Electrohydrodynamic Micropump Research Articles

Rheodynamics of viscoelastic subdiffusive channel flows: Low Weissenberg number regime

Direct numerical simulations of viscoelastic, subdiffusive, and plane Poiseuille flow, representing thick polymer solutions including polymer melts, flows of liquid crystals, as well as biological flow such as mucus, are reported. The stress strain equation is fundamentally derived by relating the timescale exponent at the microscale (tα, with 0<α≤1) with the fractional order of the time derivative, α, of the corresponding non-linear equation in the continuum. The resultant stress constitutive equation is the fractional variant of the well-known upper convected Maxwell equation. In order to quantify the formation of spatiotemporal macrostructures (or the non-homogeneous regions of high viscosity at moderate to high fluid inertia), the space of symmetric positive definite polymer conformation tensors is visualized using a Riemannian metric along with its three scalar invariants. Numerical simulations of the channel flow, in the regime of low to moderate Reynolds number and low Weissenberg number, effectively capture these flow-structures by providing (i) a better resolution of the instantaneous regions of elastic shocks (which are the alternating regions of expanded and compressed polymer volume, in comparison with the volume of the mean conformation tensor), and (ii) a better resolution to detect neighborhoods where the mean conformation tensor tends to be significantly different in comparison to the instantaneous conformation tensor, thereby corroborating the experimentally observed flow-instability transition of subdiffusive flows. Finally, the strength of the subdiffusive flow model and the invariant theory is highlighted through an application of an electrohydrodynamic micropump.

Effect of doping ferrocene in the working fluid of electrohydrodynamic (EHD) micropumps

The effect of doping ferrocene in the working fluid of electrohydrodynamic micropumps was investigated under the application of DC electric fields. The micropump consisted of 100 planar electrode pairs that were embedded along the bottom wall of a 100-micron-high, 5-mm-wide and 26-mm-long microchannel. The width of the emitter and collector electrodes was 20 and 40 µm, respectively, with inter-electrode spacing of 30 µm. A redox dopant, ferrocene, was diffused homogeneously into the working fluid HFE-7100 at 0.05, 0.1 and 0.2 % concentration by weight. The static pressure head generation and flow rate at different back pressure conditions were measured under different applied DC voltages. The current and pressure generated with the doped working fluid were significantly higher than with pure HFE-7100 under an applied DC field. A maximum static pressure of 6.7 kPa and flow rate of 0.47 mL/min at no back pressure were achieved at 700 V.

Ion drag electrohydrodynamic (EHD) micro-pumps under a pulsed voltage

The use of pulsed voltages to improve the performance of an Electrohydrodynamic (EHD) micropump with HFE7100 as the working fluid was investigated. The micropump consisted of 100 planar electrode pairs that were embedded along the bottom wall of a 100 μm high microchannel. The pressure generation was measured at different operating pulse voltage parameters. An optimum pulse repetition rate and duty cycle for the pump geometry and fluid was found for maximum static pressure. The maximum pressure at the optimum pulse repetition rate was 75% greater than the average of the pressures generated at the two DC voltage levels.

Electrohydrodynamic Injection Micropump With Composite Gold and Single-Walled Carbon Nanotube Electrodes

The presence of microfeatures/nanofeatures with sharp asperities on the emitter electrodes of ion drag electrohydrodynamic (EHD) micropumps is likely to enhance the local electric field and charge injection significantly, and thus the pressure generation and flow rates. The objective of this paper is to investigate the performance of EHD micropumps with single-walled carbon nanotubes (SWCNT) on the emitter electrodes. The micropumps had 100 pairs of planar electrodes where the width of the emitter and collector electrodes was 20 and 40 $\mu \text{m}$ , respectively, with a cross-sectional domain of $100~\mu \textrm {m} \times 5$ mm. Two micropumps with interelectrode spacing of 120 and 40 $\mu \text{m}$ were tested with a smooth emitter surface, and where SWCNT were electrophoretically deposited on the emitter electrodes using HFE7100 as the working fluid. The threshold voltage for charge injection lowered by a factor of 3 and 1.4 for the two pumps with SWCNT on the emitter electrodes compared with the smooth electrode case. The corresponding static pressure head increased by a factor 5, while the flow rate at no external back pressure increased by a factor 3 for the pump with interelectrode spacing of 120 $\mu \text{m}$ . For the pump with interelectrode spacing of 40 $\mu \text{m}$ , a maximum static pressure of 4.7 kPa was achieved at 900 V with SWCNT on the emitter electrode. [2014-0308]

Electrohydrodynamic Conduction Driven Single- and Two-Phase Flow in Microchannels With Heat Transfer

Microchannels have well-known applications in cooling because of their ability to handle large quantities of heat from small areas. Electrohydrodynamic (EHD) conduction pumping at the microscale has previously been demonstrated to effectively pump dielectric liquids through adiabatic microchannels by using electrodes that are flushed against the walls of the channel. In this study, an EHD micropump is used to pump liquid within a two-phase loop that contains a microchannel evaporator. Additional EHD electrodes are embedded within the evaporator, which can be energized separately from the adiabatic pump. The effect of these embedded electrodes on the heat transport process, flow rate, and pressure in the micro-evaporator and on the two-phase loop system is characterized. Local enhancements are found to be up to 30% at low heat fluxes. The reverse effect that phase-change has on the EHD conduction pumping phenomenon is also quantified.

Development of an EHD Micropump to Generate Oscillating Flow at Low Frequencies (Effect of Waveform on the EHD Pumping)

An electrohydrodynamic (EHD) micropump to generate oscillating flow is newly developed and experimentally tested using an arrangement of thin stainless steel wires. A working fluid is accelerated from the charged electrode to the ground electrode by a high electric field. The electric body force responsible for this acceleration is primarily the Coulomb force. In order to increase the electric field at low applied voltage, the electrode gap between the charged and ground electrodes is reduced to 0.2 mm. The size of the present EHD pump is 24 mm × 30 mm × 7.8 mm, in which ten pairs of electrodes are fabricated. In order to generate oscillating flows, the sinusoidal wave voltage and the rectangular wave voltage are applied. The present EHD pump is demonstrated to successfully generate oscillating flows at low frequencies (0.01-5 Hz).

Electrohydrodynamic pumping in microsystems

The physical principles behind the electrohydrodynamic (EHD) actuation in microsystems is presented by reviewing five different EHD micropumps. These are classified into two groups: micropumps that exert electric forces in the liquid bulk and micropumps that exert forces in the diffuse double layer. This review of five EHD micropumps allows us to analyse the EHD actuation ranging from very insulating liquids to electrolytic solutions.

On the Modeling and Simulation of Ion Drag Electrohydrodynamic Micropumps

A numerical model for ion-drag electrohydrodynamic (EHD) micropumps has been developed. The Poisson and charge conservation equations are solved to determine the electric body force within the flow domain. The charge distribution at the electrodes is assumed to depend on the magnitude and the gradient of the electric field at the surface of the electrode. The flow field is then determined by solving the momentum equation with the inclusion of the electric body force. Simulations were performed for micropump configurations that consisted of a series of planar electrode pairs embedded along the bottom wall of a microchannel. A two-dimensional segment of the channel with a single electrode pair is simulated using periodic boundary conditions at the inlet and outlet for the charge and electric fields. An empirical model was developed to estimate the charge boundary condition for the simulations. The simulation results were in good agreement with existing experimental data. The model was then used to perform a parametric study of the effect of channel height on the pump performance.

Design, fabrication and experimental research for an electrohydrodynamic micropump

This paper presented a novel electrohydrodynamic (EHD) micropump based on MEMS technology. The working mechanisms and classification of EHD micropump were introduced. The fabrication process of EHD micropump was presented with the material selection, optimal design of microelectrode and assembly process. Static pressure experiments and flow experiments were carried out using different fluid and the channel depth. The results indicated that the micropump could achieve a maximum static pressure head of 268 Pa at an applied voltage of 90 V. The maximum flow rate of the micropump-driven fluid could reach 106 μL/min. This paper analyzed the future of combining micropump with heat pipe to deal with heat dissipation of high power electronic chips. The maximum heat dissipation capacity of 87 W/cm2 can be realized by vaporizing the micropump-driven liquid on vaporizing section of the heat pipe.

Effect of micropillar electrode spacing on the performance of electrohydrodynamic micropumps

Electrohydrodynamic (EHD) micropumps with three-dimensional 50 μm × 50 μm micropillar electrodes were fabricated and tested in this study. Two basic electrode configurations were investigated: (i) micropillar emitter and collector electrodes (symmetric) and (ii) micropillar emitter and planar collector electrodes (asymmetric). The micropumps were fabricated by integrating chromium/gold planar electrodes with electroplated 3-D Nickel micropillars on a glass substrate with a 100 μm high PDMS microchannel. The effect of the spanwise micropillar spacing on the pump performance was determined. The pumps were tested using HFE-7100 as the working fluid for the maximum pressure generation under a no flow condition. The micropumps with the asymmetric electrode design generated a significantly higher pressure head than the corresponding micropumps with symmetric electrode configuration for the same applied voltage, with lower power consumption. A decrease in the spanwise spacing of the micropillar electrodes increased the pump performance for the symmetric configuration, while the performance decreased for the asymmetric configuration.

Experimental Characterization of an Electrohydrodynamic Micropump for Cryogenic Spot Cooling Applications

This article presents a study on the characterization of a planar, multistage, electrohydrodynamic (EHD) ion-drag micropump for pumping of liquid nitrogen. Two designs of the pump, consisting of different emitter configurations (flat and saw-tooth), similar emitter-collector spacing (50 microns), and similar gaps between successive electrode pairs (100 microns), were tested at DC voltages ranging from 0 to 2.5 kV. The electric currents they generated and the corresponding static pressure heads were measured to characterize the pumping performance. Pressure and current onset voltages as well as pressure-voltage (P-V) and pressure-current (P-I) relationships were investigated. The highest pressure head (30 Pa at 1700 V) was generated with the saw-tooth design. After collecting and processing the data for various prototypes, it was evident that incorporating saw-tooth electrodes can significantly improve the performance of the micropump.

Development of an Electrohydrodynamic (EHD) Micropump to Generate Oscillating Flow at Low Frequencies

An electrohydrodynamic (EHD) micropump to generate oscillating flow is newly developed and experimentally tested using an arrangement of thin stainless steel wires. A working fluid is accelerated from the charged electrode to the ground electrode by a high electric field. The electric body force responsible for this acceleration is primarily the Coulomb force. To increase the electric filed, the distance between the charged and ground electrodes is 0.2 mm. The size of the present EHD pump is 24×30×7.8 mm. Since the pressure increases with the increase in the number of the electrode pairs, a pumping channel fabricated in this EHD pump is bent in parallel so as to increase the number of electrode pairs. This channel has the dimensions of 24×48×0.9 mm, in which ten pairs of electrodes are fabricated. The maximum static pressure generated by the present EHD pump is approximately 550 Pa at an input of DC 1 kV, and the maximum flow rate is 4.3 ml/min at the unloaded condition. In order to generate symmetric oscillating flows, alternating voltage is applied. The present EHD pump is demonstrated to successfully generate symmetric oscillating flows at low frequencies (0.01 Hz ∼ 0.05 Hz)

1804 EHDマイクロポンプにおける電極の非対称性と流路高さの影響(OS18-2 ナノ・マイクロ流体のダイナミクス,オーガナイズドセッション)

The effect of asymmetry in the electrode geometry and channel height on the performance of electrohydrodynamic(EHD) micropumps was studied. The micropumps consisted of two glass substrate on which chromium/gold planar electrodes were designed. The pumps were tested using HFE-7100 as the working fluid. The micropumps with an asymmetric-electrode design, where the emitter and collector electrode widths were different, generated a lower pressure head than the corresponding micropumps with symmetric-electrode designs for same applied voltage. The micropumps with a channel height of 100 μm generated a higher pressure head than the corresponding micropumps with 50 μm and 150 μm channel height for same electric field. It was found that maximum static pressure was generated with the symmetric-electrode design and the channel height of 100 μm.

Effect of Electrode Asymmetry on Performance of Electrohydrodynamic Micropumps

The effect of asymmetry in the electrode geometry and interelectrode spacing on the performance of ion-drag-type electrohydrodynamic micropumps was studied. The micropumps consisted of chromium/gold planar electrodes on a glass substrate that was integrated within a polydimethylsiloxane microchannel that was 100 mum in height. The pumps were tested using HFE-7100 as the working fluid for the maximum-pressure generation under a no-flow condition and the maximum flow rate under a no-back-pressure condition. The micropumps with an asymmetric-electrode design, where the emitter and collector electrode widths were different, generated a significantly higher pressure head and flow rate than the corresponding micropumps with symmetric-electrode designs for the same applied voltage. The power consumption of the pumps with asymmetric electrodes was significantly lower than that with symmetric electrodes.

Electrohydrodynamic micropumps with asymmetric electrode geometries for microscale electronics cooling

The development of effective microscale thermal management solutions is important to further advance microscale electronics because of increasing heat flux densities in these devices. There is an increasing trend towards liquid based cooling solutions because of their much higher heat removal capacities compared to air cooling methods. Electrohydrodynamic (EHD) micropumps are ideally suited for these applications due to their small form factor, low power consumption and ability to work with dielectric heat transfer fluids. In addition, EHD micropumps have no moving parts and are amenable to conventional microfabrication techniques. Current EHD micropump designs, however, generate very low flowrates and pressure head to be practically useful. Here, we demonstrate for the first time, that an asymmetry in the electrode geometry (both 2D and 3D) will result in significantly higher pressure generation with lower power consumption than conventional symmetric electrode designs.

Ac-field-induced fluid pumping in microsystems with asymmetric temperature gradients

We present two different designs of electrohydrodynamic micropumps for microfluidic systems. The micropumps have no movable parts, and their simple design allows for fabrication by microsystems technology. The pumps are operated by ac voltages from 1 to 60 V and were tested with aqueous solutions in the conductivity range of 1-112 mS m(-1). The pump effect is induced by an ac electric field across a fluid medium with an inhomogeneous temperature distribution. It is constant over a wide range of the ac field frequency with a conductivity-dependent drop-off at high frequencies. The temperature-dependent conductivity and permittivity distributions in the fluid induce space charges that interact with the electric field and induce fluid motion. The temperature distribution can be generated either by Joule heating in the medium or by external heating. We present experimental results obtained with two prototypes featuring Joule heating and external heating by a heating filament. Experimental and numerical results are compared with an analytical model.

Accumulation and filtering of nanoparticles in microchannels using electrohydrodynamically induced vortical flows

We present an approach for the accumulation and filtering of nano- and microparticles in microfluidic devices that is based on the generation of electric traveling waves in the radio-frequency range. Upon application of the electric field via a microelectrode array, complex particle trajectories and particle accumulation are observed in well-defined regions in a microchannel. Through the quantitative mapping of the 3-D flow pattern using two-focus fluorescence cross-correlation spectroscopy, two vortices could be identified as one of the sources of the force field that induces the formation of particle clouds. Dielectrophoretic forces that directly act on the particles are the second source of the force field. A thorough 2-D finite element analysis identifies the electric traveling wave mechanism as the cause for the unexpected flow behavior observed. Based on these findings, strategies are discussed, first, for avoiding the vortices to optimize electrohydrodynamic micropumps and, secondly, for utilizing the vortices in the development of microdevices for efficient particle accumulation, separation, and filtering. Such devices may find numerous biomedical applications when highly diluted nano- and microsuspensions have to be processed.

Effects of discrete-electrode configuration on traveling-wave electrohydrodynamic pumping

Traveling-wave electrohydrodynamic (EHD) micropumps can be incorporated into the package of an integrated circuit chip to provide active cooling. They can also be used for fluid delivery in microdevices. The pump operates in the presence of a thermal gradient through the fluid layer such that a gradient in electrical conductivity is established allowing ions to be induced. These ions are driven by a traveling electric field. Such a traveling electric field can be realized in practice only via discrete electrodes upon which the required voltages are imposed. The impact of using discrete electrodes to create the traveling wave on the flow rates generated is explored through numerical modeling. The change in performance from an ideal sinusoidal voltage boundary condition is quantified. The model is used to explore the widths of electrodes and the intervening isolation regions that lead to optimized pumping. The influence of the choice of working fluid on the performance of the pump is determined using an analytical model.

A circular microchannel integrated with embedded sprial electrodes used for fluid transportation

This paper proposes a novel method to fabricate a circular microchannel with embedded spiral electrodes used for fluid transportation by inserting glass capillary as sacrificial mould. Utilizing a rolling exposure technique in the photolithography process, the continuous spiral electrode has been formed on the non-planar surface of a glass capillary successfully. Moreover, using the concept of sacrificial layer, the spiral electrodes are transferred on the inner surface of a SU-8 circular microchannel with a diameter of 350 μm. The fabricated device was regarded as an electrohydrodynamic (EHD) micropump, and has a pumping capacity of 4.5 μl/min herein.

Controlling electrohydrodynamic pumping in microchannels through defined temperature fields

An electrohydrodynamic micropump driven by a high-frequency traveling electric wave (1–10MHz) at low voltage (4–10V) is presented. The pumping rate is dependent on the profile (inhomogeneities) of the dielectric properties of the medium. Defined temperature fields serve as a versatile mean for the control of these profiles. We produce temperature fields in two ways: by the electric wave itself and by external Peltier elements. We investigated experimentally the influence of two-dimensional and three-dimensional electrode arrays on the pumping behavior and compared it to theoretical predictions of temperature field calculations using finite element analysis. The two results are in good agreement. Furthermore, we demonstrate the effect of an additional external temperature field that results in an advanced performance of the pump.