On the Choking of a Gas Flow by a Granular Bed

Journal of Engineering Physics and Thermophysics - A study has been made of the effect of choking of a gas flow by isothermal and heat-releasing granular beds under the conditions of a...     

Theoretical investigation of gas separation inside a microchannel by thermal diffusion

 Microscale gas separation using thermal diffusion is investigated. Under the effects of a thermal loading, different gas species move at different velocities which results in gas separation. This approach to separation may be especially applicable in micro- and nanosystems, since the requirement for relatively bulky pumps, typically required in conventional membrane filtration or gas chromatography, is eliminated. In this paper, we report our theoretical investigation of the separation effect caused by a thermal gradient in a mixture gas flow. The dependence of separation performance on various parameters, including temperature loading, molecular weight, and channel size, is investigated.     

Effect of motion of a gas medium on the accuracy of measurement by acoustic methods

The effect of velocity and direction of motion of a gas medium on the propagation time of an acoustic signal is treated in the regions of unidirectional radiation and echo ranging.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 3, pp. 457–463, September, 1984.     

The Effect of the Variability of Density on the Propagation of Heat in a Gas

The qualitative and quantitative effect of compressibility on the propagation of heat in an ideal gas in the absence of mass forces is investigated. Based on the assumption of the constancy of pressure throughout a closed cavity, a physical and a mathematical models are constructed for a flat layer of gas. Criteria of similarity are revealed which characterize the propagation of heat in the gas being compressed. Using the flat layer as an example, the processes of the propagation of heat in gas and solid are compared.     

Electron number density measurement on a DC argon plasma jet by stark broadening of Ar I spectral line

In thermal plasma processing, input power and gas flow rate play a major role in controlling the plasma jet temperature, velocity and density. Emission spectroscopy study is an important method for plasma diagnostics. A DC atmospheric plasma spray torch was operated at different power levels and flow rates of plasma gas (argon). Electron number density of the plasma jet, the corresponding temperature and the degree of ionization were determined using stark broadening of the Ar I (430.010 nm) line, the atomic Boltzmann plot method and the Saha equation, respectively. In the present work, we have investigated the effect of input power, axial position of the plasma jet and gas flow rate on the electron number density in the plasma jet. While an increase in input power considerably increased the electron number density, gas flow rate did not show any significant effect on the same.     

The effect of gas injection on the protection of body surfaces streamlined by a two-phase flow

The first results of physical simulation of the effect of gas injection on the characteristics of gas stream with solid particles at flow around bodies are presented. The possibility of ensuring an effective protection of the body surface from the negative effects of particles (droplets) is demonstrated. A dimensionless criterion (the Stokes number) is proposed that characterizes the inertia of particles near the critical point of the body and the intensity of their deposition on the surface under injection conditions.     

Catalyst effect on the preparation of single-walled carbon nanotubes by a modified arc discharge

Single-walled carbon nanotubes (SWCNTs) were prepared by a modified arc discharge furnace using 500?Torr helium as buffer gas at 600?°C. The effect of the catalyst type on the production of SWCNTs was studied by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The experimental results indicated that the catalyst composition plays an important role in the production rate and purity of the SWCNTs product. Fe-Ni-Mg and Co-Ni powder catalysts demonstrated excellent catalytic effect at a catalyst content of 3?wt%. The soot production rate was up to 15?g/hr and the mean diameter of SWCNTs was about 1.3?nm.     

Possibility of cleaning a channel in a snowy atmosphere by a supersonic off-design jet

It has been found that the threshold value of the product of the excess gas pressure in the forechamber by the area of the nozzle throat is responsible for the appearance of the cleanup effect for a fixed nozzle-photodetector distance. The thermodynamic and dynamic criteria for the occurrence of the cleanup of the laser-beam trajectory have been formulated. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 1, pp. 165–170, January–February, 2008.     

HFCVD diamond deposition parameters optimized by a Taguchi Matrix

A Taguchi Matrix was used for the experimental design to study the CVD diamond deposition parameters in a cold-wall HFCVD reactor. Gas composition, total gas pressure, total mass flow and substrate temperature were considered as controllable factors, and three levels for each of these factors were selected, in an L9 orthogonal array. A new Figure-of-Merit (FOM) is proposed to assess the best combination of film properties: grain size, residual stress, structural quality and growth rate. Substrate temperature affects mostly grain size and diamond quality, while methane content mostly determines residual stresses and the growth rate. The latter is also mainly affected by the total pressure as well as is grain size, while total gas flow has a neutral effect. Under the limits of deposition conditions, the best FOM is obtained at the highest total gas pressure and mass flow, average CH₄ content, and lowest substrate temperature.     

Temperature stratification under suction of the boundary layer from a supersonic flow

A carried out numerical simulation showed that a considerable difference can be achieved between the temperatures of a gas in the boundary layer and a suctioned gas under the gas suction from a turbulent boundary layer in a supersonic flow on a permeable surface. The effect of the Prandtl and Mach numbers of the incident flux on the temperature stratification, which depends on the gas suction intensity, is studied. The stratification is the most pronounced for low-Prandtl-number gases. It was established that, due to laminarization of the boundary layer under an intense gas suction, in the region of the impermeable plate following the permeable wall, the wall temperature drops abruptly.     

Multiple-scattering effects on differential absorption for the transmission of a plane-parallel beam in a homogeneous medium

The transmission, including all scattering orders, of a plane-parallel beam in a homogeneous scattering medium containing aerosols (e.g., water cloud) mixed with an absorbing gas (e.g., ozone) is computed with a two-stream radiative transfer model. From differential transmission the concentration of the gas is deduced. The effect of multiple-scattering on the deduced concentration is shown for conservative scattering aerosols for which the multiple scattering by the aerosols is differentially absorbed by the gas and for nonconservative scattering aerosols for which the multiple scattering is differentially absorbed by the aerosols as well as differentially absorbed by the gas. The two-stream analytical model (with no dependence on the field of view) shows good qualitative agreement (especially for a small field of view) with a numerical radiative transfer model in which the trace gas concentration is computed for the different detector's field of view.     

Study of Postdetonation Waves after the Counter Collision of Detonation Waves in a Bubble Liquid

High Temperature - The counter interaction of detonation waves in a liquid with bubbles of a combustible gas is considered based on numerical simulation. The effect of the initial volumetric gas...     

The effect of turbulent mixing on the dynamics of a liquid layer accelerated by a compressed air flow

The influence of a turbulent mixing (TM), developed at the unstable boundary of a liquid layer accelerated by a hot compressed gas flow, on the efficiency of the subsequent energy transfer from the accelerated liquid layer to a gas layer compressed by the liquid was experimentally studied. It was found that the TM development may significantly decrease the energy takeoff by the accelerated liquid layer, which is explained by cooling of the hot compressed gas as a result of the increased heat transfer from gas to liquid in the TM zone. The experimental data indicate that the gas energy losses can reach several tens percent.     

Variable-energy Blast Waves Generated by a Piston Moving in a Dusty Gas

This paper presents a similarity solution for strong blast waves of variable energy propagating in a dusty gas. It is assumed that the equilibrium-flow condition is maintained and the variable energy input is supplied by a driving piston or surface according to a time-dependent power law. Three cases have been investigated: Case I corresponds to a decelerated piston, Case II to a piston of constant velocity, and Case III to a continuously accelerated piston starting from rest. Except in the case of constant front velocity, the similarity solution is valid for adiabatic flow as long as the effect of the counter-pressure is neglected. The effects of a parameter characterizing the various energy input of the blast wave on the similarity solution have been examined. The computations have been performed for various values of mass concentration of the solid particles and for the ratio of density of solid particles to the constant initial density of gas. Tables and graphs of numerical results are presented and discussed.     

Heterogeneous processes affect the hydrodynamic resistance of a surface streamlined by a nonequilibrium gas flow

A mechanism responsible for a decrease in the turbulent friction of bodies moving in (or streamlined by) a vibrationally-nonequilibrium gas flow is proposed. Heating of the gas in the immediate vicinity of the surface as a result of heterogeneous relaxation may decrease the transverse velocity gradient and reduce the friction resistance coefficient.     

Calculation of the effect of vibration on a region filled with a perfect viscous gas

The processes of heat and mass transfer in a region subjected to the vibration effect have been studied numerically. The effect of the vibration frequency on the behavior of the characteristics of gas located inside the region has been described. The one-dimensional problem has been solved.     

Experimental Investigations of Decomposition of Gas Hydrate in a Pipe under the Impact of a Microwave Electromagnetic Field

Results are given of experimental investigations of the decomposition of propane hydrate in a microwave electromagnetic field developed in a pipe. Procedures are developed for preparing hydrate and for measuring the temperature and pressure in a model of pipeline, as well as of the volume of gas released during the decomposition of gas hydrate. The effect of increasing rate of decomposition of gas hydrate is found as compared to the natural process unassociated with the impact of electromagnetic field. The possibility is demonstrated of complete decomposition of gas hydrate in a pipe due to the impact of a microwave electromagnetic field.__________Translated from Teplofizika Vysokikh Temperatur, Vol. 43, No. 4, 2005, pp. 612–617.Original Russian Text Copyright © 2005 by M. A. Fatykhov, and N. Ya. Bagautdinov.     

Investigation of a mixed effect absorption chiller powered by jacket water and exhaust gas waste heat of internal combustion engine

CCHP (combined cooling heating and power) system based on ICE (internal combustion engine) has been widely used. A key issue is to efficiently recover the jacket water and exhaust gas waste heat for refrigeration. In this work, a mixed effect absorption chiller (AC), which couples single effect and double effect processes together, is investigated to recover these two kinds of waste heat simultaneously. The high pressure generator is powered by exhaust gas while one low pressure generator is powered by jacket water waste heat. Thermodynamic characteristics and off-design performance are simulated. Considering thermodynamic constraints, the start point temperature in low pressure generator should be 77°Cor lower. For a 16 kW ICE, the cooling output can reach 34.4 kW with COP of 0.96 and exergy efficiency of 0.186. Comparing with double effect or single effect AC, it can make a better use of different waste heat in CCHP system.     

Analysis of a Swirling Flow of Gas in the Diaphragmed Channel of a Plasma Generator

A two-temperature magnetogasdynamic model of plasma is used to calculate a swirling flow of gas (argon) in the diaphragmed channel of a plasma generator and the heating of this flow and to investigate the dependence of the flow on the strength of the current, geometry of the channel, and the flow rate and swirling moment of gas. The effect of the velocity field of swirling flow on the disequilibrium of plasma and on the arc characteristics in varying-area channels is treated. The calculation results are in qualitative agreement with the experimental data.     

Investigation of Heat Transfer in the Case of Upward and Downward Turbulent Flow of a Mixture of Gas and Solid Particles in a Pipe

The continual model developed by us is used to investigate the effect of the force of gravity on a nonisothermal turbulent flow of a gas suspension in a vertical pipe for upward and downward motion. The reasons behind the intensification of heat transfer in the case of a downward locally nonequilibrium motion of gas suspension are found.