Modeling Iron Pentacarbonyl Vaporization Accompanied by Vapor Condensation on a Flowing Down Liquid Film

Using iron pentacarbonyl distillation as an example, we analyze the vaporization process in a closed vaporization–condensation system where vapor condenses on a flowing down liquid film. We jointly analyze the mechanisms behind vaporization, vapor transport, condensation, and flowing of the condensate on the inner surface of a vertical tube. We calculate the thickness of the flowing down liquid film, determine the vaporization coefficient for a closed system using experimentally determined temperature dependences of the vaporization rate and saturated vapor pressure, and present the vaporization rate as a function of the vaporization and condensation temperatures, the radius and height of the condensation tube, and the vaporization area of the still residue.     

Modeling the thermal processes of laser synthesis for the nitrides in refractory metals

We examine the thermal processes which include the motion of phase melt and vaporization fronts in the laser synthesis of nitrides in high-melting refractory metals. The integral radiant flux, on reaching the surface of its target, is determined by a longitudinal x-ray method. We demonstrate that the extreme relationship between the thicknesses of the synthesized layers and the pressure of the gas is a result of the competition between the process of surface vaporization in the region of lower pressures and the increase in the optical density of the beam in the region of higher pressures.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 60, No. 3, pp. 357–363, March, 1991.     

Formation and growth of steam bubbles in channel boiling

The rate of bubble growth and the critical size of a nucleus are evaluated from an analysis of the dynamic equilibrium between vaporization and condensation.     

Analysis of helium II film boiling

The heat flux removed in the boundary transition from a vapour film to helium II is studied. It was found that the properties of the heat flux can be essentially explained physically by non-equilibrium molecular-kinetic effects at the vaporization condensation interface. A method of calculating the value of the heat flux is proposed.     

Effects of vaporization on debris cloud dynamics

Experimental techniques are discussed for studying the debris products produced by plane shock loading of specimens to final temperatures sufficient to cause vaporization. These techniques have been applied to a study of the shock-induced vaporization of cadmium. The expansion products produced by shock reflection from a free surface were studied by allowing the debris to stagnate against a time-resolved interferometer gauge that allowed measurement of the stagnation pressure history. The experimental results were modeled in one dimension with Eulerian and Lagrangian computer wave codes utilizing detailed equations of state for cadmium. These comparisons illustrate that vaporization of cadmium occurs under essentially equilibrium conditions and that good agreement with experimental results is obtained under the assumption of instantaneous vaporization. Another observation is that the vapor expansion appears to be a centered expansion wave, with a density distribution differing from the computer calculation.     

Analysis of the motion of a subsonic vapor flow in a quasi-closed volume

The motion of a vapor is described for the case in which the influence of geometry is isolated. The parameters are determined for a subsonic vapor flow on the outer boundary of a gas-kinetic layer near a surface of vaporization. Profiles of the gas-dynamic variables as a function of the dimensionless coordinate are calculated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 3, pp. 460–466, September, 1973.     

A tissue-mimicking ultrasound test object using droplet vaporization to create point targets

Ultrasound test objects containing reference point targets could be useful for evaluating ultrasound systems and phase aberration correction methods. Polyacrylamide gels containing albumin-stabilized droplets (3.6 μm mean diameter) of dodecafluoropentane (DDFP) are being developed for this purpose. Perturbation by ultrasound causes spontaneous vaporization of the superheated droplets to form gas bubbles, a process termed acoustic droplet vaporization (ADV). The resulting bubbles (20 to 160 μmm diameter) are small compared with acoustic wavelengths in diagnostic ultrasound and are theoretically suitable for use as point targets (phase errors < 20° for typical f-numbers). Bubbles distributed throughout the material are convenient for determining the point spread function in an imaging plane or volume. Cooling the gel causes condensation of the DDFP droplets, which may be useful for storage. Studying ADV in such viscoelastic media could provide insight into potential bioeffects from rapid bubble formation.     

The influence of ice formation on vaporization of LNG on water surfaces

The spillage of LNG on water surfaces can lead, under certain circumstances, to a decrease in the surface temperature of water and subsequent freezing. A model for heat transfer from water to LNG is proposed and used to calculate the surface temperature of water and examine its influence on the vaporization rate of LNG. For this purpose LNG was modeled based on the properties of pure methane. It was concluded that when LNG spills on a confined, shallow-water surface the surface temperature of water will decrease rapidly leading to ice formation. The formation of an ice layer, that will continue to grow for the duration of the spill, will have a profound effect upon the vaporization rate. The decreasing surface temperature of ice will decrease the temperature differential between LNG and ice that drives the heat transfer and will lead to a change of the boiling regime. The overall effect would be that the vaporization flux would first decrease during the film boiling; followed by an increase during the transition boiling and a steady decrease during the nucleate boiling.     

Assessment of the upper particle size limit for quantitative analysis of aerosols using laser-induced breakdown spectroscopy

The laser-induced plasma vaporization of individual silica microspheres in an aerosolized air stream was investigated. The upper size limit for complete particle vaporization corresponds to a silica particle diameter of 2.1 microm for a laser pulse energy of 320 mJ, as determined by the deviation from a linear mass response of the silicon atomic emission signal. Comparison of the measured silica particle sampling rates and those predicted based on Poisson sampling statistics and the overall laser-induced plasma volume suggests that the primary mechanism of particle vaporization is related to direct plasma-particle interactions as opposed to a laser beam-particle interaction. Finally, temporal and spatial plasma evolution is discussed in concert with factors that may influence the vaporization dynamics of individual aerosol particles, such as thermophoretic forces and vapor expulsion.     

Preparation of ultrafine particles of silicon base intermetallic compound by arc plasma method

The purpose of this paper was to prepare ultrafine particles of Si-based intermetallic compounds, TiSi₂, MoSi₂ and VSi₂, by an arc plasma method with hydrogen addition. The properties of the prepared particles were affected by the vapor pressure ratio (Ti/Si, V/Si: 10⁻¹; Mo/Si: 10⁻³) of the constituent metals. The vaporization and condensation rates of the constituent metals should be controlled to prepare intermetallic compound particles in the case of large different vapor pressures. The vaporization rate can be controlled by H₂ concentration in the arc; for example, an increase in H₂ concentration leads to an increase in Ti fraction in the prepared particles in a Si---Ti system. The preparation of ultrafine particles of TiSi₂ was most successful from the 60-wt.% Ti raw material with the 50%-H₂ arc. MoSi₂ particles were prepared from the 85-wt.% Mo raw material with the 50%-H₂ arc. A single phase of VSi₂ particles was prepared successfully from the 60-wt.% V raw material with the 50%-H₂ arc. Another purpose was to investigate the mechanism of vaporization enhancement of particular metals from a metal mixture by hydrogen in arc plasmas. The vaporization enhancement was mainly attributed to the formation of intermediate products such as hydride and/or activity modification by hydrogen in molten metals.     

Determination of vaporization enthalpies of polychlorinated biphenyls by correlation gas chromatography

The vaporization enthalpies of 16 polychlorinated biphenyls have been determined by correlation gas chromatography. This study was prompted by the realization that the vaporization enthalpy of the standard compounds used in previous studies, octadecane and eicosane, were values measured at 340 and 362 K, respectively, rather than at 298 K. Adjustment to 298 K amounts to a 7-8 kJ/mol increment in the values. With the inclusion of this adjustment, vaporization enthalpies evaluated by correlation gas chromatography are in good agreement with the values determined previously in the literature. The present results are based on the vaporization enthalpies of several standards whose values are well established in the literature. The standards include a variety of n-alkanes and various chlorinated hydrocarbons. The vaporization enthalpies of PCBs increased with the number of chlorine atoms and were found to be larger for meta- and para-substituted polychlorinated biphenyls.     

Condensation phenomena in supersonic nozzles

Summary The heat addition in a Laval-nozzle flow and in a Prandtl-Meyer corner expansion caused by condensation of water vapor in moist air is investigated. In both flow fields at the onset of condensation density, pressure and temperatur increase due to the release of the latent heat of vaporization. Experiments show that the energy addition is related to a relaxation process, and that the changes of the flow parameters can be expected in three different forms. In steady flow the thermodynamic state may change smoothly or it is discontinuous. At high rates of heat addition the flow becomes unsteady and it follows a repetitive cycle. The comparison of steady and unsteady flow fields allows the extraction of simple similarity rules by a dimensional analysis in conjunction with the laws of gasdynamic.With 17 Figures     

Grain growth at the free surface of WC-Co materials

The grain growth rate at the free surface of a WC-Co material was measured at different high temperatures and the microstructure and elemental composition of the material were characterized at various stages of the grain growth process. It was found that free surface grains grew at an abnormally fast rate, and this fast growth rate coincided with the vaporization of the binder phase from the free surface. It is suggested that this abnormal rate of growth is related to a change in the growth mechanism from interfacial reaction limited growth in the bulk of the material to a surface diffusion rate limited growth at the free surface. It is shown that the contact points between grains provide bridges for atomic transport from the high free-energy regions (the small grains) to the low free-energy regions (the large grains); hence, the contiguity of the material strongly influences the rate of growth. It is believed that vaporization of the binder phase allows for an increased atomic mobility at the surface, a reduction in the energy barrier to chemisorption and consequently an accelerated grain growth.     

Heat transfer in condensation on a grooved surface

The process of condensation on a grooved surface is analyzed and the basic parameters of the process determined. Expressions are obtained for the heat-transfer coefficient.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 6, pp. 1022–1028, June, 1981.     

Analysis of the influence of drop diameters on the intensity of heat transfer in dropwise condensation

An analysis of the contribution of drops of different sizes to the intensity of heat transfer is performed for dropwise condensation of water vapor on a surface that is stimulated by fluorine-containing disulfide. The fraction of the heat-exchange surface and the lifetime of different classes of drops for specified values of the temperature difference are determined. A comparison with the results of other investigators is made.     

可凝性气体抽除的一些措施

本文详细叙述了抽除可凝性气体时所利用的两种抽气设备,即气镇泵与冷凝器.首先介绍了可凝性气体的形成、饱和状态、汽化与凝结.讨论了油封机械泵抽除可凝性气体对泵性能所造成的不良影响及其防止的措施,通常有如下两种方法:即去除泵中的凝结液的加热法和泵油的再生法及防止可凝性气体在泵中凝结的气镇法和双泵串联法.其次还介绍了气镇泵的结...     

Nanometer-scale modification and welding of silicon and metallic nanowires with a high-intensity electron beam

We demonstrate that a high-intensity electron beam can be applied to create holes, gaps, and other patterns of atomic and nanometer dimensions on a single nanowire, to weld individual nanowires to form metal-metal or metal-semiconductor junctions, and to remove the oxide shell from a crystalline nanowire. In single-crystalline Si nanowires, the beam induces instant local vaporization and local amorphization. In metallic Au, Ag, Cu, and Sn nanowires, the beam induces rapid local surface melting and enhanced surface diffusion, in addition to local vaporization. These studies open up a novel approach for patterning and connecting nanomaterials in devices and circuits at the nanometer scale.     

Breakdown of the protective oxide on 11 % Cr steel at high temperature in the presence of water vapor and oxygen,the influence of chromium vaporization

Abstract

We report on the effect of water vapor and oxygen on the oxidation of a ferritic/martensitic 11 % Cr steel (CrMoV11 1). The influence of pH₂O, exposure time, gas velocity and temperature was investigated. The samples were exposed to dry O₂, O₂+10 or 40 % H₂O for up to 336 hours. Total pressure was 1 atm (1.02 × 10⁵ Pa). The gas velocity was between 0.05 and 10 cm/s while temperature was in the range 450–700°C. The samples are investigated by thermogravimetry, GI-XRD, SEM/EDX, GDOES, FIB and TEM/EDX. Oxidation is strongly affected by the vaporization of CrO₂(OH)₂ in H₂O/O₂ environment. The mechanism of vaporization of CrO₂(OH)₂ from a Cr₂O₃ surface is modelled by DFT calculations. In the absence of chromium vaporization the alloy forms a protective oxide consisting of a corundum-type solid solution (Fe_1–xCr_x)₂O₃. The vaporization of chromium tends to deplete the oxide in chromium. In some cases the oxide remains protective in spite of chromium depletion while in other cases there is a transition to breakaway oxidation. In the latter case a thick layered scale forms, consisting of an outer hematite part and an inner iron-chromium spinel. Oxidation behavior in an O₂+H₂O environment is to a large extent determined by the ability of the metallic substrate to supply the oxide with chromium by diffusion in order to compensate for the losses by vaporization. The corrosivity of the environment increases with the concentration of water vapor and oxygen, with the gas velocity and with temperature.     

Particularities of condensation of atoms with increased kinetic energy

Novel universal method for measurement of the condensation coefficient α is developed. Using this method, noticeable difference between measured (α≈0.8) and expected (α≈1) values of the condensation coefficient for sputtered Cr atoms was revealed for the first time. The effect is assumed to be a result of considerable elevation of the surface temperature during atomic condensation induced by the energy delivered to the condensation surface by sputtered atoms and from the plasma.     

微肋表面强化液氮温区冷凝传热特性的数值模拟研究

开展了微肋表面强化氮蒸气凝结传热的机理研究,基于CFD数值方法建立了竖直方向平板和微肋板上氮蒸气冷凝的三维数值模型,对比分析了平板表面和微肋表面的冷凝换热效果,通过表面冷凝的液膜分布和速度分布等内在参数揭示平板和微肋表面的冷凝换热机理。结果表明,氮的冷凝传热性能在微肋表面上得到显著提升,在1.5 K的冷凝传热温差下,其平均传热系数提高1.6倍,初步揭示了微肋表面(肋高H=0.6 mm、节距p=1 mm)对强化氮冷凝的有效性。分析显示,微肋的弯曲结构改变了液膜的空间分布,通过减薄局部液膜厚度实现了冷凝的强化。