DYNAMIC MODELS FOR INDUCTION CHARGING OF SPHERICAL PARTICLES WITH SURFACE CONDUCTIVITY

The purpose of this research was to investigate the dynamics of induction charging for spherical particles assuming finite volume and surface conductivities, and arbitrary particle permittivity. All results, presented in this thesis, were based on numerical simulations on the COMSOL commercial software using the Finite Element Method. Simulations were performed for a conducting spherical particle with finite surface conductivity. The particle was resting on a ground electrode and exposed to an external electric field. The model was then extended to investigate multiple spherical particles stacked in an arbitrary pattern structure. Saturation charge and actual charging time constant were investigated. The rate of charge accumulation was affected significantly by the particle’s volume and surface conductivities, contact area with the ground electrode, and electric shielding due to proximity of stacked particles. To a less extent, the actual charging time was affected by particle permittivity. Furthermore, shielding the electric field from a given particle reduced its saturation charge significantly

The effect of environmental plasma interactions on the performance of the solar sail system

Interaction between the solar sail and the natural plasma environment were examined for deleterious impacts upon the operation of the sail and its associated payload. Electrostatic charging of the sail in the solar wind and in near earth environment were examined. Deployment problems were studied. An analysis of electromechanical oscillations coupling the sail to the natural plasma was performed. As a result of these studies, it was concluded that none of these effects will have a significant negative impact upon the sail operation. The natural environment will be significantly perturbed and this will preclude measurements of electric and magnetic fields from an attached payload

Wet electrostatic scrubbing for high efficiency submicron particle capture

Exposure to fine particulate matter has been associated with serious health effects, including respiratory and cardiovascular disease, and mortality. Very fine inhalable particles can remain suspended in the atmosphere for a long time, travel long distances from the emitting sources and, once inhaled, they can reach the deepest regions of the lungs and even enter in the circulatory system. Therefore, the smaller the particle size, the higher its toxicity. In typical combustion units used in process industry, the end-of-pipe technologies include trains of consecutive abatements devices. Nevertheless, the traditional particle abatement devices are mainly designed and optimized to treat particles with sizes above or around 1µm, and they are far less effective towards the submicron dimensions. Among the end-of-pipe technologies, the Wet Scrubbers (WS) are widely utilized in industry due to their capacity to capture simultaneously gaseous pollutants and particles. The main particle collection mechanisms involved in WS are those related to directional interception and inertial impact, which allow high particle abatement efficiency for particles in micrometric range. Both the mechanisms are instead ineffective in the submicron range, thus resulting in low collection efficiencies. It the past 40 years, it was demonstrated that the presence of electric charge of opposite polarities on the particles and the sprayed droplets can increase the capture efficiency due to Coulomb forces between the two phases. The presence of this additional contribution in a scrubber is an upgrade of the traditional wet scrubbing and the new process is commonly referred as Wet Electrostatic Scrubbing (WES). Experimental investigation of the pertinent literature confirmed the ability of WES to increase the particle capture efficiency respect to the classic wet scrubber, but submicron range is generally not directly investigated so that the best operating conditions to increase submicron particle abatement efficiency is still an unsolved problem. This optimization problem is mainly related to the difficulties to model wet electrostatic scrubbing process due to the high number of the variables involved, resulting in a complex experimental evaluation of the main collection mechanisms that are responsible of the particle capture. Above all, a significant hindrance to the assessment of a proper description of wet electrostatic scrubbing is the complexity of the electro-hydrodynamics of the charged water spray. In this work, a new experimental methodology was adopted to perform experiments in controlled conditions in order to allow an easier investigation of the effects of the main physical variables on the abatement of submicron particles emission. This experimental approach is based on the use of a lab scale batch reactor, in which charged particles produced by combustion are inserted. In the reactor, a train of uniform droplet size and charge is used to remove the suspended particles. This approach has the main advantages to make possible to investigate specific parameters (like the effect of droplet charge or its size) under well-defined conditions and therefore model the particle abatement process. Therefore, the objective of this work is the experimental analysis and the modeling of wet electrostatic scrubbing process for submicron particles with the new methodology developed and the evaluation of the influence of the main physical variables on the capture of submicron particles. The results obtained confirm that the particle abatement is significantly enhanced by charging both particles and droplets, and that the particle abatement rate is directly proportional to the particles and droplet charges and droplet concentration. Furthermore, tests with uncharged particles and charged droplets do not show any relevant increase in the scrubbing efficiency with respect to common wet scrubbing in the investigated conditions. The experimental results obtained were compared with the predictions of classical particle scavenging models valid for ambient temperature and humidity conditions. These models were rarely applied to submicron particles and found a reliable experimental support from the performed experiments. On the other hand, this comparison also confirm the reliability of the experimental methodology in the study of wet electrostatic scrubbing and encourage the development of further tests in experimental conditions more similar to that of industrial scrubbers

Charging Level and Deposition of Droplets in Electrostatic Painting

The process of electrostatic painting has become a very important method of coating in a wide range of industrial applications including those used in the automobile industry. The general principle of spray coating is to deposit liquid droplets or solid powder particles on coated targets having various shapes. The electrostatic coating process consists of three main stages: droplet formation and charging, transportation and deposition. The complication of this process is caused by various factors, such as the physical properties of the material to be used, the appropriate electrical and mechanical conditions and the target surface to be coated, which affects significantly the deposition uniformity and the finish quality, especially when it contains some sharp edges and recessed areas. In this thesis, a numerical investigation of the charging level on a spherical droplet formed out of a cylindrical ligament in an external uniform electric field is presented. The droplet charge on a single ligament was predicted for different droplet sizes, ligament lengths, ligament diameters and electrode widths. The effect of these model parameters on the charge levels was found to be significant. A mathematical approximation for the charge magnitude as a function of the droplet radius to some exponent and ligament length is also formulated. The value of the radius exponent decreases dramatically with increasing the ligament length. Also, the estimated values of the droplet charge were compared for linear and circular arrays of ligaments, which show a great influence of the geometry of the sprayer on the charge levels. A very good agreement between the experimental and numerical results in the case of a circular array of ligaments, including a specified space charge, was obtained. All numerical simulations were performed using COMSOL, a Finite Element commercial software. A further study is carried out to investigate the deposition thickness profile on a stationary and moving flat target by incorporating a numerical simulation of the industrial electrostatic coating process via ANSYS, a CFD commercial software. A modified injection pattern was suggested to achieve a closer agreement with the experimental data. The injection pattern includes 15 bands of different particle sizes (i.e. polydispersed particles) and charge to mass ratios. A combination of different injection angles and fractions of mass flow rates was suggested in each size band. A very good agreement between the experimental and numerical deposition patterns was obtained in both cases of a stationary and moving target. Also, the deposition thickness profile was calculated on a target surface with a small perturbation at the center using ANSYS numerical model. Different model parameters of a perturbed surface, such as the size of the indentation or the protrusion and the radius of the corner were investigated in this study. The numerical results reveal a very low particle concentration inside the indentation, which is caused by the Faraday cage effect and it is strongly affected by the depth of the indentation, while the edge effect, which shows the high concentration of deposited particles at the corner, increases with decreasing the radius of curvature. The predicted deposition patterns were very consistent with the calculated values of the electric field for different surface perturbations

Novel fine pitch interconnection methods using metallised polymer spheres

There is an ongoing demand for electronics devices with more functionality while reducing size and cost, for example smart phones and tablet personal computers. This requirement has led to significantly higher integrated circuit input/output densities and therefore the need for off-chip interconnection pitch reduction. Flip-chip processes utilising anisotropic conductive adhesives anisotropic conductive films (ACAs/ACFs) have been successfully applied in liquid crystal display (LCD) interconnection for more than two decades. However the conflict between the need for a high particle density, to ensure sufficient the conductivity, without increasing the probability of short circuits has remained an issue since the initial utilization of ACAs/ACFs for interconnection. But this issue has become even more severe with the challenge of ultra-fine pitch interconnection. This thesis advances a potential solution to this challenge where the conductive particles typically used in ACAs are selectively deposited onto the connections ensuring conductivity without bridging. The research presented in this thesis work has been undertaken to advance the fundamental understanding of the mechanical characteristics of micro-sized metal coated polymer particles (MCPs) and their application in fine or ultra-fine pitch interconnections. This included use of a new technique based on an in-situ nanomechanical system within SEM which was utilised to study MCP fracture and failure when undergoing deformation. Different loading conditions were applied to both uncoated polymer particles and MCPs, and the in-situ system enables their observation throughout compression. The results showed that both the polymer particles and MCP display viscoelastic characteristics with clear strain-rate hardening behaviour, and that the rate of compression therefore influences the initiation of cracks and their propagation direction. Selective particle deposition using electrophoretic deposition (EPD) and magnetic deposition (MD) of Ni/Au-MCPs have been evaluated and a fine or ultra-fine pitch deposition has been demonstrated, followed by a subsequent assembly process. The MCPs were successfully positively charged using metal cations and this charging mechanism was analysed. A new theory has been proposed to explain the assembly mechanism of EPD of Ni/Au coated particles using this metal cation based charging method. The magnetic deposition experiments showed that sufficient magnetostatic interaction force between the magnetized particles and pads enables a highly selective dense deposition of particles. Successful bonding to form conductive interconnections with pre-deposited particles have been demonstrated using a thermocompression flip-chip bonder, which illustrates the applicable capability of EPD of MCPs for fine or ultra-fine pitch interconnection

Elektrokeemilise voogkondensaatori arendamine ja optimiseerimine

Väitekirja elektrooniline versioon ei sisalda publikatsiooneElektrokeemiline voogkondensaator (EFC) on kontseptuaalne lahendus elektrienergia mastaapseks salvestamiseks. Kõnealune seade sarnaneb tööpõhimõttelt superkondensaatorile, aga olulise erinevusena kasutab tahkete elektroodide asemel süsniniku mikro ja nano-osakestest ning elektrolüüdist koosnevat suspensiooni. Elektrolüüdiga suspensioon on eraldatud poorse, ioonjuhtiva membraaniga ja seadmes on tüüpiliselt mõne millimeetrilise diameetriga kanalid, mille sein on voolkollektoriks ning millest pumbatakse läbi eelpool kirjeldatud suspensiooni. Just nimelt süsinikupõhiste vedelate elektroodide kasutamine võimaldab arendatavat seadet olulisel määral skaleerida ning tulevikus integreerida olemasolevatesse elektrivõrkudesse ja/või rakendada seda efektiivselt taastuvate energiaallikate poolt toodetud elektrienergia salvestamiseks. Doktoritöö keskseks eesmärgiks on EFC-tehnoloogia fundamentaalsete omaduste interpreteerimine. Sellest tulenevalt on töös on läbi viidud EFC elektrokeemilised karakteriseerimised ja arvutisimulatsioonid seadme disainlahenduste optimeerimiseks. Simulatsioonide valdkonnas on sobitatud EFC modelleerimiseks nii olemasolevaid elektrokeemilisi mudeled kui on arendatud ka uudne nn stohhastiline Monte-Carlo põhimõtetel baseeruv mudel. Väljatöötatud mudelid kalibreeriti ja valideeriti põhjalikult võrdluses elektrokeemiliste tulemustega ning neid kasutati voogelektroodide laadimisprotsessi sügavamaks mõistmiseks kolmes fundamentaalses EFC-seadme konstruktsioonis. Sarnaste elektrokeemiliste seadmete modelleerimiseks kasutatakse tihti Nernst-Planki võrranditel või kontsentreeritud lahuse teooriatel baseeruvaid mudeleid. Luuakse teist järku osatuletsitega diferentsiaalvõrrandite süsteemid, mis kirjeldavad nii ioonide kontsentratsioone kui ka seadmes tekkivaid laenguülekande protsesse. Nende mudelite rakendamine iseloomustas ilmekalt difusiooni tõttu seadmes tekkivaid laengu salvestamise ja osakeste transpordi piiranguid. Efektiivne elektroodimaterjali tsirkulatsioon ning piisavalt kiire laengu transport on teineteisele vastanduvad protsessid – kui esimesel juhul on oluliseks näitajaks piisavalt suur elektroodi voolukanalite diameeter, siis teisel juhul on nõutav just nimelt sama kanali diameetri minimiseerimine. Samas ilmnes eksperimentaalsest tulemustest, et mitte ainult difusioonist tingitud nähtused pole olulised, vaid märkimisväärset mõju omavad ka nn kõrvalreaktsioonid. Töö käigus loodud stohhastiline mudel võimaldas saavutada edukalt elektrokeemiliste mõõtmistulemuste ning Nernst-Planki võrranditel baseeruvate mudelitega leitud tulemuste kokkulangevuse. Enamgi, loodud stohhastiline mudel võimaldab edukalt simuleerida vedelate elektroodide laadumise dünaamikat ja kirjeldada suspensioonis asetleidvaid protsesse ning hinnata kõrvalreaktsioonide mõjusid. Kokkuvõtvalt avab loodud lähenemisviis võimaluse leidmaks lahendust voogkondensaatori disaini kesksele probleemile – kuidas tagada seadmest piisav elektroodimaterjali läbivool ning samas hoiduda laengu transpordi limiteerimisest difusiooni tõttu. EFC-tehnoloogia edasise arengu puhul võib eeldada taastuvatest allikatest toodetud energia salvestamisvõimsuse märkimisväärset kasvu. Samas tuleb lisada, et EFC võimsustiheduse parandamiseks, ilma et see kahjustaks nende seadmete energiatihedust ning tsükleeritavust, on vaja jälgida arenduste kooskõla ka muude energiasalvestus- ja muundamis-tehnoloogiatega. Olulisteks faktoriteks on nii seadme töötingimuste valik, elektroodide disain, elektrolüüdi materjalid, kuid samuti ka sobilikud katalüsaatorid.An electrochemical flow capacitor (EFC) is a conceptual approach to meet large-scale electricity storage. This device is similar in operation to a supercapacitor but uses a concentrated solution of carbon micro and nanoparticles and an electrolyte instead of solid electrodes. It typically flows in channels with a diameter of a few millimeters, the wall of which is a flow collector and through which the liquid electrode material is pumped. A porous ion-conducting membrane separates the electrodes. Using carbon-based liquid electrodes in the device under development will allow the technology to be significantly scaled up and integrated into existing electricity grids and used effectively to support renewable energy production. The central goal of the work presented is to understand the fundamental properties of EFC technology. As a result, EFC laboratory tests and computer simulations have been performed to design and optimize the device architecture. In the field of simulations, both existing electrochemical models have been adapted for EFC modeling, and a new stochastic model based on Monte-Carlo principles has been developed. Both implemented and developed models were thoroughly calibrated and validated against laboratory experiments and used to understand the flow electrode charging process in three fundamental EFC device designs. Models based on Nernst-Planck equations or concentrated solution theories are often used to model similar electrochemical devices. Second-order differential equations systems with partial derivatives describe both the ion concentrations and the charge exchange processes occurring in the device. The application of these models was characterized by the limitations of charge storage and transport processes in the device due to diffusion. If the electrode material circulation and sufficiently fast charge transport are critical processes, then a sufficiently large diameter of the electrode flow channels is important. Otherwise, it is necessary to minimize the diameter of the same channel. At the same time, the experimental work showed that the phenomena caused by diffusion are critical side effects and have a significant effect on electrode charging processes. The models based on the Nernst-Planck equations and the stochastic model developed successfully matched the experimental results. Moreover, the developed stochastic model allows to simulate the convection and mixing processes of liquid electrodes successfully and to apply the effects of side reactions. Thus, the developed approach opens the possibility to find a solution to the central problem of the flow capacitor design - how to ensure sufficient flow of electrode material from the device and at the same time avoid limiting the transport of charge due to diffusion. Due to the development of EFC technology, a significant increase in the storage capacity of energy from renewable sources can be expected. At the same time, to improve the power density of EFCs without compromising their high energy density and cyclicality, it is necessary to monitor the coherence of developments with other energy storage and conversion technologies. Important factors are the choice of operating conditions of the device, the design of the electrodes, the materials of the electrolyte, as well as suitable catalysts.https://www.ester.ee/record=b549496

Bioelectric Effects of Intense Nanosecond Pulses

Electrical models for biological cells predict that reducing the duration of applied electrical pulses to values below the charging time of the outer cell membrane (which is on the order of 100 ns for mammalian cells) causes a strong increase in the probability of electric field interactions with intracellular structures due to displacement currents. For electric field amplitudes exceeding MV/m, such pulses are also expected to allow access to the cell interior through conduction currents flowing through the permeabilized plasma membrane. In both cases, limiting the duration of the electrical pulses to nanoseconds ensures only nonthermal interactions of the electric field with subcellular structures. This intracellular access allows the manipulation of cell functions. Experimental studies, in which human cells were exposed to pulsed electric fields of up to 300 kY/cm amplitude with durations as short as 3 ns, have confirmed this hypothesis and have shown that it is possible to selectively alter the behavior and/or survival of cells. Observed nanosecond pulsed effects at moderate electric fields include intracellular release of calcium and enhanced gene expression, which could have long term implications on cell behavior and function. At increased electric fields, the application of nanosecond pulses induces a type of programmed cell death, apoptosis, in biological cells. Cell survival studies with 10 ns pulses have shown that the viability of the cells scales inversely with the electrical energy density, which is similar to the ‘dose’ effect caused by ionizing radiation. On the other hand, there is experimental evidence that, for pulses of varying durations, the onset of a range of observed biological effects is determined by the electrical charge that is transferred to the cell membrane during pulsing. This leads to an empirical similarity law for nanosecond pulse effects, with the product of electric field intensity, pulse duration, and the square root of the number of pulses as the similarity parameter. The similarity law allows one not only to predict cell viability based on pulse parameters, but has also been shown to be applicable for inducing platelet aggregation, an effect which is triggered by internal calcium release. Applications for nanosecond pulse effects cover a wide range: from a rather simple use as preventing biofouling in cooling water systems, to advanced medical applications, such as gene therapy and tumor treatment. Results of this continuing research are leading to the development of wound healing and skin cancer treatments, which are discussed in some detail