Numerical and experimental study on the flow history effects of axial flow on the Couette–Taylor flow

In this research, experimental and numerical techniques are used to study the flow history effects of axial flow on the Couette–Taylor flow. For the experimental investigation, the flow is visualized using the PIV technique with reflective particles with a density of 1.62 g/cm³. Dispersed in a solution, the particles have a strong refraction index equal to 1.85. In this study, two protocols are adopted to study the effect of an axial flow superimposed on a Couette–Taylor flow, and of the history of the flow. The first one, the direct protocol, consists of imposing an azimuthal flow to the inner cylinder. In this case, when the regime is established, the axial flow is superimposed. The second protocol, the inverse protocol, consists of imposing first the axial flow in the gap of the system, after which an azimuthal flow is conveyed. The Couette–Taylor flow with axial flow is strongly dependent on the flow history (the protocol). Thus, the flow structures and development for different protocols are studied and analyzed here experimentally and numerically. In addition, from the numerical results, mathematical models for the two protocols are presented. For the direct protocol, a new relation between the axial Reynolds number, which stabilizes the Couette–Taylor flow, and the Taylor number is presented; for the inverse protocol, a new mathematical model for the critical Taylor number is developed as a function of the axial Reynolds number and also the first critical Taylor number without axial flow.     

Boundary layer flow of ideally-dissociated chemically “frozen” gas — Influence of Pr-number

Summary This investigations treats the ideally-dissociated gas boundary layer flow in the chemically frozen state. With that aim the universalisation of the appropriate mathematical model is performed in accordance with the Loitsianskii's definition. The obtained system of universal multiparametrical equations is integrated numerically with the biparametrical once-localised approximation at certain values of Pr-number. Based upon the graphically presented results, the conclusions about the Pr-number variation influence upon the development of dynamical and thermal boundary layer, are made.With 11 Figures     

Influence of an axial uniform magnetic field on the solid/liquid interface curvature and macrosegregation in directionally solidified the Al–0.85 wt.% Cu alloy

Effect of a uniform magnetic field on the solid/liquid interface curvature and macrosegregation in directionally solidified the Al–0.85 wt.% Cu alloy has been investigated. Results show that the interface curvature and macrosegregation increase to a maximum when B is about 0.1 T; and then decreases as B still increases. This is good agreement with the computed velocities of the thermoelectric magnetic convection. Above results reveal that the uniform magnetic field induces the new convection and further modifies the interface curvature and macrosegregation.     

Influence of Laser Coating on Microstructure and Properties of an Al-Si Alloy

The microstructure and wear resistance of acast Al-Si alloy coated with metal and rare earthelements and treated by the laser rapidmelt-solidification(LRMS)are studied in the pres-ent work.Optical and SEM micrographic analysesshowed that a superfine microstructure was ob-tained,and the hardness was remarkably enhancedby the LRMS treatment.Wear test showed that therapid melt-solidified microstructure had higherwear resistance than that treated by ordinary solidsolution treatment.     

Numerical simulation of flow behavior of liquid and particles in liquid–solid risers with multi scale interfacial drag method

Formation of particle clusters in liquid–solid circulating fluidized beds significantly affects macroscopic hydrodynamic behavior of the system. A multi scale interfacial drag coefficient (MSD) is proposed to determine effects of particle clusters on the mesoscale structure, by taking momentum and energy balance of dense phase, dilute phase and interphase into account. Based on the transportation and suspension energy-minimization method, the multi scale interfacial drag coefficient model used in this work is combined with the Euler–Euler two fluid model to simulate the heterogeneous behaviors of liquid–solid circulating fluidized bed. It was found that the reduction in drag coefficient is at least an important factor for the simulation of clusters formation, and the core-annulus flow is observed in the riser. The liquid–solid flow regime was significantly affected by the down-flow of particles in the form of clusters near the walls of the riser. The calculated concentration of particles inside the riser compared reasonably well with the available experimental data obtained by Razzak et al.     

Experimental and numerical investigation of effects of particle shape and size distribution on particles’ dispersion in a coaxial jet flow

In this study, an experimental and a numerical investigations are performed to investigate the effect of particle’s shape and size distribution on its dispersion behavior. Firstly, particle dispersion of pulverized coal and spherical polymer particles is observed by Particle Image Velocimetry (PIV) technique in the experiment. Secondly, a simulation is performed to analyze the particle dispersion in detail. Spherical and spheroidal motion models are applied to particle’s movement to investigate the shape effect. Furthermore, monodisperse and polydisperse for particles are applied to investigate the size distribution effect on the dispersion. Experimental results show that in the jet turbulence flow, pulverized coal particles, which have complex shapes and various sizes, have quite different dispersion behavior compared to spherical particles. In terms of the results of the simulation, this difference is mainly caused by the size distribution effect. Although particle’s shape affects the dispersity, it is weakened by the size distribution effect.     

Ultimate behaviour of FRP wrapped sections under axial force and bending: Influence of stress–strain confinement model

In the present work, the influence of the adopted confined concrete constitutive law, among those available in the technical literature, on the flexural strength and curvature ductility of reinforced concrete sections strengthened by FRP (fibre reinforced polymer) wrapping is investigated. An important issue to be underlined is that the stress–strain relationship of confined concrete depends not only on the number of layers and on the type of FRP used for wrapping, but also on the size and the shape of the section. By using the main constitutive laws proposed in the technical literature to model the confined concrete behaviour, the moment–curvature diagrams have been evaluated for a significant number of study cases by means of a specifically developed computer program based on a refined fibre model. The results show that even if the different constitutive laws exhibit large differences in the resulting stress–strain behaviour, they lead to negligible differences in terms of flexural resistance, but to very significant differences in terms of curvature ductility. Therefore, the accurate evaluation of the ultimate strain seems of paramount importance compared to the whole stress–strain curve. In addition, the influence of pre-existing loads acting on the structure at the time of the strengthening intervention has been investigated showing that it affects the knee region of the moment–curvature relationship, while the ultimate flexural resistance remains almost unaffected.     

The Influence of Electron–Phonon Coupling and Lattice Vibrations on the Rashba Coupling Induced Domain Wall Spin Current and Spin Torque

In the current work, a detailed calculation has been presented for spin-current and spin torque in a domain wall (DW). Specifically, we analyze both spin and momentum relaxation that are relevant to the spin-transport process. It was shown that the vibrational induced relaxations play important roles in the amount of the spin-current generated by the Rashba interaction.     

Influence of damage on ultrasonic velocity and strength—analysis and experiments

Measurements of ultrasonic velocity in creep damaged material are reviewed. The influence of damage on ultrasonic velocity is analysed and the relation between them is derived. It is shown that measurements of ultrasonic velocity can be used to predict the remaining life. Measurements of ultrasonic velocity in a damaged beam are presented along with measurements of the ultimate strength. A relation is found to exist, between reductions in ultrasonic velocity and ultimate strength, which might be used to assess the load carrying capacity of a structural element.     

Process flow industry—scheduling and control using theory of constraints

This paper discusses the applicability of the Theory of Constraints (TOC) in the process flow industry and compares TOC to the current practice. The Drum-Buffer-Rope methodology is altered to meet the needs of the process flow environment. Guidelines for the strategic location of and determination of the reduced WIP inventory levels are provided.     

Numerical study of solid–liquid two-phase flow and erosion in ball valves with different openings

In the coal chemical industry, petrochemical industry, and other industries, ball valve is a common and important valve due to its reliable structure. The conveying medium has particles that affect the valve surface under the drive of water flow, thereby making the ball valve face the risk of erosion and damage. In this study, the CFD-DEM method was adopted to study the influence of different openings and particle diameters on the two-phase flow and erosion characteristics inside the ball valve. The two-phase flow and particle distribution of the ball valve were analyzed, and the main erosion wall surfaces were determined. The erosion distribution of these walls was obtained. The variation rule of particle number with erosion rate was analyzed, which shows that particle number played a dominant role in erosion degree. Result also showed that in the case of small opening, the erosion decreased with the increase in particle diameter.     

Accurate wet-type centrifugal classification using an almost rigidly rotating flow — classification principle and performance of the batch-type classification

We have proposed a new system for an accurate wet-type centrifugal classification to which an almost rigidly rotating through-flow is applied. This flow can be produced within a highly rotating double-walled container, without any turbulent fluctuation. In the present paper, we have employed the batch-type classification with a cylinder-sphere-shaped container in classification experiments, theoretical and numerical flow analyses, and flow-visualization measurements. Consequently, we have obtained the following main conclusions: (i) with decreasing Ekman number (i.e. increasing rotation rate) at a constant Rossby number or with decreasing Rossby number (decreasing through-flow rate) at a constant Ekman number, the cut size and fine yield decrease and the classification accuracy increases, and (ii) for the occurrence of the rigid-rotation region which is indispensable to collect the coarse product, it is necessary to make the flow field inverse-C-shaped towards the rotation axis.     

Effects of tangential and radial velocity on fluid flow and heat transfer for flow through a pipe with twisted tape insert—laminar flow

The present study reports the numerical analysis of fluid flow and heat transfer in a pipe with full length twisted tape insert. The investigation is carried out for five different twist ratios of 4, 5, 6, 8 and 10 at 100 ≤ Re ≤ 1000. The velocity field in terms of streamwise, tangential and radial velocity and temperature field are studied as a function of Reynolds number and twist ratio. The variation of friction factor and Nusselt number with Reynolds number for different twist ratios is also presented. The heat transfer enhancement due to insertion of twisted tape mainly comes from the tangential and radial components of velocities, which are regarded as secondary fluid motion. It is evident from the results that with increase in Reynolds number the axial convection increases. However, with the decrease in the twist ratio, the tangential and radial convection increases, leading to increased heat transfer. The secondary flow affects the thermal boundary layer inside the tube and increases the cross-flow mixing, which increases the heat transfer. The correlations for prediction of friction factor and Nusselt number based on the numerical data are also proposed.     

Influence of austenitising temperature on austempering of an Mn-Mo-Cu alloyed ductile iron Part 1—Austempering kinetics and the processing window

X-ray diffraction, optical microscopy, and hardness measurements were used to determine the austempering kinetics of an alloyed ductile iron of composition (wt-%) Fe-3·49C-2·33Si-0·42Mn-0·25Cu-0·23Mo-0·035Mg at austempering temperatures of 300, 350, 375, and 400°C and austenitising temperatures of 870 and 920°C. The stage I reaction during austempering occurs in two steps, the first in the eutectic cell and the second in the intercellular area. Decreasing the austenitising temperature is shown to increase the driving force for the stage I reaction but to have a lesser effect on the stage II reaction. Decreasing the austenitising temperature produces a more uniform austempered microstructure and reduces the amount of martensite in this structure. These changes move the processing window to shorter austempering times and increase the temperature at which the processing window closes.

MST/3390     

Influence of Co addition on microstructure evolution and mechanical strength of solder joints bonded with solid–liquid electromigration

Journal of Materials Science: Materials in Electronics - The influence of solid–liquid electromigration on Cu-xCo/Sn-3.0Ag-0.5Cu/Cu-xCo (x?=?0, 30 and 50 wt.%) joints bonded at...     

Construction of algorithm for calculation of the flow rate of a gas–liquid mixture in a horizontal pipeline for the microprocessor of an information measurement system

Features of an algorithm for calculation of the flow rate of the liquid phase of a gas–liquid mixture with the use of a variable pressure-drop flow meter with constricting devices are considered. Corresponding dependences for use in calculating the concentration of liquid in a mixture and a correction factor based on the readings of the flow meter for use in determining the flow rate of a single-phase flow are obtained.     

Hydration of lime—marine sediment blends: Influence of mineralogical composition and lime content

There is a need to find alternatives to the extraction of non-renewable mineral resources for the production of new binders. Some specific building materials such as plant-aggregate-based concretes do not require high-strength binders. In this context, the lime-pozzolan technology, inherited from Roman times, can help reduce the carbon footprint of finished materials by the use of low amounts of lime. In this paper, three different marine dredged sediments were used as natural alumino-silicate resources and blended with hydrated lime. Based on previous literature dealing with the pozzolanic activity of cristallized minerals, the sediments were reduced to micronized powders. The hydration of these systems was investigated through hardening and reaction kinetics up to 365 days at 20 °C and 50 °C. The sediments used revealed two kinds of mineral assemblages and the best pozzolanic reactivity was found with quartz-rich sediments. In addition, the optimum lime content was found to be 20 wt% until 180 days.     

Influence of the α/β-SiC phase transformation on microstructural development and mechanical properties of liquid phase sintered silicon carbide

The transformation kinetics and microstructural development of liquid phase sintered silicon carbide ceramics (LPS-SiC) are investigated. Complete densification is achieved by pressureless and gas pressure sintering in argon and nitrogen atmospheres with Y2O3 and AlN as sintering additives. Studies of the phase transformation from to -SiC reveals a dependency on the initial -content and the sintering atmosphere. The transformation rate decreases with an increasing -content in the starting powder and in presence of nitrogen. The transformation is completely supressed for pure -SiC starting powders when the additive system consists of 10.34 wt% Y2O3 and 2.95 wt% AlN. Materials without phase transformation showed a homogeneous microstructure with equiaxed grains, whereas microstructures with elongated grains were developed from SiC powders with a high initial /-ratio (>1:9) when phase transformation occurs. Since liquid phase sintered silicon carbide reveals predominantly an intergranular fracture mode, the grain size and shape has a significant influence on the mechanical properties. The toughness of materials with platelet-like grains is about twice as high as for materials with equiaxed grains. Materials exhibiting elongated microstructures show also a higher bending strength after post-HIPing.     

Influence of crystal—melt interface shape on self-seeding and single crystalline quality

The growth of Sb-based crystals (InSb, GaSb etc) was undertaken using resistive heater furnace by vertical directional solidification (VDS) technique. Crystal—melt interface shape during the growth was shown to convert from concave to convex along the crystal axis of the ingots. Many antimonide (Sb) crystals of 8 mm to 18 mm diameter were grown by optimized growth parameters. The forced convection and absence of conducting support to ampoule showed improvement in crystal quality of as grown ingots. Crystals showed preferred orientation and self-seeding. Results on interface shape and crystallinity of ingots were found to be in good agreement with the experiments.