiles and Tmax < 50?C under different heat flux. Natural convection heat transfer in the rectangular and parallelogram enclosures with positive and negative angular adiabatic walls were simulated. The average wall temperature under heat flux boundary condition has been studied to predict optimal levels of effective factors to control the maximum wall temperature. The results illustrated parallelogram enclosures with positive angle of case 1 and case 3 and 4 with rectangular enclosures were best cases for considering physical conditions. Average of temperature for these cases were 37.9, 29.7 and 38.2, respectively.

Thermal Control Utilizing an Electrohydrodynamic Conduction Pump in a Two-Phase Loop With High Heat Flux Source

2004 ◽  
Author(s):  
Seong-il Jeong ◽  
Jeffrey Didion
Keyword(s):  
Heat Flux ◽  
Electric Field ◽  
Axial Flow ◽  
Thermal Control ◽  
High Heat ◽  
High Heat Flux ◽  
Recombination Reaction ◽  
Two Phase ◽  
New Device ◽  
Dielectric Fluids

The electric field applied in dielectric fluids causes an imbalance in the dissociation-recombination reaction generating free space charges. The generated charges are redistributed by the applied electric field resulting in the heterocharge layers in the vicinity of the electrodes. Proper design of the electrodes generates net axial flow motion pumping the fluid. The electrohydrodynamic (EHD) conduction pump is a new device that pumps dielectric fluids utilizing heterocharge layers formed by imposition of electrostatic fields. This paper evaluates the experimental performance of a two-phase breadboard thermal control loop consisting of an EHD conduction pump, condenser, pre-heater, high heat flux evaporator (HE), transport lines, and reservoir (accumulator). The generated pressure head and the maximum applicable heat flux are experimental determined at various applied voltages and sink temperatures. Recovery from dryout condition by increasing the applied voltage to the pump is also demonstrated.

scholarly journals On heat transfer to pulsatile flow of a two-phase fluid

2005 ◽  
Vol 2005 (15) ◽  
pp. 2497-2510
Author(s):  
A. K. Ghosh ◽  
S. P. Chakraborty
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pulsatile Flow ◽  
Particle System ◽  
Temperature Fields ◽  
Two Phase ◽  
Unsteady Temperature ◽  
Flow Parameters ◽  
Temperature Distributions ◽  
Phase Fluid

The problem of heat transfer to pulsatile flow of a two-phase fluid-particle system contained in a channel bounded by two infinitely long rigid impervious parallel walls has been studied in this paper. The solutions for the steady and the fluctuating temperature distributions are obtained. The rates of heat transfer at the walls are also calculated. The results are discussed numerically with graphical presentations. It is shown that the presence of the particles not only diminishes the steady and unsteady temperature fields but also decreases the reversal of heat flux at the hotter wall irrespective of the influences of other flow parameters.

Thermal Control Utilizing an Electrohydrodynamic Conduction Pump in a Two-Phase Loop With High Heat Flux Source

2007 ◽  
Vol 129 (11) ◽  
pp. 1576-1583 ◽  
Author(s):  
Seong-II Jeong ◽  
Jeffrey Didion
Keyword(s):  
Heat Flux ◽  
Electric Field ◽  
Thermal Control ◽  
High Heat ◽  
High Heat Flux ◽  
Recombination Reaction ◽  
Two Phase ◽  
New Device ◽  
Dielectric Fluids ◽  
Phase Loop

The electric field applied in dielectric fluids causes an imbalance in the dissociation-recombination reaction generating free space charges. The generated charges are redistributed by the applied electric field, resulting in the heterocharge layers in the vicinity of the electrodes. Proper design of the electrodes generates net axial flow motion pumping the fluid. The electrohydrodynamic (EHD) conduction pump is a new device that pumps dielectric fluids utilizing heterocharge layers formed by imposition of electrostatic fields. This paper experimentally evaluates the performance of a two-phase (liquid-vapor) breadboard thermal control loop consisting of an EHD conduction pump, condenser, preheater, evaporator, transport lines, and reservoir (accumulator). This study is performed to address the feasibility of the EHD two-phase loop for thermal control of a laser equipment with high heat flux source. The generated pressure head and the maximum applicable heat flux are experimentally determined at various applied voltages and sink temperatures. Recovery from the evaporator dryout condition by increasing the applied voltage to the pump is also demonstrated. The performance of the EHD conduction pump in this study confirms that the EHD conduction pump can be used as a stand-alone system for high heat flux thermal control.

THE MECHANISM OF RAISING AND QUANTIFICATION OF SPECIFIC HEAT FLUX AT BOILING OF NANOFLUIDS IN FREE CONVECTION CONDITIONS

2017 ◽  
pp. 25-34
Author(s):  
V.N. Moraru
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Capacity ◽  
Specific Heat ◽  
Chemical Properties ◽  
Heating Surface ◽  
Physical Models ◽  
Superheated Liquid ◽  
Two Phase ◽  
Boiling Process

The results of our work and a number of foreign studies indicate that the sharp increase in the heat transfer parameters (specific heat flux q and heat transfer coefficient _) at the boiling of nanofluids as compared to the base liquid (water) is due not only and not so much to the increase of the thermal conductivity of the nanofluids, but an intensification of the boiling process caused by a change in the state of the heating surface, its topological and chemical properties (porosity, roughness, wettability). The latter leads to a change in the internal characteristics of the boiling process and the average temperature of the superheated liquid layer. This circumstance makes it possible, on the basis of physical models of the liquids boiling and taking into account the parameters of the surface state (temperature, pressure) and properties of the coolant (the density and heat capacity of the liquid, the specific heat of vaporization and the heat capacity of the vapor), and also the internal characteristics of the boiling of liquids, to calculate the value of specific heat flux q. In this paper, the difference in the mechanisms of heat transfer during the boiling of single-phase (water) and two-phase nanofluids has been studied and a quantitative estimate of the q values for the boiling of the nanofluid is carried out based on the internal characteristics of the boiling process. The satisfactory agreement of the calculated values with the experimental data is a confirmation that the key factor in the growth of the heat transfer intensity at the boiling of nanofluids is indeed a change in the nature and microrelief of the heating surface. Bibl. 20, Fig. 9, Tab. 2.

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