A Correlation Study for the Positional Dependence of Friction Factor in Dilute Phase Flows

Results of a comprehensive study on the flow friction factor data collected on suspensions of solid granular particles of semolina, fly ash, and alumina having a size range of 75.5?µm ≤ d_p ≤ 275?µm in air are presented. The experimental study was composed of 250 separate test cases in which airflow Reynolds number Re = UD/ν and loading ratio M_p/M_a were varied systematically covering the ranges of 50,000 ≤ Re ≤ 100,000 and 5% ≤ M_p/M_a ≤ 25%. An upward flow field with variable inclinations α of 10°, 20°, and 30° with the horizontal plane and a horizontal flow field, i.e, 0° inclination, were used to determine the influence of gravitational forces. Local static pressure gradients measured along the flow field with distance x were used to determine local air-particle friction factor f_{p + a}, which was observed to be under the influence of particle type, M_p/M_a, Re, and flow line inclination, α. The proposed correlation for the variation of f_{p + a} with x/D was evaluated to reach a generalized form exhibiting interactive influence of Re, M_p/M_a?, α, and particle type.     

Thermal analysis of airflow inside a refrigerated container

A numerical study of conjugated heat transfer in ceiling-slot refrigerated containers is carried out to analyze the temperature distribution effectiveness and to determine the ventilation characteristics. The effect of slot size on thermal characteristics is studied by considering half-span and full-span injection. The container walls are defined as conductive opaque and are interacting with outside environment. The outer surface heat transfer coefficients of conductive walls are computed by studying the flow around the refrigerated truck. The Reynolds number at the slot exit varied between 2 × 10⁴ ≤ Re ≤ 2 × 10⁵. The gravity effect is taken into account, and the coupled mass, momentum, and energy equations are discretized in finite volumes. The heat transfer coefficients of inner flow are presented as plots of the mean Nusselt number versus the modified Reynolds number. The maximum dispersion in the numerical data being at 14.54-percent, the mean Nusselt number, the modified Reynolds number, and the aspect ratio of the container are correlated.     

Aerodynamic Heating of a Thin Sharp-Nose Circular Cone in Supersonic Flow

The assumption of flow symmetry is made to investigate a supersonic flow (M_∞ = 5) past a thin circular cone with a half-angle θ _c = 4° and an isothermal surface (T _w0 = 0.5) by way of numerical integration of unsteady-state three-dimensional Navier-Stokes and Reynolds equations. The calculations are performed in a discrete range of variation of the Reynolds number (10⁴ ≤ Re ≤ 10⁸) and angle of attack (0° ≤ α ≤ 15°). The effect of the determining parameters of the problem on the structure of flow field and on aerodynamic heating of the body surface subjected to flow is demonstrated.     

Mass transfer study of an extractive electrochemical sulfide/sulfur reaction in a parallel plate reactor

Abstract

The mass‐transfer phenomenon between an aqueous‐organic phase and an electrode producing sulfur from sulfide ions in a parallel plate reactor is studied. A kinetic model of the electrochemical conversion and extraction process is developed and tested. Under steady‐state conditions, the electrochemical reaction rate at limiting operation, defined as K‘_m A (1 – θ) C_R/α, is equal to the extraction rate, defined as K‘_d A θ (C^sat _s/β ‐ C_s/β ) for this extractive electrochemical system. Experimental parameters include volume fraction (X_d ) and fluid velocity (Re‘). The mass transfer coefficients, K‘_m and K‘_d, were obtained as K‘_m = 7.044 × 100^–5 Re‘ ^? (1.073 + 0.575 X_d – X ² _d ) and K‘_d = 5.15 × 10^–4 Re‘ ^? X_d with a Reynolds number between 18～54 and volume fraction under 70% for this two‐phase solution.     

High-frequency actuator control of air flow near a circular cylinder: Impact of the discharge parameters on the cylinder aerodynamic drag

The impact of capacitive high-frequency surface discharge on a flow around a circular cylinder is studied at airflow velocity of 20–100 m/s and the Reynolds numbers Re < 2.4 × 10⁵. The power of the discharge was modulated at a frequency of 10²–10⁴ Hz, corresponding to the Strouhal number St = 0.1–10. It is shown that the distribution of pressure in the wake behind the cylinder is significantly influenced by the discharge. A decrease in the average diameter of the wake is observed. The parameters of the discharge were measured: the gas temperature, heating rate in the discharge region, and velocity of discharge propagation.     

Investigation of the influence of free convection on the heat transfer of cylinders with different aspect ratios

Electrically heated cylindrical wires are used in research and industry for fluid velocity and turbulence measurements. At very low free-stream velocities (u≤0.1 m/s), hot-wire measurements are significantly influenced by buoyant convection. Below a certain Reynolds number Re* this effect degrades the accuracy of the measurements. To assess the contribution of free-convection heat transfer to the heat balance of hot-wires in cross flow, measurements under normal gravity and microgravity (µg) conditions are compared keeping all other parameters constant. Under gravity conditions, the acceleration of gravity, the hot-wire axis and the direction of the free stream are all perpendicular to each other. The microgravity experiments were carried out in the Drop-Tower Bremen in which the residual acceleration is less than 10^?5 g during a period of 4.7 s. The present investigation is concerned with a velocity range of 0≤u≤0.35 m/s corresponding to a Reynolds number range Re<0.1 in standard air. This range includes pure free convection for Re→0 and forced-convection-dominated heat transfer for Re=0.1. At intermediate Reynolds numbers both transport mechanisms must be considered.     

Modeling an increase in the lift and aerodynamic efficiency of a thick Göttingen airfoil with optimum arrangement

The Reynolds equations closed using the Menter shear-stress-transfer model modified with allowance for the curvature of flow line have been numerically solved jointly with the energy equation. The obtained solution has been used to calculate subsonic flow (at M = 0.05 and 5° angle of attack) past a thick (24% chord) Göttingen airfoil with variable arrangement of a small-sized (about 10% chord) circular vortex cell with fixed distributed suction Cq = 0.007 from the surface of a central body. It is established that the optimum arrangement of the vortex cell provides a twofold decrease in the bow drag coefficient Cx, a threefold increase in the lift coefficient Cy, and an about fivefold increase in the aerodynamic efficiency at Re = 10⁵ in comparison to the smooth airfoil.

     

Numerical simulation of the separated fluid flows at large Reynolds numbers

The variety of flow regimes (steady separated, periodically separated-‘Karman vortex street’, unsteady turbulent) and their characteristic peculiarities (separation and reattachment points, secondary separation, boundary layer, instability of the shear mixing layer, etc.) require the construction of effective numerical methods, which will be able to simulate adequately the considered flows. MERANGE ? SMIF–a splitting method for physical factors of incompressible fluids¹-is used for calculations of the steady and unsteady fluid flows past a circular cylinder in a wide range of Reynolds numbers (10° < Re < lo6). The finite-difference scheme for this method is of second order accuracy in the space variables, has minimal numerical viscosity and is also monotonic. Use of the Navier-Stokes equations with the corresponding transformation of Cartesian co-ordinates allows the calculations to be made by one algorithm both in a boundary layer and out of it. The method allows calculations at Re = ∞ cc and simulation of d‘Alembert’s paradox. Some results on the classical problem of the flow around a circular cylinder for a wide range of Reynolds numbers are discussed. The crisis of the total drag coefficient and the sharp rise of the Strouhal number are simulated numerically (without any turbulence models) for the critical Reynolds numbers (Re ≈ 4 × 10⁵), and are in a good agreement with experimental data.     

Investigation of laminar-turbulent transition in supersonic boundary layers in an axisymmetric aerophysical flight complex and in a model in a wind tunnel in the presence of heat transfer and suction of air

Analysis is made of the problems associated with laminar-turbulent transition in wall boundary layers, as well as of scale effects observed in the investigation of laminar-turbulent transition in wind tunnels and laminarization of flow. Flight-performance data are given on the Reynolds number and on the gradient criterion of stability at the beginning of transition on the nose part of the Oblako aerophysical complex in the presence of heat transfer for the numbers Re _{L, ∞} ≤ 2 × 10⁷, M_∞ ≤ 2.0, and acceleration a ≤ 12g. Experimental data are given on laminarization of flow past a porous plate in a wind tunnel under the effect of suction for M_∞ = 2.5. The theory of Emmons turbulent spots is generalized to the flight conditions of flow past the nose part of the Oblako aerophysical flight complex in the presence of heat transfer and to the case of laminar-turbulent transition on a porous plate for M_∞ = 2.5 in the presence of suction of air.     

Numerical study of bluff body flow structures

Our recent progress in numerical studies of bluff body flow structures and a new method for the numerical analysis of near wake flow field for high Reynolds number flow are introduced. The paper consists of three parts. In part one, the evolution of wake vortex structure and variation of forces on a flat plate in harmonic oscillatory flows and in in-line steady-harmonic combined flows are presented by an improved discrete vortex method, as the Keulegan-Carpenter number (KC) varies from 2 to 40 and ratios ofU _m toU ₀ are ofO(10⁻¹),O(1) andO(10), respectively. In part 2, a domain decomposition hybrid method, combining the finite-difference and vortex methods for numerical simulation of unsteady viscous separated flow around a bluff body, is introduced. By the new method, some high resolution numerical visualization on near wake evolution behind a circular cylinder at Re=10², 10³ and 3×10³ are shown. In part 3, the mechanism and the dynamic process for the three-dimensional evolution of the Kármán vortex and vortex filaments in braid regions as well as the early features of turbulent structure in the wake behind a circular cylinder are presented numerically by the vortex dynamics method. This study was supported by the National Natural Science Foundation of China and the Laboratory for Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, as well as by the National Basic Research project “Nonlinear Science”.     

General characteristics of supersonic vortical boundary layers

Results are shown of a study concerning the velocity profile, the velocity of discrete vortices, and the thickness of supersonic vortical boundary layers. Measurements were made with the Mach number M = 1.7–3.0 and with the Reynolds number Re = 4.4 · 10⁵-4.0⁷.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.22, No. 5, pp. 885–889, May, 1972.     

Development of a flow field structure in the vicinity of a circular cylinder in the presence of a laminar-turbulent transition

The Reynolds equations and the two-parameter differentialq-Ω model of turbulence are used to investigate a flow past a circular cylinder with an isothermal surface (temperature factorT _w0 = 0.5) at the Mach numberM _∞ = 5 in the range of Reynolds numbers Re = 10⁴-10⁸. It is demonstrated that the turbulization of flow leads to a shift of the separation point downstream, a reduction and stabilization of the separation zone length, a decrease in the maximum velocity in the separation zone, and an increase in the heat flux at the rear stagnation point compared with its value at the forward stagnation point.     

Yield strength anomaly and dynamic strain ageing behaviour of recently developed advanced ultra-supercritical boiler grade wrought Ni-based superalloy IN 740H

The yield strength anomaly (YSA) and dynamic strain ageing (DSA) behaviour of advanced ultra-supercritical boiler grade wrought nickel-based superalloy IN 740H is studied by conducting tensile tests in temperature range 28–930°C and by employing strain rates 1 × 10^?2, 1 × 10^?3, 1 × 10^?4 and 1 × 10^?5 s^?1 followed by extensive electron microscopic examination. Increase in yield strength accompanied by impairment of ductility indicates that YSA exists in alloy IN 740H in temperature range of 650–760°C. The electron microscopic observation confirms that YSA is due to pinning of dislocations by γ′ precipitates and shearing of γ′ precipitates in IN 740H. DSA is observed in the temperature range of 200–500°C and is predominant at 300°C. The nature of serrated plastic flow due to DSA is dependent on the temperature and strain rate.     

Sorption-atomic-absorption determination of platinum,palladium, and rhodium in dead autocatalysts

The conditions for determination and group concentration of platinum metals (PMs) in the presence of matrix components using new S,N-containing complex-forming sorbents in solutions obtained after decomposition of decontaminated autocatalysts are proposed. The technique of atomic-absorption determination of PMs from a solution (n × 10⁻⁴−n × 10⁻²; s _r = 0.15–0.07) and a solid phase (n × 10⁻⁵−n × 10⁻⁴; s _r = 0.20–0.12) is developed.     

Round-handle decomposition of S 2×S 1

A round-handle decomposition is associated with a non-singular Morse–Smale flow on 3-manifolds prime to S ²× S ¹. This decomposition has been built only for the 3-sphere S ³. In this paper we obtain the round-handle decomposition of non-singular Morse–Smale flows on S ²× S ¹, in order to get all the different fattened round handles in this manifold. Some of them include non-separating boundary components that induce the topology of the links of periodic orbits.     

Some General Remarks on Consulting in Statistics

This paper deals with obtaining a prediction interval on a future observation X, in an ordered sample of size n from a two-parameter exponential distribution for the situation where some or all the first r observations X ₁ < X ₂ < … < X _r , 1 ≤ r < s ≤ n, have been observed. The intervals are based on the statistic Z = (X _s , – X _r )/S _v , where S _v , is a function of the observations X ₀ ≡ A < X ₁ < X ₂ < … < X _r , such that X _s – X _r , and S _v , are independent variables and 2vS_v /σ has the distribution χ²(2v). The expressions for the quantiles z_p are given and some problems of numerical determination of z_p 's are discussed. The results can be also applied to related distributions.     

Aerodynamic quality management for the NACA 23012 airfoil model using the surface high-frequency discharge

The effect of the surface capacity HF discharge on airfoil flow-around has been studied in the situation when the oncoming flow velocity is 20 m/s and the Reynolds numbers are Re = 10⁵. The power delivered to discharge was modulated with a frequency of 3 × 10²–2 × 10⁴ Hz, which corresponds to a Strouhal number of St = 1.2–80, and the average electric power (W _av) was 50–400 W. It has been indicated that the aerodynamic drag decreased and the lift increased at stall and post-stall angles of attack when the HF dielectric barrier discharge was turned on. A nonstationary stochastic change in the C _x and C _y aerodynamic characteristics was observed at a stall angle in the St = 4–10 range of Strouhal numbers when the power was insufficient (W _av ≈ 100 W).     

Superplastic behaviour of as received superplastic forming grade IN718 superalloy

Abstract

Tensile specimens of superplastic forming grade IN718 superalloy, containing banded microstructure in the as received state, were deformed at high temperatures T to investigate the stress σ versus strain rate ? · behaviour, the nature of the stress versus strain ? curves, ductility, and microstructure upon failure. The log σ–log ? · plot for the ? · range ～5 × 10^-6–3 × 10^-2 s^-1 at T = 1173–1248 K exhibited a strain rate sensitivity index m = 0·62 at low strain rates and m = 0·26 at high strain rates, representing region II and III behaviour, respectively. The activation energies were estimated to be 308 and 353 kJ mol^-1, respectively. All the σ–? curves, obtained at ? · = 1 × 10^-4 s^-1 for the temperature range 1173–1273 K, and at T = 1198 K for the strain rate range 1 × 10^-4–1 × 10^-2 s^-1, exhibited initial flow hardening, followed by flow softening. The microstructures revealed dynamic recrystallisation, grain growth, cavitation, and a variation in the amount of second phase particles. Grain growth and cavitation were found to increase with temperature in region II. Excessive grain growth at 1273 K led to the elimination of region II. Grain growth and cavitation were both found to be less pronounced as the strain rate increased in region III.     

Frequency-dependent dielectric properties and electrical conductivity of CdIn<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

The real (ɛ) and imaginary (ɛ″) parts of complex dielectric permittivity and ac conductivity (σ_ac) of CdIn₂S₄ single crystals (cubic structure) have been measured in the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. The results demonstrate that the dielectric dispersion in the crystals has a relaxation nature. In the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz, the ac conductivity of single-crystal CdIn₂S₄ follows the relation σ_ac ∼ f ^0.8, characteristic of hopping conduction through localized states near the Fermi level.     

Special features of heavy metal ion reduction from liquid electrolytes

The ion exchange reduction of heavy metal ions from electrolytes has been studied by theoretical and experimental methods. It is established that high efficiency of the ion exchange is provided by metal ion diffusion through a thin subsurface layer of an ion exchanger with a thickness of [`(d)] = 1.6 ×10 ^{- 4}\bar \delta = 1.6 \times 10^{ - 4} under conditions of the optimum solution flow velocity U ₀, such that the time of ion penetration through the layer of water molecules adsorbed on the surface of pores in this layer is on the order of 10⁻² s. In this case, the effective diffusion coefficient of metal ions in the subsurface layer is 4.5 × 10⁻⁷ m²/s, which is more than two orders of magnitude higher than the value in solution.