Low Volumetric Fractions Research Articles

Self-organization of Janus particles: Impact of hydrodynamic interactions in substrate consumption for structure formation.

We show that the formation of active matter structures requires them to modify their surroundings by creating inhomogeneities such as concentration gradients and fluid flow around the structure constituents. This modification is crucial for the stability of the ordered structures. We examine the formation of catalytic Janus particle aggregates at low volumetric fractions in the presence of hydrodynamic interactions (HIs). Our study shows the types of structures formed for various values of the kinetic constant of the catalytic reaction. The presence of HI causes the aggregate particles to have higher mobility than in the case of the absence of such interactions, which is reflected in the behavior of the pair distribution function. Although HI decreases energy conversion efficiency, they play a significant role in the formation of complex structures found in nature. Self-organization of these structures is driven by direct feedback loops between structure formation and the surrounding medium. As the structures alter the medium by consuming substrate and perturbing fluid flow, the substrate concentration, in turn, dictates the kinetics and configuration of the structures.

RSM-based sensitivity analysis of hybrid nanofluid in an enclosure filled with non-Darcy porous medium by using LBM method

The emphasis of this study is the numerical analysis via D2Q9-based Lattice Boltzmann Method of free convection MHD non-Darcy flow in hybrid nanofluid (TiO2/Cu–water) occupying a differentially heated square enclosure. A key novelty of the work is the inclusion of a response surface methodology (RSM)-based sensitivity analysis. The current investigation has been done considering the variation in Rayleigh number (103 ≤ Ra ≤ 106), Darcy number (0.0001 ≤ Da ≤ 0.1), and Hartmann number (0 ≤ Ha ≤ 50). From RSM, high Darcy parameter, low volumetric fraction, and low Hartmann number are identified as the optimum functioning conditions for heat transfer rates.

Empirical equations for flexural residual strengths in concrete with low volumetric fractions of hook‐end steel fiber

AbstractThe characterization of steel fiber concrete in a flexural test or tensile uniaxial test requires greater control of loading rate by the speed applied in the test machine, to be able to report more accurately the behavior of displacements or crack openings in micro‐scale possible. In general, in the pre‐dimensioning process, it is often discarded the characterization tests and the main standards do not provide theoretical design recommendations concerning the residual strengths of fibrous concrete. Some empirical models in the literature attempt an approximation of the theoretical design values, but they present greater dispersion in the results. This article proposes empirical equations for predicting the residual strengths of the steel fiber reinforced concrete (SFRC), for small fiber volume fractions (approx. < 0.8%). Experimentally notched beams subjected to three‐point bending tests were collected, with the concrete matrix composed of hook‐end steel fiber and the experimental residual strengths presenting the softening behavior in the load‐opening ratio curve of the crack. The experimental residual strengths were compared with other empirical models found in the literature. The results showed that the maximum stress of the steel fiber pullout model established satisfactory relationships with the residual stresses in flexure. The empirical proposed residual strength model presented lower variability of dispersion around 10%, the mean absolute percentage error of 8%, compared to other usual empirical models and had the same material class with the experimental results, proving to be a viable alternative for pre‐design and dosage optimization for SFRC.

Cu/Oil nanofluids flow over a semi‐infinite plate accounting an experimental model

AbstractIn this study, the flow of Cu/oil nanofluids over an impermeable semi‐infinite plate was investigated. A complete single‐phase modeling of nanofluids flowing over a semi‐infinite plate was performed, bringing into account, real experimental data of oil‐based nanofluids. The empirical correlations revealed that the viscosity and thermal conductivity of the pure oil and oil‐based nanofluids strongly depend on temperature. The similarity transformation method was utilized to transform governing partial differential equations into coupled nonlinear ordinary differential equations solved by employing the standard Runge–Kutta. The results showed that even low volumetric fraction of copper/oil nanofluids noticeably enhanced the heat transfer; however, such behavior was not predicted accounting the classic modeling of nanofluids. Furthermore, both hydrodynamics and thermal characteristics were reliant on the thermal boundary conditions, which this seems to have received a marginal focus in the existing literature.

Piezoresistive epoxy resin films with carbon black particles for small-strain sensors

Materials that change resistance after undergoing deformation have various types of applications as sensors. Among the materials that may be used for this purpose, there are some in which conducting particles are immersed in an isolating polymeric matrix. Carbon black (CB) particles have high electrical conductivity, allowing them to be included in a resin epoxy (EPX) matrix and resulting in an electrical conductor composite; this can be done even in the case of low volumetric fractions of CB. The goal of this work was crafting a conducting polymeric film that has piezoresistive behavior for utilization as strain sensors for low deformations. A relevant aspect of the film development was the search for a solvent to lower the viscosity of the EPX to enhance the homogeneity of the composite. Acetone showed good potential as the solvent for this composite. The sensor showed efficiency under small strain, especially when used with a substrate.

Experimental analysis applied to an evacuated tube solar collector equipped with parabolic concentrator using multilayer graphene-based nanofluids

Solar collectors are essential to enable the direct use of solar energy. Graphene nanoparticles stand out among other nanoparticles because it presents high thermal conductivity. The aim of this study is to evaluate the thermal efficiency increase achieved applying multilayer graphene (MLG) in low volumetric fractions dispersed in water. An evacuated tube solar collector equipped with parabolic concentrator was herein used in a closed circuit. Thermal efficiency was evaluated considering different recirculating flow rates (6, 24, 42 and 60 L h−1), two volumetric fractions of MLG (0.00045% and 0.00068%) with and without concentrator. A semi-empirical equation was developed to estimate thermal efficiency based on hydraulic- and thermal-flow parameters. In relation to the flow rate the best performance was obtained at 42 L h−1. Furthermore, the use of the parabolic concentrator increased by approximately 298% the thermal efficiency in comparison to the collector without concentrator. An excellent fit (R2 = 0.970) was obtained between efficiencies estimated through the semi-empirical equation and those estimated through measurements performed in the current study. MLG nanofluid in concentrations of 0.00045 vol% and 0.00068 vol% increased the thermal efficiency of the solar collector by 31% and 76%, respectively in comparison to the base fluid.

Investigating the Provenance of Iron Artifacts of the Royal Iron Factory of São João de Ipanema by Hierarchical Cluster Analysis of EDS Microanalyses of Slag Inclusions

Microstructural characterization techniques, including EDX (Energy Dispersive X-ray Analysis) microanalyses, were used to investigate the slag inclusions in the microstructure of ferrous artifacts of the Royal Iron Factory of Sao Joao de Ipanema (first steel plant of Brazil, XIX century), the D. Pedro II Bridge (located in Bahia, assembled in XIX century and produced in Scotland) and the archaeological sites of Sao Miguel de Missoes (Rio Grande do Sul, Brazil, production site of iron artifacts, the XVIII century) and Afonso Sardinha (Sao Paulo, Brazil production site of iron artifacts, XVI century). The microanalyses results of the main microconstituents of the microstructure of the slag inclusions were investigated by hierarchical cluster analysis and the dendrogram with the microanalyses results of the wustite phase (using as critical variables the contents of MnO, MgO, Al2O3, V2O5 and TiO2) allowed the identification of four clusters, which successfully represented the samples of the four investigated sites (Ipanema, Sardinha, Missoes and Bahia). Finally, the comparatively low volumetric fraction of slag inclusions in the samples of Ipanema (~1%) suggested the existence of technological expertise at the ironmaking processing in the Royal Iron Factory of Sao Joao de Ipanema.

Performance of copper oxide/water nanofluid in a flat plate solar water heater under natural and forced circulations

Flat plate solar water heater is widely used for heating of water in low-temperature residential applications. In this paper, Copper Oxide/water (CuO/H2O) nanofluid is prepared from Copper Acetate and its thermal performance was investigated experimentally on a 100 Liters per Day (LPD) thermosyphon based indirect-type flat plate solar water heater. The volumetric fraction of CuO/water nanofluid chosen was 0.05%. Significant improvement in performance was observed in thermosyphon circulation compared to forced circulation, for the low volumetric fraction considered. The CuO/water nanofluid was prepared with the inclusion of surfactant Sodium Dodecyl Benzene Sulfonate (SDBS), as it provided the best CuO nanoparticle dispersion stability compared to pure water suspension and Triton X-100 surfactant suspensions. Also, the thermophysical properties of the synthesized nanoparticle and prepared nanofluid were compared theoretically and experimentally.

The great potential of nanomaterials in drilling & drilling fluid applications

The continuous development of global economy with decreasing in available hydrocarbon sources and increasing discovery and extraction costs due to decrease in-situ oil and gas reservoir, displays the necessity of using new techniques for the improve rate of penetration and productivity in well. Nanotechnology has already contributed significantly to technological advances in the energy industries. Nanotechnology has the potential to introduce revolutionary change in drilling industry. Nanotechnology produces nanomaterials with many attractive properties, which can play an important role in intensifying mud cake quality, reducing friction, eliminating differential pipe sticking, maintaining borehole stability, protecting reservoir, and enhancing oil and gas recovery. Nano fluids can be designed by adding nano-sized particles in low volumetric fractions to a fluid. The nano particles modify the fluid properties, and suspensions of nano-sized particles can provide numerous advantages. This paper presents an extensive literature review of assessing the applications of nanomaterials in drilling and drilling fluids, and evaluates the potential technical benefits that these nanomaterials might provide to petroleum development and production.

ENHANCEMENT OF OXYGEN MASS TRANSFER IN PNEUMATICAL BIOREACTORS USING N-DODECANE AS OXYGEN-VECTOR

In biotechnology, oxygen mass transfer is a key parameter involved in the design and operation of bioreactors and it can be analyzed by means of the oxygen mass transfer coefficient (kLa). Due to the fact that oxygen has a very low solubility in an aqueous media (8–10 ppm at 20˚C), actively growing cells can consume all the dissolved oxygen very fast, therefore, it has to be supplied continuously into the broths. In conventionally aerated bioreactors, low oxygen solubility combined with slow oxygen transfer rates often results in reduced growth and culture productivity. Due to their higher oxygen solubility, non-toxicity to microbes, antifoaming action, oxygen-vectors addition is one of the most effective methods to improve oxygen mass transfer rate in aerobic fermentations. The aim of this study was to investigate the use of n-dodecane as oxygen-vector in bubble column and air-lift bioreactors, under different working conditions (air superficial velocity, volumetric fraction of the organic phase, medium temperature). The results show that volumetric fraction of oxygen-vector (φ) has a great influence on kLa; in the presence of low volumetric fraction (φ=0.005 (v/v)), the oxygen mass transfer coefficient’s value in bubble column bioreactor was increased by almost 100% at 35˚C and for φ=0.02 (v/v) by 5% at 25˚C, while in air-lift bioreactor, at 25˚C and φ=0.005 (v/v), the kLa value was enhanced by approximately 50%.

English

The addition of nanoparticles to the fluids such as water has improved load carrying capacity of such fluids. The key idea is to exploit the viscoelastic properties of nanofluids which can withstand higher loads by adding nanoscale particles in low volumetric fractions to a fluid in order to improve their rheological, mechanical, and thermal properties. The behaviour of shear stress and the viscosity of nanofluids have been studied based on some of the empirical models developed. In this paper an overview of the recent developments in the study of heat transfer using nanofluids is presented. The nonmaterial in base fluid shows some agglomeration in 5µm -8µm, however and the load carrying capacity of the fluid are found to be improved due to the addition of nanoparticles in the base fluid. The viscoelastic properties of the nanofluids are found to be improved with increasing concentration.

Cracking control of concretes modified with short AR-glass fibers at early age. Experimental results on standard concrete and SCC

At early ages (less than 24 h), cracking can occur in concrete because it can be subjected to dimensional changes, due to shrinkage, can generate loads which are greater than the low strength capacity of the material at this age. This is especially the case in members with highly exposed surfaces, such as floor slabs or precast panels. As any other cement based composite, Self Compacting Concrete (SCC) shrinks at an early age and can crack when shrinkage is restrained. One possible solution to reduce the impact of early age shrinkage on concrete durability is to include low volumetric fractions of short fibers in order to control crack growth. To evaluate the cracking control ability of Alkali Resistant (AR) glass fibers in standard concrete and SCC, an experimental program, developed in accordance with the AR-glass fiber producer, was conducted. Two different types of AR-glass dispersible fibers, two concrete compositions and several volumetric fractions of fiber have been studied. The experimental program included a mechanical characterization of the different concrete compositions (compression and flexural strength tests), free shrinkage tests, with and without air flow over the samples, and double restrained slab cracking tests (Kraai slab modified test). The results obtained show that the inclusion of low volumetric fractions of the two types of AR-glass fiber under study can control the cracking produced due to very early age shrinkage on both standard concrete and SCC in two different ways: reducing the total cracked area and the maximum length of the cracks. Although, a non-linear dependence of cracked area on AR-glass fiber amount was found. A microscopic study of the cracked surface confirms the favorable effect of the presence of dispersed AR-glass fibers on cracking control. When standard concrete and SCC results were compared, it was observed that, although SCC drying shrinkage was larger, standard concrete with a similar performance in the hardened state produced equivalent cracking area.

On the dependence of circular Bragg phenomenon of noble metals helicoidally periodic sculptured thin films on visible and IR wavelengths

The concept of local homogenization in the visible and infra-red frequencies is used by estimating the permittivity dyadics of noble metals (Cu, Ag, and Au) in the form of thin film helicoidal bianisotroptic media (TFHBM). Despite the fact that the absorption transitions of dielectric to metal (percolation threshold) in metallic TFHBMs occur at long wavelengths at lower volumetric fraction of metallic particles, at these wavelengths the transition from dielectric to metal in composite relative permittivity scalar occurs at higher volumetric fraction of metallic particles. The latter is responsible for the increase of circular Bragg phenomenon.

Fire performance of recycled rubber-filled high-strength concrete

The paper presents the behavior of a high-strength concrete (HSC) with silica fume (SF) modified with different amounts of solid particles recycled from crumbed used truck tires. The aims of including elastomeric materials in a cementitious matrix are reducing the stiffness of HSC in order to make it compatible with other materials and elements of the building, unexpected displacement of foundations and shrinkage, recycling of solid wastes and improving fire performance. The inclusion of low volumetric fractions of rubber reduces the risk of explosive spalling of HSC at high temperatures because water vapor can exit through the channels left as the polymeric particles get burnt. The temperature reached at a fixed depth of the fire-tested specimens is reduced as the percentage of rubber increase. A set of mechanical, destructive and nondestructive tests were accomplished in order to obtain optimum quantities of crumbed used tires rubber in the composition, taking into account workability, stiffness and, obviously, strength. The results obtained show that a relatively high-volume fraction of rubber (3%) does not reduce significantly the strength, although it reduces the stiffness. Higher values of rubber produce a progressive reduction of strength and stiffness but might improve the dynamic behavior.

Microstructure and properties of alumina-SiC nanocomposites prepared from ultrafine powders

Alumina-Silicon Carbide nanocomposites were produced and studied under different aspects: characteristics of the starting materials, processing, microstructure and mechanical properties. The raw materials were two kinds of fine SiC powders (30 and 45 nm) and two Al2O3 powders (60 and 140 nm). Different compositions (amounts of SiC in the range 0.5–5 vol%) were performed and the characteristics of the resulting materials compared. The oxygen enrichment in SiC nanopowder due to specific powder treatments was controlled, in order to optimize powder processing routes. Densification tests of Al2O3-SiC powder mixtures were performed both by pressureless sintering and hot pressing route. The addition of SiC reduced the densification rate and favoured a refinement of the matrix. Improvement of mechanical properties over monolithic alumina was obtained in composites with the 45 nm SiC. The study pointed out that the critical factor for the success of these materials is the choice of the raw SiC powders in terms of grain size and state of agglomeration. The addition of this ultrafine SiC strongly affected the microstructural evolution, even at low volumetric fractions. The results do not substantiate any remarkable effect by dispersoids in the tested nanosize range.