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.

Effects of Mach number on turbulent separation behaviours induced by blunt fin

An experimental study of the interaction between shock wave and turbulent boundary layer induced by blunt fin has been carried out at M-infinity = 7.8 using oil flow visualization and simultaneous measurements of fluctuating wall pressure and heat transfer. This paper presents the effects of Mach number on turbulent separation behaviours induced by blunt fin.

Effects of adiabatic exponent on Richtmyer-Meshkov instability

We present a systematical numerical study of the effects of adiabatic exponent gamma on Richtmyer-Meshkov instability (RMI) driven by cylindrical shock waves, based on the gamma model for the multi-component problems and numerical simulation with high-order and high-resolution method for compressible Euler equations. The results show that the RMI of different gamma across the interface exhibits different evolution features with the case of single gamma. Moreover, the large gamma can hold back the development of nonlinear structures, such as spikes and bubbles.

Gain saturation effects of a flowing chemical oxygen-iodine laser

A new oxygen-iodine medium gain model is developed to include pumping and deactivation of the upper laser levels of the iodine atoms, hyperfine and translation relaxation, as well as the flowing effect. The rate equations for gain of a supersonic flowing cw oxygen-iodine laser (COIL) are described when the medium is stimulated by a single-mode field. The general solution of the self-consistency integral equation is obtained. The result shows that the saturation behaviour in low pressure of the COIL differs from both the inhomogeneous and homogeneous broadening, and exhibits an 'anomalous' saturation phenomenon.

Coupling effects of heterogeneity and stress fluctuation on rupture

The coupling of mesoscopic strength distribution and stress fluctuation on damage evolution and rupture are examined. The numerical simulations show that there is only weak stress fluctuation at the initial damage stage when the mean field approximation is in effect. As the damage fraction becomes larger than the threshold value, the fluctuation is amplified significantly, and damage localization appears. The coupling between stress fluctuation, disordered heterogeneity and the damage localization may play an essential role in catastrophic rupture. (C) 2003 Elsevier Ltd. All rights reserved.

Effects of physical parameter range on dimensionless variable sensitivity in water flooding reservoirs

The similarity criterion for water flooding reservoir flows is concerned with in the present paper. When finding out all the dimensionless variables governing this kind of flow, their physical meanings are subsequently elucidated. Then, a numerical approach of sensitivity analysis is adopted to quantify their corresponding dominance degree among the similarity parameters. In this way, we may finally identify major scaling law in different parameter range and demonstrate the respective effects of viscosity, permeability and injection rate.

Effects of physical parameter range on dimensionless variable sensitivity in water flooding reservoirs

The similarity criterion for water flooding reservoir flows is concerned with in the present paper. When finding out all the dimensionless variables governing this kind of flow, their physical meanings are subsequently elucidated. Then, a numerical approach of sensitivity analysis is adopted to quantify their corresponding dominance degree among the similarity parameters. In this way, we may finally identify major scaling law in different parameter range and demonstrate the respective effects of viscosity, permeability and injection rate.

A nanoindentation analysis of the effects of microstructure on elastic properties of Al2O3/SiC composites

Nanoindentation tests were carried out to investigate certain elastic properties of Al2O3/SiCp composites at microscopic scales (nm up to mu m) and under ultra-low loads from 3 mN to 250 mN, with special attention paid to effects caused by SiC particles and pores. The measured Young's modulus depends on the volume fraction of SiC particles and on the composite porosity and it can compare with that of alumina. The Young's modulus exhibits large scatters at small penetrations, but it tends to be constant with lesser dispersion as the indentation depth increases. Further analysis indicated that the scatter results from specific microstructural heterogeneities. The measured Young's moduli are in agreement with predictions, provided the actual role of the microstructure is taken into account. (C) 2007 Elsevier Ltd. All rights reserved.

Effects of entry conditions on cracked kerosene-fueled supersonic combustor performance

Supersonic combustion of thermally cracked kerosene was experimentally investigated in two model supersonic combustors with different entry cross-section areas. Effects of entry static pressure, entry Mach number, combustor entry geometry, and injection scheme on combustor performance were systematically investigated and discussed based on the measured static pressure distribution and specific thrust increment due to combustion. In addition, the methodology for characterizing flow rate and composition of cracked kerosene was detailed. Using a pulsed Schlieren system, the interaction of supercritical and cracked kerosene jet plumes with a Mach 2.5 crossflow was also visualized at different injection temperatures. The present experimental results suggest that the use of a higher combustor entry Mach number as well as a larger combustor duct height would suppress the boundary layer separation near the combustor entrance and avoid the problem of inlet un- start.

Atomistic investigation of the effects of temperature and surface roughness on diffusion bonding between Cu and Al

Molecular dynamics (MD) simulations are carried out to analyze the diffusion bonding at Cu/Al interfaces. The results indicate that the thickness of the interfacial layer is temperature-dependent, with higher temperatures yielding larger thicknesses. At temperatures below 750 K, the interface thickness is found to increase in a stepwise manner as a function of time. At temperatures above 750 K, the thickness increases rapidly and smoothly. When surface roughness is present, the bonding process consists of three stages. In the first stage, surfaces deform under stress, resulting in increased contact areas. The second stage involves significant plastic deformation at the interface as temperature increases, resulting in the disappearance of interstices and full contact of the surface pair. The last stage entails the diffusion of atoms under constant temperature. The bonded specimens show tensile strengths reaching 88% of the ideal Cu/Al contact strength. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.