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1 – 10 of over 8000Shalini Saha, Amares Chattopadhyay and Abhishek Kumar Singh
The purpose of this paper is to develop a numerical (finite-difference) model exploring phase and group velocities of SH-wave propagation in initially stressed transversely…
Abstract
Purpose
The purpose of this paper is to develop a numerical (finite-difference) model exploring phase and group velocities of SH-wave propagation in initially stressed transversely isotropic poroelastic multi-layered composite structures and initially stressed viscoelastic-dry-sandy multi-layered composite structures in two distinct cases.
Design/methodology/approach
With the aid of relevant constitutive relations, the non-vanishing equations of motions for the propagation SH-wave in the considered composite structures have been derived. Haskell matrix method and finite-difference scheme are adopted to deduce velocity equation for both the cases. Stability analysis for the adopted finite-difference scheme has been carried out and the expressions for phase as well as group velocity in terms of dispersion-parameter and stability-ratio have been deduced.
Findings
Velocity equations are derived for the propagation of SH-wave in both the composite structures. The obtained results are matched with the classical results for the case of double and triple-layered composite structure along with comparative analysis. Stability analysis have been carried out to develop expressions of phase as well as group velocity in terms of dispersion-parameter and stability-ratio. The effect of wavenumber, dispersion parameter along with initial-stress, porosity, sandiness, viscoelasticity, stability ratio, associated with the said composite structures on phase, damped and group velocities of SH-wave has been unveiled.
Originality/value
To the best of authors’ knowledge, numerical modelling and analysis of propagation characteristics of SH-wave in multi-layered initially stressed composite structures composed of transversely isotropic poroelastic materials and viscoelastic-dry-sandy materials remain unattempted inspite of its importance and relevance in many branches of science and engineering.
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Korti Mohammed Choukri, Korti Abdel Illah Nabil and Abboudi Said
High-pressure die casting is one of the manufacturing techniques used for the rational mass production of metal parts. Due to the high velocity of the molten metal during the…
Abstract
Purpose
High-pressure die casting is one of the manufacturing techniques used for the rational mass production of metal parts. Due to the high velocity of the molten metal during the injection phase, the die casting of aluminum is so complex and it is almost impossible to calculate these exact performances. Numerical simulation is an effective way to optimize the injection phase and minimize air entrapment that causes porosity defects in the metal. Generally, the filling phase of the molten metal in the shot sleeve is neglected in most scientific work. This phase is followed by a rest period to allow the escape of the resident air bubbles (gravity effect). The paper aims to discuss these issue.
Design/methodology/approach
It is relatively clear that the model described poses a great challenge for numerical implementation, especially for 3D geometries. The governing transport equations are solved numerically using the commercial CFD solver Fluent and the equations are discretized using a pressure-based finite volume method. The coupling pressure–velocity was solved by the PISO algorithm. The PISO algorithm takes relatively more CPU time per solver iteration, but it significantly decreases the number of iterations required for the convergence of the transient flow problems. Laminar flow inside air and molten metal was assumed. In order to describe the behavior of the molten metal, a VOF model has been activated. The model makes it possible to account for the moving boundary due to the variation of the shot sleeve volume caused by the plunger displacement. The scheme used in the discretization of momentum equation was the first-order upwind scheme, and the scheme used for the pressure was the PRESTO. The profile of the plunger velocity, boundary conditions change with time and the physical properties change with liquid fraction were used by implementation of a user-defined function. For the discretization of the domain, an unstructured mesh with triangular elements is used. After conducting mesh sensitivity study, a mesh having 53,813 triangular elements has been chosen for the present study. The convergence criterion was set equal to 10–4 for all parameters.
Findings
The results show that the rest and global filling times increase by 2.5 and 8.57 percent with decreasing the pouring velocity by 10 percent. In addition, the rest and global filling times decrease by 5.77 and 8.12 percent with increasing the pouring velocity by 10 percent.
Originality/value
After the filling phase, it is necessary to offer a rest period before the injection phase. However, the rest and global filling times increase by 2.5 and 8.57 percent with decreasing the pouring velocity by 10 percent. In addition, the rest and global filling times decrease by 5.77 and 8.12 percent with increasing the pouring velocity by 10 percent. Increasing the pouring velocity by 10 percent leads increasing of the molten metal velocity in the shot sleeve and requires a delay of time of the beginning of the faster plunger movement by 7–10.5 percent. On the other hand, Figure 12 shows that increasing the pouring velocity requires increasing of the plunger velocity during the injection phase, thus increasing the pouring velocity. In order to overcome this problem, it is necessary to reduce the injection velocity and prolong the period of the slower plunger movement.
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J.D. Lavers, G.R. Tallbäck and L.S. Beitelman
To use an experimentally calibrated turbulent flow model to determine whether two‐ and three‐phase electromagnetic stirrers provide equivalent stirring when continuously casting…
Abstract
Purpose
To use an experimentally calibrated turbulent flow model to determine whether two‐ and three‐phase electromagnetic stirrers provide equivalent stirring when continuously casting steel billets and blooms.
Design/methodology/approach
The results obtained in this paper were obtained by using a 3D quasistatic electromagnetic model to obtain the Lorentz forces that act on the liquid steel. A computationally efficient method was used to account for the effect of the conducting fluid motion on the forces. A 3D turbulent flow model that incorporated Reynolds stresses and high order upwinding was used to predict the fluid flow. The model has been calibrated using the experimental data.
Findings
The paper shows that for square and rectangular cross section casting moulds, having inside dimensions of 140 × 140 mm and 140 × 196 mm, respectively, a two‐phase electromagnetic stirrer consistently produces stirring velocities that are 12‐15 percent below those produced by an equivalent three‐phase design.
Research limitations/implications
The impact on the fluid entering the casting mould through the submerged nozzle has been neglected. The model should be further developed to consider this important factor.
Practical implications
A two‐phase stirrer is much more compact than the equivalent three‐phase design, and since space is at a premium in the vicinity of the casting mould, being able to use a compact design is desirable. The two‐phase design was long believed to produce inferior stirring due to the negative impact of electromagnetic space harmonics. This paper shows that for the range of mould dimensions considered in the paper, there is a good trade‐off between the compact two‐phase design and the slightly lower stirring velocities that result.
Originality/value
The paper presents the first quantitative comparison between two‐ and three‐phase electromagnetic stirrers that illustrates, in a practical sense, the stirring effectiveness of each approach. The paper will be of value to users of this equipment.
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Sam Ban, William Pao and Mohammad Shakir Nasif
The purpose of this paper is to investigate oil-gas slug formation in horizontal straight pipe and its associated pressure gradient, slug liquid holdup and slug frequency.
Abstract
Purpose
The purpose of this paper is to investigate oil-gas slug formation in horizontal straight pipe and its associated pressure gradient, slug liquid holdup and slug frequency.
Design/methodology/approach
The abrupt change in gas/liquid velocities, which causes transition of flow patterns, was analyzed using incompressible volume of fluid method to capture the dynamic gas-liquid interface. The validity of present model and its methodology was validated using Baker’s flow regime chart for 3.15 inches diameter horizontal pipe and with existing experimental data to ensure its correctness.
Findings
The present paper proposes simplified correlations for liquid holdup and slug frequency by comparison with numerous existing models. The paper also identified correlations that can be used in operational oil and gas industry and several outlier models that may not be applicable.
Research limitations/implications
The correlation may be limited to the range of material properties used in this paper.
Practical implications
Numerically derived liquid holdup and holdup frequency agreed reasonably with the experimentally derived correlations.
Social implications
The models could be used to design pipeline and piping systems for oil and gas production.
Originality/value
The paper simulated all the seven flow regimes with superior results compared to existing methodology. New correlations derived numerically are compared to published experimental correlations to understand the difference between models.
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In engineering applications, gas-solid two-phase reaction flow with multi-moving boundaries is a common phenomenon. The launch process of multiple projectiles is a typical…
Abstract
Purpose
In engineering applications, gas-solid two-phase reaction flow with multi-moving boundaries is a common phenomenon. The launch process of multiple projectiles is a typical example. The flow of adjacent powder chambers is coupled by projectile’s motion. The purpose of this paper is to study this flow by numerical simulation.
Design/methodology/approach
A one-dimensional two-phase reaction flow model and MacCormack difference scheme are implemented in a computational code, and the code is used to simulate the launch process of a system of multiple projectiles. For different launching rates and loading conditions, the simulated results of the launch process of three projectiles are obtained and discussed.
Findings
At low launching rates, projectiles fired earlier in the series have little effect on the launch processes of projectiles fired later. However, at higher launching rates, the projectiles fired first have a great influence on the launch processes of projectiles fired later. As the launching rate increases, the maximum breech pressure for the later projectiles increases. Although the muzzle velocities increase initially, they reach a maximum at some launching rate, and then decrease rapidly. The muzzle velocities and maximum breech pressures of the three projectiles have an approximate linear relationship with the charge weight, propellant web size and chamber volume.
Originality/value
This paper presents a prediction tool to understand the physical phenomenon of the gas-solid two-phase reaction flow with multi-moving boundaries, and can be used as a research tool for future interior ballistics studies of launch system of multiple projectiles.
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This work focuses on the laminar flow of a two‐phase particulate suspension induced by a suddenly accelerated infinite vertical permeable surface in the presence of fluid…
Abstract
This work focuses on the laminar flow of a two‐phase particulate suspension induced by a suddenly accelerated infinite vertical permeable surface in the presence of fluid buoyancy, magnetic field, heat generation or absorption, and surface suction or blowing effects. The governing equations for this modified Stokes problem are developed based on the continuum representation of both the fluid and the particle cloud. Appropriate dimensionless variables are introduced. The resulting dimensionless equations are solved numerically by an accurate implicit finite‐difference method for two situations. The first case corresponds to an impulsive start of the surface from rest while the second case corresponds to a uniformly accelerated surface. The numerical results for these cases are illustrated graphically. Comparisons with previously published work are performed and the results are found to be in good agreement. Typical fluid‐ and particle‐phase velocity and temperature distributions as well as wall shear stress and heat transfer results are reported for various values of the particle loading, Hartmann number, wall mass transfer coefficient and the heat generation or absorption coefficient.
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Faheem Ejaz, William Pao and Hafiz Muhammad Ali
In plethora of petroleum, chemical and heat transfer applications, T-junction is often used to partially separate gas from other fluids, to reduce work burden on other separating…
Abstract
Purpose
In plethora of petroleum, chemical and heat transfer applications, T-junction is often used to partially separate gas from other fluids, to reduce work burden on other separating equipment. The abundance of liquid carryovers from the T-junction side arm is the cause of production downtime in terms of frequent tripping of downstream equipment train. Literature review revealed that regular and reduced T-junctions either have high peak liquid carryovers (PLCs) or the liquid appears early in the side arm [liquid carryover threshold (LCT)]. The purpose of this study is to harvest the useful features of regular and reduced T-junction and analyze diverging T-junction having upstream and downstream pipes.
Design/methodology/approach
Volume of fluid as a multiphase model, available in ANSYS Fluent, was used to simulate air–water slug flow in five diverging T-junctions for eight distinct velocity ratios. PLCs and LCT were chosen as key performance indices.
Findings
The results indicated that T (0.5–1) and (0.8–1) performed better as low liquid carryovers and high LCT were achieved having separation efficiencies of 96% and 94.5%, respectively. These two diverging T-junctions had significantly lower PLCs and high LCT when compared to other three T-junctions. Results showed that the sudden reduction in the side arm diameter results in high liquid carryovers and lower LCT. Low water and air superficial velocities tend to have low PLC and high LCT.
Research limitations/implications
This study involved working fluids air and water but applies to other types of fluids as well.
Practical implications
The novel T-junction design introduced in this study has significantly higher LCT and lower PLC. This is an indication of higher phase separation performance as compared to other types of T-junctions. Because of lower liquid take-offs, there will be less frequent downstream equipment tripping resulting in lower maintenance costs. Empirical correlations presented in this study can predict fraction of gas and liquid in the side arm without having to repeat the experiment.
Social implications
Maintenance costs and production downtime can be significantly reduced with the implication of diverging T-junction design.
Originality/value
The presented study revealed that the diameter ratio has a significant impact on PLC and LCT. It can be concluded that novel T-junction designs, T2 and T3, achieved high phase separation; therefore, it is favorable to use in the industry. Furthermore, a few limitations in terms of diameter ratio are also discussed in detail.
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Prodyut Chakraborty and Pradip Dutta
The purpose of this paper is to present a new numerical approach for modeling the multi‐phase flow during an alloy solidification process. In many solidification processes…
Abstract
Purpose
The purpose of this paper is to present a new numerical approach for modeling the multi‐phase flow during an alloy solidification process. In many solidification processes, advection of solid may have a dramatic effect on bulk convection field as well as on the solid front growth and hence on the macro‐segregation pattern. In the present work, a numerical model is developed to simulate directional solidification in presence of melt convection as well as solid advection in the form of sedimentation. A 2D cavity filled with hyper‐eutectic aqueous ammonium chloride solution (25 wt.% of ammonium chloride) being chilled from one of the side walls has been chosen as the model problem for the numerical simulation.
Design/methodology/approach
A fixed grid volume averaging technique has been used for solving mass, momentum, energy, and species equation while taking into account the solid phase advection and local re‐melting. Two different criteria have been identified for the solid particles in the mushy zone to be mobile. These two criteria are represented by a critical solid fraction, and a critical velocity. Based on these two criteria, the mushy zone has been subdivided into two different regions namely, an immobile coherent zone consisting of packed equiaxed crystals and a mobile non‐coherent zone where the solid crystals are able to move.
Findings
The numerical results are compared with corresponding experimental observations.
Originality/value
The solid advection velocity and source terms dealing with solid velocity have been calculated using an explicit scheme, whereas the main conservation equations are solved using an implicit scheme.
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Manmatha K. Roul and Sukanta K. Dash
The purpose of this paper is to compute the pressure drop through sudden expansions and contractions for two‐phase flow of oil/water emulsions.
Abstract
Purpose
The purpose of this paper is to compute the pressure drop through sudden expansions and contractions for two‐phase flow of oil/water emulsions.
Design/methodology/approach
Two‐phase computational fluid dynamics (CFD) calculations, using Eulerian–Eulerian model, are employed to calculate the velocity profiles and pressure drops across sudden expansions and contractions. The pressure losses are determined by extrapolating the computed pressure profiles upstream and downstream of the expansion/contraction. The oil concentration is varied over a wide range of 0‐97.3 percent by volume. The flow field is assumed to be axisymmetric and solved in two dimensions. The two‐dimensional equations of mass, momentum, volume fraction and turbulent quantities along with the boundary conditions have been integrated over a control volume and the subsequent equations have been discretized over the control volume using a finite volume technique to yield algebraic equations which are solved in an iterative manner for each time step. The realizable per phase k‐ ε turbulent model is considered to update the fluid viscosity with iterations and capture the individual turbulence in both the phases.
Findings
The contraction and expansion loss coefficients are obtained from the pressure loss and velocity data for different concentrations of oil–water emulsions. The loss coefficients for the emulsions are found to be independent of the concentration and type of emulsions. The numerical results are validated against experimental data from the literature and are found to be in good agreement.
Research limitations/implications
The present computation could not use the surface tension forces and the energy equation due to huge computing time requirement.
Practical implications
The present computation could compute realistically the two‐phase pressure drop through sudden expansions and contractions by using a two‐phase Eulerian model and hence this model can be effectively used for industrial applications where two‐phase flow comes into picture.
Originality/value
The original contribution of the paper is in the use of the state‐of‐the‐art Eulerian two‐phase flow model to predict the velocity profile and pressure drop through industrial piping systems.
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Z.B. Xing, Xingchao Han, Hanbing Ke, Q.G. Zhang, Zhiping Zhang, Huijin Xu and Fuqiang Wang
A combination of highly conductive porous media and nanofluids is an efficient way for improving thermal performance of relevant applications. For precisely predicting the flow…
Abstract
Purpose
A combination of highly conductive porous media and nanofluids is an efficient way for improving thermal performance of relevant applications. For precisely predicting the flow and thermal transport of nanofluids in porous media, the purpose of this paper is to explore the inter-phase coupling numerical methods.
Design/methodology/approach
Based on the lattice Boltzmann (LB) method, this study combines the convective flow, non-equilibrium thermal transport and phase interactions of nanofluids in porous matrix and proposes a new multi-phase LB model. The micro-scale momentum and heat interactions are especially analyzed for nanoparticles, base fluid and solid matrix. A set of three-phase LB equations for the flow/thermal coupling of base fluid, nanoparticles and solid matrix is established.
Findings
Distributions of nanoparticles, velocities for nanoparticles and the base fluid, temperatures for three phases and interaction forces are analyzed in detail. Influences of parameters on the nanofluid convection in the porous matrix are examined. Thermal resistance of nanofluid convective transport in porous structures are comprehensively discussed with the models of multi-phases. Results show that the Rayleigh number and the Darcy number have significant influences on the convective characteristics. The result with the three-phase model is mildly larger than that with the local thermal non-equilibrium model.
Originality/value
This paper first creates the multi-phase theoretical model for the complex coupling process of nanofluids in porous structures, which is useful for researchers and technicians in fields of thermal science and computational fluid dynamics.
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