Effect of a High Electric Field on the Thermal and Phase Change Characteristics of an Impacting Drop

2019 ◽  
Author(s):  
Abhishek Basavanna ◽  
Prajakta Khapekar ◽  
Navdeep Singh Dhillon
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Phase Change ◽  
Electric Fields ◽  
High Speed ◽  
Impact Behavior ◽  
Liquid Drops ◽  
Active Interest ◽  
Post Impact ◽  
High Electric Fields

Abstract The effect of applied electric fields on the behavior of liquids and their interaction with solid surfaces has been a topic of active interest for many decades. This has important implications in phase change heat transfer processes such as evaporation, boiling, and condensation. Although the effect of low to moderate voltages has been studied, there is a need to explore the interaction of high electric fields with liquid drops and bubbles, and their effect on heat transfer and phase change. In this study, we employ a high speed optical camera to study the dynamics of a liquid drop impacting a hot substrate under the application of high electric fields. Experimental results indicate a significant change in the pre- and post-impact behavior of the drop. Prior to impact, the applied electric field elongates the drop in the direction of the electric field. Post-impact, the recoil phase of the drop is significantly affected by charging effects. Further, a significant amount of micro-droplet ejection is observed with an increase in the applied voltage.

Numerical study of electric field effects on the deformation of two-dimensional liquid drops in simple shear flow at arbitrary Reynolds number

2009 ◽  
Vol 626 ◽  
pp. 367-393 ◽  
Author(s):  
STEFAN MÄHLMANN ◽  
DEMETRIOS T. PAPAGEORGIOU
Keyword(s):  
Steady State ◽  
Shear Flow ◽  
Electric Field ◽  
Electric Fields ◽  
Simple Shear ◽  
Simple Shear Flow ◽  
Physical Parameters ◽  
Shear Stresses ◽  
Two Dimensional ◽  
Liquid Drops

The effect of an electric field on a periodic array of two-dimensional liquid drops suspended in simple shear flow is studied numerically. The shear is produced by moving the parallel walls of the channel containing the fluids at equal speeds but in opposite directions and an electric field is generated by imposing a constant voltage difference across the channel walls. The level set method is adapted to electrohydrodynamics problems that include a background flow in order to compute the effects of permittivity and conductivity differences between the two phases on the dynamics and drop configurations. The electric field introduces additional interfacial stresses at the drop interface and we perform extensive computations to assess the combined effects of electric fields, surface tension and inertia. Our computations for perfect dielectric systems indicate that the electric field increases the drop deformation to generate elongated drops at steady state, and at the same time alters the drop orientation by increasing alignment with the vertical, which is the direction of the underlying electric field. These phenomena are observed for a range of values of Reynolds and capillary numbers. Computations using the leaky dielectric model also indicate that for certain combinations of electric properties the drop can undergo enhanced alignment with the vertical or the horizontal, as compared to perfect dielectric systems. For cases of enhanced elongation and alignment with the vertical, the flow positions the droplets closer to the channel walls where they cause larger wall shear stresses. We also establish that a sufficiently strong electric field can be used to destabilize the flow in the sense that steady-state droplets that can exist in its absence for a set of physical parameters, become increasingly and indefinitely elongated until additional mechanisms can lead to rupture. It is suggested that electric fields can be used to enhance such phenomena.

Transient Thermal Characteristics for a Liquid Drop Impacting a Hot PCM Substrate

2018 ◽  
Author(s):  
Abdul Ahad Khan ◽  
Dilip Choudhary ◽  
Abhishek Basavanna ◽  
Salman Najmee ◽  
Jessica Crisantes ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
High Speed ◽  
Liquid Drop ◽  
Imaging Techniques ◽  
Thermal Characteristics ◽  
Heat Of Fusion ◽  
Performance Parameters ◽  
Transient Heating ◽  
Thermal Transients

The physics of the transient behavior of liquid drops impacting hot or cold surfaces are of significance in many different applications such as spray cooling, aircraft icing, etc. Further, the transient heating and cooling of vapor spots and liquid patches is of significance in determining the heat transfer performance parameters in phase change processes such as boiling and condensation. The thermal transients in all these processes are primarily dictated by the passive thermal properties of the solid substrate (e.g. thermal conductivity, specific heat) and by the flow conditions. An active control (or manipulation) of these thermal transients could provide a means to enhance the performance parameters in various phase change-based heat transfer processes. In this study, we experimentally explore the effect of a solid-liquid phase change material (PCM) coating on the thermal characteristics of a liquid drop impacting a hot surface. High-speed optical and infrared imaging techniques are employed for visualizing the flow and measuring the temperatures, respectively. The PCM, depending on its melting temperature and due to its latent heat of fusion, disrupts the normal process of the heating of the drop and cooling of the substrate. The insights obtained from these findings can have a significant impact on several technologies in the areas of phase change-based heat transfer and thermal management.

The extended Rayleigh theory of the oscillation of liquid droplets

1981 ◽  
Vol 104 ◽  
pp. 295-309 ◽  
Author(s):  
C. A. Morrison ◽  
R. P. Leavitt ◽  
D. E. Wortman
Keyword(s):  
Dielectric Constant ◽  
Electric Field ◽  
Frequency Shift ◽  
Electric Fields ◽  
Optical Field ◽  
Liquid Droplets ◽  
Dynamical Equations ◽  
Resonant Frequencies ◽  
Small Oscillations ◽  
Liquid Drops

The Rayleigh theory of oscillation of liquid drops is extended to include the effects of viscosity and a uniform external electric field. The resonant frequencies of the modes of the drop are shown to be shifted by the electric field. The magnitude and sign of the frequency shift depends on the dielectric constant of the drop. The condition for instability of drops in large electric fields is given and found to differ from that given by previous workers. This difference is attributed to the assumption by previous workers that the drops, under the influence of an electric field, distort into ellipsoids of revolution about the field direction. The dynamical equations are derived and the solution for small oscillations is given in an oscillating field and in an amplitude-modulated optical field.

The Influence of External Electric Field on Heat Transfer at Boiling on Non-Uniform Surfaces

2010 ◽  
Author(s):  
Alexey A. Eronin ◽  
Stanislav P. Malyshenko ◽  
Anton I. Zhuravlev
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Electric Fields ◽  
Heated Surface ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Major Mechanism ◽  
External Electric Fields ◽  
Different Types ◽  
Field Traps

Characteristics of heat transfer and hydrodynamics of boiling of liquid nitrogen on the surfaces with different types of non-uniformities at the presence of external electric fields are experimentally investigated. It is shown that the formation of field traps is a major mechanism of heat transfer enhancement. And this effect result in noticeable change of two-phase hydrodynamics in vicinity of heated surface.

A Mathematical Model of Thermal Oil Recovery in Linear Systems

1965 ◽  
Vol 5 (03) ◽  
pp. 196-210 ◽  
Author(s):  
B.S. Gottfried
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Chemical Reaction ◽  
Oil Recovery ◽  
High Speed ◽  
Thermal Recovery ◽  
Recovery Processes ◽  
Three Phase ◽  
Three Phase Flow ◽  
Thermal Oil

Gottfried, B.S., Junior Member AIME, Gulf Research and Development Co., Pittsburgh, Pa. Introduction Thermal oil recovery refers to a class of recovery processes where heat is supplied to a reservoir to provide the necessary expulsive energy. This thermal energy can be supplied externally as steam or hot water, or it can be generated in situ by forward or reverse combustion. In either case, however, thermal recovery processes are characterized by the simultaneous flow of two or three fluid phases in a variable-temperature field, accompanied by possible chemical reaction or phase-change effects. Although a physical understanding of the thermal recovery processes is far from complete, it is possible to construct mathematical models which describe approximately all of the principal physical and chemical phenomena. However, attempts to solve such models, even with high-speed computers, involve formidable mathematical difficulties. Consequently, theoretical solutions have been obtained only for idealized cases in which important physical phenomena are neglected. For example, consider the process of forward in situ combustion. All such theories which have been developed consider only certain aspects of the Process, such as heat transfer, heat transfer with phase change, heat transfer with chemical reaction, or the hydrodynamics of three-phase flow. A general theory including all of the above phenomena has not been developed to date. This paper presents a unified theory of thermal recovery processes in linear systems. A mathematical model is developed which explicitly includes conduction-convection heat transfer with convective external heat loss, chemical reaction between air and oil, aqueous phase change, and the hydrodynamics of three-phase flow. A system of equations is developed which can be solved numerically on a high-speed digital computer, resulting in predicted temperature, pressure, and saturation histories in space and time. The model allows a more detailed simulation of thermal recovery tube experiments than had previously been possible. THEORETICAL DEVELOPMENT Consider the linear flow of gas, water and oil in a homogeneous porous medium. Assume that the oil will react with gaseous oxygen, and that mass is transferred between the water and gas phase by evaporation or condensation. SPEJ P. 196ˆ

OBIC Analysis of Different Edge Terminations of Planar 1.6 kV 4H-SiC Diodes

2007 ◽  
Vol 556-557 ◽  
pp. 1007-1010 ◽  
Author(s):  
Christophe Raynaud ◽  
Daniel Loup ◽  
Phillippe Godignon ◽  
Raul Perez Rodriguez ◽  
Dominique Tournier ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Breakdown Voltage ◽  
High Voltage ◽  
Semiconductor Devices ◽  
Optical Beam ◽  
Induced Current ◽  
Bipolar Diodes ◽  
High Electric Fields ◽  
Optical Beam Induced Current

High voltage SiC semiconductor devices have been successfully fabricated and some of them are commercially available [1]. To achieve experimental breakdown voltage values as close as possible to the theoretical value, i.e. value of the theoretical semi-infinite diode, it is necessary to protect the periphery of the devices against premature breakdown due to locally high electric fields. Mesa structures and junction termination extension (JTE) as well as guard rings, and combinations of these techniques, have been successfully employed. Each of them has particular drawbacks. Especially, JTE are difficult to optimize in terms of impurity dose to implant, as well as in terms of geometric dimensions. This paper is a study of the spreading of the electric field at the edge of bipolar diodes protected by JTE and field rings, by optical beam induced current.

Electrorheology

MRS Bulletin ◽  
1991 ◽  
Vol 16 (8) ◽  
pp. 38-43 ◽  
Author(s):  
Therese C. Jordan ◽  
Montgomery T. Shaw
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
High Speed ◽  
Flow Properties ◽  
Electric Field Effects ◽  
Properties Of Materials ◽  
Strong Electric Fields ◽  
Silica Suspensions ◽  
Type Of Behavior ◽  
Damping Systems

The influence of electric fields on the deformation and flow properties of materials has been a subject of interest for many years. Recently, there has been renewed interest in a particular branch of these electric field effects—the electrorheological (ER) effect. The ER effect is also known as the Winslow effect after its founder Willis Winslow. Winslow observed that applying strong electric fields to nonaqueous silica suspensions activated with a small amount of water caused rapid solidification of the originally fluid material. This type of behavior was seen as instrumental in the development of high-speed valves, reactive damping systems, and a host of other applications.

Electrowetting-Based Coalescence of Droplets During Dropwise Condensation of Humid Air

2019 ◽  
Author(s):  
Enakshi Wikramanayake ◽  
Vaibhav Bahadur
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Electric Fields ◽  
Applied Electric Field ◽  
Growth Dynamics ◽  
Condensation Heat Transfer ◽  
Droplet Growth ◽  
Dropwise Condensation ◽  
Condensation Rate ◽  
Humid Air

Abstract Dropwise condensation yields higher heat transfer coefficients by avoiding the thermal resistance of the condensate film, seen during filmwise condensation. This work explores further enhancement of dropwise condensation heat transfer through the use of electrowetting to achieve faster droplet growth via coalescence of the condensed droplets. Electrowetting is a well understood microfluidic technique to actuate and control droplets. This work shows that AC electric fields can significantly enhance droplet growth dynamics. This enhancement is a result of coalescence triggered by various types of droplet motion (translation of droplets, oscillations of three phase line), which in turn depends on the frequency of the applied AC waveform. The applied electric field modifies droplet condensation patterns as well as the roll-off dynamics on the surface. Experiments are conducted to study early-stage droplet growth dynamics, as well as steady state condensation rates under the influence of electric fields. It is noted that this study deals with condensation of humid air, and not pure steam. Results show that increasing the voltage magnitude and frequency increases droplet growth rate and overall condensation rate. Overall, this study reports more than a 30 % enhancement in condensation rate resulting from the applied electric field, which highlights the potential of this concept for condensation heat transfer enhancement.

scholarly journals Solar and geomagnetic activity effects on mid-latitude F-region electric fields

2008 ◽  
Vol 26 (9) ◽  
pp. 2911-2921 ◽  
Author(s):  
V. V. Kumar ◽  
M. L. Parkinson ◽  
P. L. Dyson ◽  
R. Polglase
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Geomagnetic Activity ◽  
High Speed ◽  
Theoretical Models ◽  
Solar Flux ◽  
Quiet Time ◽  
F Region ◽  
Diurnal Patterns ◽  
Ae Index

Abstract. Diurnal patterns of average F-region ionospheric drift (electric field) and their dependence on solar and geomagnetic activity have been defined using digital ionosonde Doppler measurements recorded at a southern mid-latitude station (Bundoora 145.1° E, 37.7° S geographic, 49° S magnetic). A unique database consisting of 300 907 drift velocities was compiled, mostly using one specific mode of operation throughout 1632 days of a 5-year interval (1999–2003). The velocity magnitudes were generally larger during the night than day, except during the winter months (June–August), when daytime velocities were enhanced. Of all years, the largest drifts tended to occur during the high speed solar wind streams of 2003. Diurnal patterns in the average quiet time (AE<75 nT) meridional drifts (zonal electric field) peaked at up to ~6 m s−1 poleward (0.3 mV m−1 eastward) at 03:30 LST, reversing in direction at ~08:30 LST, and gradually reaching ~10 m s−1 equatorward at ~13:30 LST. The quiet time zonal drifts (meridional electric fields) displayed a clear diurnal pattern with peak eastward flows of ~10 m s−1 (0.52 mV m−1 equatorward) at 09:30 LST and peak westward flows around midnight of ~18 m s−1 (0.95 mV m−1 poleward). As the AE index increased, the westward drifts increased in amplitude and they extended over a greater fraction of the day. The perturbation drifts changed in a similar way with decreasing Dst except the daytime equatorward flows strengthened with increasing AE index, whereas they became weak for Dst<−60 nT. The responses in all velocity components to changing solar flux values were small, but net poleward perturbations during the day were associated with large solar flux values (>192×10−22 W m−2 Hz−1). These results help to more fully quantify the response of the mid-latitude ionosphere to changing solar and geomagnetic conditions, as required to refine empirical and theoretical models of mid-latitude electric fields.

Calculations of Some Transport Coefficients in Simple Semiconductors at Low Temperatures and High Electric Fields

1971 ◽  
Vol 49 (7) ◽  
pp. 876-880 ◽  
Author(s):  
Jyoti Kamal ◽  
Satish Sharma
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Low Temperatures ◽  
Transport Coefficients ◽  
Drift Mobility ◽  
Temperature Dependent ◽  
Hall Constant ◽  
The Difference ◽  
High Electric Fields ◽  
Model Semiconductor

In this paper the authors have calculated Hall mobility, drift mobility, and Hall constant for a non-degenerate simple model semiconductor at low temperatures for an arbitrary electric field strength. Following Paranjape the modified distribution of phonons has been taken into account. The difference between the calculations of transport coefficients made by taking into account the modified phonon distribution and by not taking it into account is quite appreciable at high electric field. Calculations also show that for Ne = 1016/cm3 the mobility of electrons remains temperature dependent.

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