The importance of effective thermal management technology in microgravity is increasingly recognised with the advancement of space exploration. Cooling techniques based on phase change materials (PCMs) have shown potential in recent thermal management applications; however, the suppression of natural convection in microgravity limits heat transfer and melting rates. This study investigates the enhancement of thermal management of heat loads in microgravity using an electric field. A numerical solver for melting was developed on the OpenFOAM platform, coupling electric and thermal fields. The effects of injection intensity (C) and gravity on melting rates, thermal management, and thermal energy storage were systematically analysed. Results indicate that electrohydrodynamic (EHD) effects promote melting by altering vortex structures and temperature distribution. The melting enhancement coefficient based on the increase of liquid fraction reaches 20.3% at 0.17 g and 10 kV, with C = 10. Three peaks in the Nusselt number are observed after the thermal conduction stage due to EHD. The uniform development of vortices enhances performance in low-gravity environments at C = 0.1. Higher melting rates increase latent heat storage, while slower melting leads to a rapid rise in sensible heat, indicating a trade-off between storage efficiency and effective thermal management. This study demonstrates the capability of heat transfer to regulate the operating temperature of heat loads in microgravity using an electric field, providing a promising solution for advanced thermal management in space applications with reduced energy consumption.

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.

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.

The proper orthogonal decomposition (POD) algorithm was applied to reconstruct the instantaneous velocity field of the EHD jet in this work. Particle image velocimetry (PIV) measurements were conducted on EHD jets in a bladeplane configuration at different voltages and electrode spacings. The acquired instantaneous flow fields were used as input to yield the orthogonal spatial modes, the temporal coefficients and the eigenvalues that are automatically ranked by kinetic energy magnitudes. It is shown that the dominant spatial modes obtained by POD usually correspond to large-scale coherent structures, while the higher modes characterize finer-scale turbulent vortex structures. Although POD-based flow field reconstruction allows for the elimination of non-coherent noise and spurious vectors in the original PIV data, the number of modes available for reconstructing the instantaneous flow field tends to increase due to the decrease in the energy content of the dominant modes.

This study numerically investigates the flow structures and bifurcations of three-dimensional (3D) electro-convection (EC) between concentric cylinders. The flow motion is driven by the volumetric Coulomb force exerting on the free ions introduced by a strong unipolar injection. Three different sets of cases with periodic or symmetric boundary conditions are carried out. The finite volume method is used to numerically resolve the model problem. The co-effect of 2D roll mode and 3D polygon mode at the initial period of the EC flow is identified. The EC flows are made up of different types of regular or irregular centrally downflowing polygonal cells and are characterized by the central charge density cores surrounded by the charge void regions. The symmetry, periodicity, and staggered distribution characteristics of polygonal cells are identified. The cell patterns of EC flow are strongly influenced by the computational domain and the electric Rayleigh number (T). The subcritical bifurcation of linear instability together with a hysteresis loop is observed. In addition, the stability of the triangular flow pattern is analyzed at a large range of T and found that the annular EC flow is more likely to be unstable in three dimensions than in two dimensions.

This study set out to systematically investigate the structural characteristics of plane electrohydrodynamic jets through the particle image velocimetry (PIV) techniques. Due to the wide range of applied voltages and electrode gaps under various experimental conditions, an assessment of the image quality and a statistical analysis of the velocity fields are first performed to ensure the validity of the PIV measurements, which were originally applied purely to fluid mechanics. The results indicate that the time interval between two consecutive images should be pre-adjusted to reduce the number of uncorrelated vector fields. Moreover, the minimum number of instantaneous fields should be achieved for an accurate calculation of the time-averaged fields. An equivalent electric field criterion adapted to the asymmetric electrode configuration is defined to find similarities in flow structures under different voltage and electrode gap conditions. As the applied electric field increases, three injection regimes are identified and the current increases almost linearly, indicating a large conduction current component. The decrease in charge density due to recombination proves to be relevant in all cases of this study. Analogous to the parametric analysis approach for classical jets and thermal plumes, the evolution of the coefficients of axial velocity, half-width and turbulence intensity are investigated.

Surface dielectric barrier injection (SDBI) actuators have received increasing interest due to the presence of dielectric barriers, which can greatly improve the applied voltage. The success of SDBI actuators in driving silicone oil makes silicone flow a very promising application in the field of microfluidics. However, polarity-dependent flows that are different from conventional cases are observed experimentally under bipolar pulsed DC signals. To interpret this specific phenomenon, a new model of electrohydrodynamic (EHD) wall jet considering both electrochemical injection and the initial presence of an electrical double layer (EDL) at the dielectric solid/liquid interface is developed for the first time based on the finite element method. The results show that the flow field in the simulation is consistent with the experimental bidirectional flow field. The silicone vortex movement is accompanied by charge injection, migration, and accumulation in the near-wall region. Through studies of the effect of signal parameters on flow behavior, including voltage amplitude, duty cycle, frequency, and waveform, a square wave signal with a frequency of 0.2 Hz proves to be the most efficient in generating a high-velocity silicone flow.

In this work, we extend the investigation of the injection-induced electro-convection (EC) between two-dimensional concentric electrodes from perfectly insulating dielectric liquids to dielectric liquids with residual conductivity. A dissociation-injection model of the EC system is implemented by a finite-volume framework of OpenFOAM®. The morphology of hetero-charge layers in a hydrostatic regime is presented. The flow characteristics including the spatial and temporal features of the flow field, electric field, and positive/negative charge density of the EC are analyzed. The subcritical bifurcation phenomenon of EC is observed. The residual conductivity postpones the onset of EC flow and inhibits the flow strength as EC takes place. The difference between onset (Tc) and cessation (Tf) of EC flow decreases as the residual conductivity grows. Gradually increasing the electric Rayleigh number (T), the EC system sequentially evolves via hydrostatic, steady, periodic, and chaotic states with abundant bifurcations. The initialization of the calculation could also strongly influence the instability of the EC system. Furthermore, the effect of residual conductivity on the transition sequences of the EC system is investigated. Four different transition sequences for EC develop from the hydrostatic state to chaos as T increases, and three distinct transition routes from the chaotic state to the motionless state when T reduces are observed and discussed.

This work deals with the mixing of two miscible dielectric liquids enhanced by electro-convection mean. We have improved the numerical model presented in the previous ICDL conference in 2022. This model can now account for the case where the two liquids in presence have different permittivities and ionic mobilities. It appears that the permittivity ratio has a direct impact on the flow dynamics. According to he permittivity ratio, the ripples that we have highlighted in the early growth of instability have an increased amplitude and may last longer before electro-convection takes place. For a given electric Rayleigh number T and for small values of this permittivity ratio, it is even noticed that the growing instability suddenly decreases before the flow returns to rest, although for the same T but with permittivity ratio higher, electro-convection takes place. When permittivity ratio or ionic mobility ratio are increased, we have observed that the electro-convection strength is higher.

Silicone oils acting as alternatives to mineral oils have received increased attention in electrical installations cooling fields, and thus electroconvective silicone flows induced by a surface dielectric barrier injection (SDBI) actuator is worth studying. The flow behavior is recorded through the Particle Image Velocimetry (PIV) method and a polarity-dependent flow direction is obtained by using phase analysis of velocity data. In an attempt to explain this unusual phenomenon, an EHD wall jet model considering electrochemical injection and adsorption mechanism of electrical double layer (EDL) at dielectric solid/liquid interface as well as charge accumulation effect is built based on the finite element method. The time-averaged velocity field of each phase in experiment is consistent with that observed in simulation. With the aid of simulation, coupling characteristics of flow convection and charge motion are obtained, which is usually hard to capture in experiment.

When a blade-plane actuator is subjected to a high voltage, an electrohydrodynamic (EHD) force is exerted on the dielectric liquid to produce an electroconvective flow. Experimental estimation of the electrical force can be carried out through the momentum integration method based on the velocity fields of particle image velocimetry (PIV) measurements. It is a force-averaged approach which is conducted by integrating the instantaneous Navier-Stokes' momentum equation over a designated control volume. Theoretically, a new method inspired by turbulent plume model is proposed to estimate the EHD force through the axial velocity curve and half-width curve of the time-averaged field. It is found that the calculation error of this effective calculation is within an acceptable range when compared with results obtained by the PIV based method.

This work addresses the characterization of the subcritical electroconvection instability that occurs in two plane layers of two miscible dielectric liquids subjected to strong unipolar injection. It appears that electro-convection is a very efficient way to increase the mixing of two miscible liquids. It is shown that the Lacey index, which characterizes the level of mixing between the liquids, is directly impacted by the electrical Rayleigh number T. Linear and non-linear instability criteria, T-c and T-f, featuring a typical hysteresis loop, are determined. We have exhibited a very intriguing phenomenon in the time evolution of the maximum velocity Vmax in the domain. Above the linear criterion T-c, for given values of the Schmidt number S-c, one can observe the emergence of some ripples in the V-max vs time, curve. This unexpected behavior is analyzed and an explanation in terms of modal dynamic is proposed.

Experiments on the electrohydrodynamic (EHD) flow characteristics of a dielectric liquid in a sharp needle-plate configuration under direct current (DC) and alternating current (AC) electric field are carried out. The current-voltage characteristics and the velocity field are simultaneously recorded for understanding the flow behavior and its mechanism. For the DC case, a critical voltage separating the conduction and injection regimes and the corresponding flow reverse is observed. Results indicate the polarity of voltage only influences the flow's intensity in the injection regime. For the AC case, two types of signals with the same 50% duty cycle are considered. For the pulsed voltage (−2.0kV to 0), the flow generally keeps the plume structure and shows weaker strength than the corresponding DC case. For the AC signal (-2.0kV–+2.0kV), the velocity amplitude first decreases and then tends to be constant with the increase of frequency. The weak flow motion with high frequency AC field is due to conduction.

Numerical analysis of the 2D radial and azimuth electro-convection (EC) flow of dielectric liquid between two eccentric cylindrical electrodes driven by unipolar injection of ions is presented. The finite volume method is used to resolve the spatiotemporal distributions of the flow field, electric field, and charge density. The flow instability is studied in various scenarios where the radius ratio Gamma = R-i/R-o ranges between 0.1 and 0.7 and the eccentricity eta between 0.1 and 0.5. The bifurcation of the flow patterns depends on the electric Rayleigh number T, a ratio of the electric force to viscous force, and the two geometric parameters Gamma and eta. For an increasing T, the EC system develops from a weak steady convective state to chaos via different intermediate states experiencing pitchfork and Hopf bifurcations. The influence of Gamma and eta on the bifurcation behavior is also investigated. When Gamma lies between 0.1 and 0.3, a novel periodic oscillation of the flow patterns has been observed.

In this study a full 3D numerical simulation of the flow induced by the dissociation of neutral molecules in a weakly conductive liquid between a blade shaped electrode and a vertical plane electrode is undertaken. It turns out that even in the conduction situation where neutral molecule dissociate into ions, although the flow is expected to be directed from the plane to the blade a reversed flow occurs after a transition when some circumstances are met. To the best knowledge of the authors, this intriguing phenomenon has never been reported. In this study, this unexpected behavior is analyzed, and an explanation is proposed. The conditions leading to this particular flow inversion pattern are examined and highlighted.

Nowadays, heat transfer enhancement devices are becoming very essential in many applications. Most of electronic devices, from the simplest to the most sophisticated, contain processors. Advanced processors require efficient cooling for an optimal performance. Due to the growing interest in faster and lighter devices, researchers always seek to innovate and optimize cooling strategies. In spatial applications, the use of typical cooling systems can cause complications due to the vibrations during takeoff and due to zero gravity effects. Electrohydrodynamic (EHD) pumping, which is based on the interaction of a dielectric liquid with an electric field, could present a solution to all these challenges. EHD pumps were considered a breakthrough in the field of cooling since they demonstrate many advantages over other types of pumps. EHD devices are less power consuming, lighter and cheaper. They don't have moving parts and they are suitable for microgravity applications. The hydrofluoroethers (HFE) are dielectric liquids that could be ideally utilized in these pumps for many applications. Being dielectric fluids with eco-friendly properties, HFEs could replace CFCs, HFCs, HCFCs, and PFCs. Due to their promising EHD applications, studies must be done to investigate the variation of their dielectric behavior with electric field and with temperature. This work presents an experimental investigation of the dielectric characteristics of HFE-7000 with temperature variations. Understanding this aspect can help enhance and optimize the performance of EHD systems.

When an external electric field is applied on a weakly conducting liquid, next to each metallic electrode two layers with a net electric charge of opposing polarity appears. These are called heterocharge layers. The electric field exerts a force on these layers. If the electrodes of different polarity have different geometric characteristics a net electric force is produced, creating a net flow. This is the basis of EHD conduction pumping. This technique has a great number of interesting applications, notably in heat exchange devices to be applied in satellites and aerospace systems. Here we consider a flexible EHD conduction pump. An array of symmetric electrodes is deployed on a flexible non-conducting substrate. This flexibility allows the pump to be installed in conduits of complicated geometries, increasing the applicability of the EHD conduction pumping concept. Specifically, we present the results of numerical simulations with a conic flexible pump with several pairs of electrodes. We discuss the structure of the fluid flow and of the heterocharge layers along the pump.

In this paper, the electrohydrodynamic flow generated by nine electrode pairs of asymmetric electrodes is experimentally investigated. Electrodes are flushed into a cavity wall and a DC voltage is applied to the electrodes in order to set the liquid in motion. The liquid flow patterns are recorded by the use of a particles velocity Image system. Flows have been recorded during more than 500s and time variations are presented. According to the theory the flow over each electrode pair is most of the time directed from to small electrode to the large one but unpredicted flow patterns have also been obtained. It can be noticed that an unexpected reversed flow has even been observed in some configurations. In order to explain these behaviors, a joint analysis of both flow patterns and measured electric current is made. This last point is more particularly discussed in the last part.

This study aims to demonstrate the capability of simulating the flow induced by the dissociation of neutral molecules in a weakly conductive liquid in a full 3D channel. We investigate numerically the EHD pumping through pure conduction phenomenon in a 3D rectangular channel. It is important to verify if the assumptions allowing us to consider that the flow remains 2D are always valid and in which circumstances some 3D phenomena may occur ? Not very surprisingly it is observed that while increasing the electric Reynolds number in increasing the electric potential difference between the two electrodes makes the flow becoming turbulent. In such situation 2D computations are not anymore valid.

In this article we analyse the results of a numerical simulation of an electro-thermo-convective flow induced in a dielectric liquid layer by the simultaneous action of an external electric field and a thermal gradient. A low conductivity liquid is placed between two horizontal electrodes and subjected to strong unipolar charge injection which set the fluid in motion under the combined action of Coulomb and buoyancy forces. The motion induced by the charge injection has a vigorous character and strongly increases the electric charge transfer and heat transfer between the electrodes. The full set of governing equations including Navier-Stokes equation, the conservation equations of electric charge and energy and Poisson equation for electric potential is solved by a finite volume method. We define an electric Nusselt number (Ne) as the ratio of the effective current and the current existing without liquid motion, number which can be considered as the analog of Nusselt number (Nu) for a pure thermal problem. The case of heating and strong injection of electric charges from lower electrode is considered. The variation of the electric Nusselt number Ne with electrical parameter T for different values of the non-dimensional parameter mobility number M and Rayleigh number is then analyzed. It is shown that the mobility number M is a parameter which plays an important role in the characterization of electro-thermo-convective flows and also that the physical mechanisms of the different instability regimes can be better understood considering the electric Nusselt number Ne.