Parallel Computation of Electric Potential in the EHD Ion-Drag Micropump and the Performance Analysis of the Parallel System

The numerical solution of a computationally intensive model becomes more complex in terms of execution time required by a single processor. To speedup the computation, a suitable parallel computing architecture is required. This paper attempts to achieve a fast finite difference solution of electric potential in an EHD ion-drag micropump. A 2D Poisson’s equation is solved on a cluster of low cost computers using MATLAB. Numerical solution is obtained for the different mesh refinements and then the execution time, communication time, speedup and efficiency of parallel system are analyzed. The results showed that the speedup and efficiency of the system increases by increasing the grid points. The results also reveal that for each data size there is an optimum number of workers for obtaining the parallel numerical solution in minimum processing time

Micro Electromechanical Systems (MEMS) Based Microfluidic Devices for Biomedical Applications

Micro Electromechanical Systems (MEMS) based microfluidic devices have gained popularity in biomedicine field over the last few years. In this paper, a comprehensive overview of microfluidic devices such as micropumps and microneedles has been presented for biomedical applications. The aim of this paper is to present the major features and issues related to micropumps and microneedles, e.g., working principles, actuation methods, fabrication techniques, construction, performance parameters, failure analysis, testing, safety issues, applications, commercialization issues and future prospects. Based on the actuation mechanisms, the micropumps are classified into two main types, i.e., mechanical and non-mechanical micropumps. Microneedles can be categorized according to their structure, fabrication process, material, overall shape, tip shape, size, array density and application. The presented literature review on micropumps and microneedles will provide comprehensive information for researchers working on design and development of microfluidic devices for biomedical applications

Electrohydrodynamic Enhancement of Heat Transfer and Mass Transport in Gaseous Media, Bulk Dielectric Liquids and Dielectric Thin Liquid Films

Controlling transport phenomena in liquid and gaseous media through electrostatic forces has brought new important scientific and industrial applications. Although numerous EHD applications have been explored and extensively studied so far, the fast-growing technologies, mainly in the semiconductor industry, introduce new challenges and demands. These challenges require enhancement of heat transfer and mass transport in small scales (sometimes in molecular scales) to remove highly concentrated heat fluxes from reduced size devices. Electric field induced flows, or electrohydrodynamics (EHD), have shown promise in both macro and micro-scale devices. Several existing problems in EHD heat transfer enhancements were investigated in this thesis. Enhancement of natural convection heat transfer through corona discharge from an isothermal horizontal cylindrical tube at low Rayleigh numbers was studied experimentally and numerically. Due to the lack of knowledge about local heat transfer enhancements, Mach-Zehnder Interferometer (MZI) was used for thermal boundary layer visualization. For the first time, local Nusselt numbers were extracted from the interferograms at different applied voltages by mapping the hydrodynamic and thermal field results from numerical analysis into the thermal boundary layer visualizations and local heat transfer results. A novel EHD conduction micropump with electrode separations less than 300 µm was fabricated and investigated experimentally. By scaling down the pump, the operating voltage was reduced one order of magnitude with respect to macro-scale pumps. The pumping mechanism in small-scales was explored through a numerical analysis. The measured static pressure generations at different applied voltages were predicted numerically. A new electrostatically-assisted technique for spreading of a dielectric liquid film over a metallic substrate was proposed. The mechanism of the spreading was explained through several systematic experiments and a simplified theoretical model. The theoretical model was based on an analogy between the Stefan’s problem and current problem. The spreading law was predicted by the theoretical approach and compared with the experimental results. Since the charge transport mechanism across the film depends on the thickness of the film, by continuing the corona discharge exposure, the liquid film becomes thinner and thinner and both hydrodynamic and charge transport mechanisms show a cross-over and causes different regimes of spreading. Four different regimes of spreading were identified. For the first time, an electrostatically accelerated molecular film (precursor film) was reported. The concept of spreading and interfacial pressure produced by a corona discharge was applied to control an impacting dielectric droplet on non-wetting substrate. For the first time, the retraction phase of the impact process was actively suppressed at moderate corona discharge voltages. At higher corona discharge strengths, not only was the retraction inhibited but also the spreading phase continued as if the surface was a wetting surface

EXPERIMENTAL AND COMPUTATIONAL INVESTIGATION OF PLANAR ION DRAG MICROPUMP GEOMETRICAL DESIGN PARAMETERS

To deal with increasing heat fluxes in electronic devices and sensors, innovative new thermal management systems are needed. Proper cooling is essential to increasing reliability, operating speeds, and signal-to-noise ratio. This can be achieved only with precise spatial and temporal temperature control. In addition, miniaturization of electric circuits in sensors and detectors limits the size of the associated cooling systems, thereby posing an added challenge. An innovative answer to the problem is to employ an electrohydrodynamic (EHD) pumping mechanism to remove heat from precise locations in a strictly controlled fashion. This can potentially be achieved by micro-cooling loops with micro-EHD pumps. Such pumps are easily manufactured using conventional microfabrication batch technologies. The present work investigates ion drag pumping for applications in reliable and cost effective EHD micropumps for spot cooling. The study examines the development, fabrication, and operation of micropumps under static and dynamic conditions. An optimization study is performed using the experimental data from the micropump prototype tests, and a numerical model is built using finite element methods. Many factors were involved in the optimization of the micropump design. A thorough analysis was performed of the major performance-controlling variables: electrode and inter-electrode pair spacing, electrode thickness and shape, and flow channel height. Electrode spacing was varied from 10 µm to 200 µm and channel heights from 50 µm to 500 µm. Also, degradation of the electrodes under the influence of an intense electric field was addressed. This design factor, though important in the reliability of EHD micropumps, has received little attention in the scientific and industrial applications literature. Experimental tests were conducted with prototype micropumps using the electronic liquid HFE7100 (3M®). Flow rates of up to 15 ml/min under 15 mW power consumption and static pumping heads up to 750 Pa were achieved. Such performance values are acceptable for some electronic cooling applications, where small but precise temperature gradients are required

EXPERIMENTAL AND COMPUTATIONAL ANALYSIS OF AN ELECTROHYDRODYNAMIC MESOPUMP FOR SPOT COOLING APPLICATIONS

As electronic products become faster, more compact, and incorporate greater functionality, their thermal management becomes increasingly more challenging as well. In fact, shrinking system sizes, along with increasing circuit density, are resulting in rapid growth of volumetric heat generation rate and reduction in surface area for adequate heat dissipation. Moreover, system miniaturization by employing microfabrication technology has had a great influence on thermal and fluid research Smaller systems have many attractive characteristics and can be more conveniently fabricated using batch production technologies. One of the fields showing promising potential in microsystems and electronics cooling is the use of the phenomenon of electrohydrodynamics or EHD defined as a direct interaction between the electric and hydrodynamic fields where the electric field introduces fluid motion. The objectives of the present study were to identify the physics of these phenomena as related to the present study, to simulate it numerically, and to verify the modeling through experiments. More specifically, the goals were to develop a novel numerical methodology to simulate the highly complex interaction between fluid flow and electrical fields. Next, to verify the model a mesoscale ion-injection pump was designed and fabricated, followed by a set of experiments that characterized the pump's performance. The experiments will also demonstrate the application potential of the concept in electronics cooling and particularly for spot cooling applications. Experimental tests were conducted on an EHD ion-injection mesopump to measure the flow rates and generated pressure heads with HFE -7100 as working liquid. It is shown that the results of two different flow rate measurement techniques that were employed, are in agreement. The experimental results also show that maximum flow rate of about 30 ml/min and pressure head of 270 Pa for the electrode gap of 250 m and voltage of 1500 V are achievable. A novel numerical modeling method was developed that incorporates both the injection and dissociation of ions. This modeling method is used to simulate the EHD mesopump. The numerical results show a fairly good agreement with experimental data

Characterisation of electrohydrodynamic fluid accelerators comprising highly asymmetric high voltage electrode geometries

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University London.Electrohydrodynamics (EHD) is a promising research field with several trending applications. Even though the phenomenon was first observed centuries ago, there is very little research until the middle 20th century, as the mechanisms behind it were very poorly understood. To this date, the majority of research is based on the development of empirical models and the presentation of laboratory experiments. This work begins with an extensive literature review on the phenomenon, clarifying conflicts between researchers throughout the history and listing the findings of the latest research. The literature review reveals that there are very few mathematical models describing even the most important parameters of the EHD fluid flow and most are either empirical or greatly simplified. As such, practical mathematical models for the assessment of all primary performance characteristics describing EHD fluid accelerators (Voltage Potential, Electric Field Intensity, Corona Discharge Current and Fluid Velocity) were developed and are begin presented in this work. These cover all configurations where the emitter faces a plane or another identical electrode and has a cylindrical surface. For configurations where the emitter faces a plane or another identical electrode and has a spherical surface, Corona Discharge Current and Fluid Velocity models have been presented as well. Laboratory experiments and computer simulations were performed and are being thoroughly presented in Chapter 4, verifying the accuracy and usability of the developed mathematical models. The laboratory experiments were performed using two of the most popular EHD electrode configurations - wire-plane and needle-grid. Finally, the findings of this research are being summarized in the conclusion, alongside with suggestions for future research. The step-by-step development of the equipotential lines mathematical model is presented in Appendix A. Appendix B covers the mathematical proof that the proposed field lines model is accurate and that the arcs are perpendicular to the surface of the electrodes and to all of the equipotential lines

IMECE2002-39584 ELECTRONICS SPOT COOLING WITH LIQUID NITROGEN

ABSTRACT This paper describes an ongoing research to evaluate and characterize electrohydro-dynamic (EHD) meso-and micropumps for spot cooling of sensors. In the proposed concept, the localized cooling is achieved by means of a flow of liquid nitrogen that is driven by an ion-drag pump towards the heat source, where heat is directly removed. First, a numerical heat transfer model will illustrate the advantages of the proposed concept of spot cooling with liquid nitrogen against a conventional conduction cooling. Next, we will present experimental results for pumping of liquid nitrogen via (EHD) a pump at the meso-scale, as well as experiments with EHD micro-pumps for pumping of HFE-7100 at room temperature. The objective of this research is to establish the optimum operational and design conditions for micro-pumping of liquid nitrogen for spot cooling applications