The hydrodynamics of countercurrent two-phase flow in vertical channels

Countercurrent flow of gas and liquid in vertical tubes is investigated. Processes that occur under various conditions of flow (including the “flooding” mode) are treated. Equations are suggested that describing the hydrodynamic characteristics of countercurrent two-phase flow.     

Numerical simulation of gas-particle flows behind a backward-facing step using an improved stochastic separated flow model

An improved stochastic separated flow (ISSF) model developed by the present authors is tested in gas-particle flows behind a backward-facing step, in this paper. The gas phase of air and the particle phase of 150 μm glass and 70 μm copper spheres are numerically simulated using the k–ɛ model and the ISSF model, respectively. The predicted mean streamwise velocities as well as streamwise and transverse fluctuating velocities of both phases agree well with experimental data reported by Fessler. The reattachment length of 7.6H matches well with the experimental value of 7.4H. Distributions of particle number density are also given and found to be in good agreement with the experiment. The sensitivity of the predicted results to the number of calculation particles is studied and the improved model is shown to require much less calculation particles and less computing time for obtaining reasonable results as compared with the traditional stochastic separated flow model. It is concluded that the ISSF model can be used successfully in the prediction of backward-facing step gas-particle flows, which is characterised by having recirculating regions and anisotropic fluctuating velocities. Received 20 June 2000     

Influence of steady shear flow on dynamic viscoelastic properties of un-reinforced and Kevlar,glass fibre reinforced LLDPE

An experimental study was conducted to observe the effects of parallel-superposed flow condition on viscoelastic properties of LLDPE, Kevlar fibre reinforced LLDPE and hybrid of short glass fibre and Kevlar fibre reinforced LLDPE. Parallel-plate rheometer was employed for these tests. Rheological parameters such as loss modulus (G″) and dynamic viscosity (η′) do not vary significantly on superposing steady state shear with oscillatory shear in the studied range of experiment at 185°C in un-reinforced LLDPE. Kevlar fibre reinforced LLDPE and Kevlar/glass fibre reinforced LLDPE showed significant changes in the flow behaviour under various sets of superposed conditions. Storage modulus (G′), andG″ become highly sensitive to low oscillatory angular frequencies (ω) under superposed conditions. These curves show two different regions with increased ω value. At low ω values, parametersG′ andG″ change sharply reaching a certain value, thereafter, changes are moderate with increased ω. In case of η′ a maxima is observed, position of which, depends upon the value of steady shear rate. Maxima shifts towards higher frequencies with the increased steady shear rate.     

Experimental Investigation of a Bubbly Two-Phase Flow in an Open Capillary Channel under Microgravity Conditions

The study of a bubbly laminar two-phase flow in an open capillary channel under microgravity conditions was conducted aboard the sounding rocket, Texus-45. The channel geometry, the liquid (FC-72) and the experimental conditions were chosen based on an analysis for application toward liquid management in space. The channel consists of two parallel plates that were b = 25 mm wide and separated by a distance of a = 10 mm. The flow along the length l = 80 mm is bounded by a free surface on one side and a plate on the opposite side. Bubbles are injected at the inlet of the capillary channel via six capillary tubes. The features of the gas injection were chosen with regard to the required bubble size, the injection frequency, and the gas and liquid flow rates. Different liquid and gas flow rates were tested leading to a volumetric quality ranging between 0.07 and 0.11. The experimental results show the interaction among bubbles and with the liquid free surface.     

Experimental Study on Boiling Flow of Liquid Nitrogen in Inclined Tubes—Liquid Slug Length Distribution

An experimental study was carried out to understand the phenomena of the boiling flow of liquid nitrogen in inclined tubes with closed bottom by using the high speed motion analyzer. The tube in the experiment is 1.0 m length and 0.018 m and 0.014 m inner diameter respectively. The range of the inclination angles is 45–90° from the horizontal. The statistical method is employed to analyze the experiment data. The experiment focused on the effect of the inclination angle on the distributions of the liquid slug length along the tube. The experimental results show that the Taylor bubble is easier to coalescence with inclination angle decreasing, but coalescence lessening at 45°. The liquid slug length distributions extend to much larger values for the large tube when x/D is 40 and 50. The mean liquid slug lengths increased first, and then decreased with decreasing θ for two tubes, maximum at 60°.     

The fracture energy of brittle crystals

An expression is derived for the fracture energy, γ, in brittle crystals, namely, γ = kd ₀ E, d ₀ being the lattice spacing, E Young’s modulus perpendicular to the fracture plane, and k is a constant. The value of γ obtained through this expression is compared to experimental data for cubic crystals. Despite the fit, we conclude that because the fracture energy is dominated by the elastic constant, comparisons between a computed γ and experimental data cannot be used to distinguish between bonding functions.     

Mass spectroscopic measuring of SiCl<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 0–2) radicals in SiCl<Subscript>4</Subscript> RF glow discharge plasma

The relative densities of SiCl _n (n = 0–2) in SiCl₄ radio frequency (rf) glow discharge plasma are measured by mass spectrometry. The effects of discharge parameters, i.e., rf power, discharge pressure, substrate temperature, and SiCl₄ flow rate on the relative densities of SiCl _n (n = 0–2) are investigated in detail. An optimum configuration of discharge parameters (low rf power, high discharge pressure, low substrate temperature, and low flow rate), which enhanced the formation of SiCl _n (n = 0–2) radicals, is searched by a great deal of measurements and discussions. In the optimum configuration of discharge parameters, we measure the spatial distribution of SiCl _n (n = 0–2) radicals in the most optimized plasma parameters. The experimental results reveal that Si and SiCl may be the dominant precursors in forming the thin film.     

Hot deformation behavior of an 8% Cr cold roller steel

An 8% Cr cold roller steel was compressed in the temperature range 900–1200 °C and strain rate range 0.01–10 s⁻¹. The mechanical behavior has been characterized using stress–strain curve analysis, kinetic analysis, processing maps, etc. Metallographic investigation was performed to evaluate the microstructure evolution and the mechanism of flow instability. It was found that the work hardening rate and flow stress decreased with increasing deformation temperature and decreasing strain rate in 8% Cr steel; the efficiency of power dissipation decreased with increasing Z value; flow instability was observed at higher Z-value conditions and manifested as flow localization near the grain boundary. The hot deformation equation and the dependences of critical stress for dynamic recrystallization and dynamic recrystallization grain size on Z value were obtained. The suggested processing window is in the temperature range 1050–1200 °C and strain rate range 0.1–1 s⁻¹ in the hot processing of 8% Cr steel.     

Nonstationary heat and mass transfer in evaporative cooling of flowing liquid films

A mathematical model of nonstationary evaporative cooling of a laminar liquid film flowing down a vertical surface in its blowing with a countercurrent steam-air flow has been developed. The problem of heat and mass transfer has been formulated in a conjugate statement. The calculated data on the time change in the temperature and concentration fields in the steam-air flow and the liquid film as well as in the density of the heat flux on the flowing-film surface have been given. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 1, pp. 3–10, January–February, 2006.     

High-T c superconductivity in thed-p electron system

The relaxation time with spin flipτ _s and the parametersξ, δ, χ of superconducting phase have been calculated on the basis of the kinematical mechanism of superconductivity in strongly correlated oxide models. An inter-relation between the superconducting gap Δ₀ and the specific heat jump Δ _c allowing the experimental verification was obtained and the Ginsburg-Landau equation derived.     

Formation of coulomb clusters from charged diamagnetic microparticles in inhomogeneous magnetic field

The possibility of levitating Coulomb clusters formed by charged diamagnetic microparticles in an inhomogeneous magnetic field has been theoretically substantiated and experimentally confirmed. An experimental setup is described, in which the Coulomb clusters can be formed from charged graphite particles 100–300 μm in size and maintained stable between the poles of an electromagnet generating a magnetic field with induction B ∼ 10⁴ G and gradient |∂B| ∼ 10⁵ G/cm.     

Application of non-linear k–ω model to a turbulent flow inside a sharp U-bend

Simulation of the complex flow inside a sharp U-bend needs both refined turbulence models and higher order numerical discretization schemes. In the present study, a non-linear low-Reynolds number (low-Re) k–ω model including the cubic terms was employed to predict the turbulent flow through a square cross-sectioned U-bend with a sharp curvature, R _C/D = 0.65. In the turbulence model employed for the present study, the cubic terms are incorporated to represent the effect of extra strain-rates such as streamline curvature and three-dimensionality on both turbulence normal and shear stresses. In order to accurately predict such complex flowfields, a higher-order bounded interpolation scheme (Song et al., 1999) has been used to discretize all the transport equations. The calculated results by using both the non-linear k–ω model and the linear low-Reynolds number k–ɛ model (Launder and Sharma, 1974) have been compared with experimental data. It is shown that the present model produces satisfactory predictions of the flow development inside the sharp U-bend and well captures the characteristics of the turbulence anisotropy within the duct core region and wall sub-layer.     

Increasing in the rate constant for dissociative attachment of electrons to hydrogen molecules by vibrational pumping during flow in a channel

An investigation is made of the electron-vibrational kinetics in a stream of vibrationally excited hydrogen flowing in a channel. It is shown that for suitably organized flow and a suitable choice of material for the channel walls, the rate constant 〈K _DA〉 for dissociative attachment of electrons to hydrogen molecules may be increased substantially. The effect is controlled by the mean vibrational energy 〈E _v ⁽⁰⁾ 〉 of the H₂ molecules entering the channel. Pis’ma Zh. Tekh. Fiz. 24, 69–75 (December 26, 1998)     

Optimization of the contrast, brightness, and modulation amplitude of light in electrooptic devices based on polymer-encapsulated ferroelectric liquid crystals

An analysis is made of the relations connecting the maximum optical transmittance, the light modulation amplitude, and the contrast in a polymer-encapsulated ferroelectric liquid-crystal device to the geometry of device and the tilt angle θ of the director. The correctness of the calculations is confirmed by their agreement with experimental measurements. Pis’ma Zh. Tekh. Fiz. 24, 63–67 (June 26, 1998)     

About temperature dependence of the rheological properties of human blood at low shear rates

Measurements of the human blood flow curve as a function of temperature are reported. The blood was sampled from healthy donors. The measurements were made at the shear rates from 0.2 to 5.0 sec⁻¹ in the temperature range 30–45°C. The blood flow curve was investigated by the nonstationary measurement method using a specially designed viscosimeter. An experimental study of the human blood flow curve at low shear rates allowed investigation of the temperature dependence of the Casson’s model parameters describing it. It is shown that these parameters have a complicated temperature dependence that exhibits a specific feature at 42°C. Academic Scientific Complex “A. V. Luikov Heat and Mass Transfer Institute, Academy of Sciences of Belarus,” Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 3, pp. 386–389, May–June, 1996.     

Master apparatus for calibrating water meters

A master flow meter is required for calibrating the majority of flow meters and water meters. An apparatus for calibrating water meters was constructed at the Venturorganization under the direction of Test St. Petersburg. Translated from Izmeritel'naya Tekhnika, No.5, pp. 31–32, May, 1998.     

Experimental estimation of contact conditions in problems of mechanics of a solid deformable body

An experimental technique for estimating the conditions acting on the contact surfaces of mutually deformable bodies as applied to geomechanical measurements is considered. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 3, pp. 506–509, May–June, 1997.     

Numerical simulation of planar shear flow passing a rotating cylinder at low Reynolds numbers

Two-dimensional shear flow over a rotating circular cylinder is investigated using lattice Boltzmann method. Simulations are performed at a fixed blockage ratio (B = 0.1) while the Reynolds number, nondimensional shear rate (K) and absolute rotational speed range as 80 ≤ Re ≤ 180, 0 ≤ K ≤ 0.2 and −2 ≤ β ≤ 2, respectively. To verify the simulation, the results are compared to previous experimental and numerical data. Quantitative information about the flow variables such as drag and lift coefficients, pressure coefficient and vorticity distributions on the cylinders is highlighted. It is found that, generally, with the increment in |β|, the absolute value of time average lift coefficient increases and time average drag coefficient decreases, and beyond a certain magnitude of β, the vortex shedding vanishes. It is also revealed that the drag coefficient decreases as the Reynolds number increases while the effect of the Reynolds number on lift is almost negligible. At the end, correlations for drag and lift coefficients ([`(C<sub>D</sub> )] ,[`(C_L )]){(\overline {C_D } ,\overline {C_L })} are extracted from the numerical data.     

Investigation of gas-dynamic processes in optical discharges with an ablating polymer wall in air and vacuum conditions

Experimental research results are presented on the formation dynamics and macrostructure of optical discharges of condensed matter of a polymer series ((C₂F₄) _n , (CH₂O) _n ) under the action of a femtosecond laser (τ _0.5 ∼ 45–70 fs) pulses (I ₀ ∼ 10¹³−10¹⁵ W/cm²) in the UV — NIR spectral region (λ ∼ 266, 400, 800 nm) under air and vacuum conditions. Electron density distributions in the near-surface area of the optical discharge, vapor expansion, and velocities of shock-wave front propagation are determined for the first time by precise laser pulse micro-interferometry with high spatial and time resolution. The correspondence is shown of the values of the laser ablation spectral-energy threshold, as determined by interference microscopy and the interferometry of a gas-plasma flow. An estimation technique for the total momentum of light-erosion gas-plasma flow in the sub-nanonewton range is proposed and implemented for the first time. The results of comparative analysis are presented on the laser radiation conversion efficiency at different stages of femtosecond optical discharges.     

Rise of a Single Bubble in Ascending Laminar Flow: Slip Velocity and Wall Friction

An experimental study has been made of the motion of single bubbles in ascending laminar flow in a vertical pipe. An electrodiffusion procedure has been used for visualization of wall friction in passage of a single bubble. Time realization of friction stress is considered as the structure frozen-in into the flow and moving along the flow together with the bubble. The experiments have revealed the complex structure of wall-friction stress, which corresponds to different components of interaction of the bubble with the wall. The evolution of these components as a function of the Reynolds numbers of the bubble and the pipe is discussed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 4, pp. 129–135, July–August, 2005.