Wire Emitter Research Articles

Heat transfer performance and electrohydrodynamic characteristics optimization of a dividing-wall-type ionic wind heat exchanger

Heat exchangers play a major role in reducing emissions and conserving energy. There is a plethora of theoretical research on the enhancement of heat transfer caused by ionic wind, but there is still a lack of studies on the practical application of ionic wind in heat exchangers to increase heat exchange capacity. This work developed an original ionic wind heat exchanger with a dividing wall. It may be applied to difficult circumstances when conventional heat exchangers fail for air-to-air heat exchange. The study conducted experiments to investigate the impact of many factors, including intake air velocity, discharge spacing, and electrode distribution scheme, on the ionic wind intensity and the heat exchanger's increased heat transfer coefficient. A two-dimensional model was used to analyze the internal flow and thermal properties of the heat exchangers with wire emitters. By combining active and passive heat exchange technologies, an ionic wind heat exchanger with serrated grounded electrodes was presented. The outcomes demonstrated that a suitable intake air velocity enhances the heat exchanger's capacity for heat exchange. The improved heat exchange effect of ionic wind is more important when the inlet wind speed is less than 1 m/s. When the intake air velocity approaches 1.3 m/s, the ionic wind has less of an impact on the heat exchanger's capacity for heat exchange. The benefits of improved heat transfer are promoted by placing the emitter closer to the channel entry. Increasing the operating voltage further enhances the heat transfer enhancement ratio (HTER). The number and arrangement of wire electrodes should be chosen with consideration for the 'barrier effect' between neighboring emitters and the distance from the entrance when utilizing multiple wire electrodes. In comparison to the three-wire and five-wire electrodes, the four-wire electrode heat exchanger's HTER values were increased by 5.9 % and 14.3 %, respectively. The ionic wind heat exchanger's capacity for heat transfer is further increased using a zigzag grounding electrode. The zigzag uses a decreased aspect ratio, and the emitter is positioned slightly above the tip, improving the system's heat transfer capabilities. When compared to a heat exchanger with a flat plate grounded electrode, the four-wire electrode heat exchanger produced a 158 % increase in HTER value.

Blade emitters for atmospheric ionic thrusters

In the field of atmospheric ionic thrusters, the objective of this work is to evaluate the possibility of an alternative ionic emitter to the traditional thin wire emitter, in order to overcome the technical issues of the EHD technology related to the fragility of the wires and to make it more suitable to applications outside the laboratory. For the presented experiments, emitters in the form of metallic blades have been produced. These were tested while varying the geometric parameters of both the emitters themselves and of the thruster configuration. Through this measurement campaign, the electrical characteristics, as well as the feasibility and the performances of the new proposed solutions have been evaluated and compared with wire emitters. Results indicate that the blade emitters can work as alternative emitters, however the performance of the present prototypes does not reach that of wire emitters and therefore further research is needed in order to make them a valid alternative.

Molecular ion formation on activated field emitters in atmospheric pressure field desorption mass spectrometry

Atmospheric pressure field desorption (APFD) mass spectrometry (MS) has recently been explored as a new contribution to the field of ambient desorption/ionization (ADI). Depending on the selected polarity applied to the field emitter, ionic and polar analytes were demonstrated to deliver positive as well as negative ions. Whereas this recent study solely reported on the formation of even-electron ions of either polarity, the present work on APFD-MS demonstrates the abundant formation of positive molecular ions, M+•, from polycyclic aromatic compounds. Molecular ions were formed on and desorbed from standard 13-µm activated tungsten wire emitters at atmospheric pressure. The commercial field emitters were positioned at about 2 mm distance in front of the atmospheric pressure interface of a Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometer and the entrance electrode of the interface was set to –4.5 to –5.5 kV with respect to the emitter. Emitter-disrupting electric discharges did normally not occur under these conditions. The electric field strengths achieved at the dendritic microneedles were sufficient to allow for the abundant formation of M+• ions of various polycyclic aromatic compounds such as benzo[a]pyrene, anthracene, fluoranthene, 1,1,4,4-tetraphenyl-butadiene, and 1-aza-[6]helicene. In case of the extremely basic 1-aza-[6]helicene protonation strongly competed with molecular ion formation and tended to suppress the field ionization process. All molecular ion compositions were assured by accurate mass-based formula assignments.Graphical

Evaluating the optimum electric power consumption for forced convection of an EHD induced circulating flow through a circular tube: A numerical study

In this study, the effect of using EHD forced convection heat transfer through a circular tube is numerically investigated to prepare the required data sets to find the optimum configuration considering the Nusselt number and friction factor. To gain the required results, the Reynolds numbers and the applied voltages are set to 3000–7000 and 9–13.5 kV, respectively. Moreover, the variety of using miscellaneous placement positions of the central wire emitter, up to 30%, in combination with collector section angles in the range of θ = 90°–360°, are simultaneously investigated. The results of different section angles show that the Nusselt number has increased between 2.35 and 4.76 times compared to the non-EHD mode. Similarly, for the various eccentricities, the Nusselt number has increased between 2.35 and 5.05 times. In the final step, upon the gathered data, a Pareto front of optimal points was deduced for the hydraulic-thermal performances against the power consumption, and the optimum design was highlighted.

Prospects of application and possibilities of electric modular-launch furnaces with a new design of the heating system

We perform the analysis of the methods aimed at improving the energy efficiency of the electric modular-launch furnaces for firing of vermiculite. The first method is reduced to the analysis of the energy efficiency of the original six-module furnace with heat emitters made of U-shaped nichrome and structural transformation of the furnace unit with reinstallation of the least efficient bottom module in parallel with the most efficient top module. In this way, we get a furnace with series-and-parallel pairing of modules (SPP-furnace). The second method proposed in the previous works of the author is based on the application of new heating systems with top arrangement of wire emitters with round cross sections mounted on the thermal covers made of ceramic-vermiculite plates. Both these methods are implemented in modified SPP furnaces and give a synergistic effect with lowering of the specific energy intensity of firing of the vermiculite concentrates down to 105.9 mJ/m3 in a six-module SPP furnace and to 63.5 mJ/m3 in a four-module furnace with the use of a “zero” nonelectrified module.

ULTRA-WIDEBAND SCANNING ANTENNA ARRAY WIRE EMITTERS

The aim of the work is to determine the properties of the ultra-wideband scanning antenna array of wire emitters. A single element of the grid is a three-dimensional antenna Vivaldi. Numerical simulation of antenna arrays and single Vivaldi emitters was carried out by the method of integral equations in the thin-wire approximation using the original program and the MMANA program. The dimensions of all elements of a single emitter are determined by the criterion of matching and the shape of the radiation pattern for operation in the frequency range 2–18 GHz. The described variant of the antenna according to the matching criterion (SWR < 2) has a frequency overlap coefficient of 12. The narrowing of the frequency band of a single emitter in the composition of non-scanning and scanning gratings within the angle of 30 degrees is determined. The article deals with the range properties of antenna arrays depending on the parameters of the emitters and the possibility of phase scanning. It is shown that the greatest frequency band in agreement has a lattice with a minimum step of placement of emitters. In a flat antenna array, when scanning in the H-plane, the frequency band according to the matching criterion decreases by 2–3 times. It is shown that the linear lattice without scanning has a frequency overlap coefficient equal to 6 according to the criterion of matching emitters. This ratio decreases as the phase scan sector increases. In a flat lattice, the frequency overlap coefficient and the phase scan sector are smaller than in a linear lattice and decrease with the number of rows. The reduced antenna array has a number of design advantages and can be used in systems with ultra-wideband signals.

Electrohydrodynamic drying of multiple food products: Evaluating the potential of emitter-collector electrode configurations for upscaling

Electrohydrodynamic (EHD) drying is a promising, non-thermal drying technology, based on ionic wind generation between an emitter and a collector electrode. This simulation-based study evaluates impact of various emitter-collector configurations for EHD drying in order to assess their potential towards industrial upscaling. The conventional wire-to-plate configuration, which creates impinging flow, is found not to be an optimal solution for EHD drying of multiple food products in a fast and uniform way. With a single wire (emitter), it is found that the products placed more downstream dry slower due to the progressive loading of the air with water vapor. With multiple emitters, up to a threefold increase in drying time of the food products is found, compared to a single wire. This increase is caused by the recirculation of most air. To avoid water vapor accumulation in the drying zone, a wire-to-mesh configuration is proposed. The mesh collector minimizes interference of neighboring airflows and avoids recirculation of moist air in the drying zone. As such, the wire-to mesh configuration provides more uniform drying between adjacent products, but also within a product, as it can dry from all its surfaces. An increase in emitter density for the wire-to-mesh configuration leads to an overall increase in air speed, but, surprisingly, not to increased product drying rates. The reason is that the high-speed EHD airflow is always generated very locally in the vicinity of the emitter and collector. Thereby the convective drying process is not affected so much by the emitter density.

Junction temperature estimation of IGBT module via a bond wires lift‐off independent parameter V gE‐np

An electrical method for junction temperature estimation of insulated-gate bipolar transistors (IGBTs) is presented in this study. Owing to the parasitic inductance between bond wire and main emitter terminal L E . The temperature-dependent falling collector current during turn-off transition would cause a negative voltage drop in the gate-main emitter voltage waveform v gE . Therefore, this negative voltage drop V gE-np is proportional to the junction temperature. A double-pulse test circuit is developed to verify the accuracy and feasibility of the proposed method. The impacts of collector-emitter voltage V ce , collector current I c and bond-wires cut-off are also be discussed theoretically and experimentally. The experimental results show that the proposed V gE-np has a linear relationship with junction temperature as theoretical analysis and it is a bond-wires cut-off independent parameter in some special test point, which offers an effective way to estimate junction temperature without package destruction. The advantages of the proposed method include good linearity, bond-wires failure immunity and adequate sensitivity with junction temperature.

Fast power cycling protocols implemented in an automated test bench dedicated to IGBT module ageing

This paper presents fast test protocols for ageing IGBT modules in power cycling conditions, and a monitoring device that tracks the on-state voltage VCE and junction temperature TJ of IGBTs during ageing test operations. This device is implemented in an ageing test bench described in previous papers, but which has since been modified to perform fast power cycling tests.The fast test protocols described here use the thermal variations imposed on IGBT modules by a test bench operating under Pulse Width Modulation conditions. This test bench reaches the maximal values of power cycling frequencies attainable with a given module packaging in order to optimize test duration.The measurement device monitors VCE throughout the ageing test that is needed to detect possible degradations of wire bonds and/or emitter metallization. This requires identifying small VCE variations (a few dozen mV). In addition, the thermal swing amplitude of power cycling must be adjusted to achieve a given ageing protocol. This requires measuring junction temperature evolution on a power cycle, which is carried out by means of VCE measurement at a low current level (100mA).Experimental results demonstrate the flexibility of this test bench with respect to various power cycling conditions, as well as the feasibility of the proposed on-line monitoring methods.

Excitonics of semiconductor quantum dots and wires for lighting and displays

In the past two decades, semiconductor quantum dots and wires have developed into new, promising classes of materials for next-generation lighting and display systems due to their superior optical properties. In particular, exciton–exciton interactions through nonradiative energy transfer in hybrid systems of these quantum-confined structures have enabled exciting possibilities in light generation. This review focuses on the excitonics of such quantum dot and wire emitters, particularly transfer of the excitons in the complex media of the quantum dots and wires. Mastering excitonic interactions in low-dimensional systems is essential for the development of better light sources, e.g., high-efficiency, high-quality white-light generation; wide-range color tuning; and high-purity color generation. In addition, introducing plasmon coupling provides the ability to amplify emission in specially designed exciton–plasmon nanostructures and also to exceed the Förster limit in excitonic interactions. In this respect, new routes to control excitonic pathways are reviewed in this paper. The review further discusses research opportunities and challenges in the quantum dot and wire excitonics with a future outlook.

Ageing and Failure Modes of IGBT Modules in High-Temperature Power Cycling

This paper presents an experimental study on the ageing of insulated-gate bipolar transistor (IGBT) power modules. The aim is to identify the effects of power cycling on these devices with high baseplate temperatures (60 °C to 90 °C) and wide temperature swings (60 °C to 100 °C). These values for thermal stresses have been defined according to automotive applications. The test conditions are provided by two types of test benches that will be described in this paper. The changes in electrical and thermal indicators are observed regularly by a monitoring system. At the end of the test (reaching damage criterion or failure), different analyses are performed (acoustic scanning and SEM imaging), and the damage is listed systematically. Nineteen samples of 600-V 200-A IGBT modules were thus aged using five different power-cycling protocols. The final summary of results shows that ageing mechanisms mainly concern wire bonds and emitter metallization, with gradual impact depending on protocol severity.

Electric propulsion using an alternating positive/negative corona discharge configuration composed of wire emitters and wire collector arrays in air

We present a study on a corona discharge configuration exclusively composed of thin wires that provides maximal thrust performance and a compact unit staging method. The ion and air flow behaviors were experimentally and numerically investigated. The basic characteristics derived from the experiments are reported for three discharge configurations (positive, negative, and positive/negative alternation). The proposed alternating positive/negative configuration enhanced the thrust (5.4 N/m2 of maximum thrust to air flow area ratio) through the ability to achieve compact staging, compared to a previous study. In addition, two useful equations as criteria in the evaluation of the thrust performance were derived.

CNX (Carbon‐Nano‐eXit): a unique carbon‐nano‐structure to be employed for excellent electron‐emitters

AbstractCarbon materials including Carbon‐Nano‐Tubes (CNT), Nano‐Diamonds and other Nano‐Carbon‐relatives (such as Carbon‐Nano‐Walls [CNW]) have received intense attention as good candidates for electron‐emitters. The present authors and co‐workers have long been trying to fabricate good electron‐emitters, employing a variety of carbon‐nano‐materials. Until some months ago, we claimed that CNW was the best structure for high emission‐capability among the carbon‐nano‐materials. However, by introduction of a unique structure into the CNW, we have recently succeeded to obviously improve the capability of the emitter while achieving and far shorter fabrication or deposition times.The unique structure has been named Carbon‐Nano‐eXit (CNX) and patented. The introduction of this CNX into the CNW structure can be done by some modification of plasma parameters during emitter fabrication or deposition by plasma CVD process. Now the emitter has shown a world‐top‐ranking property: very low turn‐on‐voltage (0.5 V/µm to induce 10 µA/cm2) and high emission current at low applied voltage with a gap distance of 1 mm (1 mA/cm2 current at 1.1 V/µm and 100 mA/cm2 at 2 V/µm). The emitter a is wire or pipe type emitter to avoid the so‐called “edge‐effect”. Owing to the presence of CNX which shortens the fabrication time, we are able to fabricate or deposit the emitters totally about 50∼100 km long per month by one CVD‐reactor. Then using these emitters, we are able to fabricate Mercury‐free fluorescence lamps with high efficiency (∼70 lm/watt) and a high brightness of 105 cd/m2 (white‐light). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Field emission investigations of RuO 2-doped SnO 2 wires

Field emission studies of a bunch and a single isolated RuO 2:SnO 2 wire have been performed. A current density of 5.73 × 10 4 A/cm 2 is drawn from the single wire emitter at an applied field of 8.46 × 10 4 V/μm. Nonlinearity in the Fowler–Nordheim (F–N) plot has been observed and explained on the basis of electron emission from both the conduction and the valence bands of the semiconductor. The current stability recorded at the preset value of 1.5 μA is observed to be good. Overall the high emission current density, good stability and mechanically robust nature of the RuO 2:SnO 2 wires offer advantages as field emitters for many potential applications.

COMPARISON OF BARE WIRES AND ACTIVATED EMITTERS FOR FD MS OF OLIGOSACCHARIDES

Ion formation in field desorption (FD) from activated wire emitters covered with field enhancing microneedles has been compared with that from bare wires for some oligosaccharides doped with NaCl. The experiment revealed a close similarity between both types of emitters in the ion formation by electrohydrodynamic disintegration processes at temperatures near the onset of ion emission. In contrast, at higher temperatures above the melting point the sample layers are removed from smooth wires while on activated emitters they are retained in part between the microneedles. In this temperature range surface mobile molecules were found to be ionized not only by FI processes on microneedle tips but also by alkali ion attachment on charged alkali ion donating solid deposits. The latter mechanism has not been considered in FD mass spectrometry yet.

Study of the synthesis of ammonia by field desorption mass spectrometry

In this study the synthesis of ammonia from a nitrogen—hydrogen mixture has been investigated, both in the presence and absence of catalyst, under field desorption conditions. Both promoted and unpromoted catalysts have been used. There is strong evidence for formation of ammonia on the reduced catalyst surface at room temperature in the strong electrostatic field; room-temperature formation of ammonia is also observed on a wire emitter with gold microtips in the absence of catalyst, indicating that the electrostatic field itself may act as a catalyst. This may be rationalized in terms of the high polarization energy of the ammonia molecule.

Electrodynamic effects in field desorption mass spectrometry

The electrohydrodynamic disintegration of sample droplets deposited onto 10-μm tungsten wire emitters has been studied under conditions of field desorption mass spectrometry, by optical microscopy. In these experiments droplets were taken from concentrated aqueous solutions of sucrose and polyethylene oxide, both containing alkali salts, and of tartaric acid. Various stages of disintegration of the samples are distinguished. The final and almost stationary state of the samples corresponding to the best anode temperature for the emission of quasimolecular ions is also displayed. The emission of desolvated ions is attributed to the formation of very fine tips and fibers projecting out of the sample layer. The threshold field strength required to initiate the observed electrohydrodynamic effects resulting in the final ion-emitting state of the sample is estimated to be of the order of 10 8 V m −1.

Field desorption of non‐electrolytes using simply activated wire emitters

AbstractThe high field strengths obtained with activated emitters are necessary to accomplish field desorption of non‐electrolytes, i.e. samples containing neither salts nor acids. A simple procedure to produce activated emitters in a few seconds for this mode of field desorption is described. The method was applied to W and Pt wires, as well as carbon fibres.

Field desorption of electrolytic solutions using untreated wire emitters

AbstractSimple untreated wire emitters can be used for field desorption of electrolytic solutions, e.g. acids or substances containing alkali salts. The ionization is achieved by the attachment of protons or alkali ions to molecules in the condensed phase which are subsequently desolvated by the action of high electric fields. This field desorption mode is demonstrated and discussed for a few characteristic examples. It is shown that the addition of substances of high viscosity and low vapour pressure in the liquid state favours the field desorption behaviour of many compunds. In general the mass spectra of untreated wires are less complicated than those of activated emitters since field ionization processes occurring at the tip of the field‐enhancing microneedles are avoided.

Characterization of multipoint field ionization sources

The characteristics of multipoint field ionization (FI) sources are described. In addition, efficiency comparisons are made with the more commonly used activated tungsten wire emitters. The multipoint FI source has been found to be more efficient due to more effective sample feed to the ionizing volume.