Tunable Lens Driven by Electrohydrodynamic Pumping

In recent years, functional fluidic and gas electrohydrodynamic (EHD) pumps have received considerable attention due to their remarkable features, such as simple structure, quiet operation, and energy-efficient utilization. EHD pumps can be applied in various industrial applications, including flow transfer, thermal management, and actuator drive. In this paper, the authors reviewed the literature surrounding functional fluidic and gas EHD pumps regarding the following aspects: the initial observation of the EHD effect, mathematical modeling, and the choice of pump structure, electrode configuration, and working medium. Based on the review, we present a summary of the development and latest research on EHD pumps. This paper provides a critical analysis of the current limitations of EHD pumps and identifies potential areas for future research. Additionally, the potential application of artificial intelligence in the field of EHD pumps is discussed in the context of its cross-disciplinary nature. Many reviews on EHD pumps focus on rigid pumps, and the contribution of this review is to summarize and analyze soft EHD pumps that have received less attention, thus reducing the knowledge gap.

EHD gas pump as a cooling device for electronic components in a horizontal channel

Electrohydrodynamic (EHD) pumps are a promising driving source for various fluid-driven systems owing to features such as simple structure and silent operation. The performance of EHD pumps depends on the properties of the working fluid, such as conductivity, viscosity, and permittivity. This implies that the tuning of these parameters in a working fluid can enhance the EHD performance. This study reports a method to modify the properties of a liquid for EHD pumps by mixing an additive. Specifically, dibutyl adipate (DBA) and polyvinyl chloride (PVC) are employed as the working fluid and the additive, respectively. The results show that when the concentration of PVC is 0.2%, the flow rate and pressure at applied voltage of 8 kV take highest value of 7.85 μL/s and 1.63 kPa, respectively. These values correspond to an improvement of 109% and 40% for the flow rate and pressure, respectively, compared to the pure DBA (PVC 0%). When the voltage is 10 kV, the flow rate of 10.95 μL/s and the pressure of 2.07 kPa are observed for DBA with PVC concentration of 0.2%. These values are more than five times higher than those observed for FC40 at the same voltage (2.02 μL/s and 0.32 kPa). The results also suggest that optimal conductivity and viscosity values exist for maximizing the EHD performance of a liquid. This demonstrates the validity of the proposed method for realizing high-performance EHD pumps by using additives in the working fluid.

The effect of electrode orientation in an electrohydrodynamic (EHD) gas pump inside a square channel is experimentally examined for its effective use in thermal management. The two-stage gas pump with electrodes flush mounted on two parallel walls in each stage is powered by DC voltages ranging from 24 to 28 kV. In addition to the volume flow rate produced, the performance of the pump is evaluated using an energy efficiency factor, which is defined as the volume flow rate delivered by a unit power input. It is found that this parameter has a larger value for the EHD pump with aligned electrodes. However, the EHD pump with offset electrodes can produce more mixing of flow inside the channel, which may be more favorable for the application in thermal management. Most importantly, EHD gas pumps with either electrode configuration have a greater energy efficiency than conventional fans, and thus have a greater advantage for applications in the thermal management. This advantage is even more prominent when pumps are operated with uneven applied voltages.

Flow control and heat transfer enhancement represent critical research in the aerospace field, facing challenges such as complex environments, long-term thermal management requirements, low energy consumption, and high integration. As an emerging fluid-driven and thermal management technology, the electrohydrodynamic (EHD) pump is independent of gravity, and it demonstrates significant application potential. This study presents a modular EHD pump and systematically tests its flow control, heat transfer enhancement, and dynamic response characteristics. Experimental results indicate that as the applied voltage increases, the flow rate of the EHD pump increases significantly. At a heat flux of 10 000 W/m2, the enhancement efficiency of the pump reaches 107.59%. By constructing an energy consumption characteristic curve, the energy consumption of the EHD pump is evaluated, showing a maximum of 0.046 W at 10 kV. Dynamic response tests reveal that the startup and shutdown processes of the pump can be divided into four stages: initiation, progression, stabilization, and decay. Owing to its compact, gravity-independent, and modular design, the pump shows potential for use in spacecraft thermal management and compact electronic cooling systems.

So far, electrohydrodynamic (EHD) pumps based on the injection or the field-enhanced dissociation (the Wien effect) at the surface of metal electrodes have been studied. This paper proposes and studies both numerically and experimentally a fundamentally new pump scheme, namely, the EHD pump operating due to the Wien effect in a conical hole located in the solid insulation barrier. An experimental setup of the pump has been created, and performance (pressure vs flow rate) characteristics have been measured that satisfactorily agree with the results of computer simulation. With the size of the hole being a fraction of a millimeter, the proposed system performance is comparable to that of the previously studied EHD pumps.

Designing and manufacturing actuators using soft materials are among the most important subjects for future robotics. In nature, animals made by soft tissues such as the octopus have attracted the attention of the robotics community in the last years. Suckers (or suction cups) are one of the most important and peculiar organs of the octopus body, giving it the ability to apply high forces on the external environment. The integration of suction cups in soft robots can enhance their ability to manipulate objects and interact with the environment similarly to what the octopus does. However, artificial suction cups are currently actuated using fluid pressure so most of them require external compressors, which will greatly increase the size of the soft robot. In this work, we proposed the use of the ElectroHydroDynamics (EHD) principle to actuate a suction cup. EHD is a fluidic phenomenon coupled with electrochemical reaction that can induce pressure through the application of a high-intensity electric field. We succeeded in developing a suction cup driven by EHD keeping the whole structure extremely simple, fabricated by using a 3D printer and a cutting plotter. We can control the adhesion of the suction cup by controlling the direction of the fluidic flow in our EHD pump. Thanks to a symmetrical arrangement of the electrodes, composed by plates parallel to the direction of the channel, we can change the direction of the flow by changing the sign of the applied voltage. We obtained the pressure of 643 Pa in one unit of EHD pump and pressure of 1428 Pa in five units of EHD pump applying 6 kV. The suction cup actuator was able to hold and release a 2.86 g piece of paper. We propose the soft actuator driven by the EHD pump, and expand the possibility to miniaturize the size of soft robots.

Electrohydrodynamic (EHD) pumping of two-phase media has potential applications related to both pure pumping as well as heat transfer enhancement. Utilization as pumping mechanism is attractive for terrestrial and outer space systems. Augmentation of mass flow rate in two-phase heat transfer applications, such as boiling and condensation, leads to enhanced heat transfer coefficients, thus making EHD pumping an attractive candidate for these situations. A theoretical model is presented for EHD induction pumping of a stratified liquid/vapor medium accounting for electric shear stresses due to interfacial and bulk charges. Bulk charges are a result of temperature gradient in the liquid phase of the fluid. Conditions are established under which the bulk effect plays a significant role in the pumping process.

In this study, fluid flow induced by a two stage electrohydrodynamic (EHD) gas pump in a square channel has been evaluated by experimental measurement and numerical simulations. This study is implemented for a two stage EHD gas pump with three emitting electrode configurations: 8, 24, and 56 respectively to seek the relation between the number of stages and emitting electrodes. The EHD pump is evaluated for a wide range of operating voltages starting from 20 kV up to 28 kV for further improvement in its performance over a single stage. To achieve the maximum enhancement, the emitting electrodes of the EHD gas pump are flush mounted on the channel walls so that the corona wind produced directly disturbs the boundary layer thickness and improves the heat transfer. This is leading to a higher velocity near the channel walls and resulting in an inverted parabolic velocity profile at the center of the channel, which is opposite to the fully developed velocity profile of a forced flow. Velocities are measured at three cross-sections along the tube length and then integrated to obtain the volume flow rate. The results show that EHD technique has a great potential for many engineering applications.

The electrohydrodynamics (EHD) technique has shown promising results in enhancing heat transfer and mass transport. It has endless potential in industrial applications such as drying technology, design of evaporators, condensers, electrostatic precipitator, plasma actuator, and micropumps in microfluidic, chip-integrated cooling, and drug delivery systems. In recent years, a significant amount of research has been directed to design EHD micropumps as researchers realize their attractive features (e.g., no moving part, simple fabrication process) are most suitable in the aforementioned microelectro-mechanical systems (MEMS). This paper evaluates the performance of an EHD pump in a vertical square (4 × 4 inch) channel with a non-intrusive wire-electrode configuration. The voltage and current characteristics of the EHD pump are measured such that numerical simulations can be carried out. Measurements were taken from the corona threshold voltage to the occurrence of sparkover with a 1 kV increment. Due to the corona wind generated, the average volume flow rate in the channel was as high as 10 liter per second subjected to a voltage difference of 25 kV.

Rolling motions have been observed in many animals and insects. In the previous fluidic rolling system, a deformed chamber and long cables were imperative to drive the soft rolling actuators, which required high pressure and a sophisticated controlling strategy. In this study, we propose a soft fluidic roller using a simple structure composed of a bendable and twistable electrohydrodynamic (EHD) pump and a layer of natural latex. To realize the rolling motion, we first optimized the electrode and channel height of the EHD pumps using different patterns and designs. We also examined the output power, efficiency, pressure loss, bending, and twisting performance. Subsequently, the optimized electrodes and channel height were selected to design the power source of the EHD roller. This roller was lightweight (0.7 g) with an amount of liquid (0.6 g). This EHD robot can roll as the EHD liquid oscillates under a duty-controlled voltage realized using a high-voltage circuit. Next,we investigated the influence of frictional forces on rolling performance. Finally, the rolling motion in the liquid was demonstrated. This study extends the EHD pumps to independent soft actuators integrated with a soft power source.

This paper provides a summary of recent experimental work in electrohydrodynamic (EHD) conduction pumping of dielectric liquid, done by the authors and others in the Multi Scale Heat Transfer Laboratory at WPI. The primary objective of all experiments was to gain a fundamental understanding of interaction of flow fields and electrical fields in the presence and absence of phase change (liquid-vapor) and presence and absence of gravity. This fundamental research has led to development of potential applications in electrically-driven heat transfer enhancement. Meso- and micro-scale EHD conduction pumps were studied as mechanisms for flow generation in single- and two-phase heat transport systems. In addition, EHD conduction pumping was studied as a technique to augment pool boiling and liquid film boiling heat transfer. An analytical model was developed to characterize the influence of an electrical field on pool boiling critical heat flux. Most recently, two experiments were conducted on board a parabolic flight to study EHD conduction-driven liquid film boiling and micro-scale, single-phase flow in microgravity.

One of the most promising applications of electrohydrodynamic (EHD) pumps occurs at the microscopic scale. However, microscopic dimensions do not always imply microscopic characteristics, and stringent requirements are sometimes imposed on the values of certain variables—for instance, a flow rate of the order of 10 ml/s and a pumping pressure of 100 kPa. This study proposes an EHD pump system based on a holed metal-clad insulation barrier pair that generates high-performance characteristics. A feature of the system is the focusing of electric field lines inside the holes, which increases the electric field strength and activates charge formation processes. Dodecane with 10% Span 85 was used as the working dielectric liquid with a conductivity of 8 × 10−9 S/m. The Onsager effect is believed to be the dominant charge formation mechanism in the pump with some injection contribution. We measured the characteristics of the electric current (curves of current–voltage and current–time) as well as the performance-related characteristics of the pump in experiments (curves of pressure–voltage and flow rate–pressure at different voltages). The scalability of the flow rate of the proposed EHD pump was investigated by comparing single-hole and nine-hole configurations. As a result, a non-linear growth of the pump performance on the number of holes was obtained, with the distance between the holes comparable to the inter-electrode gap. The estimated flow rate and pressure for the proposed modulus EHD pump with dimensions of 1 cm3 can reach values of 82 ml/s and 620 kPa, respectively.

Flow characteristics of a two-stage electrohydrodynamic (EHD) gas pump in a circular tube have been experimentally investigated for two different sizes (61.8 and 127.8 mm in diameter). Each stage uses eight emitting electrodes flush mounted on the tube wall. Two electrode configurations, aligned and offset, with fixed spacing between electrodes have been considered in this study. The main objective of the study is to verify whether or not a two-stage EHD pump can sustain or even increase the volume flow rate produced by a single-stage pump over a greater tube length. To this end, electrodes at both stages are charged at the same voltages in positive polarity from 18 to 22 kV. Velocities are measured at three cross sections along the tube length and then integrated to obtain the volume flow rate. The velocity profile and volume flow rate delivered by the single top stage of the pump are compared with those produced by the two stages combined to give additional insight to the problem. The results obtained have important implications for practical applications of EHD gas pump.

Numerical simulation and design optimization of an electrohydrodynamic pump for dielectric liquids