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This paper presents a fundamental study of electro-thermo-convective flows within a layer of dielectric liquid subjected to both an electric field and a thermal gradient. A low-conductivity liquid enclosed between two horizontal electrodes and subjected to unipolar charge injection is considered. The interplay between electric and thermal fields ignites complex physical interactions within the flows, all governed by a set of coupled electro-thermo-hydrodynamic equations. These equations include Maxwell, Navier–Stokes, and energy equations and are solved numerically using an in-house code based on the finite volume method. Electro-thermo-convective flows are driven by two dimensionless instability criteria: Rayleigh number Ra and the stability parameter T, and also by the dimensionless mobility parameter M and Prandtl number Pr. The electric Nusselt number (Ne) analogue to the Nusselt number (Nu) in pure thermal problems serves as an indicator to monitor the shift from a thermo- to an electro-convective flow and its eventual evolution into unsteady, and, later, chaotic flow. This change in regime is observed by tracking the electric Nusselt number's behavior as a function of the stability parameter (T), for different values of the non-dimensional parameters (M, Ra, and Pr). The important role of mobility parameter M for the development of the flow is shown. The flow structure during different development stages in terms of the number of convective cells is also discussed. [ABSTRACT FROM AUTHOR]

This article investigates the behavior of two parallel layers of different miscible dielectric liquids enclosed and sandwiched between two electrodes. By applying an electric potential to one electrode while grounding the other, electro-convection occurs when the electric Rayleigh number exceeds a critical value, setting the fluid into motion and resulting in rapid mixing between the two liquids. A numerical model is developed to account for the varying ionic mobility and permittivity of the two liquids, considering their evolution based on the relative concentration field. The simulations confirm that electro-convection significantly enhances the mixing between the two liquids, as expected. Additionally, intriguing ripples are observed near the initial interface during the early stages of electro-convection instability growth. To explain and describe the flow dynamics in terms of stability analysis, a semi-analytical model is presented. This study provides insights into the mixing behavior and flow dynamics of miscible dielectric liquids under the influence of electro-convection. The findings contribute to a better understanding of the underlying mechanisms and can be valuable for applications such as microfluidics, energy conversion, and mixing processes. Further research is encouraged to explore additional parameters and optimize the control of electro-convection for practical applications. [ABSTRACT FROM AUTHOR]

This paper is an experimental study on electroconvective flows produced by an asymmetric electric field in a cavity. It is part of a scientific project aiming to develop electrohydrodynamic (EHD) flow actuator in order to enhance heat transfer and mixing efficiency in fluidic and microfluidic systems. In this study, the EHD flow is obtained by applying a dc voltage between two electrodes (cylinder/plane) immersed in a working liquid. The produced velocity fields strongly depend on the applied voltage. Whatever may be the applied voltage, the fluid goes from the cylinder toward the plate or the other way round. The velocity fields obtained by particle image velocimetry for different potentials are analyzed in both cases with the usual mechanisms (injection and conduction) at the origin of the motion of the liquid. A discussion on the transition between injection and conduction phenomena is finally presented. [ABSTRACT FROM AUTHOR]

For several years, our research group has developed electrohydrodynamic (EHD) actuators able to set dielectric liquid in motion. More precisely, these actuators are designed to produce electroconvective flows up to 1 m/s. These flows are jets (impinging jet, wall jet, etc.) that can be used in various applications such as mixing, flow control, cooling systems, etc. The main advantages of these actuators are direct conversion of electric energy into inertial energy (without moving parts), low cost, and easy miniaturization. EHD pumps could be used in microfluidic applications. Nevertheless, the fundamental physics of these flows remains complex, and in order to have a better understanding of these electroconvective flows, we need a more reliable analysis method. The best method to date is particle image velocimetry. However, in order to show liquid movement, this method requires seeding particles, which can be electrically charged and so on can be influenced by the electric field produced by the electrodes. In this work, we study the behavior of three types of seeding particles under high electric field in order to estimate the error induced by the electric field on the measurement of the liquid velocity. [ABSTRACT FROM PUBLISHER]

Two-dimensional numerical simulations are carried out to evaluate the enhancement of natural convection heat transfer in a dielectric liquid resulting from injection induced annular electro-convection. The liquid is confined between two concentric horizontal cylinders and subjected to the simultaneous actions of a direct current electric field and a thermal gradient. A unipolar injection from the inner cylinder introduces free space charges into the liquid. Numerical results are presented for the configuration of inner to outer diameter ratio of 0.5 and silicon oil as the working medium. It is found that the charge injection may induce a strong radial fluid motion, which consequently augments the heat transfer rate. Due to the linear stability nature of electro-convection, there exists a threshold value of the electric driving parameter, above which the electrical enhancement becomes manifest. In addition, when the electric driving parameter is sufficiently high, the flow is fully dominated by the Coulomb force, and thus heat transfer becomes independent of the thermal driving parameter. [ABSTRACT FROM AUTHOR]

In this paper, the interaction between a plane Poiseuille channel flow and an electroconvective movement induced by the electric field is numerically investigated. A flow is generated by an inlet parabolic profile in a rectangular duct. Space charges are injected in the flow through a metallic electrode placed on one of the channel walls and brought to a given potential. Transient numerical simulations have been carried out to investigate the structure of the flow. The entire set of the coupled Navier-Stokes and EHD equations is solved using an efficient finite volume technique. The behavior of the flow subjected to an applied voltage between the two electrodes is analyzed and time evolution of the charge density distributions is presented. The interaction between the convective movement induced by space charge injection and electric field and the mainstream flow, emphasizes the appearance of periodic transverse traveling waves convected in the channel. The dynamic of the flow through the variation of the ionic mobility parameter M is investigated. For a given Reynolds number and ionoc mobility parameter M it exists a threshold value Tc of the instability parameters T above which the transverse traveling rolls appear or not. When T is increased, different flow regimes have been highlighted starting from a complete steady state up to a fully unsteady electro-plumes flow configuration. [ABSTRACT FROM AUTHOR]

We numerically investigated the annular electroconvection that takes place in a dielectric liquid lying between two concentric cylinder electrodes. A uniform injection of arbitrary strengths either from the inner or outer cylinder introduces free charge carriers into the system, and the resulting Coulomb force induces electroconvection. The problem is characterized by a linear instability that corresponds to the onset of flow motion. The linear stability criteria were determined from direct numerical results and by linear stability analysis, and the results obtained with the two approaches show an excellent agreement. We focused on the fully developed flow pattern in the finite amplitude regime. We observed very different flow motions that were highly dependent on the injection strength. [ABSTRACT FROM AUTHOR]

This paper addresses the numerical investigation of an electrohydrodynamic (EHD) plume induced by a sharp blade electrode in a dielectric liquid. Different injection laws, namely, autonomous and nonautonomous ones, are considered, and the importance of the blade shape is emphasized, especially for nonautonomous injection laws. Different flow regimes arise according to the value of the Reynolds number based on the ionic mobility and the distance $d$ between the blade and the vertical plate. It is found that the critical Reynolds number for which the transition between steady and unsteady regimes occurs depends on the injection law, on the blade shape, on the $M$ parameter, and on the injection strength $C$. For much higher Reynolds number, the flow turns to be chaotic and behaves as a jet flow with the development of a Kelvin–Helmoltz instability. The use of different sharp blades indicates that a higher electric field at the tip of the blade plays a significant effect on the development of the EHD plume. The plumes have been characterized by their charge density distribution which shows, in the early stages of the simulation, that its dynamics is significantly dependent on the blade shape as well as on the nonautonomous injection law. [ABSTRACT FROM AUTHOR]

In this paper, we numerically explored the potential application of electrohydrodynamic (EHD) plumes in cooling local regions with high temperature. The EHD plume is induced by ion injection from a sharp metallic blade immersed in a dielectric liquid. A 2-D simulation which took into account all relevant physical variables for EHD plumes in a nonisothermal liquid was performed. It is found that both the local and average Nusselt numbers dramatically increase with the increase of the electric Rayleigh number $(T)$ and the injection strength parameter $(C)$. However, for the same $T$ and $C$, the heat transfer augmentation effect is stronger for small Rayleigh numbers $(Ra)$, which can be understood by comparing the relative importance between Coulomb force and buoyancy force. [ABSTRACT FROM AUTHOR]

Two-dimensional numerical calculations were carried out for the isothermal electroconvection in a dielectric liquid induced by the unipolar charge injection. In the dimensionless form, the system is mainly governed by the injection strength number $C$, the electric Rayleigh number $T$, and a mobility number $M$. A strong injection case with $C = 10$ was considered. Along with the increase in driving parameter $T$, oscillatory electroconvection occurs. Critical values of $T$ corresponding to the onset of such oscillatory convection were shown to be highly dependent on $M$ and were accurately determined. Some precautions, including the algorithm for the charge density equation, were taken to reduce the numerical diffusion and to ensure the reliability of our findings. [ABSTRACT FROM AUTHOR]

An impinging jet in a dielectric liquid is generated by applying a high potential difference to a blade–plane geometry. This kind of jet is both a fluid flow and an electrical phenomenon. In our study, an overview of the flow field is easily obtained by using the classical particle velocity method. Two patterns of electrohydrodynamic velocity profiles of the jet can be observed when the applied high voltage varies. A typical method for a classical impinging jet is used in order to point out the specific characteristics of electrohydrodynamic jets. Electric current measurements and particle-image-velocimetry investigations are conducted synchronously, which contribute to the analysis of this electrohydrodynamic phenomenon. Two electrical current regimes are presented according to the potential difference. [ABSTRACT FROM AUTHOR]

Abstract: A new approach for diffusive flux discretization on a nonorthogonal mesh for finite volume method is proposed. This approach is based on an iterative method, Deferred correction introduced by M. Peric [J.H. Fergizer, M. Peric, Computational Methods for Fluid Dynamics, Springer, 2002]. It converges on highly skewed meshes where the former approach diverges. A convergence proof of our method is given on arbitrary quadrilateral control volumes. This proof is founded on the analysis of the spectral radius of the iteration matrix. This new approach is applied successfully to the solution of a Poisson equation in quadrangular domains, meshed with highly skewed control volumes. The precision order of used schemes is not affected by increasing skewness of the grid. Some numerical tests are performed to show the accuracy of the new approach. [Copyright &y& Elsevier]

Objective. The purpose of this study was to determine the clinical and biological characteristics at diagnosis in children and adolescents with chronic myelogenous leukemia (CML)in contemporary practice. Methods. Analysis was conducted on data from 3 prospective trials conducted in children and adolescents with CML. Forty pediatric patients were evaluated in 16 French pediatric oncology units between 1991 and 2003. Results. The disease predominately affected children who were older than 10 years (67% of the patients), with a higher prevalence in boys than girls (gender ratio: 1.5). Approximately 20% of cases were diagnosed incidentally. The main presenting symptoms were asthenia, weight loss,and complaints related to splenomegaly. Occasional patients presented with signs evocative of leukostasis. Symptoms were more common in patients with splenic enlargement,which was present in 70% of patients, and higher leukocyte counts. Markedly raised leukocyte counts were common (median white blood cell count: 242 x 109/L).The age and the gender of the patients had no effect on the leukocyte count, the hemoglobin level, or the platelet count. A predominance of b3a2 transcript was observed in the 16 children who were studied for the type of chimeric BCR-ABL mRNA. Conclusions. This is largest reported series of CML at diagnosis in children and adolescents. It shows that the characteristics of CML seem to differ in children compared with previously published adult series; in particular, the presenting leukocyte counts are often higher in children. [ABSTRACT FROM AUTHOR]