Effect of ambient condition for coaxial dielectric barrier discharge reactor on CO2 reforming of CH4 to syngas

A coaxial dielectric barrier discharge reactor was used for the CO₂ reforming of CH₄ to syngas. The reactor was operated under two ambient conditions for comparison, namely, immersion in electrical insulating oil and total exposure in an air ambient. Immersion of the reactor in insulating oil increased the electrical power efficiency into the generation of plasma discharge due to the prevention of micro-arcing on the reactor surface. Operation in the insulating oil bath showed higher conversion and selectivity of major reactants and products rate than operation in an air ambient.     

Possibility of Improvement on Ozone Production by Using the Back-Corona Effect

Electrostatic precipitators’ problems and experimental results in point-to-plane or wire-to-cylinder systems indicate that the presence of a thin layer of porous dielectric material on the electrodes increases the discharge current for the same applied potential. This socalled Back-Corona effect, which generally reduces the sparking potential, depends on the active electrode polarity; nature, and thickness and porosity of the insulating layer; and position on the active or passive electrode of the deposited particles or insulating layer. In laboratory experiments in a point-to-plane device, with a dielectric porous layer on the plane, the current may be many times higher than its “normal” value (clean electrodes). In a DC negative wire-to-cylinder system, where the ozone concentration depends quasi directly on the discharge current, it appears possible to increase the ozone production, for the same running conditions (gas flow, electrical circuit, etc.).     

Effects of Scrap Rubber Particles on the Mechanical Behavior of Epoxy

Abstract

The conductive properties of carbon black filled polymers have already found many qualitative applications while quantitative ones remain infrequent because of the number of unexpected parameters which influence the conductance of samples of the material. We have tried to connect the anomalous electrical behaviour of such materials with three particular phenomena which influence d-c conduction:

–Percolation, which is a process expected to occur in mixtures of conducting and insulating solids.

–Volumic polarization and ionic heterocharge near the electrodes which supply a new explanation for the variable contact resistance.

–Filamentary conduction and localized thermal effects which produce under some conditions, regions of negative resistance in the current-voltage characteristics of samples. Possible electrical applications for filled polymers are deduced from this analysis.     

MD simulations of the collision between a copper ion and a polyethylene surface: an application to the plasma-insulating material interaction

To allow a better understanding of the physical phenomena occurred between a plasma and an insulating material, we have developed a specific MD code to study this type of interaction. We report results of MD simulations of the interaction of an incoming copper ion with a polyethylene crystal surface. Three initial incoming velocities and four impact angle values are used to check the influence of both the incident energy and impact direction to the resulting surface damage. When the incoming ion velocity is sufficiently high, MD results show that the impact can cause bond breaking leading to uncoordinated carbon atoms and free hydrogen atoms. The values of local temperatures associated with the structural changes show a possible ablation of the polyethylene surface.     

Ozone and Nitrogen Oxides Generation in Gas Flow Enhanced Hollow Needle to Plate Discharge In Air

Siemens made the first ozone generation system by corona discharge about hundred and fifty years ago. At present mainly two types of atmospheric pressure electrical discharges - corona discharge and dielectric barrier discharge are used for production of ozone. Another type of discharge, which can be used for this purpose, is multineedle to plate electrical discharge enhanced by the gas flow. Contrary to the conventional arrangement when the gas is flowing around the needles we studied the discharge in which the gas was pumped through the needles. Results of studies of ozone and nitrogen oxides production by DC electrical discharge in air at atmospheric pressure with a single hollow needle to plate electrode configuration enhanced by the flow of air through the needle for both polarities of the needle, different airflow rates and currents are presented in this paper.     

Development of functionally graded vapor‐grown carbon‐fiber/polymer materials

We successfully produced vapor‐grown carbon‐fiber (VGCF)‐incorporated polymer‐based functionally graded materials (FGMs) using a centrifugal method. Gradual VGCF incorporation within an epoxy resin effectively produced depth gradients in the fiber distribution, microstructure, mechanical, and electrical conductivities and microwave absorbing properties. This VGCF‐grading capability indicated that it is possible to tailor desired gradient filler content distributions by careful selection of the processing parameters to control variations in the property and microstructure precisely. The results confirmed that the volume content of VGCF in the epoxy substrate increased as a function of the normalized thickness along the centrifugal force direction, which caused a gradient. A uniform VGCF gradient in the composite can also be observed using field‐emission scanning electron microscopy. In the case of the electrical properties, for example, the volume resistance exhibited a depth‐graded distribution in the matrix as the electrical conductivity of the FGM nicely followed the grading direction; this is considered to be ideal for applications demanding an electrically conductive surface and an insulating core for FGMs. The results of microwave absorption behavior of FGMs indicate that the grading structure can lead to a graded absorption ability, which could be a better design for microwave absorption materials. The concept of FGMs bridges conventional materials and nanocomposites and will be effective for wider material applications. POLYM. COMPOS., 34:1774–1781, 2013. © 2013 Society of Plastics Engineers     

Organic free montmorillonite-based flexible insulating sheaths for Nb3Sn superconductor magnets

Nb₃Sn is a superconductor that exhibits higher performances than NbTi alloy currently used in superconducting magnets, regarding both the critical magnetic field and critical current. However, Nb₃Sn is an intermetallic compound prepared by thermal treatment, which loses ductility and plasticity once reacted. Since organic materials cannot be used as insulating sheaths and applied before the thermal treatment required for the synthesis of Nb₃Sn, a clay mineral-based organic-free sheath was prepared, which can be applied to Nb₃Sn magnetic coils prepared by the wind & react method, before the thermal process. This process allows for facile shaping of the superconductor precursor, before reaction, along with the application of the insulating coating, the sintering of this coating being achieved by the thermal treatment required for the synthesis of Nb₃Sn. This process has been designed for industrial developments and facile scale-up. The final material is an organic-free ceramic ribbon that can be stored before further use as an insulating sheath of Nb₃Sn wires, and electrical and magnetic tests on both the material and a specific demonstrator made with a 20 m superconducting reel, demonstrate that this material can be used as an insulating sheath, with no side-effect on superconductor properties.     

气流辅助聚合物熔体微分电纺流道优化设计

为进一步降低熔体微分电纺的纤维直径,使其达到纳米尺度,在现有直线狭缝电纺喷头的基础上设计了可以使高速气流汇聚的“V”形风道,通过高速气流对熔体微分射流进行二次牵伸细化。采用实验研究和数值模拟相结合的方法,以射流间距和喷头端电场强度为指标,研究了“V”形风道结构、材质对电纺微分射流的影响。研究结果表明,风道结构会不可避免地削弱喷头端的电场强度、降低射流的效率。增加风刀与喷头尖端的头端凸出量以及采用不导电的聚醚醚酮作为风刀材质都可以有效地降低风刀对射流效率的影响,而风道的宽度对喷头端电场强度影响不大。在优化的风刀结构和材质的基础上,成功制备了平均直径为825 nm的熔体电纺超细纤维。研究证实在气流辅助牵伸的作用下,直线狭缝电纺能够实现熔体电纺超细纤维的批量制备。     

Effect of a glow discharge on the formation of a surface layer on polycaproamide fibres in the presence of an organophosphorus compound

Conclusions The interaction of a glow discharge with polycaproamide fibres which have been impregnated with an involatile, unreactive liquid has been investigated.It has been shown that plasmochemical treatment of the impregnated fibres leads to immobilization of the impregnating agent.It has been established for the first time that on contact of a glow discharge plasma with an impregnated material, migration processes of the impregnating preparation take place both along the surface of the fibre and also in its volume. The intensity and ratio of these processes are determined by the discharge conditions.Translated from Khimicheskie Volokna, No. 2, pp. 38–40, March–April, 1990.     

Production of BL-0.5 lightweight brick with combustible additives

Conclusions Lightweight brick with a bulk density of 0.5 g/cm² made with combustible additives is an effective refractory insulating material and can be used for purposes of insulation at 1000 – 1200.The use of BL-0.5 lightweight refractory for insulating blast furnace blowpipes at a blast temperature of 930 – 950, apart from preserving the ends of the blowpipe and saving heat, creates better conditions for servicing the furnace in the tuyere zone.     

Etude des nombres de transport ioniques dans les mélanges cryolithe-alumine selon le principe de la methode de Hittorf—I. mise en oeuvre de la methode

We describe a boron nitride cell permitting the direct application of Hittorf's method for the study of ionic transference numbers in cryolite-alumina melts, as used in practice. The grade of purity of the material, more especially its electrical conductivity, is discussed. We show that in spite of its defects, it is utilizable for the purpose. Other phenomena to be dealt with, especially the evaporation of the baths, are pointed out.     

Electrical conductivity of YSZ-SDC composite solid electrolyte synthesized via glycine-nitrate method

Yttria-stabilized zirconia (YSZ) is a common solid electrolyte for solid oxide fuel cells (SOFCs) because of its high electrical conductivity and high ionic transference number in both oxidizing and reducing atmospheres. Samarium doped ceria (SDC) has also been considered as an alternative electrolyte material to YSZ for intermediate temperature SOFC because of its high conductivity at relatively low temperatures. Due to improved ionic conductivity of YSZ at high temperature (~ 800 °C) and good conductivity of SDC in the intermediate temperature range (600–800 °C), the electrical properties of YSZ-SDC composites were investigated. Composites of YSZ and SDC with weight ratio 9.5:0.5, 9:1 and 8.5:1.5 were synthesized via glycine-nitrate route. XRD pattern of the systems revealed the formation of composite phases. Biphasic electrolyte microstructures were observed, in which SDC grains are dispersed in YSZ matrix. Relative density of the compositions was found to be more than 92% to the theoretical density. It was observed that the interface provides a channel for ionic transport, leading to a notable ionic conductivity. With increase in SDC weight ratio the electrical conductivity was found to increase. For weight ratio 8.5:1.5 the electrical conductivity was found to be greater than that of YSZ in the temperature range 400–700 °C. Further, for weight ratio more than 8.5:1.5, conductivity was found to decreases due to the formation of a few other insulating impurity phases. The electrode polarisation was also found to reduce significantly with SDC in the composite electrolyte system. Thus, such composite system may be useful for improving the ionic conductivity of the composite electrolytes.     

多级针-网式离子风散热系统性能

为探究多级针-网式离子风散热系统的性能和针对多级离子风散热装置进行优化设计，提出一种多级针-网式离子风散热系统装置，研究多级级数、级间隙、放电电压对离子风最大风速和发热片的散热温降的影响。结果表明，在相同电压时，多级比单级散热性能更好，能把11 W的发热片降低到更低的温度，并获得更大的离子风最大风速。多级装置离子风最大风速可达2.6 m/s，能把11 W的发热片温度降到90℃左右，温降可达105℃左右，而单级只能降到110℃，温降约85℃。     

Performance of multistage pin-mesh ionic wind cooling system

In order to explore the performance of the multistage pin-mesh ionic wind cooling system and optimize the design for the multistage ionic wind heat dissipation device, a multistage pin-mesh ionic wind cooling system device was proposed to study the effect of multistage number, stage clearance, and discharge voltage on the maximum wind velocity of the ionic wind and the heat dissipation temperature drop of the heating plate. The results show that at the same voltage, the multistage heat dissipation performance is better than the single-stage, which can reduce the 11 W heating plate to a lower temperature and obtain a larger maximum wind velocity of the ionic wind. When the maximum wind velocity of the ionic wind reaches the maximum value, it does not mean that the heat dissipation performance is the best, because the optimal heat dissipation performance can be achieved when the average wind velocity reaches the maximum value. The multistage device using the pin-mesh integrated structure has a maximum wind velocity of 2.6 m/s, which can reduce the temperature of the 11 W heating plate to about 90℃ and the temperature drop to about 105℃, while the single-stage can only drop to 110℃ and the temperature drop is about 85℃.     

Percolation threshold in ceramic composites with isotropic conducting nanoparticles

The percolation threshold for electrical conductivity of a binary system of electrically insulating and conducting spheres was studied theoretically to yield a roadmap for electrically conductive ceramic composites. Although the crystal grains in such matrix are of irregular shape, the spheres of different sizes are used in the model to keep calculations tractable, where insulating spheres (matrix) are considered to be much larger than conducting ones (filler). This difference influences spatial distribution of conducting spheres. Besides the rough analytical estimation of the percolation threshold, we also use the Metropolis algorithm. The latter must be adapted for the system of conducting spheres which are positioned at the surface of large insulating spheres. We give a suggestion for the modification of this algorithm. Analytical estimation and Metropolis method give qualitatively similar dependence of the percolation threshold on the radii of geometrical objects, but there are significant quantitative differences in the results.     

Adsorption and surface properties of silica with transformer insulating oils

The presence of polar species in transformer insulating oil may cause degradation and electric discharges in the power transformer. Such oil polar fraction can originate either from the neat oil and/or from its oxidative degradation in the power transformer. The aim of this study is to examine the relation between the insulating oil and the electrical properties of its polar fraction in order to predict eventual failure in the power transformer.We investigate at ambient temperature the adsorption of the polar fractions of various transformers insulating oils (a new and two used oils) from the neat oils onto silica particles. The adsorbed amount was higher for the used oils as compared to the new one. Infrared spectra of the polar fraction indicate the presence of hydroxyl, aromatic and carboxyl functional groups that are found in the asphaltenes compounds. Microelectrophoresis study of the oil polar fraction covered silica particles gives negatively charged oil polar fraction. Such oil surface charge depends on the pH and results from the ionisation of the oil acidic surface groups. Finally, we obtain a good correlation between the amount of the oil polar fraction and the magnitude of the zeta potential at the water/oil-silica interface.     

Use of thermal-shock resistant electric-insulating phosphate ceramics based on corundum for making high-temperature tensosensors

Conclusions On the basis of the results of a study of the temperature dependence of the resistance of insulation and the tensometric sensitivity of sensors, and an evaluation of the adhesion and thermal-shock resistance of ceramic material KPN-3, it can be expected that the use of this material for making high-temperature tensosensors will increase the application limits (as regards the properties of the bond) to a temperature of about 800°C.Repeat cyclic heating of the coating KPN-3 to 850°C not only does not reduce its electrical insulating properties, but somewhat increases them. The continuity of the material and its adhesion properties are also preserved.Translated from Ogneupory, No. 5, pp. 59–61, May, 1971.     

Development of a Large Particle Aerosol Distribution System for Testing Manikin-Mounted Samplers

Personal samplers used to determine the inhalable fraction of workplace dust are tested while mounted on a manikin, which simulates a worker. To understand the mechanisms affecting the performance of such samplers, researchers must measure the airflow around the body where the samplers are mounted. Therefore, wind tunnel facilities to determine both airflow conditions around samplers and sampling efficiency are needed. A wind tunnel system was developed that was large enough to accommodate the top half of a life-sized manikin and employed a laser Doppler velocimeter for velocity measurements around the manikin. For generating particles up to 70 mu m, an aerosol generation system, using a two-dimensional scanning system to cover an extended area, was developed and tested. The generation system had carriages with linear bearings mounted on rod assemblies for scanning in the horizontal and vertical directions. Screw drives, powered by stepper motors under computer control, moved the carriages in a preprogrammed pattern. The generation system was characterized for its ability to generate uniform concentrations of aerosols over an extended area at wind speeds of 0.5 and 2 m/s and particle sizes of 7 and 70 mu m. Uniformity of concentration over the area studied, in the absence of the manikin, was 10% relative standard deviation (RSD) or better, except for 7 mu m particles at a wind speed of 0.5 m/s where some nonuniformity was observed. The uniformity under these conditions was improved by rearranging the distances between components in the wind tunnel.     

Impact damage sensing in glass fiber reinforced composites based on carbon nanotubes by electrical resistance measurements

In this article, we report an interesting employment of multi‐walled carbon nanotubes as a filler in the epoxy matrix of a glass fiber reinforced composite (FRP). The intrinsic electrical conductivity of carbon nanotubes made the development of a nanocomposite with enhanced electrical properties possible. The manufactured nanocomposite was subsequently employed in the production of a glass FRP. Due to the high aspect ratio of carbon nanotubes, very small amounts of these particles were sufficient to modify the electrical properties of the obtained glass fiber composites. Basically, a three‐phases material was developed, in which two phases were electrically insulating—epoxy matrix and glass fiber—and one phase highly conductive, the carbon nanotubes. The main goal of this study was to investigate the possibility of developing a glass fiber reinforced nanocomposite (GFRN), which is able to provide measurable electrical signals when subjected to a low‐velocity impact on its surface. Following this goal, the drop in the mechanical performance of the composite was evaluated before and after the impact. At the same time, the variation in its electrical resistance was measured. The results have shown that it is possible to associate the increase in electrical resistance of the composite with the formation of damages caused by impact. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal and insulating properties of epoxy/aluminum nitride composites used for thermal interface material

We synthesized an epoxy matrix composite adhesive containing aluminum nitride (AlN) powder, which was used for thermal interface materials (TIM) in high power devices. The experimental results revealed that adding AlN fillers into epoxy resin was an effective way to boost thermal conductivity and maintain electrical insulation. We also discovered a proper coupling agent that reduced the viscosity of the epoxy‐AlN composite by AlN surface treatment and increased the solid loading to 60 vol %. For the TIM sample made with the composite adhesive, we obtained a thermal conductivity of 2.70 W/(m K), which was approximately 13 times larger than that of pure epoxy. The dielectric strength of the TIM was 10 to 11 kV/mm, which was large enough for applications in high power devices. Additionally, the thermal and insulating properties of the TIM did not degrade after thermal shock testing, indicating its reliability for use in power devices. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012