基于气体捕捉法的泡沫Ti-6Al-4V等温发泡规律研究

为了确定气体捕捉法制备泡沫Ti-6Al-4V等温发泡过程中孔隙率和微观孔洞的变化规律,在不同发泡温度及发泡时间下制备了泡沫Ti-6Al-4V.运用阿基米德原理对泡沫Ti-6Al-4V的孔隙率进行测量,通过OM和SEM对其微观特征进行观察.研究表明:泡沫Ti-6Al-4V的孔隙率及孔径均随等温发泡温度升高而增加;但当发泡温度大于950℃时,孔隙率和孔径均减小,且孔洞形态由球形变成多边形,这是由于基体内生成大尺寸β相造成的.增加发泡时间能以促进孔洞长大的方式提高泡沫Ti-6Al-4V的孔隙率,球形孔洞数量随着发泡时间的增加逐渐增多.经950℃/10 h发泡得到了孔隙率34.2%、孔径平均值156μm、孔洞为球形且分布弥散的泡沫Ti-6Al-4V.     

A thermogravimetry-capillary gas chromatography/mass spectrometry interface

An interface and gas chromatograph oven are described that couple a thermogravimetric analyzer with a mass spectrometer and permit multiple capillary gas chromatographic separations of volatile thermal decomposition products generated during a single thermogravimetric analysis. Examples of the use of this apparatus for identifying the volatile products generated during poly(vinyl butyral) thermal decomposition in the presence of γ-alumina and catalytic cracking of poly(styrene) and poly(ethylene) are described. TG-GC/MS analyses employing isothermal, temperature programmed, and subambient temperature ramp gas chromatography separations are described. The apparatus permits repetitive temperature-programmed capillary gas chromatographic analyses of thermogravimetric effluent containing more than 25 constituents in 3-min intervals.     

热丝CVD方法中气体状态参数的二维模拟计算

使用在连续介质中建立的二维流场数学模型，模拟计算了在用HFCVD方法生长金刚石薄膜过程中影响气体温度分布的多个沉积工艺参数，研究了气体的速度和体密度的空间分布．结果表明，在优化工艺参数条件下，高温热丝的热阻塞作用导致气体状态参数的不均匀空间分布；在热丝附近气体的速度大而靠近反应腔体侧壁处小；热丝附近处气体体密度减小而靠近冷反应腔体侧壁处增加，采用绝热或高等温边界的反应腔管道壁可以消除气体的热绕流现象，有利于大面积金刚石薄膜的快速均匀生长．     

Thermal polarization of a viscous gas flow accompanied by slip in a channel with a nonuniform surface

A theoretical model of heat transfer is proposed and measurements are made of the temperature field in a gas flow in an isothermal channel with a nonuniform surface.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 4, pp. 566–571, October, 1988.     

Constant holdup times in gas chromatography by programming of column temperature and inlet pressure

The requirements for attaining constant holdup times in capillary gas chromatography (GC), while linearly programming both column temperature and inlet pressure, are illustrated. A scheme, which is based on a series of responses from isothermal and isobaric conditions, is proposed. The responses from two commonly used GC instruments, one with a mass-selective detector operating at near-vacuum pressure and another with a flame-ionization detector at ambient pressure, are analyzed. A significant deviation from Poiseuille flow is noted due to the use of helium as a carrier gas. Nonetheless, the experimental holdup times are approximately constant over a range of temperatures and pressures. Theoretical analysis reveals the spatial and temporal dependence of flow rates inside the column during the programmed runs.     

Isothermal creep of a binary gas mixture along a flat surface

The method of half-space moments [1] is used to derive an analytic expression for the velocity of isothermal creep of a binary gas mixture along a flat surface. The distribution functions for the gas molecules are found from the solution of the Boltzmann kinetic equation with a model collision integral.     

Stable diffusion boundaries in three-component gas mixtures

Within the framework of the Boussinesq approximation, as a function of the relationship between the partial diffusion factors, we have investigated an isothermal three-component gas mixture with respect to linear stability. In the stable diffusion region the process of isothermal mass transfer is described by standard Fick equations. We have determined the regions of increasing (diminishing) monotonie and oscillatory perturbations. We have investigated the relationship between the Rayleigh numbers and the parameters of the mixture.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 60, No. 3, pp. 419–425, March, 1991.     

Computer simulation (based on a linear-elution-strength approximation) as an aid for optimizing separations by programmed-temperature gas chromatography

If the dependence of retention on temperature is specified for the various components of a sample in isothermal gas chromatography (GC), it is possible to predict retention, bandwidth, and resolution for programmed-temperature GC separations as a function of experimental conditions. The use of a linear-elution-strength (LES) approximation for isothermal retention allows these predictions to be carried out more easily and conveniently, in turn facilitating rapid simulations with a personal computer. This approach to GC method development appears promising, especially if segmented-temperature programs are used. The LES approximation also provides added insight into how different factors affect separation in programmed-temperature GC.     

Isothermal slip of a binary gas mixture along a solid surface

This paper investigates Couette flow of a binary mixture of a rarefied gas between two flat plates. An analytical expression for the rate of isothermal slip of a binary mixture of the rarefied gas along the surface is obtained.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 4, pp. 683–686, April, 1977.     

Measurement of unsteady gas flow under anisothermic conditions

We describe a dynamic method for measuring unsteady gas flow under anisothermic conditions. We show that the value of the flow sensitivity determined under isothermal conditions can be used for molecular flow.     

Self-similar solutions of one-dimensional problems of gas filtration with a quadratic resistance law

One-dimensional problems of isothermal gas filtration in a porous medium with a quadratic resistance law are considered. For the cases of plane and axial symmetry of the problem under constant initial conditions, analytical expressions for the gas pressure and velocity are obtained and an empirical formula for calculating the gas pressure is proposed.     

Radiation in a layer of nongray gas between gray walls

Radiative heat transfer formulas are derived for an isothermal layer of gas and gray walls; they are compared with previously published formulas. The method of derivation makes it possible to refine the formulas obtained.     

Heat transfer effects on dusty gas flow past a semi-infinite inclined plate

Heat transfer effects on dusty gas flow past a semi-infinite isothermal inclined plate are considered here-with. The governing boundary layer equations for the above problem are set up and non-dimensionalised. The non-dimensional governing equations are solved by an implicit finite difference scheme of Crank–Nicolson method, which is fast convergent and unconditionally stable. Gas-velocity, dust particle-velocity, temperature, skin friction and Nusselt numbers are calculated numerically for various parameters occurring into the problem and are shown graphically. It is observed that the velocity of the dusty-gas decreases with decreasing inclination angle ϕ to the horizontal. An increase in the mass concentration of dust also causes a fall in the gas-velocity.     

Experimental studies on an indigenous coconut shell based activated carbon suitable for natural gas storage

Experimental studies are carried out to characterize an indigenous, coconut shell based, activated carbon suitable for storage of natural gas. Properties such as BET surface area, micropore volume, average pore diameter and pore size distribution are obtained by using suitable instruments and techniques. An experimental setup is developed to estimate the equilibrium methane adsorption capacity and adsorption/desorption kinetics. The experimental isothermal uptake data is used to fit four different isotherm models. Using the constants obtained for the D–A isotherm model the variation of heat of adsorption and adsorbed phase specific heat with equilibrium pressure and temperature are obtained. Similarly Henry’s Law coefficients, important at low pressure and low uptake regime are also obtained. Finally using the kinetic data and a linear driving force model, constants in the kinetic equation are obtained. Results show that the indigenous material used in this study offers reasonably high natural gas storage capacity and fast kinetics and is suitable for adsorbed natural gas (ANG) applications. It is expected that this study will be useful in the design and development of ANG systems based on this indigenous material.     

Effect of a transverse thermal gradient on the microstructure of a directionally solidified 73C eutectic alloy

The thermal stability of a directionally solidified (d. s.) eutectic CoCrCAl-alloy in a thermal gradient is compared to isothermal conditions. A device has been designed and constructed for examination of d. s. eutectics in high temperature gradients at temperatures above 1300 K in different atmospheres and vacuum. Experiments in this gradient furnace show coarsening of the carbide fibres forming the aligned strengthening phase. A microstructural instability resulting from the transformation of carbide fibres has been observed. These effects are discussed in relation to isothermal conditions and their implications on the applicability of the alloy as high temperature gas turbine blade material.     

碳纳米管及其掺杂氧化物半导体气敏传感器

碳纳米管气敏传感器以其工作温度低和最低检出限较低等优点而备受关注,而碳纳米管掺杂氧化物半导体气敏传感器兼备了氧化物半导体气敏传感器和碳纳米管气敏传感器二者的优点,具有灵敏度较高、最低检出限低和工作温度低等特性。综述了这两类传感器的研究进展,介绍了其气敏机理,并对相应存在的问题及今后的发展趋势进行了概述。     

Simulated pulsed flow of gas and particles in a horizontal oppose-pulsed gas jets of bubbling fluidized bed

Flow behavior of gas and particles with a horizontal oppose-pulsed gas jets are simulated by means of a three dimensional Computational Fluid Dynamics (CFD) model with the kinetic theory of granular flow in a gas-particles bubbling fluidized bed. The effects of amplitudes and frequencies on the hydrodynamics of gas and particles are analyzed. The simulation results are presented in terms of phase velocity vector plot, volume fraction of phases, granular temperature, power spectrum and Reynolds stresses in the bed. Results show that the impingement caused by the oppose-pulsed gas jets oscillates with the variation of pulsed gas velocity. The impingement zone with the high solid volume fraction reciprocates from the left side to the right side through the bed center with the variation of pulsed jet gas velocities. The lateral velocity and gas turbulent kinetic energy, granular temperature and Reynolds stresses of gas and particles are larger near the pulsed gas jets than that at the center of the bed. The large dispersion coefficients of particles using the horizontal oppose-pulsed gas jets enhance the mixing of particles in gas-solid fluidized bed.     

Transient flow in response to a pressure pulse in gas chromatography

The analysis of flow through a gas chromatography column has traditionally assumed the presence of steady-state conditions. However, when rapid changes in inlet pressure are introduced, a significant transient period is observed, leading to a failure of the steady-state model. Through the introduction of a one-dimensional continuity equation into the basic set of equations, a nonlinear partial differential equation is derived to describe the evolution of pressure profiles in a capillary gas chromatography column. A numerical solution is used to solve the differential equation for the case of a pulse injection under isothermal conditions, and comparisons with experimental holdup and retention times show very good agreement.