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1.
Kyoungjin Kim 《Journal of Thermal Spray Technology》2008,17(4):517-524
An electrothermal gun is the device that produces high-temperature and high-velocity plasma vapor using high current pulsed
power and has a potential to be an efficient method for producing a variety of nanomaterials. Pulsed plasma discharge from
the electrothermal gun into the open air has been investigated numerically, and the time-dependent inviscid gas dynamics equations
are solved for the two-dimensional computational domain including electrothermal gun and the open-air space using flux-corrected
transport (FCT) scheme. The modeling of the Joule heating and the mass ablation from the bore wall are incorporated in the
computation. The computational results yield the details of the plasma discharge behavior inside and outside the capillary
bore including choked condition at the bore exit and complex shock structure of external plasma discharge. The flow structure
of freely expanding plasma discharge in the open air is essentially the highly underexpanded supersonic jet featuring Mach
disk, barrel shock, contact surface, and spherical blast wave. Compared to the experiments, the numerical simulation agrees
well with the experimental data such as the capillary mass ablation and shock structure of the plasma jet. 相似文献
2.
E. Kadyrov 《Journal of Thermal Spray Technology》1996,5(2):185-195
A model is developed to describe dynamic interaction of particles with the carrier gas during detonation spraying. Equations
of mass, energy, and momentum conservation are integrated numerically for the two-phase particle-gas flow with the Hugoniot
boundary conditions at the detonation wave front. Velocity and temperature of the sprayed powder and the gas parameters are
calculated self-consistently, taking into account effects of friction and cooling of the gas in the vicinity of the gun barrel
and effects of particle-gas interaction on the parameters of the gas phase. Calculations are performed for tungsten carbide
particles of 30 μm diam and a 1.8 m long detonation gun using a stoichiometric mixture of oxygen and propane. Distributions
of gas and particle parameters along the barrel are calculated for various moments of time. Tungsten carbide particles of
30 μm reach an exit velocity of 1278 m/s and a temperature of 1950 K. Exit particle velocity is a nonmonotonic function of
the loading distance,L, with a distinct maximum atL = 75 cm. The proposed model can be applied to a broad range of problems related to detonation coating technology and allows
evaluation of the effectiveness of various designs and optimization of operational parameters of detonation spraying systems. 相似文献
3.
A numerical simulation analysis for reactions of chalcopyrite and pyrite particles coupled with momentum,heat and mass transfer between the particle and gas in a flash smelting furnace is presented.In the simulation.the equations governing the gas flow are solved numerically by Eular method.The particle phase is introduced into the gas flow by the particle-source-in-cell technique(PSIC),Predictions including the fluid flow field,temperature field,concentration field of gas phase and the tracks of particles have been obtained by the numerical simulation.The visualized results show that the reaction of sulfide particles is almost completed in the upper zone of the shaft within 1.5m far from the central jet distributor (CJD)type concentrate burner,The simulation results are in good agreement with data obtained from a series of experiments and tests in the plant and the error is less than 2%. 相似文献
4.
R. Nickel K. Bobzin E. Lugscheider D. Parkot W. Varava H. Olivier X. Luo 《Journal of Thermal Spray Technology》2007,16(5-6):729-735
A new method for a combustion-free spraying is studied fundamentally by modeling and simulation in comparison with first experiments.
The article focuses on the numerical simulation of the gas-particle nozzle flow, which is generated by the shock reflection
at the end wall section of a shock tube. To study the physical fundamentals of this process, at present only a single shot
operation is considered. The particles are injected downstream of the nozzle throat into a supersonic nozzle flow. The measurements
of the particle velocity made by a laser Doppler anemometry (LDA) set up show that the maximum velocity amounts to 1220 m/s
for stainless steel particles of 15 μm diameter. The CFD-Code (Fluent) is first verified by a comparison with available numerical
and experimental data for gas and gas-particle flow fields in a long Laval-nozzle. The good agreement implied the great potential
of the new dynamic process concept for cold-gas coating applications. Then the flow fields in the short Laval nozzle designed
and realized by the Shock Wave Laboratory (SWL) are investigated. The gas flow for experimentally obtained stagnation conditions
is simulated. The gas-particle flow without and with the influence of the particles on the gas flow is calculated by the Surface
Engineering Institute (IOT) and compared with experiments. The influence of the injection parameters on the particle velocities
is investigated, as well.
This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been
expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain
Montavon, Ed., ASM International, Materials Park, OH, 2007. 相似文献
5.
环面节流静压推力轴承气膜入口区流动机理的研究与计算 总被引:1,自引:0,他引:1
对静压气体轴承流场研究结果进行了归纳与分析,指出常规气体轴承,在正常的供气压力和工作间隙下,可以采用雷诺方程求解;随着供气压力和气膜厚度的增加,供气孔与气膜相交处可能出现边界层发展区、惯性流区,此时气体流动则应分别采用边界层方程和全N—S方程求解,并采用膨胀波和拟激波揭示了惯性流区压力剧降然后回升的变化机理。在此基础之上提出了采用全N—S方程计算气膜内压力分布方法,计算与试验结果的比较表明,该计算方法可准确预测激波位置和流场的压力分布。 相似文献
6.
Investigation into laser shock processing 总被引:2,自引:0,他引:2
B. S. Yilbas A. F. M. Arif S. Z. Shuja M. A. Gondal J. Shirokof 《Journal of Materials Engineering and Performance》2004,13(1):47-54
Laser shock processing is a good candidate for surface industry due to its rapid processing, localized ablation, and precision
of operation. In the current study, laser shock processing of steel was considered. The numerical solutions for temperature
rise and recoil pressure development across the interface of the ablating front and solid are presented. The propagation of
elastic-plastic waves in the solid due to recoil pressure loading at the surface is analyzed and numerical solution for the
wave propagation was obtained. An experiment was conducted to ablate the steel surfaces for shock processing. Scanning electron
microscopy was carried out to examine the ablated surfaces shock processing while transmission electron microscopy was conducted
to obtain dislocation densities after the shock processing. It was found that surface hardness of the workpiece increased
in the order of 1.8 times of the base material hardness, and the dislocation was the main source of the shock hardening in
the region affected by laser shock processing. 相似文献
7.
An investigation is conducted of the gas dynamics of a gas detonation coating process and the mechanism of particle acceleration
by the shock wave inside the coating apparatus. Velocities of gas detonation in different gas mixtures are analyzed by applying
the conventional hydrodynamic theory of detonation, and the effect of addition gases on the velocity of detonation in oxygen/hydrogen
and oxygen/acetylene mixtures is studied. The authors propose a model that allows calculation of particle acceleration and
final velocity. This model utilizes the Chapman-Jouquet picture of detonation and assumptions about the linear distribution
of the velocity of detonation products behind the front of the detonation wave. The kinetics of particle acceleration by a
detonation wave exhibits several novel features and is distinctly different from particle acceleration in other methods of
spraying, such as plasma and high-velocity oxyfuel. There is a nonmonotonic dependence of particle velocity upon its coordinate
and change in the direction of particle acceleration. Loading distance and total barrel length are important parameters that
affect final particle velocity. Results indicate that final particle velocity and, as a consequence, the quality of detonation
coatings can be significantly affected by changing the gas mixture composition and the powder loading distance while keeping
the remaining operational parameters constant. 相似文献
8.
The fluid and particle dynamics of a high-velocity oxygen-fuel torch are analyzed using computational fluid dynamic techniques.
The thermal spray device analyzed is similar to a Metco Diamond Jet torch with powder feed. The injection nozzle is axisymmetric
with powder and a carrier gas injected on the centerline, premixed fuel and oxygen fed from an annulus, and air cooling injected
from an annulus along the interior surface of the aircap. The aircap is a conically converging nozzle that achieves choked
flow conditions at the exit; a supersonic, underexpanded jet develops externally. A two-dimensional, axisymmetric geometry
is assumed; the equations for mass, momentum, and energy conservation are solved for both the gas and the particle phases.
The combustion process is modeled using approximate equilibrium chemistry with dissociation of the gas with a total of nine
species. Turbulent flow is modeled by a two-equation model for turbulent kinetic energy and dissipation rate that includes
compressibility effects on turbulent dissipation. Particles are modeled as a lumped-heat-capacity system and are considered
to melt upon attaining the required latent heat of fusion. An iterative, implicit, finite-volume numerical method is used
to solve the coupled gas and particle equations inside and outside the torch. A companion paper presents the results of the
numerical simulation and discusses in detail the gas and particle dynamics. 相似文献
9.
GAO Juxian SHAO Binghuang ZHANG Ke ZHENG Zhemin Institute of Mechanics Academia Sinica Beijing China 《金属学报(英文版)》1991,4(8):121-126
Two dimensional explosive consolidation under cylindrical converging shock wave has beenstudied by use of coated fine iron filaments compacts to replace conventional metallic powder,so the randomness of three-dimensional spatial distribution of metallic powder might beavoided.The deformation and surface flow pattern of particles as well as the mechanism ofconsolidation have been clarified experimentally.The distribution of high temperature area isin agreement with the result of numerical simulation by Williamson.A model for the explosiveconsolidation was given. 相似文献
10.
Jacob E. Cannon Mohammad Alkam P. Barry Butler 《Journal of Thermal Spray Technology》2008,17(4):456-464
Pulsed detonation thermal spray coating is used to enhance the material properties at the surface of an object. The present
research implements computational fluid dynamic modeling to identify the efficiency of energy and mass delivered to potential
target locations. Six cases of a hydrogen-air mixture are used to investigate the gas flow from the instant of ignition to
the instant of flow reversal at the tube exit. Flow monitors are included in the model to represent potential target locations.
These monitors are placed at different axial locations in order to record mass flow rate and the flow rate of enthalpy over
time. The results indicate that there exists a quasi-steady jet that is efficient and predictable in delivery of energy and
mass from the tube exit to potential target locations positioned on the centerline. The duration of the quasi-steady jet is
dependent on the fraction of combustible gas (i.e., % fill). Much of the initial energy and mass delivered from the jet avoids
the flow monitors. This is found to be related to the evolution of the jet behind the blast wave where energy is lost in expansion
and vorticity production. It is also found that nearly 11-18% of the available energy and 20-23% of the available mass remains
in the tube after flow reversal. 相似文献
11.
目的 为克服激光冲击强化现有离线检测方法的缺点,提出了一种基于空气中冲击波信号能量的激光冲击强化在线检测方法。方法 利用波长为1064 nm、脉宽为14 ns、单脉冲能量为5~7 J的Nd:YAG激光器对经过振动时效处理的TC16钛合金试件进行激光冲击强化处理。用自主研制的信号放大器对空气中的冲击波信号进行一级放大后,再经前置放大器、数据采集卡传输到计算机控制系统,从而实现对空气中冲击波信号的采样、存储、滤波和数据分析,并从中提取冲击波信号能量。用X-350A型X射线应力测定仪测量TC16钛合金试件经激光冲击强化处理后的表面残余应力。最后对所得实验数据进行多项式拟合,以获得材料表面残余压应力与冲击波信号能量之间的经验公式。结果 经激光冲击强化处理后,材料表面形成了一定大小的残余压应力。随着激光能量的增加,材料表面残余压应力及冲击波信号能量均增加,且二者的增加趋势一致。结论 在激光冲击强化过程中,对空气中传播的冲击波信号进行采集和提取其信号能量,可以预测试件经激光冲击强化处理后的残余应力,能够准确判断激光冲击强化质量,从而实现工业过程的在线检测。 相似文献
12.
This paper presents an eigenstrain (misfit strain) model of the residual stresses generated by laser shock peening (LSP). The shock wave is first modelled as a dynamic pressure load in an explicit finite element (FE) model and the stabilised plastic strain distribution is extracted. This strain distribution is then incorporated as an eigenstrain distribution in a static FE model and the residual stresses generated by the original shock wave are obtained as the elastic response to the eigenstrain. In order to focus on the basic mechanics, an elastic-perfectly plastic material model is assumed. Similarly, a simplified pressure/time variation (a triangular ramp with the peak pressure occurring at the half the total pulse duration) is assumed in order to characterise the pressure pulse. The peak pressure and the duration of the pressure pulse are determined in a way that they are consistent with experimental results. The analysis is extended to study the case of multiple pulses and the results show that the process generates compression in a surface layer of about 1.5-2 mm deep. Furthermore, the results demonstrate that the magnitudes of subsurface tensile stresses are of the order of one fifth of the material's yield strength for typical peening conditions. 相似文献
13.
14.
15.
Mathematical modeling of the gas and powder flow in HVOF systems 总被引:1,自引:0,他引:1
A mathematical model was developed to describe the gas dynamics and heat-transfer mechanism in the gas/particle flow of high-
velocity oxyfuel (HVOF) systems. A numerical solution was carried out using a PC- based computer program. One- dimensional
predictions of the temperature and velocity profiles of gas and particles along the axis of flow were obtained to conduct
cost- effective parametric studies and quality optimization of thermal spray coatings produced by HVOF systems. The numerical
computer model allows for the variation of the HVOF system parameters, such as air/fuel ratio and flow rates, cooling water
inlet temperature and flow rate, barrel length, standoff distance, particle size, and gun geometry.
Because of the negligible volume of the powder relative to the gas, the gaseous phase was modeled as continuous nonadiabatic,
and friction flow with variable specific heats and changing cross- sectional areas of flow. The generalized continuity, momentum,
and energy equations with the influence parameters were used to model the gaseous flow regime and predict its thermodynamic
properties. Empirical formulas for the mean axial decay of both velocity and temperature in the supersonic jet plume region
were generated from published measurements of these parameters using laser Doppler velocimeter and Ray leigh scattering techniques,
respectively. The particle drag and heat- transfer coefficients were calculated by empirical formulas in terms of Reynolds,
Nusselt, and Prandtl numbers to evaluate both the momentum and heat transferred between the combustion gases and the powder
particles. The model predictions showed good agreement with the particle and gas temperature and velocity measurements that
are available in the literature. 相似文献
16.
A computational study of pulsed detonation thermal spraying is conducted using an axisymmetric two-dimensional transient gaseous
detonation model. The variations of the particle velocity and temperature at impact on the target surface with the particle
initial loading location are analyzed for different conditions. The geometry of the system and the loading locations of the
particulate phase are key parameters in pulsed detonation thermal spraying. Since the process is extremely transient and the
gas phase experiences a wide range of transient stages all on a timescale of a millisecond, the particle characteristics are
strongly dependent on the instantaneous location in the gas stream. One cycle of detonation thermal spraying occurs on a time
scale on the order of a millisecond due to the high gas velocities associated with detonation. Thus, a precise control of
the process variable parameters is required to have a successful detonation coating process. 相似文献
17.
18.
《International Journal of Cast Metals Research》2013,26(1-4):204-207
AbstractThe presence of bulk and interdendritic flow during solidification can alter the microstructure, potentially leading to the formation of defects. In this paper, a numerical model is presented for the direct simulation of dendritic growth in the presence of fluid flow in both liquid and mushy zones. The Navier–Stokes equations are solved for multiphase flow using a projection method. The energy conservation and solute diffusion equations are solved via a combined stochastic nucleation approach and finite difference solution to simulate dendritic growth. The predicted microstructures illustrate typical asymmetric dendritic growth behaviour under forced convection, which is consistent with prior similar simulations of a single dendrite during unconstrained growth (both 2D and 3D). The micromodel was coupled with a macromodel to investigate the effects of forced fluid flow on equiaxed dendritic growth and micro-segregation during vacuum arc remelting. 相似文献
19.
A. Blais B. Jodoin J-L. Dorier M. Gindrat C. Hollenstein 《Journal of Thermal Spray Technology》2005,14(3):342-353
Low pressure plasma spraying (LPPS) is a thermal spraying technique that has found a niche for low oxidation products. It
uses a low pressure environment (i.e., chamber pressure between 2 and 90 kPa) and yields supersonic plasma jets. The enthalpy
probe technique is a common measurement method in plasmas. However LPPS jets are difficult to diagnose as their supersonic
nature forces the apparition of a shock wave in front of any measuring device inserted in the jet. Incomplete or erroneous
assumptions are usually invoked to overcome the difficulties associated with this shock wave and carry out the LPPS jet diagnosis
from enthalpy probe measurements. In this work, a new device is designed to gain access to an additional physical quantity,
which is needed to assess the aerodynamic non-equilibrium state of the jet. It is combined with enthalpy probe measurements,
and the resulting set of experimental data is used with a numerical procedure based on gas dynamics theory, yielding free-stream
supersonic plasma jet values from the measurements behind the induced shock wave. The results agree well with the phenomenology
of supersonic jets in aerodynamic nonequilibrium. However this new method is restricted by the local thermodynamic equilibrium
assumption, which is directly linked with the pressure and temperature conditions of the plasma jet. 相似文献
20.
O. B. Kovalev A. V. Zaitsev D. Novichenko I. Smurov 《Journal of Thermal Spray Technology》2011,20(3):465-478
The results of theoretical and experimental investigations of direct metal deposition (DMD) processes involving a CO2-laser with the power up to 5 kW and wave length of 10.6 μm are presented. The physical and mathematical model of multi-layer
gas flows with gas-jet transportation of metal powder particles has been developed. To simulate the flows of carrier and shaping
gases in annular channels of a triple coaxial nozzle, Navier-Stokes equations were applied for an axisymmetric flow. Thermodynamics
and powder particles transport are calculated from a discrete-trajectory model with due regard to particle collision with
solid walls of the transport nozzle. It is shown that particles may overheat on their way between the nozzle and substrate;
the overheating depends on the trajectories by which particles move, on their size, and time of their retention in the laser-radiation
region. The results of performed experimental researches on DMD processes visualization are presented. Some results of numerical
simulation and experimental data are compared and analyzed. 相似文献