Increase In Solid Volume Fraction Research Articles

CFD-DEM numerical investigation of the effects of water content and inclination angle on interactions between debris flows and slit dam

Debris flows, composed of sediment–water mixtures, can pose significant risks to downstream populations and infrastructure in mountainous regions. Slit dams have been demonstrated as being effective measures for decreasing the destructivity of debris flows. Reliable evaluations of the interactions between debris flows and slit dams are challenging if the complicated component characteristics of debris flows, such as the water content, are not considered. Here, a multi-scale study of debris flows impacting a slit dam is conducted via computational fluid dynamics and discrete element method (CFD-DEM) simulations to understand the influences of the water content (controlled by solid volume fraction in this study) and the channel inclination angle on flow–slit dam interactions. The results indicate that both the initial solid volume fraction and the channel inclination angle have significant effects on the impact kinematics of flow–slit dam interactions and regulation functions of the slit dam: (i) For gentle slopes, the deposition of debris flows is primarily influenced by flume basal friction, and the normalized peak total impact forces have little difference for a given inclination angle, whereas for steep slopes, an overtopping can occur, further result in the increasing of the normalized peak total impact forces with the increase of solid volume fraction. (ii) The run-up height and retention efficiency are also analyzed to provide a scientific reference for optimizing the design of slit dams.

Computational analysis of entropy generation minimization and heat transfer enhancement in magnetohydrodynamic oscillatory flow of ferrofluids

Improvements in heat transfer rate and entropy generation minimisation are critical issues in many engineering and industrial applications where efficient heat transfer is essential to achieve optimal performance and lower energy consumption. This study investigates the entropy generation of the mixed convection flow of ferrofluids in the presence of viscous and Joule dissipation. The flow is oscillatory and induced by the sinusoidal oscillations of a flat plate in its plane. Two Newtonian fluids, namely, kerosene oil C12H26C15H32 and methanol CH3OH are considered base fluids containing magnetite Fe3O4 nanoparticles. Governing equations are first modelled by employing the fundamental laws of transport phenomena. Then, using scaling analysis, these equations are transformed into a dimensionless system of partial differential equations. Numerical simulations are performed using the Gear-Generalized Differential Quadrature Method (GGDQM), and the model is validated with special cases from the literature. It has been found through numerical analysis that the convergence of GGDQM can be guaranteed by using only a small number of grid points. The thermal boundary layer of methanol-based nanofluid is thicker than that of kerosene. It has been observed that the skin friction coefficient increases for both categories of nanofluids as the values of the Eckert number, solid volume fraction, and Grashof number increase. The Nusselt number increases as the solid volume fraction increases, while the opposite trend is observed when the values of the Hartman, Eckert, and Grashof numbers rise. With increasing values of the Grashof number, the rise in the velocity of methanol-based nanofluids is higher than that of kerosene oil-based nanofluids. The maximum percentage difference between the velocities is identified to be 22.2177% at Gr=4.0. The temperature of methanol-based nanofluids rises more quickly than that of kerosene oil-based nanofluids with increasing values of the Grashof number. It is determined that the largest percentage difference between the temperatures is 20.5968% at Gr=4.0. When Ec=0, the percentage difference between velocities is 29. 1721 %, while the percentage difference between temperatures is 78.7155%. Compared to methanol-based ferrofluid, the volumetric entropy production is more extensive in kerosene-based ferrofluid. On the other hand, in comparison to a kerosene-based nanofluid, thermal irreversibility predominates in a methanol-based nanofluid. The novelty of this study lies in the computational treatment of coupled partial differential equations (momentum and energy) that incorporate buoyancy force, Joule heating and viscous dissipation effects, complementing the underlying physics and mathematical modelling of the research problem.

Shear thickening of cementitious suspensions: effect of high-volume fraction and hydration

The lubrication layer (LL) formed at the concrete–pipe interface plays a crucial role in facilitating concrete pumping. Shear thickening in this layer significantly affects concrete pumping. However, very few studies are available for understanding the onset and intensity of shear thickening of the LL. In this study, the effect of solid volume fraction (SVF), superplasticiser dosage, supplementary cementitious materials and hydration on the shear thickening (continuous and discontinuous) behaviour of cementitious suspensions were investigated. Results show that an increase in SVF reduces the shear thickening intensity for systems using ordinary Portland cement (OPC), whereas the intensity is amplified for systems with fly ash (FA) or ground granulated blast furnace slag (GGBS). An increase in superplasticiser dosage results in an early onset of shear thickening and increases the shear thickening intensity, regardless of the binder used. Systems including GGBS exhibit the highest shear thickening intensity, followed by OPC- and FA-based systems. Based on these results, it is evident that the superplasticiser dosage for OPC-based systems needs to be optimised based on the structural buildup, while, for FA- or GGBS-based systems, the superplasticiser dosage needs to be optimised based on shear thickening behaviour with respect to hydration.

Study on flow and heat transfer characteristics of salt solution ice slurry

As a phase change material, ice slurry allows the storage of thermal energy in the form of latent heat. This has great advantages in terms of reducing energy consumption and environmental protection, and is being widely used. In this study, based on the Eulerian-Eulerian CFD model and the Population Balance Model (PBM), the flow and heat transfer characteristic of salt solution ice slurry was simulation studied, which included the pressure drop, friction coefficient, volume fraction, distribution of ice crystals and local heat transfer coefficient during the flow and solidification of salt solution ice slurry in different conditions. And the experimental system is set up to verify the results of the model and analyze the variation rules of these parameters. The results showed that in salt solutions with different concentrations, when the flow rate and solid phase volume fraction increase, the pressure drop and local heat transfer coefficient of the ice slurry will increase. The surface heat transfer coefficient reached to 2.5 × 103 W m-2 K-1, 2.9 × 103 W m-2 K-1, and 3.2 × 103 W m-2 K-1 when ice crystal volume fraction was 5 %, 10 %, and 15 %, respectively. The study will contribute to understanding of the changes in basic characteristics of salt solution slurry during the flow and phase transition processes.

Strategies to improve the thermal performance of solar collectors

Abstract The paper evaluates a passive method for heat transfer improvement in heat exchangers, which implies the use of nanofluids. All calculations were carried out with a constant volumetric flow rate. The study examines three fluids with 0–4 % volume concentrations of CuO, MgO, and Al2O3 particles. The results indicate an increase in the heat transfer coefficient with increasing temperature. An Al2O3 nanofluid (4 % concentration) contributed to the best thermal performance. The incorporation of a 4 % content of MgO yielded an augmentation in heat transfer ranging from 15 % to 22 %, whereas an analogous concentration of CuO led to a more substantial enhancement of 25 %. Notably, the introduction of nanoparticles of Al2O3 produces a remarkable augmentation in heat transfer performance, with potential improvements of up to 36 %. The Nusselt number increases with increasing particle volume fraction and Reynolds number, according to results obtained for several nanoparticles (Al2O3, CuO, SiO2, and ZnO) with volume percentages in the range of 1–4 % and nanoparticle diameters of 25–70 nm. For all nanofluids, the time-averaged Nusselt number rises with a solid phase volume fraction increase of less than 5 %.

Strategies to improve the thermal performance of solar collectors

Abstract The paper evaluates a passive method for heat transfer improvement in heat exchangers, which implies the use of nanofluids. All calculations were carried out with a constant volumetric flow rate. The study examines three fluids with 0–4 % volume concentrations of CuO, MgO, and Al2O3 particles. The results indicate an increase in the heat transfer coefficient with increasing temperature. An Al2O3 nanofluid (4 % concentration) contributed to the best thermal performance. The incorporation of a 4 % content of MgO yielded an augmentation in heat transfer ranging from 15 % to 22 %, whereas an analogous concentration of CuO led to a more substantial enhancement of 25 %. Notably, the introduction of nanoparticles of Al2O3 produces a remarkable augmentation in heat transfer performance, with potential improvements of up to 36 %. The Nusselt number increases with increasing particle volume fraction and Reynolds number, according to results obtained for several nanoparticles (Al2O3, CuO, SiO2, and ZnO) with volume percentages in the range of 1–4 % and nanoparticle diameters of 25–70 nm. For all nanofluids, the time-averaged Nusselt number rises with a solid phase volume fraction increase of less than 5 %.

Effects of Brownian Motions and Fractal Structure of Nanoparticles on Natural Convection

The study simulated heat transfer in alumina-water nanofluid in a natural convection flow and Rayleigh-Benard configuration considering the Brownian motions and fractal structure of the nanofluids. The simulations were based on a two-dimensional, Eulerian-Eulerian method. Many simulations have been performed to examine the effect of aspect ratio, heat flux, and para-meters related to the structure of the nanoclusters including size, fractal dimension, and volume fraction on the natural convective heat transfer coefficient. The comparison between the simulation results and the experimental data of heat transfer coefficient indicates a good agreement. The simulation results indicated that the enhancement of aspect ratio, heat flux, and fractal dimension increases the heat transfer coefficient. On the other hand, the reduction of nanoclusters and nanoparticle size decreased this coefficient. Moreover, the simulation results showed that in high heat transfer fluxes, the heat transfer coefficient first increases by increasing the nanoparticles solid volume fraction and then decreases. However, heat transfer coefficient decreased steadily with the increase in the nanoparticles solid volume fraction in low heat transfer fluxes. The results suggested that using the nanoparticles Brownian motion mechanism along with their fractal structure can be well-applied in natural-convection heat transfer modelling of nanofluids.

Assessment of flow and heat transfer of triply periodic minimal surface based heat exchangers

An efficient intermediate heat exchanger is crucial for ensuring the safe operation, lifespan and energy efficiency of the advanced nuclear systems. Benefiting from the development of additive manufacturing technology, it is possible to design and optimize heat exchangers by introducing triply periodic minimal surface (TPMS) structures. With the excellent mechanical and thermal performance of TPMS, further improvements in the energy efficiency of advanced nuclear systems are achievable. In this study, I-WP surface, Primitive surface based heat exchangers and a printed circuit heat exchanger for accelerator driven subcritical systems are constructed in three dimensions. In order to obtain the potential enhancement of thermal performance of TPMS-based heat exchangers, the fluid flow and conjugate heat transfer characteristics in TPMS heat exchangers, especially for the specific working medium of lead-bismuth eutectic (LBE) are investigated. A parametric analysis is conducted on the key design variables including the solid volume fraction and hydraulic diameter. The results indicate that TPMS-based heat exchangers could achieve about 2–3 times the total heat transfer rate with half the volume of a printed circuit heat exchanger. The TPMS topologies contribute greater heat transfer enhancement on the Helium side than the LBE side, which helps to optimize the thermal resistance allocation in Helium-LBE heat exchangers. An increase of solid volume fraction enhances the convective heat transfer of Helium in I-WP heat exchanger, while homogenizing the local thermal performance. This study provides a database for the design and optimization of TPMS-based heat exchangers, which contributes to the sustainable future target.

Inertial migration of rigid red blood cell particles in Poiseuille flow

Inertial migration of single and multiple red blood cell (RBC) particles in a tube Poiseuille flow is studied using the lattice Boltzmann method coupled with the Galilean invariant momentum exchange method. Different blockage ratios, Reynolds numbers, and solid volume fractions are considered. In the single particle case, the RBC particle migrating in tumbling and rolling modes is called the tumbling particle and rolling particle, respectively. Simulation results show that the tumbling particle has a higher equilibrium position and longer rotation period than the rolling particle. For both the tumbling and rolling particles, when the blockage ratio increases, the equilibrium position moves closer to the tube centerline, and the rotation period becomes longer. The higher Reynolds number strongly affects the angular velocity of the RBC particle, leading the RBC particle to rotate faster; however, the equilibrium position is insensitive to the Reynolds number based on the limited observation. In the multiparticle case, the second and third inner particle annuluses unexpectedly form inside the Segré–Silberberg annulus as the solid volume fraction increases. Furthermore, smaller particles form the perfect Segré–Silberberg annulus at a lower solid volume fraction than larger particles. The third inner annulus of smaller particles is located further from the tube centerline than that of larger particles. This work is beneficial for understanding the motion of RBC particles in Poiseuille flow. It can positively contribute to the design of microfluidic devices for focusing, separating, and transporting red blood cells.

Visualization and investigation of healing mechanism in carbon fiber reinforced Elium® composites

In this study, carbon fiber/Elium® composites are manufactured using the resin infusion manufacturing technique. Artificial cracks representing impact-induced delamination are incorporated during layup. The laminates are subsequently healed using several healing parameters. The bonding mechanisms are investigated through microscopic analyses and X-ray Computed Tomography (XCT). The mechanical performance of the healed composites is investigated through four-point bending tests. It is found that as the healing temperature is increased, the cracks are gradually healed by interdiffusion and macroscopic resin flow across each crack interface. The 3D models generated from XCT images show an increase in solid volume fraction from 48% to 70% at the optimum healing parameters. The flexural strength and flexural modulus of the undamaged composites subjected to optimized healing condition are significantly increased relative to the room temperature cured pristine samples. The residual flexural strength of the damaged samples healed at the optimum parameters is 96% of the reference condition. The SEM images confirm that delamination from the previously-healed crack interfaces is the most dominant failure mode in the healed samples, in contrast to fiber fracture and brittle failure in the undamaged reference composite samples. The results show that the damaged composite laminates can be effectively healed and repaired to as good as undamaged laminates using the interdiffusion mechanism.

Electrochemical modeling, Li plating onsets and performance analysis of thick graphite electrodes considering the solid electrolyte interface formed from the first cycle

Based on a crack dominated solid electrolyte interface (SEI) resistance, an electrochemical model considering the SEI formed from the first cycle is established to investigate the comprehensive influence of electrode thickness, solid volume fraction and C-rate on the performance of thick graphite electrodes. Reasonable agreement is obtained for the simulated and measured charge and discharge profiles of Li/graphite cells including the first cycle. The periodic evolution of SEI film resistance during the cycles can be well interpreted by the mechanism based on the growth of SEI crack. The potential drop over SEI is found to contribute little to the polarization during Li inter- and deintercalation, and the electrode porosity reduction caused by SEI growth has larger effect for thick electrode than traditional thin electrode. The cell voltages, total potential drop of the electrode, state of charge and ratio of SEI capacity to the total capacity at the onsets of Li plating are analyzed. A linear relationship is developed for the Li plating onset voltages with the increasing of electrode thicknesses, solid volume fractions and C-rates. Finally, the performance of Li/graphite cells with electrode thicknesses (δ) ranging from 100 μm to 500 μm, solid volume fractions (εs) ranging from 0.35 to 0.6 and C-rates ranging from 0.05C to 0.5C is simulated and compared. The ionic migration limitation is aggravated by the growth of SEI for electrodes thicker than 300 μm as the solid volume fraction increases. The maximal areal capacity appears around δ = 500 μm and εs = 0.4, with a rate performance of 13.8 mAh cm−2, 13.6 mAh cm−2 and 13.1 mAh cm−2 at 0.1C, 0.2C and 0.5C, respectively.

Modified Buongiorno’s model for biomagnetic hybrid nanoliquid past a permeable moving thin needle

PurposeThe purpose of this paper is to study the steady biomagnetic hybrid nanofluid (HNF) of oxytactic microorganisms taking place over a thin needle with a magnetic field using the modified Buongiorno’s nanoliquid model.Design/methodology/approachOn applying the appropriate similarity transformations, the governing partial differential equations were transformed into a set of ordinary differential equations. These equations have been then solved numerically using Runge–Kutta–Fehlberg method of fourth–fifth order programming in MAPLE software. Features of the velocity profiles, temperature distribution, reduced skin friction coefficient, reduced Nusselt number and microorganisms’ flux, for different values of the governing parameters were analyzed and discussed.FindingsIt was observed that as the needle thickness and solid volume fraction increase, the temperature rises, but the velocity field decreases. For a higher Peclet number, the motile microorganism curve increases, and for a higher Schmidt number, the concentration curve rises.Originality/valueOn applying the modified Buongiorno’s model, the present results are original and new for the study of HNF flow and heat transfer past a permeable thin needle.

Criticality of microstructural evolution at an early age on the buildability of an accelerated 3D printable concrete

The buildability of a 3D printed concrete structure is influenced by the layer compression during printing, which in turn is governed by the rheological and early age mechanical properties of the mix. The study aims at understanding the effect of alkali-free aluminium sulphate-based accelerator on the microstructural evolution, which affects the macrostructural behaviour governing buildability of the structure. The effect of accelerator on hydration, phase composition, location and arrangement of ettringite, and porosity evolution of two paste systems with and without viscosity modifying admixture and superplasticizer is observed at initial hours. Further, fresh properties, yield stress evolution, and mechanical strength at early and later ages of the printable mix is evaluated. The squeeze flow test, which simulates the physical process of printing, is performed to understand the rheological characteristics of the mix under compressive loading in the initial hours. It is concluded that the precipitation of ettringite in large quantities at the initial hours controls the rheological and mechanical behaviour of the mix. The total ettringite formed increases for accelerated paste system at 30 min compared to the paste without accelerator. The ettringite is located at surfaces of clinker and interstitial spaces, with the crystals interlocked physically with each other. The squeeze flow test further suggests that the flow hardening increases tremendously on increasing the accelerator dosage due to an increase in solid volume fraction of ettringite and the resultant physical interlocking. Finally, a theoretical model is proposed considering the significance of ettringite interlocking and microstructure densification under compression on the plastic flow hardening for accelerated mixes.

On the settling of spherical particles in power-law fluid at moderate Reynolds number

The present paper analyses the settling behavior of multiple spherical particles in a power-law fluid. The results were numerically solved by the lattice Boltzmann method for the fluid mass and momentum equations and the immersed boundary method for the particle dynamics. The transient particle position and velocity data were obtained for a constant Archimedes number of 1000 and density ratio of 2.25. The objects of the investigation were the solid volume fraction, between 0.2% and 3.3%, and the power-law index, from 0.6 to 1.25. The particles repel each other and avoid collision due to increased fluid viscosity in their gaps for the shear-thickening fluid. On the other hand, for shear-thinning fluids, a wake of low viscosity is formed behind the particles, which leads to a high occurrence of particle collisions. However, as the solid volume fraction increases, these effects become less noticeable, mainly because the settling transitions from viscous to collision-dominated. In all cases analyzed, the average terminal velocity was below the terminal velocity of a free particle.

Numerical analysis of MHD nanofluid flow and heat transfer in a circular porous medium containing a Cassini oval under the influence of the Lorentz and buoyancy forces

AbstractThis paper reports our study on the flow characteristics and heat transfer performance of magnetohydrodynamics (MHD) nanofluid in an innovative porous, circle‐shaped enclosure incorporating a Cassini oval cavity using the Darcy law. The MHD nanofluid considered in this study is Al2O3–H2O. A two‐dimensional (2D) mathematical model is developed based on a homogeneous model. The formulation of the vorticity stream function is then used to obtain coupled equations. Finally, the coupled partial differential equations are solved numerically using the finite element method. Model predictions are then compared against results from the previously published study to verify the accuracy and validity of the developed model, and a good agreement is achieved. Figures demonstrate the effects of nanoparticle volume fraction, inclined angle, Lorentz, and buoyancy forces on the MHD nanofluid flow. The results indicate that the convection mechanism becomes weaker with an increase in solid nanoparticle volume fraction. A significant increase in the Rayleigh number will lead to a stronger and more cohesive core vortex. In addition, when magnetic force is applied horizontally, favorable Nuave occurs. Based on the numerical results, a correlation to predict the average Nusselt number within the enclosure is developed as a function of Hartmann number (Ha), Rayleigh number (Ra), and inclined angle (γ).

Study on the Rheology of AlSi4Mg2 Alloy at Steady State

The rheological characteristics of AlSi4Mg2 alloy at steady state are studied theoretically based on the ICF model. It is shown that the solid volume fraction and shear rate have obvious effect on the rheological behaviour. Specifically, the apparent viscosity increases when the solid volume fraction increases and the shear rate decreases, the corresponding microstructure parameter n has the similar trend. It shows that there is a closely relationship between the steady state viscosity and its microstructure. The AlSi4Mg2 alloy has the pseudoplastic behaviour. The agreement of theoretical prediction and the experimental results indicates the ICF model is reliable to predict the rheological behaviour of AlSi4Mg2.

Two-Way Coupling Simulation of Solid-Liquid Two-Phase Flow and Wear Experiments in a Slurry Pump

The slurry pump is one of the most important pieces of equipment in mineral transportation and separation systems, and it has complex two-phase flow characteristics and wear mechanisms. By employing numerical and experimental methods, the solid–liquid two-phase flow characteristics and wear patterns were investigated in this study. A two-way coupling discrete phase model (DPM) method was used to predict the flow pattern and the wear location and shows good agreement with the experimental observations. The pump performance characteristics of numerical results under pure water conditions were consistent with the experimental results. The effects of particle parameters and operating conditions on the internal flow field and wear were compared and discussed. The results show that the wear degree increased with the increase in volume flow rate and solid volume fraction. With the increase in particle size, the wear range at the impeller inlet became significantly smaller, but the wear degree became obviously larger. This study provides a basis for reducing the wear and improving the hydraulic performance of slurry pumps.

Radial distribution of solid holdup and its fluctuation characteristics in a three-phase scrubbing-cooling chamber

The local solid holdup in the three-phase scrubbing-cooling chamber was measured using optical fiber probes under different solid-phase properties, liquid-phase properties, and superficial gas velocities. The root-mean-square (RMS) fluctuations of the solid fraction (v′¯) were used to describe the local solid volume fraction fluctuations quantitatively. The results showed that the bubble wake is the dominant factor affecting the radial solid holdup distribution uniformity. The bubble wake entrainment in the central area and the fluid reflux in the near-wall area resulted in the radial distribution of solids holdup with “low center and high sidewalls.” In addition, the increase of solid volume fraction and the enhanced entrainment ability of bubble wake both encourage the growth of local v′¯ and lead to a more uneven radial distribution of v′¯. A regional model of v′¯ is established, and its predicted values agree well with the experimental values.

Experimental investigations on viscosity and density of eco-friendly MoS2-sesame oil nano-lubricants and its influence on pumping power

In this study, the rheological behavior and density of MoS2/sesame oil based nano-lubricants are experimentally investigated. The transmission electron microscopy and x-ray diffraction technique were utilized to confirm the morphology of the MoS2 nano particles. The experimental measurements are carried out at temperature varying from 313 to 393 K, shear rate ranging from 10 to 70 s−1 and solid volume fraction ranging from 0.2% to 1.2%. For the both nano-lubricants and pure lubricant, shear thinning behavior is observed. The influence of temperature and nanoparticle concentration on viscosity and density of nano lubricants are examined. The viscosity and density of nano-lubricants increased with an increase of solid volume fraction, while, it decreased with an increase in temperature. Moreover, the effect of nano particle concentration on the pumping power of lubricant flow are discussed. Finally, an experimental correlation was developed for predicting the viscosity of MoS2/sesame oil based nano-lubricant.

Buoyancy Effect on a Micropolar Fluid Flow Past a Vertical Riga Surface Comprising Water-Based SWCNT–MWCNT Hybrid Nanofluid Subject to Partially Slipped and Thermal Stratification: Cattaneo–Christov Model

This paper provides a comprehensive analysis of the mixed convective flow that comprises SWCNT-MWCNT/water hybrid nanofluid containing micropolar fluid through a partially slipped vertical Riga surface. A Cattaneo–Christov heat flux model is used to examine the heat transport rate. The energy equation is gaining more significance with the effect of viscous dissipation and thermal stratification. The flow model is transformed by convenient transformation into nondimensionless form. The numerical results of nonlinear complex equations are collected using the bvp4c built-in function from MATLAB which is based on the finite difference method. The graphical results are obtained for both hybrid nanofluid and simple nanofluid. The temperature distribution for hybrid nanofluid is higher than that for simple nanofluid when the solid volume fraction increases. The axial friction factor increases with solid volume fraction, porosity parameter, and mixed convection parameter. The velocity graph varies inversely with nanofluid volume fraction and micropolar parameter.