Recent experimental advances in electrohydrodynamic conduction pumping research

Thermal boundary layer depletion in minichannels by electrohydrodynamic conduction pumping

Flow boiling in mini and microchannels has become an attractive option for many applications, such as compact and low charge heat exchangers. Microchannel heat exchangers, however, are more susceptible to maldistribution between parallel flow channels. When operating during uneven heat load conditions, the maldistribution becomes even more severe. Electrohydrodynamic (EHD) conduction pumping technology offers an innovative way to redistribute flow between parallel branches in a microchannel heat exchanger and is also being explored as a next generation mechanism of microgravity heat transport. In EHD conduction pumping, a strong electric field interacts with dissociated electrolytes in dielectric fluid to generate a net body force, and thus, a net flow, with no moving parts, no acoustical noise, lower power consumption, and the ability to operate in microgravity. An EHD conduction pump was designed, fabricated, and tested for upstream flow distribution control of a parallel microchannel evaporator in an opposing configuration. Flow redistribution capability was measured at system flowrates up to 6 ml/min. The EHD conduction pump was capable of completely blocking and reversing the flow in its branch. Recovery from near critical heat flux conditions up to a maximum heat flux of 77.5 W/cm2 was also demonstrated for the operating conditions and design of this study. This was achieved in the absence of enhanced surfaces. The working fluid is HFE 7100. The results show that EHD conduction is able to effectively control the flow distribution of the microchannel evaporator, however, its effectiveness decreases with increasing heat flux and flowrate.

Electrohydrodynamic (EHD) conduction pump is a new concept which has been recently explored. Net pumping is achieved by properly utilizing the heterocharge layers present in the vicinity of the electrodes. This paper presents an innovative electrode design which provides pressure head on the order of 600 Pa per an electrode pair operated at 20 kV with less than 0.08 W of electric power. An EHD conduction pump consisting of six pairs was designed and installed in the liquid passage of a monogroove heat pipe. The EHD conduction pump drastically increased the heat transport capacity of the heat pipe. Furthermore, the EHD conduction pump provided immediate recovery from the dryout condition.

Effect of electrode arrangement on heat transfer enhancement by electrohydrodynamic conduction pumps in a rectangular channel

Heat pipes are well-known as simple and effective heat transport devices, utilizing two-phase flow and the capillary phenomenon to remove heat. However, the generation of capillary pressure requires a wicking structure and the overall heat transport capacity of the heat pipe is generally limited by the amount of capillary pressure generation that the wicking structure can achieve. Therefore, to increase the heat transport capacity, the capillary phenomenon must be either augmented or replaced by some other pumping technique. Electro-hydrodynamic (EHD) conduction pumping has been demonstrated as an effective method for pumping liquid films by using DC electric fields and a dielectric working fluid. Beyond increased pumping capacity, EHD conduction pumping offers other advantages over capillary pumping, such as active control of the pumping capacity via the intensity of the applied electric field. This experimental study demonstrates the prospects of a macro-scale two-phase heat transport device that is driven by EHD conduction pumping. Various liquid film thicknesses are considered. In each case, the performance of the EHD-driven heat transport device at various electric field intensities is compared to the capabilities of the same device under gravity alone. The effect of tilt on the device is also considered.

Liquid film flow boiling heat transfer driven by electrohydrodynamic (EHD) conduction pumping is experimentally studied on a surface with a novel metal-plated nanofiber-mat coating. The nanotextured surface is formed on a copper substrate covered by an electrospun polymer nanofiber mat, which is copper-plated as a postprocess. The mat has a thickness of about 30 μm and is immersed in saturated HCFC-123. The objective is to study electrowetting of the copper-plated nanofiber-enhanced surface via EHD conduction pumping mechanism for the entire liquid film flow boiling regime leading up to critical heat flux (CHF), and compare it to the bare surface without EHD-driven flow. The results show that with the combination of these two techniques, for a given superheat value, enhancement in heat flux and boiling heat transfer coefficient is as high as 555% compared to the bare surface. The results are quite promising for thermal management applications.

The research in this paper extends previous liquid film flow boiling studies by including the effect of an additional electrohydrodynamic (EHD) force, namely the dielectrophoretic (DEP) force. Rather than using only EHD conduction pumping of the liquid film to electro-wet the heater surface, a localized non-uniform electric field above the heater surface is also used to generate a dielectrophoretic force for improved vapor bubble extraction during the nucleate boiling regime. The effect of liquid film height and applied potential are studied as a function of heater superheat and heat flux. The study considers the sole and combined effect of DEP with EHD conduction pumping. A brief analytical study is also used to estimate the expected dielectrophoretic force magnitude and explain the results. All of the above studies are also used to quantify the enhancement in heat transfer that can be achieved when heat transport systems are driven or augmented by these electrohydrodynamic phenomena. The results show remarkable enhancement of up to 1217% in heat flux and boiling heat transfer coefficient for a given superheat when both mechanisms are used simultaneously. The experimental data are important for applications in thermal management in terrestrial and micro-gravity conditions.

Heat transfer enhancement of backstep flow by means of EHD conduction pumping

Experimental study of electrohydrodynamic pumping through conduction phenomenon

The paper presents the computer simulation results for a single section of electrohydrodynamic (EHD) conduction pump with and without taking into account the enhancement of the dissociation rate under the action of the strong electric field (the Wien effect). The computations were carried out on the basis of the complete set of EHD equations using commercial software package COMSOL Multiphysics. The behavior of EHD flow inside the pump was investigated for different ratios between positive and negative ion mobilities and the effect of the latter on the pumping efficiency was estimated. The features of the pump operation in the case of the Wien effect presence were investigated. It was shown that the enhancement of the dissociation rate can lead to the reversion of EHD flow direction with increasing voltage. Besides, the results for the present computer model were compared to those for the simplified one (based on the hydrostatic approach), and considerable discrepancy between the calculated pressure drops was revealed.

This paper extends previous liquid film flow boiling studies by including the effect of an additional electrohydrodynamic (EHD) force, namely, the dielectrophoretic (DEP) force. Rather than using only EHD conduction pumping of the liquid film to electro-wet the heater surface, a localized nonuniform electric field above the heater surface is established to generate a DEP force for improved vapor bubble extraction during the nucleate boiling regime. The effects of liquid film height and applied potential are studied as a function of heater superheat and heat flux. A brief analytical study is also used to estimate the expected DEP force magnitude to explain the results. All of the above studies are also used to quantify the enhancement in heat transfer that can be achieved when heat transport systems are driven or augmented by these two EHD mechanisms. The results show remarkable enhancement of up to 1217% in boiling heat transfer coefficient at a given superheat when both mechanisms are used simultaneously. The experimental data are important for applications in thermal management in terrestrial and space conditions.

The ongoing development of modern electronic systems leads to smaller, more powerful devices that are expected to operate in complex environments. Due to this, advanced thermal management technologies are required to meet the growing demand, especially in space where two-phase thermal systems are limited by the absence of gravity. Electrohydrodynamic (EHD) and dielectrophoretic (DEP) forces can be used to sustain stable liquid film boiling in micro-gravity, which is otherwise impractical due to the lack of a required buoyancy force to initiate bubble departure. EHD and DEP are phenomena that are represented by the interaction between electric fields and fluid flow. The DEP force especially is characterized by the unique ability to act on liquid/vapor interfaces due to a high gradient of electrical permittivity, allowing for two phase operation. This study investigates the effect of EHD conduction pumping coupled with DEP vapor extraction on liquid film flow boiling during a microgravity parabolic flight, and it characterizes the future two-phase microgravity heat transport technology prior to testing on the International Space Station (ISS). The results of this study show that EHD and DEP raise critical heat flux, lower heater surface temperature, and successfully sustain boiling in micro-gravity all at the cost of low power consumption. Additionally, the heat transfer data captured in terrestrial, microgravity, and 1.8 g conditions compare well, indicating that this technology can provide thermal enhancement independent of gravity. This study paves the way for future implementation of EHD-driven two-phase heat transport devices into space and aeronautical electronics applications.

The ongoing development of modern electronic systems leads to smaller, more powerful devices that are expected to operate in complex environments. Due to this, advanced thermal management technologies are required to meet the growing demand, especially in space where two-phase thermal systems are limited by the absence of gravity. Electrohydrodynamic (EHD) and dielectrophoretic (DEP) forces can be used to sustain stable liquid film flow boiling in the absence of gravity, which is otherwise impractical due to the lack of a required buoyancy force to initiate bubble departure. EHD is a phenomenon that is represented by the interaction between electric fields and fluid flow. The DEP force is characterized by its ability to act on liquid/vapor interfaces due to a high gradient of electrical permittivity. This study investigates the heat transfer characteristics of EHD conduction pumping driven liquid film flow boiling coupled with DEP vapor extraction during a microgravity parabolic flight and on the ground. The results of this study show that EHD and DEP raise the critical heat flux, lower heater surface temperature, and successfully sustain boiling in both microgravity and on the ground with low power consumption. Additionally, the heat transfer data captured in terrestrial, microgravity, and 1.8 g conditions compare well, indicating that combining these mechanisms can provide thermal enhancement independent of gravity. This study provides fundamental understanding of electrically driven liquid film flow boiling in the presence of phase change, paving the way toward developing next-generation heat transport devices for space and terrestrial applications.

Steady-state 2-D electrohydrodynamic pumping through bipolar hetero-charge conduction phenomenon has been investigated numerically. In order to validate the presented numerical algorithm, the pump geometry was chosen to be identical to the device whose experimental data is available in the literature. The concentrations of the positive and negative ions and the electric field distribution of the pump were calculated. The resulting static pressure generation of the pump was predicted for the refrigerant R-123 at different applied voltages ranging between 2 to 20kV DC. The comparison between the predicted static pressure generation and the previous experimental results in the absence of fluid flow shows a good agreement with a maximum deviation of 12.5% at 20 kV applied voltage. In the present work, the electrical conductivity of R-123 was assumed to be the most recent proposed value of σ=7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> S/m. Assuming this value of electrical conductivity, the numerical model predicts the hetrocharge layer thicknesses in the order of gap spacing even at low applied voltage and weak field regime. By increasing the applied voltage, above ~15kV, the heterocharge layers of the opposite electrodes extend to the entire gap spacing and create an overlapping region. Assuming three orders of magnitude higher value of electrical conductivity for R-123 in the previous numerical studies, the thickness of the hetrocharge layer and pressure generation was underestimated by almost two orders of magnitude. Through extensive numerical experiments, the electrical conductivity of the working fluid was found to be an important parameter to determine the heterocharge layer thickness, electric body force, and predicted static pressure. The issues related to the scaling of the conduction pump when the heterocharge layers create an overlapping region in the reduced gap spacing are discussed.

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.