The effect of particles on the gas velocity in a free turbulent flow

The article describes experimental studies carrid out to investigate the interaction between gas and particles in a free turbulent two-phase flow at the outlet from a rather long vertical tube.Notation A cross-sectional area of the flow - A ₀ initial cross-sectional area of the flow - d diameter of the flow - d _p average diameter of particles - I _i initial momentum of the two-phase flow - k mass ratio of particles and gas (k=m _p/m _g) - k ₀ mass ratio of particles and gas in the initial cross-section of the two-phase flow (x=0) - m _g mass flow rate of gas - m _p mass flow rate of particles - r instantaneous radius of the flow - r ₀ radius of the initial cross-section of the flow - r _1/2 normal distance from the flow axis to the point at which the velocity of gas is equal to the half of the axial velocity - R cross-sectional radius of the flow - u velocity - u _a air velocity - u _fa gas velocity on the flow axis - u _g gas velocity - u _av average gas velocity in the initial cross-section for two-phase and single-phase flows - u ₀ gas velocity on the axis of the initial cross-section of the flow - u _p particle velocity - x distance along the axis from the original of coordinates - _g gas density Institute of Nuclear Research Vina, Laboratory of Thermal and Power Engineering, Belgrade, Yugoslavia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 3, pp. 361–365, May–June, 1995.     

Numerical study on the effect of heat loss upon the critical marangoni number in a half-zone liquid bridge

In a half-zone (HZ) liquid bridge, flow exhibits a transition from a two-dimensional steady to a three-dimensional oscillatory flow if the Marangoni number Ma exceeds a critical value Ma_c, or ΔT>ΔT_c. In case of high Prandtle number fluids, the Mac obtained in the numerical simulations deviated significantly from the ones by the experiments. One of the causes of the difference is due to the heat loss over the free surface. Most of past researches neglected effects of the heat loss through an interface of the liquid bridge. Recently several experimental and analytical works reported that the critical condition is significantly affected by the heat loss. The present study aims to include the effects of the heat loss upon the Ma_c. As the result, the calculated Ma_c agrees well with the experiment for a high Pr fluid.     

Experimental study on the fluidization discharging characteristics of Geldart-C kaolin powders in a blow tank with pulsed gas

Kaolin powders have been suggested to be able to adsorb heavy metal vapor from coal-fired flue gas. However, due to the influence of inter particle forces, such as liquid bridge force, it is difficult to realize stable pneumatic conveying. In the present work, the fluidization characteristics of kaolin powders were investigated. A series of unstable flow phenomena such as agglomeration, channeling, and slugging occurred during the fluidization process. Also, the fluidization discharging characteristics of kaolin powder in an optimized blow tank were experimentally studied. The results indicated that the introduction of pulsed gas can effectively destroy agglomeration and thus improving the stability of discharging. Visual experiments in pseudo-2D fluidized bed were also confirmed the destructive effect of pulsed gas on agglomeration. With an increase in either fluidization gas velocity U_f or pulsed gas velocity v_pulsed, the mass flow rate of kaolin powder G first increased and then decreased. Finally, drying experiments demonstrated that there is free water on the surfaces of the kaolin powders. The analysis of forces indicated that the liquid bridge force F_lb between particles is much larger than the particle gravity F_g. The liquid bridge force might be one of key reasons for kaolin powder agglomerating.     

Radiative-convective heat transfer for high-temperature two-phase flow around bodies

Some methods for determining the basic parameters of high-temperature two-phase flows and the results of investigation of radiative—convective heat transfer with a flowing body in a flow are presented.Notation x=x/d, x distance from the plasmatron nozzle exit section - d diameter of the plasmatron nozzle - q=q_p/q₀, q_p heat flux in the vicinity of the critical point of the surface in a flow given the gas flow - q₀ neat flux in the absence of particles in the flow - _p mass concentration of particles in the flow - G_p mass flow rate of the condensed phase - G_g mass flow rate of the gas phase Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 3, pp. 300–303, March 1993.     

DUST STRANDS IN CYCLONE SEPARATORS AT LOW DUST CONCENTRATION

Abstract

State of the art in calculating a cyclone separator is the application of the equilibrium theory and taking the formation of dust strands into account as well. The latter process does not depend on particle size mainly. An ideal flow pattern for the formation of dust strands is the so called Dean-vortex: it is being realized favorably in the axial flow cyclone. A dust strand can be produced down to a raw gas concentration C₀ ≈ 10^?5. Then, it is being exhausted through one or few holes in the mantle of the axial cyclone applying bleeding of about 10 % of the volume flow Separating its dust in a bin cyclone and recirculating the binflow gas to the main, axial cyclone completes this high performance cyclone separator. Dimensional analysis shows that the clean gas concentration c₁ mainly depends on the swirl W_tan/w_ax, the raw gas concentration c₀and on Reynolds number. For usual dust conditions a clean gas concentration c₁ ≤ 50 mg/m³ is feasible.     

Temperature jump across a plane interface for a phase transition in a pure liquid

We develop a theoretical model of the development of a temperature jump across the boundary between phases during a phase transition in pure liquids.Notation G₁ mass flux of molecules of the liquid into the liquid - G₂ mass flux of molecules of the liquid into the vapor - G_v mass flux of vapor molecules - T₁ vapor temperature near the liquid surface - T₂ temperature of the liquid - T_v vapor temperature - R universal gas constant - c_p, c_v specific heats - r heat of vaporization - q heat flux density - K ratio c_p/c_v - parameter of the phase transition - F₀ area of the interface - P₁ pressure of the liquid - P₂ phase transition pressure - P_v vapor pressure Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 5, pp. 793–797, May, 1988.     

A cold model study of mass transfer in Q-BOP

At steel-making temperature, chemical kinetics can rarely be the rate-limiting step. Thus most of the reactions are limited by the rate of mass transfer to and from the reaction interface. The overall rate of mass transfer may be controlled by gas phase mass transfer or liquid phase mass transfer. Since in Q-BOP, the rate of reaction may be controlled by the rate of mass transfer in gas phase or in liquid phase, both were studied in a cold model. The different variables studied were tuyere diameter, jet direction, flow rate of gas and tuyere depth. The results of gas phase mass transfer indicate that the effect of tuyere diameter and jet direction is very small. For Reynolds number less than 9000 the effect of flow rate and tuyere depth is given by the equation,K _g A/L ₀ Q = 0·02d ₀ + 0·043, whereas for Reynolds number greater than 9000 the effect of flow rate and tuyere depth is given by the equation,K _g A/L ₀ Q=0·061d ₀+0·046. Similarly the liquid phase mass transfer coefficient is independent of the tuyere diameter and the shrouding gas, and is not much affected by the jet direction. The effect of gas flow rate and tuyere depth is given by the equation,K _L A=0·077 (Q)^0·75(L ₀)^0·61.     

A generalized Ginzburg-Landau approach to the superfluidity of helium 3

The coefficients in the expansion of the free energy and supercurrents in gradients of the order parameter are calculated from the microscopic Hamiltonian for all temperatures, first for a gas model and then including Fermi liquid corrections. This provides the basis for a simple discussion of the supercurrents and collective modes. The magnitude of the intrinsic orbital angular momentum in the Anderson-Brinkman-Morel phase is calculated, and found to beT _c/E_F smaller than previous estimates.     

Diffusion in a porous system in crossed electric and magnetic fields

Diffusion in crossed electric and magnetic fields is considered; measurements are reported on accelerated diffusion in the extraction of low-molecular-weight fractions (hemicelluloses) from cellulose and of copper salts from viscose fiber.Notation j₁ current density in liquid - j_p current density inside particles - c concentration in liquid - c₀ concentration in particles - t time - D₁=mD mass-conduction factor [17] - D diffusion coefficient - m porosity - D_c=D(m/m_v) concentration-conduction factor [17] - m_v volumetric porosity - x coordinate - s=2.46 design factor (for a film) - film half-thickness Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 5, pp. 831–838, November, 1976.     

Change in the nature of hydrodynamic cavitation in nonuniform magnetic fields

It is known that in nonuniform magnetic fields the precavitation properties of aqueous media change, leading to an increase in the irreversible physicochemical changes.Notation l length of zone II - D and d diameters of tubes I, III, and II - p_I, p_II, p_III pressures in regions I, II, and III - p_cr critical pressure at which cavitation occurs - p_cr and p _cr ⁰ critical pressures in the magnetic field and when there is no magnetic field - [V_I, V_II, V_III] velocities of the liquid in regions I, II, and III - V_II, lim velocity of the liquid at which breakdown of the hydrated layer occurs for a certain value of the induction - V_cr and V _cr ⁰ critical velocities at which cavitation occurs in the magnetic field and when there is no magnetic field - p_a atmospheric pressure - p_sv saturation-vapor pressure at the given temperature - density of the liquid - kinematic viscosity - Re Reynolds number - Re_cr critical Reynolds number - c_gf and c_gd concentrations of free and dissolved gases in the magnetic field and when there is no magnetic field - c_gf and c_gd, and c _gf ⁰ and c _gd ⁰ concentrations of free and dissolved gases in the magnetic field and when there is no magnetic field - _sc space-charge density - electrical conductivity in the volume of the liquid - _b electrical conductivity in the boundary layer - _l , _g, _d dielectric constants of the liquid in the volume, of the gas in the bubbles, and of the diffusion layer - j, j_b, j_i, and j_T current density of the general, boundary layer, induced and current flow - f_MHD and f_EHD volume forces of magnetohydrodynamic and electrodynamic nature (per unit volume) - p_MHD pressure in the liquid due to the action of the magnetohydrodynamic forces - ₀ limiting shear stress in the liquid - B magnetic induction - E electric field strength in the volume of the liquid Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 5, pp. 842–850, November, 1978.     

A coupled numerical analysis of shield temperatures, heat losses and residual gas pressures in an evacuated super-insulation using thermal and fluid networks: Part III: Unsteady-state conditions (evacuation period)

This paper analyses the evacuation period of a 300 L super-insulated cryogenic storage tank for liquid nitrogen. Storage tank and radiation shields are the same as in part I of this paper. The present analysis extends application of stationary fluid networks to unsteady-states to determine local, residual gas pressures between shields and the evacuation time of a multilayer super-insulation. Parameter tests comprise magnitude of desorption from radiation shields, spacers and container walls and their influence on length of the evacuation period. Calculation of the integrals over time-dependent desorption rates roughly confirms weight losses of radiation shields obtained after heating and out-gassing the materials, as reported in the literature. After flooding the insulation space with dry N₂-gas, the evacuation time can enormously be reduced, from 72 to 4 h, to obtain a residual gas pressure of 0.01 Pa in-between shields of this storage tank. Permeation of nitrogen through container walls is of no importance for residual gas pressures. The simulations finally compare freezing H₂O-layers adsorbed on shields, spacers and container walls with flooding of the materials.     

Evaporation of additive droplets in a pulse MHD generator

Theoretical investigation into evaporation of additive droplets in the combustion chamber of a pulse MHD generator were undertaken. Flow in the chamber is considered as stationary and one-dimensional; mixing in a direction perpendicular to flow is believed to be ideal, and mixing is lacking in the flow direction. It is suggested that droplets are monodisperse, spherical, and motionless relative to the gas medium. The droplet evaporation can be taken as occurring in the diffusion mode. The specific heat c _p and heat conductivity coefficient are taken to be constant and independent of temperature and the concentration of components. The Lewis number is believed to be the unit value; and the Soret and Dufour effects, negligible. A formula for calculation of the droplet evaporation rate with allowance made for chemical reactions occurring in liquid and gas media is obtained.     

2D Electron Bubbles in Gaseous Helium

The structure of 2D electron bubbles in gaseous helium is discussed. These cavities appear under the condition n_g > n_c, where n_c ≈ 10²⁰ cm⁻³ is much less than the critical helium gas density for the appearance of 3D electron bubbles. Far from the critical density, the 2D bubble trapping energy is practically a linear function of n_g. Experiment confirms the existence of 2D electron bubbles.     

The influence of residual gas pressure on the thermal conductivity of microsphere insulations

Experimental results of investigations of the heat exchange by residual gas in microsphere insulations are presented. The results of measurements of microsphere effective thermal conductivity versus residual gas (N₂) pressure in the pressure range of 10^–3–10⁵ Pa are also given. A sample of self-pumping microsphere insulation was prepared and its thermal parameters were tested. In comparison to the standard microsphere insulation, the self-pumping insulation yielded lower thermal conductivity results over the entire pressure range. The stability of its thermal parameters as a result of considerable gas input into the insulation volume is discussed. Measurements of temperature and pressure distributions inside the microsphere layer were performed. Plots of temperature and pressure gradients inside the layer of the microsphere insulation are presented.Nomenclature d _m Mean value of the microsphere diameter - k Apparent thermal conductivity coefficient - ¯k Average thermal conductivity coefficient - k _c Component of the heat transfer by conduction - k _g Modified gas thermal conductivity under atmospheric pressure - k _r Component of the heat transfer by radiation - k _s Thermal conductivity of the sphere material - k _gc Component of the heat conduction by gas - k _go Gas thermal conductivity under atmospheric pressure - k _gr Sphere effective conductivity - k _ss Component of the heat conduction by the solid state - K 1–(k _g/k _gr) - Kn Knudsen number - ¯L Mean free path of gas molecules - m 1–_s; porosity - m Empty volume of a single sphere - p Residual gas pressure - ¯p Average pressure - p _g Pressure measured by gauge - p ₀ Residual gas pressure above the insulation bed - r Radial coordinate - T Temperature - T _c Temperature of the cold calorimeter wall - T _g Temperature of the pressure gauge - T _H Temperature of the hot calorimeter wall - T _i Gas temperature inside the bed - T _y Constant dependent on the sort of gas - v Volume - Accommodation coefficient - Density - _a Local distance between surfaces - _s Solid fraction - Constant dependent on the sort of gas - Time measured from the initiation of insulation cooling     

Explosion of Electron Bubbles Trapped on Vortices in He-II

Electrons injected into liquid helium become trapped in a spherical cavity from which the liquid is almost completely excluded. When a negative pressure is applied to the liquid the size of the electron bubble increases, and at a critical negative pressure P _c the bubble explodes. We have observed these explosions and have measured P _c as a function of temperature. At low temperatures an electron bubble can become bound to a quantized vortex. The flow of the helium around the quantized vortex leads to a reduction in the magnitude of P _c. We will report measurements of this reduction in P _c and will make a comparison of the results with theoretical predictions.     

Motion of liquid drops in one-dimensional gas flow

Formulas for calculating the velocity of liquid drops entrained by a gas flow are obtained. These formulas can be used to analyze the effect of dimensionless similarity criteria (_g, Re, We, Kn, etc.) on the velocity of the drops.     

Shear-thickening behaviour of concentrated polymer dispersions under steady and oscillatory shear

The rheological behaviour of a 58 vol.% dispersion of styrene/acrylate particles in ethylene glycol was investigated using a plate-on-plate rheometer. Experimental results showed that the concentrated polymer dispersion exhibited a strong shear-thickening transition under both steady shear and dynamic oscillatory conditions. The low-frequency dynamic oscillatory behaviour could be reasonably interpreted in terms of the steady shear behaviour. Accordingly, the critical dynamic shear rate [(g)\dot]_{\textc_d} , \dot{\gamma }_{{{\text{c\_d}}}} , agreed well with the critical shear rate obtained in steady flow [(g)\dot]_{\textc_s} , \dot{\gamma }_{{{\text{c\_s}}}} , where [(g)\dot]_{\textc_d} \dot{\gamma }_{{{\text{c\_d}}}} was calculated as the maximum shear rate by the critical dynamic shear strain γ _c and the frequency ω, i.e. [(g)\dot]_{\textc_d} = wg_\textc . \dot{\gamma }_{{{\text{c\_d}}}} = \omega \gamma_{\text{c}} . However, during high-frequency dynamic oscillation, it was observed that the shear thickening occurred only when an apparent critical shear strain was reached, which could not be fully explained by the wall-slipping effect. Based on freeze fracture microscopic observations, the effect of the micro-sized flocculation of particles on the rheology of concentrated dispersions was also discussed.     

Progress on the boundary element method to study the disturbance fields of bodies moving in an unbounded medium

For studying flow problems involved with complex physics it is now common to use numerical field methods for solving Navier-Stokes or Euler equations. However, for a large class of fluid mechanics problems, which can be dealt with linearized potential equations, the boundary element method proves to be quite useful, especially for its easy application and relatively less computational effort compared to the field methods. The boundary element method has undergone some significant advancements in the last decade with respect to the study of steady and unsteady flow problems concerning wing aerodynamics in compressible medium, flow fields of propellers and rotors and acoustical disturbance propagation from moving bodies. In this paper a few recent contributions which evolved in the DLR as research projects and as doctoral and diploma thesis of the Technical University Braunschweig are concisely described.List of symbols a Sound velocity - b Span of a wing - c _p Coefficient of static pressure - c _dp Coefficient of profile drag - c ₁, c _d, c_m Coefficient of lift, drag and moment per unit span width - c _L, c_D, c_M Total lift, drag and moment-coefficients - c _T, c_P Thrust and power-coefficient of a propeller - d Distance - D Doublet strength - e Specific heat energy - E Total energy in a moving medium element - f Frequency - F Field point - g Gravitational acceleration - h Radial distance in cylinder coordinates - I ₁, I ₂ Inducing functions - i, j, k Unit vectors in cartesian coordinates - k Wave number [/a ] - l Local wing-chord - l ₀, l _v Length of singularity element at t _oand t _v - m Notation for Fourier-component - M, M ^* Mach number based on local and critical sound speed - n Number of rotation per second - n Unit normal vector to a surface     

Transport Properties of a Tl-2201 Film Close to the Critical Temperature: The Vortex Glass Transition

We have studied the I-V characteristics of a Tl-2201 film at zero field. In the regime in which flux creep is the dominant dissipation mechanism, the J _c -T curve is divided into two parts at a temperature T _g (about 82 K), close to the critical temperature (84 K). The I-V characteristics around T _g are well described using a flux creep model. For T>T _g , J _c /J _c (0) =0.445x(l-0.525t-0.5t ² ); for T _g , J _c /J _c (0) = 0.9x(1-0.595t-0.44t ² ). Differential resistance (dV/dI) as a function of the measuring current shows a change in curvature close to T _g . The I-V curves collapsed nicely into two branches by plotting (V/I)/|T–T _g | ^v(z-1) vs. (I/T)/|T _g –T| ^2v , indicating a current–reduced vortex glass transition.     

Saturation curve equations for normal and heavy water

Compact and precise equations are obtained for the saturation curves of normal and heavy water.Notation p saturated vapor pressure - p_c critical pressure - T absolute temperature - T_c critical temperature - =T/T_c dimensionless temperature - =1 – ; r heat of vaporization - c _p ⁰ isobaric heat capacity of vapor in ideal gas state - c_s liquid heat capacity along saturation curve - v specific volume of vapor - a _i coefficients of Eq. (1) Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 5, pp. 894–897, May, 1981.