High-speed Gas Stream Research Articles

An experimental study of the effect of gas density on the distortion and breakup mechanism of drops in high speed gas stream

High velocity, gas-assisted liquid drop atomization processes were investigated under well-controlled experimental conditions at elevated gas densities and room temperature. A monodisperse stream of drops which are generated by a vibrating-orifice drop generator was injected into a transverse high velocity gas stream. The gas density and air jet velocity were adjusted independently to keep the Weber numbers constant. The Weber numbers studied were 72, 148, 270, and 532. The range of experimental conditions studied included the three drop breakup regimes previously referred to as bag, stretching/thinning and catastrophic breakup regimes. High-magnification photography was taken to study the microscopic breakup mechanisms in high velocity gas flow fields. When the Weber number is held constant at different gas densities and jet velocities, the results show that the microscopic breakup process is similar, even at high gas densities. At low Weber numbers, the photographs confirmed the existence of the bag breakup regime. The stretching/thinning breakup regime was observed for Weber numbers between 150 and 270. At Weber number = 532, the breakup in the catastrophic breakup regime occurred.

Experimental simulation of corium dispersion phenomena in direct containment heating

In a direct containment heating (DCH) accident scenario, the degree of corium dispersion is one of the most significant factors responsible for the reactor containment heating and pressurization. To study the mechanisms of the corium dispersion phenomenon, a DCH separate effect test facility of 1:10 linear scale for Zion PWR geometry is constructed. Experiments are carried out with air-water and air-woods metal simulating steam and molten core materials. The physical process of corium dispersion is studied in detail through various instruments, as well as with flow visualization at several locations. The accident transient begins with the liquid jet discharge at the bottom of the reactor pressure vessel. Once the jet impinges on the cavity bottom floor, it immediately spreads out and moves rapidly to the cavity exit as a film flow. Part of the discharged liquid flows out of the cavity before gas blowdown, and the rest is subjected to the entrainment process due to the high speed gas stream. The liquid film and droplet flows from the reactor cavity will then experience subcompartment trapping and re-entrainment. Consequently, the dispersed liquid droplets that follow the gas stream are transported into the containment atmosphere, resulting in containment heating and pressurization in the prototypic condition. Comprehensive measurements are obtained in this study, including the liquid jet velocity, liquid film thickness and velocity transients in the test cavity, gas velocity and velocity profile in the cavity, droplet size distribution and entrainment rate, and the fraction of dispersed liquid in the containment building. These data are of great importance for better understanding of the corium dispersion mechanisms.

Coaxial atomization of a round liquid jet in a high speed gas stream: A phenomenological study

Coaxial injectors have proven to be advantageous for the injection, atomization and mixing of propellants in cryogenic H2/O2 rocket engines. Thereby, a round liquid oxygen jet is atomized by a fast, coaxial gaseous hydrogen jet. This article summarizes phenomenological studies of coaxial spray generation under a broad variation of influencing parameters including injector design, inflow, and fluid conditions. The experimental investigations, performed using spark light photography and high speed cinematography in a shadow graph setup as main diagnostic means, illuminate the most important processes leading to atomization. These are identified as turbulence in the liquid jet, surface instability, surface wave growth and droplet detachment. Numerical simulations including free surface flow phenomena are a further diagnostic tool to elucidate some atomization particulars. The results of the study are of general importance in the field of liquid atomization.

サブミクロン粒子の付着力と分散性の関係

Adhesive forces of sub-micron particles of limestone were measured by using a split-cell type tensile strength tester under various vapor pressure conditions of water, ethanol and acetone. The adhesive force generated by ethanol vapor or acetone vapor adsorption was smaller than that generated by water vapor adsorption.Agglomerated particles generated from a micro-fluidized bed of the limestone sample with various atmospheric gases were dispersed by a high speed gas stream through a small pipe, and the size distribution of the agglomerates was measured. The agglomerates containing adsorbed ethanol were easily dispersed into the single particles by about half the force required for the agglomerates containing adsorbed water, which qualtatively corresponded to the decrease in the adhesive force of the particles by adsorbing ethanol vapor instead of water vapor.

Aerodynamic effects on PFBC erosion target experiments

Dust carried along by the exhaust gas from a pressurized fluidized bed combustor (PFBC) can cause erosion of the blades of the gas turbine through which the gas passes. To help quantify this erosion, experiments are performed using targets in a high speed gas stream laden with PFBC dust. The results of such experiments can be greatly affected by local aerodynamic effects on the particle trajectories. This paper examines the aerodynamic effects for a particular set of experiments with symmetric wedge targets. The flow field and particle trajectories are calculated by computer programs. The aerodynamic effects on the particle impact conditions are presented and summarized in a non-dimensional form suitable for use as a general guide to the extent of such effects. The erosion loss is derived from the calculated impact conditions and compared with that which would be obtained with no aerodynamic effects. A large influence of the aerodynamics is shown for the typical PFBC dust distribution used. An iterative method of correcting experimental erosion results for aerodynamic effects is suggested and demonstrated to converge rapidly to the true erosion function in the case considered.

Note on the experimental measurement of particles embedded in one and two in-line tubes in a high speed gas stream

Solid particle deposition on one and two in-line tubes has been measured. Experiments were conducted in a vertical duct containing the tube(s) oriented perpendicular to the mean flow. Dilute particle concentrations corresponding to 40 or 97 μm glass beads, at mass loading ratios less than 0.007, were investigated. Air approaching the tube(s) at 18.5 m s −1 and 1.4% turbulence intensity was used as the carrier fluid. Various differences observed in the circumferential depositions for the two bead sizes are attributed to the fivefold difference between their respective inertia numbers. In the case of two in-line tubes, the wake of the first substantially alters the deposition characteristics of the second. Some photographic evidence of this effect was obtained.

Disintegration of thin liquid sheet in cocurrent gas stream. Wave motion of thin liquid sheet and breakup patterns.

The breakup of thin liquid sheet in a cocurrent gas stream was investigated experimentally. The patterns of the disintegration were classified mainly into two breakup patterns. The first breakup means that the liquid film disintegrates into lumps, ligaments and droplets, and the second breakup means that the large lumps, ligaments and large droplets produced by the first breakup breakdown into the smaller droplets. Moreover, the first breakup was divided into the following four small groups : lump, ligament, bag. These breakup depended strongly on the wave motion of the liquid sheet. The scale, shape and instability (possibility of realization of the second breakup) of large lumps and droplets varied with the type of the breakups. It was also clarified that the breakup of thin liquid sheet in a high speed gas stream was caused mainly, not by an unbalance of the surface tension and the liquid flow momentum in the liquid sheet, but gas flow impact on the surface of the thin liquid film having large wave amplitude.

A new CVD technique for the preparation of transparent conducting films

A new CVD technique was proposed for preparing transparent conducting films such as SnO 2 and In 2O 3. The unique feature of this technique is the use of a V-shape high speed gas stream as carrier gas. Such a reflecting high speed gas stream (RGS) ensures superior optical properties of the films comparable to physical vapor deposition (PVD) ones, e.g.. a transparency of over 90% and a haze factor of less than 1% in the range of film thickness below ∼5000 Å. In addition, the films possess a blend of thermal, chemical, and mechanical durability which is an inherent property of CVD films. Another favorable feature of this new technique is the potentiality of both the preparation of a large transparent conducting film and mass production in the atmosphere, not in a vacuum.

Subsonic and supersonic disturbances in the generation of surface waves in a liquid layer adjacent to a high-speed gas-stream

In an effort to shed further light upon the nature of “supersonic” disturbances as distinct from that of ‘subsonic’ disturbances in parallel compressible flows, this paper makes an investigation of the stability characteristics of the surface waves generated in a liquid layer adjacent to a high-speed gas-stream. It turns out that the nature of the surface waves generated in the liquid layer depends markedly upon the type of disturbances present in the high-speed gas-stream. For the case of ‘subsonic’ disturbances it is shown that the energy transfer from the gas stream to the surface waves is contributed predominantly by the Fourier component of the normal gas-pressure force-field in phase with the slope of the wavy surface. For the case of ‘supersonic’ disturbances, this energy transfer is shown to be predominantly due to the component of the pressure-field in phase with the surface-wave displacement and is related to the presence of travelling periodic waves in the gas-stream—this energy transfer is shown to promote always the growth of the surface waves.

Shape and surrounding flowfield of a drop in a high-speed gas stream

Liquid droplet shape effect flow field velocity and pressure distribution over windward surface in high speed gas streams

Mean drop size resulting from the injection of a liquid jet into a high-speed gas stream.

The mean drop size generated by a liquid jet penetrating a gaseous environment is estimated. There are at least four regimes of interest which may be separated according to the relative dynamic pressure. The two regimes having the higher dynamic pressure are treated here. Primary drop generation is treated for the case when the unstable waves grow and are dominated by capillary action (region 3) as well as acceleration forces (region 4). The theoretical results are found to be reasonably consistent with experimental data found in the literature.

Erratum: Stability of a Liquid Layer Adjacent to a High-Speed Gas Stream

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Comments on ``Stability of a Liquid Layer Adjacent to a High-Speed Gas Stream''

Comments on ``Stability of a Liquid Layer Adjacent to a High-Speed Gas Stream''

Breakup rate and penetration of a liquid jet in a gas stream.

An analysis of a disintegrating liquid jet penetrating a high-speed gas stream is presentedc Conditions are analyzed for which two types of waves (capillary and acceleration) will be amplified and will account for the jet disintegration. The results in the form of jet trajectories and penetration are found to be consistent with experimental data (180 cases, 8 liquids, suband supersonic flows). In each case, a parameter is determined by comparison with experiment and found to be approximately constant.

Stability of a Liquid Layer Adjacent to a High-Speed Gas Stream

The interfacial stability of a liquid layer with a compressible gas flowing over it is investigated. The liquid is assumed to be incompressible and viscid; the gas to be inviscid and to obey the equations of linearized compressible flow theory. The effects of surface tension at the gas-liquid interface and a gravitational body force are included. The criteria for the stability of a chosen equilibrium configuration of the system are determined by solving the linearized equations of motion for small perturbations about the equilibrium configuration. The configuration is considered to be stable if the perturbations decrease with time and unstable if they increase. Marginal stability is defined as the periodic, oscillatory motion of the perturbations. First, the interfacial stability is analyzed by means of a steady-gas-motion approximation. The effects of viscosity are neglected. Then the analysis is extended to include viscosity and the effect of the finite depth of the layer.

Catalytic Probes for the Determination of Atom Concentrations in High Speed Gas Streams

Catalytic Probes for the Determination of Atom Concentrations in High Speed Gas Streams

The Aerothermopressor—A Device for Improving the Performance of a Gas-Turbine Power Plant

Abstract Theoretical and experimental investigations of a novel gas-dynamics device having no moving parts yet performing the function of a compressor, are described. This device, called the “Aerothermopressor,” exploits the possibility of raising the total pressure of a high-speed gas stream through cooling of the gas. When placed at the exhaust of a gas turbine, the Aerothermopressor will reduce the exhaust pressure, thereby improving both fuel economy and power capacity per unit of air flow. Basic elements of the apparatus comprise a nozzle which accelerates hot gas into an evaporation section; a water-injection system which delivers finely atomized water into the high-speed stream; an evaporation section in which the gas is cooled and most of the water evaporated; and, finally, a diffuser in which the gas stream is decelerated and the static pressure increased. Although the Aerothermopressor is simple in structural arrangement, the physical processes occurring within it are exceedingly complex in their details. The simultaneous effects on the gas stream of droplet drag, evaporative cooling, area variation, and wall friction lead to many regimes of operation, including the hitherto unknown passage from subsonic to supersonic speeds in a constant-area duct. Theoretical calculations of a one-dimensional nature, involving for the gas stream the equations of continuity, momentum, and energy, and for the liquid-droplet cloud the equations of motion, heat transfer, and mass transfer, have been carried out on a high-speed, electronic digital computer. The theory reproduces all the behavior patterns of experimental units and is in generally good quantitative agreement with the experimental data. The results of experiments on a small-scale, constant-area unit of 2.13 in. diam are presented and compared with theoretical calculations. The experiments and theory both show that a net stagnation rise is possible only with gas flows greater than about 2 lb/sec; below this value the detrimental effects of wall friction completely absorb the gains due to cooling. In the range of 25 lb/sec a net stagnation pressure rise of about 10 per cent seems assured, while 20 per cent seems possible. Early tests on a recently completed medium-scale unit of 25 lb/sec capacity have already demonstrated a net overall rise in stagnation pressure.