Vapor-gas Mixture Research Articles

Experimental study of Ga and Al oxide solubility in gas-vapor mixture at 200°C

Experimental study of Ga and Al oxide solubility in gas-vapor mixture at 200°C

High sensitive analysis of steroids in doping control using gas chromatography/time‐of‐flight mass‐spectrometry

The method of high sensitive gas chromatographic/time-of-flight mass-spectrometric (GC/TOF-MS) analysis of steroids was developed. Low-resolution TOF-MS instrument (with fast spectral acquisition rate) was used. This method is based on the formation of the silyl derivatives of steroids; exchange of the reagent mixture (pyridine and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA)) for tert-butylmethylether; offline large sample volume injection of this solution based on sorption concentration of the respective derivatives from the vapour-gas mixture flow formed from the solution and inert gas flows; and entire analytes solvent-free concentrate transfer into the injector of the gas chromatograph. Detection limits for 100 µl sample solution volume were 0.5-2 pg/µl (depending on the component). Application of TOF-MS model 'TruTOF' (Leco, St Joseph, MO, USA) coupled with gas chromatograph and ChromaTOF software (Leco, St Joseph, MO, USA) allowed extraction of the full mass spectra and resolving coeluted peaks. Due to use of the proposed method (10 µl sample aliquot) and GC/TOF-MS, two times more steroid-like compounds were registered in the urine extract in comparison with the injection of 1 µl of the same sample solution.

Preparation of stable gas mixtures with microconcentrations of volatile substances in vapor-phase sources at elevated pressures

Tools are proposed for the preparation of stable vapor-gas mixtures with microconcentrations of volatile components (vapor-phase sources of gas mixtures). These work at elevated pressures and ensure the generation of gas flows with component concentrations differing within an order of magnitude from one and the same source.

On the theory of aerosol particle growth: Non-steady transport problems

In this paper we consider continuous regime of liquid droplet growth in a vapor–gas mixture. Since we do not limit ourselves to any restrictions related with the slowness of the droplet growth, we discuss the problem in essentially non-steady formulation. It allows us to avoid the limitation of considering low supersaturations only. The use of self-similar method for solving transport problems helps us obtain analytical expressions for non-steady vapor concentration profile, temperature profile around the droplet and droplet growth rate.

Difference in the rates of evaporation and condensation in the presence of an inert gas

On the basis of experimental data on the non-steady-state evaporation and the subsequent condensation of vapors of a substance on a flat cooled surface in the presence of an inert gas, the existence of the molecular and convective regimes of the condensation of vapors depending on the ratio of the molecular weights of the components of a gas-vapor mixture is found for the first time. It is shown that the kinetics of the evaporation-condensation processes differs: if the molecular weight of a vapor MA is more than the molecular weight of an inert gas MB, evaporation occurs in the molecular regime and condensation takes place in the convective regime; if MA is less than MB, the regimes of the processes change to the opposite ones. The results of experiments performed using ethyl acetate-air, ethanol-air, carbon tetrachloride-air, methanol-air, water-air, and water-helium systems are in satisfactory agreement with the results calculated by the proposed equation. Procedures for studying the dynamics of condensation and evaporation are described.

Condensation from a vapor-gas mixture

A review of the possible approaches to calculation of vapor condensation from a binary vapor-gas mixture on a surface is presented. Emphasis is paid to justification of the application of molecular-kinetic theory methods for calculation of applied problems. Quantitative estimates for the parameters of the existence in principle of the regimes of one-dimensional stationary condensation are given.

The axial mixing influence on the number stages of countercurrent absorbers in absorbing NH3-CO2-H2O mixture in NaCl-H2O system

This paper investigates the influence of axial or longitudinal mixing of stages on the number stages in a countercurrent absorber in absorbing vapour-gas mixture of NH3-CO2-H2O in the multicomponent system NaCl-H2O. The number stages in ideal mixing of phases NT and the number of stages which involves axial mixing ND were determined. The authors of this paper conclude that the influence of axial mixing does not affect the number stages in the countercurrent absorber. Otherwise, absorption in this concrete system is practically present in the process of soda ash production.

Mathematical modeling of the treatment of the near-wellbore area with a high-temperature gas-vapor mixture in the combustion of composite solid propellants under oil-well conditions

A mathematical model for the combustion of composite solid propellants based on ammonium perchlorate in oil wells is constructed, and the effect of the propagation of the front of pressure, temperature, and gaseous combustion products is estimated. An analysis of the results of modeling is performed, and inferences about the efficiency of the use of the given technology for increasing the productivity of low-yield wells are made.

Specific features of multicomponent diffusion

Using a computational experiment, the existence of the abnormal regimes of nonequimolar diffusion in three-component gas-vapor mixtures such as acetone-methanol-air, hydrogen-water-carbon dioxide, and hydrogen-ammonia-nitrogen is shown. Due to osmotic and reverse diffusion, the molar fraction of water vapors and ammonia can be increased by more than a factor of two in the individual segments of a Stefan tube in comparison with their concentration at the inlet.

Macrokinetics and mathematical simulation of intercalated graphite particle expansion under fast heating

A mathematical model of intercalated graphite particle expansion under fast (shock) heating is introduced. The model is based on the idea of two thermodynamic forms of intercalate in the graphite particle. This theory explains the existence of a minimum-size graphite particle capable of thermal expansion, which was ascertained in many experiments, and makes it possible to estimate the effective coefficient of filtration of the gas-vapor mixture from the particle without resorting to additional experiments.

The flow of liquid past a plate with boiling and injection of gas

A classical model boundary layer problem is considered for the flow of liquid past a plate in view of injection of a vapor-gas mixture from its surface. The obtained self-similar solutions enable one to estimate the typical values of thickness of the vapor-gas layer, the value of heat-transfer coefficient as a function of temperature of liquid, intensity of injection and composition of mixture being injected, and the velocity of flow past the plate. In addition, the problem is considered of reducing the hydrodynamic drag owing to vapor and vapor-gas “lubrication” because of boiling of liquid and injection of vapor-gas mixture from the plate surface. The possibility is analyzed of the emergence of vapor film due to viscous friction forces in the case where the liquid is in the vicinity of the boiling point.

The influence of radiation heat exchange on characteristics of liquid fuel ignition by a heated metal particle

A complex of interrelated heat-mass transfer processes at gas-phase ignition of a typical liquid fuel by a hot metal particle immersed partially into a liquid is investigated numerically. The scale of influence of the radiation heat exchange at particle—liquid fuel and particle—gas—vapor mixture interfaces is found. Conditions under which the impact of this factor can be neglected are determined.

Ignition of a vapor-gas mixture by a moving small-size source

A theoretical analysis of the ignition of a liquid fuel vapor-air mixture by a moving small source of heating was performed. A gas-phase model of the ignition with consideration given to heat transfer, liquid fuel evaporation, diffusion and convective motion of fuel vapor in the oxidizer medium, crystallization of the heating source, kinetics of the vaporization and ignition processes, temperature dependence of the thermophysical characteristics of the interacting substances, and character of motion of the heating source in the vapor-gas mixture was developed. The values of the ignition delay time τd, the main characteristic of the process, were determined. It was established how τd depends on the initial temperature, heating source sizes, velocity and trajectory of the heating source, and ambient air temperature.

Kinetics of luminescence induced by sputtering metallic cadmium by a pulsed fast electron beam in helium

Results of an experimental study of the kinetics of luminescence observed when a metallic cadmium foil is bombarded in a helium medium by a 3-ns pulsed beam of 150-keV fast electrons are reported. The foil was irradiated at gas pressures from 76 to 2280 Torr. At a foil temperature of T = 240° C, the de-excitation time of the Beitler levels of the Cd II ion was measured as a function of the buffer gas pressure and the constant of collision quenching of the 5s22D5/2 level of Cd II by He atoms was determined as k ≈ 3 × 10-29 cm6/s. The experimental data were compared with calculations performed for the gas—vapor mixture in order to find the fraction of excited Cd II ions in the 5s22D5/2 state produced directly as a result of sputtering of metallic cadmium by high-energy electrons and by components of the helium plasma. At a helium buffer gas pressure of P ≤ 2.5 atm and a temperature of the cadmium target of T = 240° C, the value of this quantity was found to be α = 0.28 + 0.23P (where P is the helium pressure in atmospheres).

Letter to the Editor of HMT: Comments on the comment Y. Liao, comment on the paper D.Y. Shang and L.C. Zhong, “Extensive study on laminar free film condensation from vapor–gas mixtures” IJHMT 51 (2008), pp. 4300–4314

Letter to the Editor of HMT: Comments on the comment Y. Liao, comment on the paper D.Y. Shang and L.C. Zhong, “Extensive study on laminar free film condensation from vapor–gas mixtures” IJHMT 51 (2008), pp. 4300–4314

Distinctive features of the gas-phase ignition of a mixture of a kerosene vapor and air by a steel wire heated to high temperatures

The process of ignition of a mixture of air and a kerosene vapor by a steel wire heated to high temperatures has been modeled numerically. The investigations have been carried out on a model allowing for the combination of heat- and mass-transfer processes (evaporation of the flammable liquid, diffusion and convection of the fuel vapor in air, heat conduction, and oxidation of the fuel vapor in air). The values of the delay time of ignition of the vapor-gas mixture have been determined and the scale of influence of the initial temperature and dimensions of the wire, the distance between the heating source and the kerosene surface, and the temperature and humidity of air on the inertia of the ignition process have been established.

Dynamics of the droplet size distribution function during the gradual creation of a supersaturation state under different regimes of droplet growth

The method of the direct numerical integration of kinetic equations of droplet size distribution functions that was previously proposed by the authors is employed to solve the problem of condensation relaxation in a vapor-gas mixture during the creation of a supersaturation state at a finite rate. Two relaxation regimes are considered. In the static regime, the mixture is expanded at a constant rate until a preset supersaturation ratio is achieved; in the dynamic regime, the expansion is continued. Solutions are obtained for argon-cesium and argon-ethane mixtures, thus making it possible to study the dependence of the process character on the Knudsen number. The effects of the rate of the supersaturation creation and the relaxation regime on the droplet size distribution function are analyzed.

On peculiarities of heat and mass transfer in a hot metal particle-liquid fuel condensed substance-air system

Results of numerical modeling are used for validating the governing role of the ratio of areas of contact between the heater with the combustible liquid and the formed vapor-gas mixture in a complex of interrelated processes of heat and mass transfer at gas-phase ignition of a liquid condensed substance film by small-size hot metal particle. Critical values of the ratio at which the ignition conditions cannot be realized are marked out. Ranges of varying the main igniter parameters for which the influence of the parameter on the ignition parameters may be neglected are determined.

Variable Property Effects on Vapor Condensation with a Noncondensable Gas

In modeling condensation from vapor-gas mixtures with the heat and mass transfer analogy, there are two parallel methods in the literature to account for variable property effects: (a) the property ratio scheme using an empirical factor as a multiplier for the mass flux and (b) the reference property scheme using reference properties to calculate the mass flux. The current work focuses on the reference property scheme and establishes its relation to the property ratio scheme. From condensation boundary layer analysis, the current work proposes a reference mixture composition and a reference mixture temperature, which can be used for calculation of a variety of reference thermodynamic and transport properties. It is demonstrated that the empirical factor in the property ratio scheme used widely in the literature can be obtained from the reference property scheme derived in the current work, and thus, the two parallel methods to account for variable property effects are equivalent. A common mistake in using the reference mixture composition is highlighted as part of this investigation. The reference property scheme presented herein has a theoretical basis and is more accurate over a wide range of conditions than the empirical property ratio scheme. Finally, the reference property scheme is extended to multicomponent gases.

Nonisothermal effects in the growth of carbon clusters in the gas phase

A numerical investigation of the nonisothermal effects occurring in the process of growth of carbon clusters in the gas phase in the temperature range 2000-3000 K has been carried out. It has been established that these effects are due to the phase-transition latent heat released as a result of the volume condensation of nonequilibrium carbon vapor as well as the convective and radiative cooling of the clusters. It is shown that, under the indicated conditions, the radiative cooling of carbon clusters is the dominant cooling mechanism. A mathematical simulation was carried out for the cases of optically thin and thick layers of a vapor-gas mixture embedded in cold walls. The dependence of the growth and temperature of the carbon clusters on their porosity, the supersaturation of the carbon vapor, and the temperature of the vapor-gas mixture was detected. It has been established that the temperature of the growing carbon clusters can be higher or lower than the temperature of the vapor-gas mixture and the deviation from this temperature can exceed 500 K. The data obtained were compared with the results of experiments on shock tubes.