Effects Of Solid Volume Fraction Research Articles

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.

Hyporheic exchange driven by emergent vegetation patches: Experiment and simulations

The vegetated region is known as the “hot zone” for the exchange of substances in river systems, which causes an uneven pressure distribution at the sediment–water interface (SWI) and then forms hyporheic exchange (HE). However, as a common form of plant survival, the impact of vegetation patches on HE has received little research attention. In this study, laboratory experiment and numerical simulations were conducted to explore the effects of solid volume fraction within the patch (φ), the overlying water average velocity (U), and the streamwise distance of the patches (Sx) on HE. The results showed that the pressure along the SWI caused the spatial–temporal characteristics of HE at the vegetation patch (VP) scale and vegetation patch group (VG) scale. At the VP scale, the HE depth was influenced by φ, U, and Sx in increasing order, and increased with the increase in these values within a certain range. At the VG scale, the HE depth was positively correlated with φ and U and negatively correlated with Sx, and the spatial characteristics of HE were larger at this scale than at the VP scale. The HE flux was linearly related to φ and power functionally related to U. There was an asymptotic behavior of the effect of Sx on the HE flux, which means that the rate of change of the HE flux progressively decreases with Sx. The HE volume was influenced by Sx, φ, and U in increasing order and was positively correlated with all of these parameters. Based on the flow blockage parameter, Reynolds number (Re), and Sx, a prediction model of HE flux was developed. The results of this study provided further understanding of the role of vegetation patches in driving the HE process and may serve as a reference for vegetated river benthic habitat restoration.

Using adaptive neuro-fuzzy inference system for predicting thermal conductivity of silica -MWCNT-alumina/water hybrid nanofluid

In this study, the thermal conductivity (knf) of Silicon Oxide-MWCNT-Alumina/Water hybrid nanofluid (HNF) is predicted versus solid volume fraction (SVF) and temperature. For this reason, various combinations of SVF and temperature are considered from SVF= 0.1–0.5% and 20–60 (°C) respectively. Then, an adaptive neuro-fuzzy inference system (ANFIS) has been effectively used to model the knf of HNF as one of the effective machine learning techniques. Various shapes of membership functions are considered and the generalized bell shape membership function showed to have acceptable accuracy for knf prediction using an ANFIS-based model. Moreover, the outcomes reveal that the effect of SVF is higher than temperature influence on the knf of HNF. Specifically, when the SVF is increased from 0.1% to 0.5%, there is an approximate 25% increase in knf. Conversely, an increase in temperature leads to a smaller ratio of knf increment. When the temperature rises from 20° to 60°C, knf only increases by less than 10%. The highest error value is found at φ = 0.2% and T = 60 °C, amounting to 0.01128 W/mK.

Analysis of the absorptance and emittance in particle curtains by means of a discrete MCRT method

Apparent optical properties, absorptance and emittance, in particle curtains are analyzed by means of a discrete Monte Carlo Ray-Tracing model. The effect of solid volume fraction, particle diameter and curtain thickness on these properties is investigated for two types of particles with different absorptivity and emissivity: sand and CARBO HSP. Absorptance and emittance achieved by curtains made of these particles are greater than the values of absorptivity and emissivity of material. The increase in curtain absorptance/emittance compared to the particle absorptivity/emissivity is higher as the particle property is poorer, such as in sand. Both absorptance and emittance are maximum for opaque curtains, which entails high thicknesses. Assuming opaque curtains, the absorptance and emittance increase as the solid volume fraction decreases. The results obtained with the Monte Carlo Ray-Tracing model are used to estimate particle curtain radiative losses including emission and reflection losses. If material properties absorptivity and emissivity are used instead of the obtained curtain properties absorptance and emittance, sand curtain losses are up to 35 pp and only 9 pp in the case of CARBO HSP. Absorptivity is more important than emissivity, that is, it is preferable having high absorptivity than low emissivity to achieve low radiative losses. Emission losses are less important than reflected losses being very similar in both types of curtains. Sand curtains lose 33% of the incoming power while CARBO curtains lose only 7%. Radiative losses are significantly higher than advection losses in sand curtains. However, in CARBO curtains, advection losses are higher.

Study of the Performance of a Photovoltaic Solar Panel by Using a Nanofluid as a Cooler

Abstract In this paper, we study by numerical simulation, the cooling of a solar photovoltaic panel using a nanofluid as a cooler. The solar panel is subjected to a hot temperature that character-ises the climate of the city of Bechar located in southwestern Algeria. The nanofluid (Al2O3-water) is introduced in the cavity with a constant horizontal speed and subjected to the ambient (cold) temperature. The equations governing the hydrodynamics of the flow and the heat transfer are described by the Navier-Stockes and energy equations. The finite element method is used to solve the system of partial differential equations (PDEs) based on the Galerkin method. We consider the effect of solid volume fraction and form factor for different values of Reynolds number on the results in the form of isotherms, streamlines, temperature, velocity, average Nusselt numbers and solar panel efficiency.

An Investigation of Entropy and Exergy of Nanofluid Flow in Microchannel Heat Sinks

The current study aims at performing the thermodynamic analysis of three different scenarios of the heat sinks numerically using the finite volume method (FVM). To this effect, heat sinks are made of aluminium to provide cooling for an electronic chip. In this respect, the three cases examined throughout this study are as follows: One with one layer and two with two layers flowing in different directions, counter-current, and parallel. The parameter’s analysis of the present investigation consists of three solid volume fractions (Φ) up to 3% for Reynolds number ratio (Rer) in the range of 0.25 ≤ Rer ≤ 2. Their imprints have been highlighted on frictional, thermal, and global entropy generation, the first law of thermodynamics and exergy efficiency, heat transfer, and pumping power. The findings revealed that the first law and exergy efficiencies are higher in the single-layered heat sink. However, the effect of solid volume fraction and Reynolds number ratio on these efficiencies is minimal. On the other hand, the double-layered heat sink generates less entropy than the single-layered one, which may be reduced by raising the Reynolds number ratio and solid volume fraction. Finally, the findings show that the heat transfer is higher in the double-layered heat sink but is accompanied by a considerable rise in pumping power.

Role of Nanofluid and Hybrid Nanofluid for Enhancing Thermal Conductivity towards Exponentially Stretching Curve with Modified Fourier Law Inspired by Melting Heat Effect

The intensive of this study is to examine the melting heat and second-order slip (SoS) effect at the boundary in nanofluid and hybrid nanofluid (HN) ethylene–glycol (EG) based fluid through a curved surface using the Modified Fourier Law (MFL) and dust particles. Considering similarity transformation, the PDEs are converted to ODEs and then solved numerically by using the finite element method (FEM). The effects of solid volume fraction (SVF), melting heat factor, curvature factor, first and second-order slip factor, fluid particle concentration factor, and mass concentration factor on the velocity field, dust phase velocity (DPV), temperature field, dust phase temperature (DPT), and the Ski Friction (SF) are investigated through graphs and tables. The thermophysical properties of nanofluid and HN are depicted in tables. The novelty of the present work is to investigate the dusty- and dusty-hybrid nanoliquids over the curved surface with a melting heat effect and MFL which has not yet been studied. In the limiting case, the present work is compared with the published work and a good correlation is found. The confirmation of the mathematical model error estimations has been computed.

Controlling ettringite precipitation and rheological behavior in ordinary Portland cement paste by hydration control agent, temperature and mixing

The influence of ettringite precipitation on the rheological properties during the initial and the induction period of ordinary Portland cement (OPC) hydration is examined by combining quantitative X-ray diffraction (QXRD), thermogravimetry (TG), calorimetry, penetration test method and 1H-TD-NMR. This allows a good overview about mineralogical changes during hydration and conclusions about their effect on rheological and microstructural changes within the paste. The reaction kinetic are controlled either by varying curing temperature or by an organic additive, which allows adjustment of the initial aluminate reaction while delaying the silicate reaction for hours. A significant correlation of ettringite content and rheological behavior due to structural build-up of the paste is observed in all investigated systems. The potential influence of ettringite content on structural build-up of the paste is found to be comparable to the effect of solid volume fraction on rheology (viscosity & yield stress).

Effect of Solid Volume Fraction on the Magnetorheological Response of Nano-Fe3O4 Incorporated Cementitious Paste

Effect of Solid Volume Fraction on the Magnetorheological Response of Nano-Fe3O4 Incorporated Cementitious Paste

Effect of using hybrid nano lubricant on the thermo-hydrodynamic performance of two lobe journal bearings

Due to the wide range of journal bearings applications in the industrial machine, significant efforts have been made by tribology researchers to improve their performance in recent years. Designing new bearings geometry and using lubricants with new chemical compounds including additives are the most common solutions proposed to enhance the performance of journal bearing supports. New advancements in nanotechnology and producing the various types of nano particles have provided the chance of upgrading the properties of commercial lubricants. According to the different effect of nano fluids on the performance of mechanical systems corresponding to their composition, today they are used to achieve different goals in lubrication systems. Upgrading the steady state performance parameters including load carrying capacity, attitude angle, surface cooling and effective viscosity are among the expected results of applying nano lubricant in journal bearings. So, in this study the performance of hydrodynamic two lobe journal bearings lubricated with SiO2-multiwall carbon nano tubes /SAE40 hybrid nano fluid is presented considering the thermal effects. For this purpose, the governing Reynolds and energy equations as well as the equation of heat transfer in bearing shell are modified based on the properties of assumed rotor-bearing system. Then the effects of solid volume fraction of nano particles on the performance of two lobe bearings are studied for different amount of bearing noncircularity. The results indicate that upgrading the solid volume fraction of added nano particle to the SAE40 base oil, enhances the lubricant pressure distribution, load carrying capacity, and lubricant effective viscosity. Further, by increasing the solid volume fraction, the attitude angle and temperature of lubricant and rotor-bearing surfaces experience a decreasing trend. Generally, it's obvious from the results that choosing the appropriate solid volume fraction of SiO2-multiwall carbon nano tubes in hybrid nano oil composition, especially for high value of preload factor, can improve the performance of two lobe bearings.

Effects of boundary walls on the properties of settling spheres

Abstract Numerical Simulations are performed, using Eulerian two fluid model (TFM) to investigate the effects of solid volume fraction and no-slip side walls on the settling particles. It is found that average settling velocity decreases with increasing volume fraction for both gas-solid (GS) and liquid-solid (LS) systems, in good agreement with the Richardson-Zaki 1 − ϕ n ${\left(1-\phi \right)}^{n}$ law. It was also noted that average velocity is independent of the boundary condition for both gas-solid (GS) and liquid-solid (LS) systems. The root mean square value of the solid volume fraction shows the increasing trend with volume fraction, caused by the many particle interactions. Furthermore, no-slip sidewalls were found to damp the velocity fluctuations quantitively, while following the well-known ϕ 1 / 2 ${\phi }^{1/2}$ scaling with volume fraction. Side walls were found to act as kinetic trap for the particles, damping the fluctuation near the walls and plateauing in the mid plane. These simulations showed that the GS system shows the higher solid fraction fluctuations that the LS system at the same Reynolds number, mainly because of the higher collision frequency (higher Stokes number) among the particles.

Experimental and numerical study of catalytic combustion and pore-scale numerical study of mass diffusion in high porosity fibrous porous media

Pore structure has a significant effect on transport phenomena inside porous media. This effect can be considered in simulations by using suitable transport coefficients. Some correlations are reported in the literature, which can be applied for simple pore geometries. In the present study, a pore-scale simulation approach is presented to determine mass diffusion coefficient considering molecular and Knudsen diffusion in a fibrous porous medium as a complex porous geometry. The methodology is employed for species in catalytic combustion of Methane inside a fibrous porous structure. The effect of Solid Volume Fraction (SVF), fibers orientation, and diameter are discussed in different temperatures. It is found that SVF plays the dominant role in mass diffusion, specifically above 600K. Mass diffusion coefficients obtained in the present study and flow permeability, conduction and radiation heat transfer coefficients from the previous study are used to simulate methane combustion inside the fibrous structure on the macro scale. An experimental setup is developed for validation. The results indicated that the simulation could well predict the temperature distribution, also 6.4% error in estimating the Methane conversion rate was observed. Due to the low Peclet number, the concentration of CH4 and O2 decreased unexpectedly before entering the catalytic zone.

Viscosity and Rheological Properties of Graphene Nanopowders Nanofluids.

The dynamic viscosity and rheological properties of two different non-aqueous graphene nano-plates-based nanofluids are experimentally investigated in this paper, focusing on the effects of solid volume fraction and shear rate. For each nanofluid, four solid volume fractions have been considered ranging from 0.1% to 1%. The rheological characterization of the suspensions was performed at 20 C, with shear rates ranging from to , using a cone-plate rheometer. The Carreau–Yasuda model has been successfully applied to fit most of the rheological measurements. Although it is very common to observe an increase of the viscosity with the solid volume fraction, we still found here that the addition of nanoparticles produces lubrication effects in some cases. Such a result could be very helpful in the domain of heat extraction applications. The dependence of dynamic viscosity with graphene volume fraction was analyzed using the model of Vallejo et al.

Nanofluid MHD combined convection in a porous chamber with various thermal sources

The impact of various sizes and positions of the heater in a nanofluid-saturated porous lid-driven chamber with a uniform Lorentz force is studied numerically. In this investigation, three different lengths of heater with higher temperature at six different locations along the left sidewall of the cavity are considered. Lower temperature is maintained at the right sidewall. Further, lower and moving upper horizontal walls and the rest of left wall are supposed to be thermally insulated. Based on the finite volume method, the system of nondimensional governing equations is solved by SIMPLE algorithm. The results conclude that the average Nusselt number is reduced with the enhancement of Richardson and Hartmann numbers. When the heater length is reduced from bottom to top, the heat transfer rate is increased for all the considered Richardson, Darcy and Hartmann numbers. In the lower permeability of the porous medium, the effect of solid volume fraction of nanofluid is more vulnerable. In the case of nanofluid, the steady state is reached quickly than the pure fluid.

Experimental Evaluation in Thermal Conductivity Enhancement and Heat Transfer Optimization of Eco-Friendly Al2O3–Pure Coconut Oil Based Nano Fluids

Abstract The present study reports an experimental evaluation of thermal conductivity of Al2O3/pure coconut oil nano fluids with solid volume fraction varying from 0.1% to 1.2% at a temperature ranging from 303 K to 413 K, respectively. Additionally, the thermophysical properties such as thermal diffusivity, density, and specific heat were also measured. The effect of solid volume fraction and temperature on thermophysical properties of nano fluids was examined. The results confirmed that the thermal conductivity of nano fluids was higher than that of the base fluid with an increase in the solid volume fraction and temperature. Apart from this, the efficiency of nano fluids for the heat transfer application has been evaluated for optimization based on different figures of merit. Further, the experimental thermal conductivity data were compared with different existing models and correlations as the thermal conductivity enhancement of the nano fluid is directly or indirectly a function of almost all thermophysical properties. Hence, a novel dimensionless correlation was developed for predicting the thermal conductivity of pure coconut oil/Al2O3 nano fluids in terms of almost all the thermophysical parameters calculated from the experimental data.

Experimental and Theoretical Studies of Thermophysical Properties of MgO-Water Nanofluid

Magnesium oxide (MgO) nanoparticles were synthesized using the sol-gel technique then characterized. Cetyl Trimethyl Ammonium Bromide (CTAB) surfactant was added to reduce Van der Waal forces among MgO nanoparticles and distilled water forming a stable nanofluid using two-step method with aid of ultrasound sonication. Pure distilled water and nanofluids with different volume fractions of 0.25, 0.5, 0.75, and 1% are used as working fluids. Thermophysical properties of prepared nanofluids were measured experimentally and determined theoretically. Effect of solid volume fraction on the thermophysical properties; including thermal conductivity, heat capacity, viscosity, and density of MgO-water nanofluids are discussed. Moreover, experimental results have been compared with the suitable correlations for MgO-water nanofluid. The findings show that thermal conductivity, viscosity, and density of nanofluid increases with increasing solid volume fraction.

Comparison of disparate solid volume fraction ratio of hybrid nanofluids flow over a permeable flat surface with aligned magnetic field and Marangoni convection

Over the past decade preparation, characterization and modeling of nanofluids plentifully deliberated to improve the heat transfer effects. Hence to gratify the advancements this paper focuses on heat transfer effects of three distinct hybrid nanoparticles and with a base fluid (water). So this work numerically investigated the influence over a permeable flat surface with aligned magnetic field in the presence of suction or injection or impermeable together with the Marangoni convection of different hybrid nanofluids. The present results are validated with previous experimental and numerical results. The effect of solid volume fraction of hybrid nanoparticles, angle of inclination, magnetic parameter and wall mass transfer parameter are deliberated and offered through graphs together with the surface velocity and rate of heat transfer is presented in tabular form. It is found that the rate of heat transfer is increased with an increment of wall mass transfer parameter and an opposite effect of the rising of magnetic parameter. Among the three hybrid nanofluids water hybrid nanofluid has higher surface velocity, water hybrid nanofluid has higher temperature profile and water hybrid nanofluid has higher heat transfer rate.

Viscous Flow Over a Permeable Stretching/Shrinking Surface in a Nanofluid: A Stability Analysis

This study deals with the boundary layer flow and heat transfer near the stagnation point on a permeable stretching/shrinking surface in a nanofluid. The nanoparticles considered in this study are copper and silver. The governing nonlinear partial differential equations are transformed into a system of nonlinear ordinary differential equations using an appropriate similarity transformation which then solved numerically to study the effect of solid volume fraction or nanoparticle volume fraction parameter Φ of the nanofluid. Multiple solutions are found for a certain range of shrinking and suction parameters, therefore, a stability analysis is performed to determine which solution is stable and physically realizable. The effects of the governing parameters on the skin friction coefficient, the local Nusselt number and the velocity and temperature profiles were presented and discussed. It was found that the nanoparticle volume fraction substantially affects the fluid flow and heat transfer characteristics.

Experimental investigation of porous medium structural effects on a coupled porous media-free zone laminar flow

An experimental research program was conducted to investigate the effects of solid volume fraction, arrangement of rods, and rod shape on slow flow through and over two-dimensional model porous media. The porous media were modeled using in-line and staggered arrays of rods of circular and square cross-sections to cover a range of solid volume fraction of 0.06 to 0.49. Each model was installed into a test section so as to fill three-quarters of the total depth of the flow section; and the flow was driven through the test section by pressure. Using a refractive-index matched viscous fluid, the bulk Reynolds numbers for the respective test conditions were kept considerably lower than unity. Particle image velocimetry measurements were made across the streamwise-transverse plane of the test section. Results indicate that the flow through the free zone increases from 75% to nearly 100% as the solid volume fraction increases from 0.06 to 0.49. While the bulk distribution is independent of the shape of the rods, or the mode of arrangement, at the interface, penetration of the free flow is dependent on the solid volume fraction and arrangement of rods. The interfacial flow is predicted by a new formulation from which a boundary condition is derived which unlike others in the literature, is devoid of jumps at the interface. This work provides detailed experimental data and important predictive tools for validations of theoretical and numerical work.

Effect of viscous dissipation on finding dual solutions for mixed convection boundary layer flow for nanofluid

AbstractThe effect of viscous dissipation on mixed convection boundary layer flow for Ag‐water nanofluid under steady‐state condition has been studied numerically for both the buoyancy assisting and opposing flows over a vertical semi‐infinite flat plate. A new co‐ordinate system has been introduced to transform the governing partial differential equations (PDEs) to facilitate the numerical calculations. Then, the local similarity method has been used for approximating the transformed PDEs to ordinary differential equations. Further, the quasi‐linearization method has been introduced to linearize the nonlinear equations and then numerical integration has been carried out using implicit trapezoidal rule along with the principle of superposition. For higher Pr, the coupled differential equations behave like stiff differential equations. To overcome the situation, orthonormalization process has been introduced. The effects of solid volume fraction of nanoparticles , the mixed convection parameter , Prandtl number , and Eckart number have been analyzed on the heat transfer and flow characteristics. It has been observed that the dual solutions are obtained for buoyancy opposing flow only and the range of dual solutions have become wider with the increases in . Further, nanofluids enhance the heat transfer process as compared to conventional heat transfer fluids . Moreover, the addition of viscous dissipation causes less heat transfer in the boundary.