Modelling of Laminar Plasma Jet Impinging on a Flatplate with Approximate Box Relaxation Method

Approximate Box Relaxation method was used t'o simulate a plasma jet flow impinging on a flatplate at atmospheric pressure, to achieve a better understanding of the characteristics of plasma jet in materials surface treating. The flow fields under different conditions were simulated and analyzed. The distributions of temperature, velocity and pressure were obtained by modelling. Computed results indicate that this numerical method is suitable for simulation of the flow characteristics of plasma jet: and is helpful for understanding of the mechanism of the plasma-material processing.

(Ti,Al)N Film On Normalized T8 Carbon Tool Steel Prepared By Pulsed High Energy Density Plasma Technique

Under optimized operating parameters, a hard and wear resistant ( Ti,Al)N film is prepared on a normalized T8 carbon tool steel substrate by using pulsed high energy density plasma technique. Microstructure and composition of the film are analysed by x-ray diffraction, x-ray photoelectron spectroscopy, Auger electron spectroscopy and scanning electron microscopy. Hardness profile and tribological properties of the film are tested with nano-indenter and ring-on-ring wear tester, respectively. The tested results show that the microstructure of the film is dense and uniform and is mainly composed of ( Ti,Al)N and AlN hard phases. A wide transition interface exists between the film and the normalized T8 carbon tool steel substrate. Thickness of the film is about 1000 nm and mean hardness value of the film is about 26GPa. Under dry sliding wear test conditions, relative wear resistance of the ( Ti,Al)N film is approximately 9 times higher than that of the hardened T8 carbon tool steel reference sample. Meanwhile, the ( Ti,Al)N film has low and stable friction coefficient compared with the hardened T8 carbon tool steel reference sample.

Evaluacion de bicarbonato de sodio, caldo vizosa y caldo bordeles en el control de la cenicilla (Erysiphe cichoracearum DC) en el cultivo de pipian (Cucurbita pepo L.), en Apacunca, Chinandega

El pipián ( Cucurbita pepo.) tiene su origen en el continente americano, por lo que la diversidad genética presente en el continente ha permitido muchas denominaciones populares. El trabajo de investigación se llevó a cabo en la Reserva de Recursos Genéticos de Apacunca, en la comunidad de Asquespalapa, el objetivo fue encontrar opciones de bajo costo y no dañinas a la salud humana y ambiente, para el control de la Cenicilla del Pipián ( Erysiphe cichoracearum), Los tratamientos fueron arreglados en un diseño de bloque completo al azar (B.C.A) con tres réplicas. El ensayo fue establecido en una Area de 100m2. Cada parcela experimental estuvo constituida por 4 surcos de 6 metros de largo con distancia entre plantas de 1 metro. El área total de cada parcela experimental fue de 18 metros cuadrados. La parcela útil estuvo constituida por las 8 plantas centrales de cada parcela experimental. La variedad utilizada para el estudio fue la Criolla. Los tratamientos probados consistieron en tres caldos minerales preventivos y un testigo, se realizó un análisis de varianza con un 95 % de confianza y separación de medias según Tukey LSD (∞= 0.05) y análisis de beneficio costo. Los resultados indican que el caldo vizosa mostró únicamente entre un 5 y 10% de afectación en cuanto a la incidencia y severidad de la enfermedad, en segunda categoría encontramos al caldo bordelés con un 15 y 20 %, de afectación. En cuanto a la relación beneficio costo se determinó que el caldo Vizosa es un producto rentable ad amas de mantener la parcela libre de patógenos da un resultado económico en cuanto a la producción y compensación a la hora de vender en el mercado.

Regeneración natural del madroño (Calycophyllum candidissimum (Vahl) DC) en el bosque tropical seco de Chacocente, Nicaragua

El objetivo de este estudio fue estudiar la densidad de la regeneración natural de brinzales y latizales del Madroño ( Calycophyllum candisissimum ) en un periodo de tiempo y analizar el patrón de distribución espacial en relación con la pendiente del terreno y la exposición a la luz solar. El estudio se llevó a cabo en el refugio de Vida Silvestre de Chacocente localizado en la costa del Pacifico de Nicaragua. Se realizó un inventario forestal durante los años 2001, 2002 y 2003 y todos los individuos con alturas mayores de 10 cm y diámetro menores de 5 cm a la altura del pecho fueron inventariados. Los cambios en densidad de población de brinzales y latizales para C. candisissimum fueron positivos indicando una continua regeneración natural de la especie. La densidad de población de brinzales y latizales varió con respecto a la pendiente y la exposición a la luz solar resultando en un patrón de distribución agregado.

Regeneración natural del madroño (Calycophyllum candidissimum (Vahl) DC) en el bosque tropical seco de Chacocente, Nicaragua

El objetivo de este estudio fue estudiar la densidad de la regeneración natural de brinzales y latizales del Madroño ( Calycophyllum candisissimum ) en un periodo de tiempo y analizar el patrón de distribución espacial en relación con la pendiente del terreno y la exposición a la luz solar. El estudio se llevó a cabo en el refugio de Vida Silvestre de Chacocente localizado en la costa del Pacifico de Nicaragua. Se realizó un inventario forestal durante los años 2001, 2002 y 2003 y todos los individuos con alturas mayores de 10 cm y diámetro menores de 5 cm a la altura del pecho fueron inventariados. Los cambios en densidad de población de brinzales y latizales para C. candisissimum fueron positivos indicando una continua regeneración natural de la especie. La densidad de población de brinzales y latizales varió con respecto a la pendiente y la exposición a la luz solar resultando en un patrón de distribución agregado.

Effects Of The Length Of A Cylindrical Solid Shield On The Entrainment Of Ambient Air Into Turbulent And Laminar Impinging Argon Plasma Jets

When materials processing is conducted in air surroundings by use of an impinging plasma jet, the ambient air will be entrained into the materials processing region, resulting in unfavorable oxidation of the feedstock metal particles injected into the plasma jet and of metallic substrate material. Using a cylindrical solid shield may avoid the air entrainment if the shield length is suitably selected and this approach has the merit that expensive vacuum chamber and its pumping system are not needed. Modeling study is thus conducted to reveal how the length of the cylindrical solid shield affects the ambient air entrainment when materials processing (spraying, remelting, hardening, etc.) is conducted by use of a turbulent or laminar argon plasma jet impinging normally upon a flat substrate in atmospheric air. It is shown that the mass flow rate of the ambient air entrained into the impinging plasma jet cannot be appreciably reduced unless the cylindrical shield is long enough. In order to completely avoid the air entrainment, the gap between the downstream-end section of the cylindrical solid shield and the substrate surface must be carefully selected, and the suitable size of the gap for the turbulent plasma jet is appreciably larger than that for the laminar one. The overheating of the solid shield or the substrate could become a problem for the turbulent case, and thus additional cooling measure may be needed when the entrainment of ambient air into the turbulent impinging plasma jet is to be completely avoided.

An investigation of electromagnetic wave propagation in plasma by shock tube

This paper presents the electromagnetic wave propagation characteristics in plasma and the attenuation coefficients of the microwave in terms of the parameters n(e), v, w, L, w(b). The phi800 mm high temperature shock tube has been used to produce a uniform plasma. In order to get the attenuation of the electromagnetic wave through the plasma behind a shock wave, the microwave transmission has been used to measure the relative change of the wave power. The working frequency is f = (2 similar to 35) GHz (w = 2pif, wave length lambda = 15 cm similar to 8 mm). The electron density in the plasma is n(e) = (3 x 10(10) similar to 1 x 10(14)) cm(-3). The collision frequency v = (1 x 10(8) similar to 6 x 10(10)) Hz. The thickness of the plasma layer L = (2 similar to 80) cm. The electron circular frequency w(b) = eB(0)/m(e), magnetic flux density B-0 = (0 similar to 0.84) T. The experimental results show that when the plasma layer is thick (such as L/lambda greater than or equal to 10), the correlation between the attenuation coefficients of the electromagnetic waves and the parameters n(e), v, w, L determined from the measurements are in good agreement with the theoretical predictions of electromagnetic wave propagations in the uniform infinite plasma. When the plasma layer is thin (such as when both L and lambda are of the same order), the theoretical results are only in a qualitative agreement with the experimental observations in the present parameter range, but the formula of the electromagnetic wave propagation theory in an uniform infinite plasma can not be used for quantitative computations of the correlation between the attenuation coefficients and the parameters n(e), v, w, L. In fact, if w < w(p), v(2) much less than w(2), the power attenuations K of the electromagnetic waves obtained from the measurements in the thin-layer plasma are much smaller than those of the theoretical predictions. On the other hand, if w > w(p), v(2) much less than w(2) (just v approximate to f), the measurements are much larger than the theoretical results. Also, we have measured the electromagnetic wave power attenuation value under the magnetic field and without a magnetic field. The result indicates that the value measured under the magnetic field shows a distinct improvement.

Structure and mechanical properties of ceramic coatings fabricated by plasma electrolytic oxidation on aluminized steel

Ceramic coatings were formed by plasma electrolytic oxidation (PEO) on aluminized steel. Characteristics of the average anodic voltages versus treatment time were observed during the PEO process. The micrographs, compositions and mechanical properties of ceramic coatings were investigated. The results show that the anodic voltage profile for processing of aluminized steel is similar to that for processing bulk Al alloy during early PEO stages and that the thickness of ceramic coating increases approximately linearly with the Al layer consumption. Once the Al layer is completely transformed, the FeAl intermetallic layer begins to participate in the PEO process. At this point, the anodic voltage of aluminized steel descends, and the thickness of ceramic coating grows more slowly. At the same time, some micro-cracks are observed at the Al2O3/FeAl interface. The final ceramic coating mainly consists of gamma-Al2O3, mullite, and alpha-Al2O3 phases. PEO ceramic coatings have excellent elastic recovery and high load supporting performance. Nanohardness of ceramic coating reaches about 19.6 GPa. (c) 2007 Elsevier B. V. All rights reserved.

Theoretical and experimental studies of the bell-jar-top inductively coupled plasma

The present paper describes a systematic study of argon plasmas in a bell-jar inductively coupled plasma (ICP) source over the range of pressure 5-20 mtorr and power input 0.2-0.5 kW, Experimental measurements as well as results of numerical simulations are presented. The models used in the study include the well-known global balance model (or the global model) as well as a detailed two-dimensional (2-D) fluid model of the system, The global model is able to provide reasonably accurate values for the global electron temperature and plasma density, The 2-D model provides spatial distributions of various plasma parameters that make it possible to compare with data measured in the experiments, The experimental measurements were obtained using a tuned Langmuir double-probe technique to reduce the RF interference and obtain the light versus current (I-V) characteristics of the probe. Time-averaged electron temperature and plasma density were measured for various combinations of pressure and applied RF power, The predictions of the 2-D model were found to be in good qualitative agreement with measured data, It was found that the electron temperature distribution T-e was more or less uniform in the chamber, It was also seen that the electron temperature depends primarily on pressure, but is almost independent of the power input, except in the very low-pressure regime. The plasma density goes up almost linearly with the power input.

Study on the ions' behavior in an electron cyclotron resonance plasma

The energy, velocity, angle distribution of ions in magnetoactive electron cyclotron resonance plasma have been studied with a two-dimension hybrid mode. The dependence of these distribution functions versus position and pressure are discussed. Our simulation results are in good agreement with many experimental measurements. (C) 1997 American Institute of Physics.

Drag on an ellipsoid particle in free-molecular plasma flow

Based on the analysis of molecular gas dynamics, the drag and moment acting on an ellipsoid particle of revolution X-2/a(2) + Y-2/a(2) + Z(2)/c(2) = 1, as an example of nonspherical particles, are studied under the condition of free-molecular plasma flow with thin plasma sheaths. A nonzero moment which causes nonspherical particle self-oscillation and self-rotation around its own axis in the plasma flow-similar to the pitching moment in aerodynamics-is discovered for the first time. When the ratio of axis length c/a is unity, the moment is zero and the drag formula are reduced to the well-known results of spherical particles. The effects of the particle-plasma relative velocity, the plasma temperature, and the particle materials on the drag and moment are also investigated.

Two-dimensional fluid model simulation of bell jar top inductively coupled plasma

In the present paper, argon (Ar) plasmas in a bell jar inductively coupled plasma (ICP) source are systematically studied over pressures from 5 to 20 mtorr and power inputs from 0.2 to 0.5 kW. In this study, both a two-dimensional (2-D) fluid model simulation and global model calculation are compared, The 2-D fluid model simulation with a self-consistent power deposition is developed to describe the Ar plasma behavior as well as predict the plasma parameter distributions, Finally, a quantitative comparison between the global model and the fluid model is made to test their validity.