Electric Convection Research Articles

Nonlinear regimes of electric convection of poorly conducting fluids in weightlessness at low frequencies of an electric field

Electrothermal convection in a poorly conducting fluid in an alternating electric field of a horizontal capacitor is studied. The nonlinear regimes of electric convection in weightlessness are studies at low frequencies of the electric field on the basis of the pentamodal model within the framework of the electroconductive charge formation mechanism. Hysteresis transitions between two different synchronous and subharmonic regimes are found to exist. Transitions to chaos occur by means of either interemittance or a subharmonic cascade.

Nonlinear Regimes of Electric Convection of Poorly Conducting Fluids in Weightlessness at Low Frequencies of an Electric Field

Nonlinear Regimes of Electric Convection of Poorly Conducting Fluids in Weightlessness at Low Frequencies of an Electric Field

Investigation of electrohydrodynamic effects on sessile droplet evaporation using the lattice Boltzmann method

Droplet evaporation on hot substrates within an electric field plays an essential role during the electrospray cooling process. However, there is only a vague understanding of electrohydrodynamic (EHD) effects on droplet evaporation. In this paper, the coupled set of governing equations, including the Poisson equations, the energy equations, and the Navier-Stokes equations, is implemented within the lattice Boltzmann (LB) framework to examine the evaporation of leaky dielectric droplets. The contact angle hysteresis (CAH) as well as the influences of fluid-solid conjugate heat transfer are taken into consideration in this model. The method’s accuracy is validated quantitatively by using three basic cases. The results suggest that the sessile droplet could be elongated or flattened under EHD effects. When the droplet is elongated, the acceleration of the rate of evaporation is controlled by the interrelationship between thermal conduction and electric-induced convection in the droplet, i.e., the average Peclet number (Pe) value. As Pe is less than 1.0, the interior of the droplets is controlled by thermal conduction, and the applied electric field would prolong the droplet evaporation time. As Pe is greater than 2.0, the electric convection promotes evaporation compared to neutral droplets. In the case that the droplets are compressed inside the electric field, the evaporation time progressively decreases as the intensity of the electric field increases. These insights help us understand how EHD affects sessile droplet evaporation and illustrate the huge potential of electric fields for thermo-fluid manipulation.

Stable and decoupled schemes for an electrohydrodynamics model

In this paper, we study numerical solutions of an electrohydrodynamics model. The considered model appears in the description of electric convection dynamics arising from unipolar charge injection on the boundary of insulating liquid, which is a coupling of the Navier–Stokes equations, charge transfer equation, and potential energy equation. A class of stable numerical schemes is proposed and analysed for this coupled equation system. The advantage of the proposed schemes is twofold: (1) they are unconditionally stable, consequently the choice of time step size only concerns the accuracy requirement; (2) they decouple the charge density and potential energy from the Navier–Stokes equations, and therefore can be implemented efficiently. The numerical examples provided in the paper show that the proposed schemes achieve the expected convergence rate, and can be used to accurately simulate the changes of flow field and electric field induced by the electrical convection. We first consider the case of constant density, then extend the construction, analysis, and validation of the schemes to the case of variable density.

Модификация критерия подобия электрической конвекции

The paper is devoted to the modification of the previously obtained similarity criterion for electric convection. The criterion depends on the voltage generated at the electrodes, the distance between the electrodes, and the specific electrical resistance of the working medium (liquid hydrocarbon fuel). The modified similarity number includes the temperature difference between the wall and the coolant, as well as the heat transfer coefficient for convection conditions without the use of electric fields. The analysis of the new version of the similarity number of electric convection brings us to the conclusion that the number can be effectively used along with the previously obtained similarity criterion. The paper introduces the results of studies with liquid hydrocarbon fuel TS-1 kerosene under natural and forced convection. Electric convection similarity numbers are compared, new graphs are constructed, and criterion dependences are obtained.

Development of calculation methods of heat transfer under influence of deposit formation and electric convection in a medium of kerosene

Development of calculation methods of heat transfer under influence of deposit formation and electric convection in a medium of kerosene

Mathematical modeling of the influence of non-catalytic dissociation / recombination of water molecules in the desalination channel on electric convection

The article formulates a two-dimensional mathematical model of non-stationary transport of 1: 1 electrolyte in a potentiodynamic mode, taking into account electroconvection and non-catalytic dissociation / recombination reaction of water molecules in electromembrane systems, which are considered as the desalting channel of an electrodialysis device. The model is described by a system of coupled Navier-Stokes and Nernst-Planck-Poisson equations taking into account the electric force and physically justified boundary conditions. The article establishes the basic laws of mass transport, taking into account the dissociation / recombination of water molecules. It was shown for the first time that a double electric layer of hydrogen and hydroxyl ions arises in the recombination region. It is shown that between the region of recombination and quasi-equilibrium regions of space charge there are regions of electroneutrality and equilibrium with an almost linear distribution of concentrations. It was found that even under prelimiting, but close enough to the limiting current, modes, non-catalytic dissociation of water molecules in the quasi-equilibrium region of space charge occurs so intensely that the concentration of hydrogen and hydroxyl ions becomes comparable to the concentration of potassium and chlorine ions. At overlimiting current densities, due to the appearance of an extended space charge region and intense dissociation of water molecules in this region, as well as an increase in the electric double layer in the recombination region, the space charge and the dissociation / recombination reaction of water molecules significantly affect each other. In turn, this has a decisive effect on electroconvection and, accordingly, on the transport of salt ions.

Stationary Regimes of Electric Convection of a Low-Conductivity Fluid in the Case of Unipolar Charge Injection in a Constant Electric Field

Stationary Regimes of Electric Convection of a Low-Conductivity Fluid in the Case of Unipolar Charge Injection in a Constant Electric Field

Lattice Boltzmann modeling of double-diffusive convection of dielectric liquid in rectangular cavity subjected to unipolar injection

The lattice Boltzmann method is used to study the double-diffusive convection caused by the simultaneous effect of the temperature gradient and concentration gradient of the dielectric liquid in a rectangular cavity in the case of unipolar injection of ions. Considering that the physical model in this article is a complex dynamic system, we first conducted a linear stability analysis and obtained a neutral stability curve. Then we made a series of simulations to determine the influence of different dimensionless parameters on the movement of dielectric liquids and the distribution of charge density, temperature field, and concentration field. The variation range of the parameters is as follows: thermal Rayleigh number (1000≤Ra≤20000), electric Rayleigh number (100≤T≤800), Lewis number (1.0≤Le≤50.0), and buoyancy ratio (−2≤Nc≤0.5). The results show that the increase in electric Rayleigh number and thermal Rayleigh number will enhance the intensity of heat and mass transfer. Compared with pure electric convection, the existence of temperature field and concentration field have increased the instability of the dielectric fluid flow. When the Lewis number increases, the average Nusselt number will decrease but the average Sherwood number will increase. In addition, we noticed that the heat and mass transfer intensities have increased with the increase of the buoyancy ratio. When the buoyancy rate gradually increases from –2.0, we observe a bifurcation structure, and as the electric Rayleigh number increases, the critical value Ncc that causes convection will decrease.

Разработка критериального уравнения влияния электростатических полей на теплообмен и осадкообразование в среде керосина при естественной конвекции

The paper focuses on the problem of deposit formation in engines and power plants operating on liquid hydrocarbon fuels and coolers, and analyzes hydrocarbon deposit formation on heated fuel-delivery metal at increased temperature. First, an experimental setup was created to study the effect of electrostatic fields on the heat transfer intensification in liquid aviation kerosene TS-1 and the process of deposit formation on a heated working plate. Then, the effect of electric wind on thermal processes was visualized using the Tepler optical setup and the influence of electrostatic fields on the processes of heat transfer of deposit formation in the kerosene medium when using coaxial needles as electrodes was studied. Finally, findings of the research were generalized and a new criterion equation with a created dimensionless similarity number of electric convection and deposit formation simplex was introduced.

Mathematical modeling of nonstationary 1:1 electrolyte transfer and study of the space charge region in membrane systems taking into account electric convection and water dissociation/recombination reactions

The article formulates a mathematical model of non-stationary transfer of 1:1 electrolyte in potentiodynamic mode, taking into account electroconvection and non-catalytic reaction of dissociation/recombination of water molecules in membrane systems, which are considered the channel of desalting of the electrodialysis apparatus. Using this model, the main regularities of the space charge distribution are theoretically established, the influence of the input parameters is determined: initial concentration, potential sweep rate, etc. It is shown that the desalination channel consists of narrow quasi-equilibrium regions of space charge adjacent to ion-exchange membranes; an electric double layer appears in the central part, caused by the recombination reaction. Regions of electroneutrality are located between this double electric layer and the near-membrane space charge regions. This study will further be used to analyze the combined effect of the noncatalytic reaction of dissociation of water molecules and recombination and electroconvection on the current-voltage characteristic of the desalting channel.

Numerical simulation and analysis of natural convective flow and heat transfer of nanofluid under electric field

To study the effect of electric field on the natural convective heat transfer enhancement mechanism of nanofluid, numerical study was carried out by the lattice Boltzmann method (LBM). The physical model and boundary conditions were established based on experiments. The velocity and temperature distributions with various conditions were compared. The electric field forces on nanoparticle were also discussed. Simulation results reveal that electrophoretic force plays the most important role in the motion of the nanoparticle. The simulation values are in good agreement with the experimental results. Moreover, the electric field forces reform the velocity field and temperature field generated by natural convection. The local thermal conductivities of nanofluid are improved by the local electric field. Besides, to reveal the interaction between natural convection and EHD effect, a dimensionless number called electric convection number and fitting equations are proposed and analyzed. In addition, movements of nanoparticle and basefluid under electric field are inverse, which is beneficial to the stability of nanoparticle in the basefluid.

Spectral element method for numerical simulation of ETHD enhanced heat transfer in an enclosure with uniform and sinusoidal temperature boundary conditions

This paper presents a novel numerical framework based on the accurate spectral element method (SEM) for electro-thermo-hydrodynamics (ETHD), in which the coupled electric, flow, and heat fields are solved simultaneously. The electric field potential is estimated by the classic Galerkin variation with the electric field vectors evaluated by the spectral approximation, and the streamline upwind Petrov-Galerkin variation and consistent approximate upwind technique are applied to stabilize the numerical simulation of charge density transport. As for the flow and heat transfer, the improved time-splitting method developed in our previous work is applied to deal with the coupled pressure and velocity in the momentum equations. Three carefully selected cases of analytical solution, pure thermal and pure electric convection, and electro-thermo-convection are performed to validate the algorithm. Then, the electro-thermo-convection in an enclosure with uniform temperature distribution is simulated and the average Nusselt numbers at different electric Rayleigh numbers are presented accurately. Additionally, the sinusoidal temperature boundary conditions are considered that the contours for stream function, temperature, and charge density are analyzed in detail to depict the heat transfer enhancement with ETHD effects.

Электрическая плита ПЭ-УИЭВ

Increasing the efficiency of electric stoves currently remains an unsolved problem. The present study proposes a new design scheme for the electric convection stove with an air ionization device (Electric Stove PE-UIEV). This will reduce energy costs and speed up the cooking process. The stove in question is based on the method of electrothermal convection of heat-exchange surfaces of the frying deck. The proposed design reduces the formation of carcinogenic substances and improves the taste of fried and stewed dishes. The improved device increases the heat transfer coefficient from the burner surface to the cooker by 3 times since it creates better conditions for electrothermal convection. Treating air with electricity gives it adhesive properties: the air sticks to grounded surfaces of boilers. Ionized air intensively performs the function of heat carrier. Ionization reduces carcinogenic substances by 2–4 times and disinfects of ready-made dishes. The practical significance of the technical solution lies in the fact that the proposed design reduces the load on the ventilation and air conditioning system. In addition, the stove can be used for cooking in restricted (closed) spaces, and it improves the taste quality indicators. Unlike other stoves, this one reduces hot air circulation and, thus, its losses.

Erratum to: The Model of Electric Connection of a Low-Conductivity Liquid in High-Frequency Electric Field

In the original publication, there are several misprints. 1. In page header, the author’s name was misspelled. It should read “Ponomareva” instead of “Ponomarev.” 2. In title, it should read “The Model of Electric Convection of a Low-Conductivity Liquid in High-Frequency Electric Field” instead of “The Model of Electric Connection of a Low-Conductivity Liquid in High-Frequency Electric Field.”

Natural convection heat transfer of nanofluid in a cavity under an inhomogeneous electric field

Natural convective heat transfer of nanofluid consisted of transformer oil and Al2O3 nanoparticles in a cavity under a non-uniform high electric field intensity was experimental investigated. The main objective is looking for a coupling enhanced method by nanofluid and electric field. It is found that when the effect of gravity is ignored, the electric field forces applied on the working fluids induce an electric convection and thence induce significant heat transfer enhancement. This enhancement effect increases rapidly with the increase of electric field intensity, the nanoparticles mass concentration of nanofluid and the heat flux. When the effect of gravity exists, a coupled convection is caused by both gravity and electric field force together. For pure transformer oil, the influences of electric field force and gravity on the heat transfer almost offset each other. However, for nanofluid, the impact of the electric filed force is dominant. The study results revealed the enhanced mechanism of natural convection heat transfer of nanofluid under electric field and provided some useful technical support for practical application.

The Development of Teaching Aid in The Implementation of Natural Science in The Curriculum 2013 Junior School

The purpose of this study was to develop the teaching aid required in the curriculum implemented 2013 science subjects at the junior level.The method used in this research is the Research and Development. In this article will be described in the description of the development of the teaching aids that have been generated. Teaching aids consist of three pieces, namely water filtration magical, electric convection box and Musschenbroek bimetal. Based on the expert validation, then all three devices have fulfilled the requirements as teaching aids. Where all three can be used to demonstrate the concept of separation of mixtures, air convection, and thermal expansion of the metal. All three are decent teaching aids used to learn science subjects at junior in implementing the curriculum in 2013.

Electric convection of low-conductivity liquid in a horizontal capacitor in the presence of unipolar charge injection

Electric convection of low-conductivity liquid in a horizontal plane capacitor is analyzed with allowance for unipolar charge injection. Dynamics of charge transfer through stationary isothermal liquid in the presence of modulated electric field is studied. Effect of modulation amplitude and frequency on the spatiotemporal distribution of charge density and electric potential is considered. Nonlinear electric convection of nonisothermal low-conductivity liquid is studied in the presence of static electric field in a 2D system. Hysteresis transitions between two different (with respect to intensity) regimes of electric convection are analyzed.

Modelos de convección eléctrica y magnética en electrodeposición de celdas delgadas

Modelos de convección eléctrica y magnética en electrodeposición de celdas delgadas

Uniform and Non-uniform Thermoelement Subject to Lateral Heat Convection

A general energy equation of quasi-one-dimensional heat flow in a longitudinal thermoelement (TE) of a curved side that is subjected to an electric field and convection heat transfer on the curved surface is developed. The energy equation is solved for the temperature distribution in two cases; uniform cross-section TE and non-uniform cross-section TE. Analytical solutions for a uniform cross-section TE with uniform electrical and thermophysical properties are obtained, whereas numerical solutions are provided for a non-uniform cross-section TE. Two parameters playing a vital role in the thermal performance of the TE are identified: the heat resistance ratio (HRR) and the energy growing ratio (EGR). The HRR represents the ratio of the longitudinal conduction maximum thermal resistance to the lateral convection maximum thermal resistance. The EGR represents the ratio of Joule’s electrical heating to Fourier’s heat conduction. The effects of varying these two parameters, as well as the TE geometry, have been thoroughly investigated.