The effect of inelastic collisions on the diatomic gas temperature jump in the vicinity of a solid surface

The problem on temperature jump in the vicinity of a solid surface is solved by the method of half-space moments using the previously suggested model kinetic equation which takes into account the rotational degrees of freedom of molecules of a diatomic gas. The temperature jump coefficient is obtained in the form of a function dependent on the coefficient of accommodation of tangential momentum, the coefficients of accommodation of translational and rotational components of energy, thermophysical parameters, and the frequency of inelastic collisions of gas molecules. The temperature jump coefficient is calculated for a number of diatomic gases. Graphs are given of the dependence of the temperature jump coefficient on the inelastic collision frequency and on the accommodation coefficients.     

Rotational and translational accommodation coefficients of nitrogen on nickel,silver and gold

An electron beam excited fluorescence technique was used to make simultaneous measurements of rotational and translational accommodation of nitrogen on nickel, silver, gold and stainless steel solid surfaces. In addition to the advantage of being able to make independent measurements of rotational accommodation, this apparatus allows a wide range of solid surface temperatures to be used and operates at lower gas density than most previous experiments.Rotational accommodation coefficients for nickel and gold varied from α_R = 0.12 at 400°K to α_R = 0.18 at 850°K while the value of α_R for silver increased more quickly from α_R = 0.03 at 430°K to α_R = 0.2 at 700°K.A linear variation of translational accommodation coefficient, α_T, with surface temperature was observed. An empirical relationship based on molecular weights was able to account for variation in dα_T/dT_s observed. The metal surfaces used were thought to be free of adsorbed gas and oxide layers.     

Kinetic Coefficients in the Boundary-Value Problem on the Slip of a Multiatomic Gas with Rotational Degrees of Freedom

The boundary-value problem on the slip of an inhomogeneous multiatomic gas along the spherical surface of small curvature is solved. For this purpose, a model kinetic equation that includes the rotational degrees of freedom of molecules is proposed. The solution is performed using the method of half-space moments. Gas-kinetic slip coefficients and jumps of macroscopic parameters of gas of the first and second order in the Knudsen number are obtained. These gas-kinetic coefficients are represented in the form of functions depending on the accommodation coefficient of tangential momentum, on the accommodation coefficients of the translational and rotational components of energy, and on the Prandtl number. For a number of multiatomic gases, calculations of the above-mentioned coefficients are performed.     

The Effect of Inelastic Collisions of Molecules of a Diatomic Gas with Rotational Degrees of Freedom

The problem on Barnett slip of gas along a plane surface is solved within the suggested kinetic model for a diatomic gas with rotational degrees of freedom of molecules, which takes into account transitions from rotational degrees of freedom to translational and vice versa. The Barnett slip coefficient is obtained in the form of a function dependent on the frequency of inelastic collisions of gas molecules and on the coefficient of accommodation of tangential momentum.     

Experimental study of the influences of degraded vacuum on multilayer insulation blankets

The paper presented experimental investigation on the heat transfer of MLI with different rarefied gases at different pressures. The investigations were carried out using an innovative static liquid nitrogen boil-off rate measurement system in the case of the small temperature perturbations of cold and warm boundaries. The heat fluxes for a number of inert and some polyatomic gases have been analyzed at different heat transfer conditions ranging from molecular to continuum regime, apparent thermal conductivities of the multilayer insulation were measured over a wide range of temperature (77 K–300 K) and pressure (10⁻³–10⁵ Pa) using the apparatus. The experimental results indicated that under degraded vacuum condition, the influences of rarefied gas on the MLI thermal performance very depend on the gas rarefaction degree which impacted by the MLI vacuum degree. Under the condition of molecular regime heat transfer, the MLI thermal performance was greatly influenced by gas energy accommodation coefficients (EAC), when under the continuum regime, the performances depend on the thermal conductivity of rarefied gas itself. Compared to the results of N₂, Ar, CO₂, Air and He as interstitial gases in the MLI, Ar was the better selection as space gas because of its low EAC and thermal conductivity characteristics on the different vacuum condition ranging from high pressure to vacuum. So different residual gases can be utilized according to the vacuum level and gas energy accommodation coefficient, in order to improve the insulation performance of low vacuum MLI.     

Prediction of translational accommodation coefficient

A simple empirical equation has been developed from experimental data for prediction of the translational accommodation coefficient. It contains such basic parameters of gas-surface interaction as the atomic weights of gas and solid surface atoms, their temperatures and the ratio of specific heats of the gas. Adequate agreement with experimental data available in the literature for monatomic, diatomic and polyatomic gases is obtained for a wide range of gas-surface parameters.     

Molecular transport at a moving surface at low pressures

The rate of impingement and departure and the differential forces exerted by molecules at a moving surface in a low pressure gas are considered theoretically. Expressions for these quantities, assuming accomodation at the surface or no accommodation and assuming either specular of diffuse scattering, are derived. It is shown that in general the differential pressure exerted by a gas is either equal to or lower, under all circumstances, than the values derived earlier for specular reflexion no accomodation conditions, indicating that the details of the surface collisions cannot account for observed discrepancies between experimental measurements and theoretical predictions.     

Dynamics of inelastically colliding spheres with Coulomb friction: Relaxation of translational and rotational energy

We investigate the free cooling of inelastic rough spheres in the presence of Coulomb friction. Depending on the coefficients of normal restitution ε and Coulomb friction μ, we find qualitatively different asymptotic states. For nearly complete normal restitution (ε close to 1) and large μ, friction does not change the cooling properties qualitatively compared to a constant coefficient of tangential restitution. In particular, the asymptotic state is characterized by a constant ratio of rotational and translational energies, both decaying according to Haff's law. However, for small ε and small μ, the dissipation of rotational energy is suppressed, so that the asymptotic state is characterized by constant rotational energy while the translational energy continues to decay as predicted by Haff's law. Introducing either surface roughness for grazing collisions or cohesion forces for collisions with vanishing normal load, causes the rotational energy to decay according to Haff's law again in the asymptotic long-time limit with, however, an intermediate regime of approximately constant rotational energy. Received: 19 November 1999     

Translational and rotational dynamics of methane in ZSM-5 zeolite: A quasi-elastic neutron scattering study

The translational and rotational motions of methane adsorbed at different loadings in NaZSM-5 have been studied by quasi-elastic neutron scattering at two temperatures: 200 and 250 K. The translational motion does not simply follow Fick's law, but a jump diffusion model with a Gaussian distribution of jump lengths satisfactorily simulates the experimental results. The diffusion coefficient that is obtained for long-range translational motion does not vary much on the loading in the range that was studied: it is of ⋍ 2.7 × 10⁻⁵ cm² s⁻¹ at 200 K and ⋍ 5.5 × 10⁻⁵ cm² s⁻¹ at 250 K. Good agreement is found between the neutron and n.m.r. results for this motion, but large discrepancies are observed with the macroscopic measurements. The rotational motion is well described by an isotropic rotational diffusion model, and this motion is found to be much slower in the zeolite than in physisorbed layers or in bulk solid methane.     

Thermal accommodation coefficient of gases on controlled solid surfaces: Argon-tungsten system

The knowledge of the thermal accommodation coefficient for gases on well-controlled surfaces as a function of temperature is imperative to understanding the mechanism of interphase heat transfer on the microscopic level. With this goal in view, a heat transfer column instrument is designed, fabricated, assembled, and tested for the specific case a argon—tungsten system. With 99.9999%, pure argon, six sets of data are taken in the rarefied gas region in the maximum temperature range of 500–1500 K. Four sets of these measurements are in the temperature-jump region and are analyzed by the constant-power method to compute the thermal accommodation coefficient of argon on a controlled tungsten surface. The other two sets are taken under free-molecular flow conditions and are interpreted in accordance with the man-free-path kinetic theory for the low-pressure regime. These data are compared and discussed in the context of reported data in the literature and interpreted in the light of the surface condition and finish of the tungsten wire.Nomenclature A area of the solid surface - C _j constants in Eq. (3); j=0, 1, 2, 3, and 4 - E _i incident energy flux - E _r reflected energy flux - E _s reflected energy flux when the interaction between the gas and the solid atoms is complete - g temperature-jump distance - L half-length of the metal wire - M molecular weight of the gas - P gas pressure - Q _H total thermal energy conducted by the gas per unit time from the hot surface - Q_KT total thermal energy conducted by the gas per unit time if the striking gas molecules were to attain thermal equilibrium with the hot surface - R molar gas constant - r radial coordinate - r _f radius of the hot wire - S sticking coefficient - S_o initial sticking coefficient - T temperature - T _e linearly extrapolated gas temperature on the hot-wire surface - T _g temperature of the impinging gas molecules - T _H temperature of the hot surface - T _i temperature of the incident gas stream - T _r temperature of the gas molecules receding after collision with the solid surface - T _s temperature of the solid surface Greek Symbols thermal accommodation coefficient for the gas—solid surface - resistivity of the metal wire - gas coverage on the solid surface For an explanation of symbols, see Nomenclature.     

Plasmons: quanta for micro-region temperature measurement

An analysis is made of the shifts in the plasmon loss energies for a 1 keV electron beam scattered from pure tin as a function of temperature in ultra-high vacuum. The plasmons in tin are free-electron like and the thermal shifts are shown to arise from the volume expansion and consequent reduction in electron density as the temperature rises. The shifts for the volume plasmon of 0.49 meVK^–1 in the solid state, and 0.60 meVK^–1 in the liquid state, may be measured fairly readily to an accuracy better than 10 meV and hence provide a temperature measurement to better than 20 K. In the study of solid surfaces in an ultra-high vacuum scanning electron microscope, by a choice of electron beam energy, this method may be used to define the temperature in the outermost 1 nm at a solid surface with a lateral region limited only by the electron probe size. This may be less than 100 nm in modern surface analysis instruments and involve power of less than 10 nW. In the study of thin films by transmission electron microscopy, the temperature may be determined with a spatial resolution close to that of the imaging and involve even lower power inputs than for solid surfaces.     

Constitutive relations for a planar,simple shear flow of rough disks

Stresses developed in a rapid simple shear flow of disks are quantified. Collisional momentum transfer is considered to be the dominant stress generating mechanism. The disks are inelastic and frictional. The restitution coefficient and the coefficient of friction together determine the transfer of momentum and dissipation of energy during a collision. The frictional coefficient generates and maintains a rotational motion of disks. The total fluctuation motion of disks consists of two translational modes and one rotational mode. The rotational mode is found to depend on both the restitution and the friction coefficient. Equipartition of energy among all modes of motion is absent. The mean rotation depends only on the mean flow gradient. The analysis assumes fluctuation modes all have constant magnitudes. Comparison with a computer simulated disk flow shows good agreement. This implies that the distribution of velocity magnitude may not be crucial to the quantification of stresses.     

Measurements of the relative momentum accommodation coefficient for different gases with a viscosity vacuum gauge

The viscosity vacuum gauges are based on the gas momentum transfer phenomena between a moving part of the gauge and a stationary surface. Thus, they may be used for the study of the momentum accommodation coefficient for various combinations of gas species and surfaces. The aim of the present work is to determine the momentum accommodation coefficient by means of the viscosity vacuum gauge with vibrating metal ribbon. The relative accommodation coefficient was computed from the measurements for Xe, Ar, He and H₂ on the bronze ribbon of the gauge in the molecular conditions. The values of the relative coefficients were 0.90 for Xe, 0.95 for Ar, 1 for He (values were normalised to data obtained for He) and 0.94 for H₂.     

A viscosity gauge for pressure measurement in the range 10 to 10 torr

In this paper a direct reading molecular damping gauge for pressure measurement in vacuum system is described. By making an oscillating vane (of aluminium foil 9 × 5 cm) one element of a closed loop servo system the amplitude of swing is maintained constant independent of pressure, the power fed into the system just balancing the losses due to gas damping. The power input is monitored and taken as a measure of gas damping and hence pressure. Experiment shows there to be a linear relation between power input and pressure over the whole useful working range 10⁻⁶ to 10⁻³ torr. By taking account of such secondary factors as the influence of the finite size of the vacuum vessel on the damping forces good agreement between theory and experiment can be reported. The relative unimportance of accomodation coefficient on the behaviour of the gauge is discussed. The prediction that sensitivity is proportional to the square root of the molecular weight of the gas in the vacuum system has been checked and found correct to ± 4 percent over the range 4–350 amu. This gauge can therefore be recommended as a useful secondary calibration standard for vapours where more conventional calibrating techniques are difficult to apply.     

Solid elements with rotational degrees of freedom: Part 1—hexahedron elements

This is the first of a two part paper on three-dimensional finite elements with rotational degrees of freedom (DOF). Part I introduces an 8-node solid hexahedron element having three translational and three rotational DOF per node. The corner rotations are introduced by transformation of the midside translational DOF of a 20-node hexahedron element. The new element produces a much smaller effective band width of the global system equations than does the 20-node hexahedron element having midside nodes. A small penalty stiffness is introduced to augment the usual element stiffness so that no spurious zero energy modes are present. The new element passes the patch test and demonstrates greatly improved performance over elements of identical shape but having only translational DOF at the corner nodes.     

Relationship of porcelain insulator temperature and flashover voltage measurement procedure in vacuum

In this paper the existence of a connection between a conditioning procedure and the solid insulator temperature changes in a vacuum is shown. The increase of an insulator temperature and consolidation of the other working-temperature in the system insulator-electrodes, is a predominant feature for the high voltage measurements performed on dimensionally small insulators in a vacuum. It was found that numerous surface breakdowns influence the insulator surface strength due to its temperature changes.     

Evaluation of elastic accommodation energies during solid-state phase transformations by the finite element method

The precipitation of a solid phase in a rigid matrix leads to the creation of strain energy in the system as the transformation strain cannot be relaxed in the case of solid state transformations. A finite element model based on the initial strain approach has been presented to evaluate elastic accommodation energies during solid-state transformations. The finite element analysis (FEA) reveals that the total system energy increases with increase in the ratio of the modulus of the precipitate to that of the matrix, and with increase in misfit strain between the matrix and the precipitate. The analysis has been performed by considering the transformation to progress from the centre to the surface and from the surface to the centre of the three dimensional axisymmetric system. The elastic accommodation energies obtained by the FEA are comparable to energies obtained by continuum mathematical models.     

Radiation and dynamics of a nanoparticle in equilibrium background radiation upon translational–rotational motion

We have obtained general expressions for the intensity of radiation and tangential force of a small polarizable particle in the process of translational–rotational motion in equilibrium radiation background (thermalized photon gas) of a certain temperature at an arbitrary relative orientation of the linear and angular velocity vectors. It is shown that, in a cold vacuum background, the translational velocity of particle is independent of time and the intensity of its spontaneous emission is determined by the angular velocity and imaginary part of the particle polarizability.     

热电材料塞贝克系数测试仪研制

为避免热电材料在高温测试过程中被氧化,基于塞贝克效应(Seebeck effect)设计一种在真空高温环境下测试热电材料Seebeck系数的新型装置。装置主要包括真空系统、样品支架系统和控制总成3部分。该新型装置成本低廉,易于操作,其应用不但可以有效防止高温环境中样品测试的氧化现象,而且可以在高温真空环境下准确、快速地测量样品的Seebeck系数。