Search

The motion of solids in a viscous fluid with nonlinear complex behavior has important applications in different industries and engineering sciences. This work experimentally investigated the free-fall behavior of rotating and non-rotating spherical particles in a viscous fluid. The effects of physical parameters, including particle size, particle density, fluid viscosity, and rotational velocity, on the terminal velocity of the falling spherical particles were examined. A high-speed camera was employed to capture the phenomena and study the free-fall behavior of the spherical solid particles in a viscous fluid. The studied spherical particles had five different densities of 2800, 7800, 7900, 8660, and 8960 kg/m3 and three varying dimensions of 4, 5, and 6 mm. To explore the effect of fluid viscosity on the terminal velocity of particles, two types of fluids with the viscosities of 0.012 and 0.014 Pa.s were used. The initial rotational velocities were 0, 600, 900, and 1200 rpm for the falling particles. The obtained results revealed that increases in the particle diameter, density, and rotational velocity, along with a decrease in fluid viscosity, accelerated the terminal velocity and shortened the time of reaching this velocity. Furthermore, an increase in the Reynolds number gave rise to a decrease in the lift coefficient. On the other hand, the accelerated dimensionless rotational velocity increased the lift coefficient. [ABSTRACT FROM AUTHOR]

Objective: The objective of this article is to investigate the distinct features, morbidity and mortality of systemic lupus erythematosus (SLE) patients registered in rheumatology tertiary centers of Shiraz University of Medical Sciences from 2008 to 2018. Method: A cross-sectional study was conducted on registered patients by reviewing their medical records. The clinical presentations were classified based on each organ's distinct involvement. Result: Data of 1322 patients with a mean age of 40 at the time of the study were reviewed. The most common primary manifestation of the disease was arthralgia (37.5%), and the most common clinical presentation in course of the disease was skin involvement (61.8%). The most common cause of hospital admission was disease flare (27.8% (108/388)), and mortality was mainly due to pulmonary complications (27.5% (8/29)). Patients who had hypothyroidism had statistically significantly lower rates of constitutional symptoms (p = 0.006), gastrointestinal involvement (p = 0.024), hypertension (p = 0.002), headache (p = 0.019), depression (p = 0.049) and anemia (p = 0.014). Patients who presented with malar rash and photosensitivity in their course of disease were detected to have statistically significantly lower ages of disease onset (p = 0.013 and 0.003, respectively). Conclusion: This study is an update to an epidemiologic study conducted in 2008 in the south of Iran. By comparing results between the two studies, we have tried to investigate the change in morbidity and mortality of SLE during these years. [ABSTRACT FROM AUTHOR]

Applying a high-voltage electric field in a flow (electro-hydrodynamics or EHD) is a highly effective approach to locally accelerate a fluid to a desired speed. In this paper, a finite volume implementation is used to study the fluid flow around a fixed cylinder at a low Reynolds number. Two pairs of wire-plate electrodes are used to generate the electric field for fluid acceleration. Two Reynolds numbers are considered: Re=40, 100. We show that by increasing the Reynolds number, the relative effect of EHD is decreased. Further, we study the change in drag force due to EHD actuation. Finally, we showed that under certain voltage, electrode placement and Reynolds number the EHD fluid acceleration does not increase the total drag on the cylinder and yet leads to an increase in the total streamwise momentum transfer by augmenting the velocity at the top of the boundary layer. [ABSTRACT FROM AUTHOR]

When charged particles are exposed to an electric field the well-known Coulomb force acts on them. In this investigation, this force is utilized to induce vertical motion of spherical steel particles submerged in a dielectric liquid. The interelectrode space of a two parallel electrode system is filled with the liquid and dispersed steel particles, which become charged after contact with the electrodes. Experiments were carried out to measure the effect of this particle motion on the heat transfer between an electrode surface and an adjacent stagnant dielectric liquid. In order to interpret the experimental data, the dynamics of particles was analytically studied for low particle volume concentrations. Experimental results demonstrate significant heat transfer enhancement on low viscosity dielectric liquids. A detailed discussion is presented on the possible mechanisms responsible for such an enhancement. [ABSTRACT FROM AUTHOR]

An experimental study of stationary and non-stationary dielectric barrier discharge (DBD) plasma actuator is presented to control the flow around a NACA0024 airfoil. First, an induced air velocity of ~5 m/s is generated on a flat plate in still air using an AC-DBD actuator to find the optimal setup of the actuator (voltage, frequency, electrode width and gap size). Using the same actuator in the optimal position/setup on a NACA0024 airfoil at Reynolds number of 0.48 106, we are able to increase the stall angle of the airfoil to 18°, compared to 16° in no-actuator state. Furthermore, during the plasma actuation, the lift is increased by up to 5%. We show that non-stationary actuation, while yielding a performance similar to stationary actuation, leads to a considerable reduction of ~51% in plasma power consumption. [ABSTRACT FROM AUTHOR]

In this paper, the air flow around a blunt flat plate with a rounded leading edge has been experimentally examined with and without the presence of a plasma actuator. Tests have been conducted with Reynolds numbers ranging from 104 to 105. Significant phenomena in this flow field is the flow separation at the leading edge of the body, which called separation bubble. There are two considerably dimensionless parameters in this experiment. One of them is the leading edge radius ratio to body thickness and other one is the ratio of maximum velocity induced by plasma actuator to free stream velocity. Geometries with the values of R/D=0, 1/16, 2/16, 4/16 were tested. For each geometry, the effectiveness of plasma actuator on the separation bubble is studied in different values of velocity ratio. The results show that, the effect of plasma actuator for the geometry with sharp edge (R/D=0), is negligible, while in geometry with rounded edge, the plasma actuator has significant effect on the separation bubble domain. This effectiveness is enhanced, by increasing of leading edge radius and velocity ratio, so that in rounded edge geometry (R/D=4/16) length of separation bubble is reduced about 75%. [ABSTRACT FROM AUTHOR]

Abstract: An experimental study was carried out to investigate heat transfer and friction factor characteristics of γ-Al2O3/water nanofluid through circular tube with twisted tape inserts with various thicknesses at constant heat flux. In this work, γ-Al2O3/water nanofluids with two volume concentrations of 0.5% and 1% were used as the working fluid. The twist ratio of twisted tape remained constant at 3.21, while the thicknesses were changed through three values of 0.5 mm, 1 mm and 2 mm. The experiments were performed in laminar flow regime from 150 to 1600 Reynolds numbers. Results indicated that twisted tape inserts enhanced the average convective heat transfer coefficient, and also more the thickness of twisted tape is more the enhancement of convective heat transfer coefficient is. Also, the highest enhancement was achieved at maximum volume concentration. Results showed that nanofluids have better heat transfer performance when utilized with thicker twisted tapes. At the same time, the increase in twisted tape thickness leads to an increase in friction factor. In the end, the combined results of these two phenomena result in enhanced convective heat transfer coefficient and thermal performance. Finally, two new correlations were offered for Nusselt number and thermal performance based on our experimental observation. [Copyright &y& Elsevier]

In this paper, characteristics of the flow induced in the boundary layer by an AC-Dielectric Barrier Discharge (DBD) plasma actuator are compared against those of a DC-corona wind actuator. This is achieved by visualization of the induced flow using smoke injection and measuring the horizontal induced velocity. Our measurements show that the maximum induced velocity of an AC-DBD actuator is about one order of magnitude larger than that of a DC-corona actuator. For an AC-DBD actuator, the induced velocity is maximized on the plate surface while for a DC-corona actuator the induced velocity peaks at about 20mm above the surface. Using flow visualization, we demonstrate that the induced velocity of an AC-DBD actuator is parallel to the surface, while the induced velocity of a DC-corona actuator has components perpendicular to surface. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, hydrodynamics and heat transfer characteristics of γ-Al2O3 nanoparticles inside a circular tube in laminar flow with constant heat flux was investigated. For this purpose, γ-Al2O3 nanoparticles with 15 nm diameter and distilled water as base fluid were used. The primary objective is to evaluate the effect of different volume concentration on convective heat transfer. In addition, the effect of volume concentration is also studied on friction factor. Increasing the particle volume fraction leads to enhancement of convective heat transfer coefficient. Results revealed that the average heat transfer coefficient increased 6.8% with 0.5% volume concentration and enhanced 19.1% at 1% volume concentration in comparison with distilled water. More the heat flux is more the heat transfer coefficient is. From the results, there is no significant change of friction factor for nanofluids in comparison with base fluid. A new correlation was proposed based on our experimental observation in order to present a deep insight into the current issue. [Copyright &y& Elsevier]

Abstract: In the present study, electrohydrodynamic conduction pumping of n-hexane and n-decane liquid films in an open channel has been investigated experimentally. These two dielectric liquids have nearly the same electrical properties but with their different viscosities. The effects of film thicknesses, the arrangement of electrodes and the gap between pumps on the flow rate of liquid films have been also studied. The pumps with cylindrical electrodes have been installed in the channel. The best performance of the conduction pumps, revealing with experimental results, has been achieved at 8mm thickness of liquid film with the gap size of 55mm for both dielectric liquids in the present layout of the pumps. [Copyright &y& Elsevier]

The effects of a nonuniform electric field on the formation, detachment, and breakup of a single inert bubble surrounded by a dielectric liquid were studied experimentally and numerically. In experiments, air bubbles were injected into kerosene at a constant flow rate through an orifice at the bottom wall of the test cell. The liquid was subjected to a nonuniform electric field, applied between the horizontal and vertical electrodes. During the experiments, the behavior of bubbles was recorded continuously, and the position, shape, and volume departure of the bubbles were digitally extracted from the sequential frames with the aid of graphical software. The experimental results show that in the presence of the nonuniform electric field, bubbles take a prolate shape and skew to the opposite direction of the ground electrode. With an increase in the electric potential, the bubble growth time and departure volume will decrease continuously. Bubble breakup is also observed at high enough voltages. As a further study, a 3-D numerical simulation was performed, using a commercial finite element code (Comsol Multiphysics) to determine the distribution of electric stresses along the bubble surface. The numerical results show that the nonuniform electric field generates some inhomogeneous stresses at the bubble surface. The bubble is compressed and deviated by the horizontal component and elongated by the vertical component. Numerical outcomes prove the physical behavior of the bubble observed in the experiments. [ABSTRACT FROM AUTHOR]

Abstract: The effects of an external electric field on the stability and dynamics of a planar interface between Transformer/Silicone oils (Tr/Si) layers are studied experimentally. Experiments performed in a configuration help in clarifying the effects of electrical stresses on the interface dynamics. Results demonstrate that application of electric field, higher than the critical value (E ≥ E cr ), to the considered system enhances the spontaneous fluctuations at the interface and leads to an instability and formation of a filamentary structure at the interface. It is found that the presence of free charges made by dissociation process plays the main role in interface instability under applied electric field. Migration of the generated charge carriers drags fluid into motion and forms two counter-rotating vortices in the enclosure. Moreover, results confirm that application of electric field is an effective method for promoting mixing of two fluids, which can be helpful to step forward in design of new generation of fluid mixers here we call “EHD Mixers”. [Copyright &y& Elsevier]

• Cerium doped alumina/PANI nanocomposite particles were prepared. • The nanocomposite particles are proven to be pH responsive. • Ce(III) is released in acidic or alkaline solutions. • The nanocomposite particles were incorporated into epoxy coatings. • Protective system with superior corrosion protection performance was achieved. Alumina/polyaniline hybrid nanoparticles doped with cerium nitrate corrosion inhibitor was synthesized via a chemical polymerization method. The morphology and structure of the synthesized nanoparticles were investigated by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and X-Ray diffraction (XRD) techniques. Incorporation of alumina/polyaniline nanocomposite particles doped with cerium nitrate into epoxy coating on aluminum alloy 2024-T3 resulted in a protective system with superior corrosion protection performance confirmed by potentiodynamic scanning method (PDS) and electrochemical impedance spectroscopy (EIS). The corrosion current density of the nanocomposite coating was (7.35 ± 0.22)×10−9 A/cm2, which was reduced by two orders of magnitude compared with that of the control epoxy sample. Moreover, the embedding of cerium nitrate doped alumina/polyaniline nanoparticles into epoxy coating provides active protection against corrosion. The low frequency impedance values of the scratched area of this coating after 6 days immersion was three orders of magnitude higher than that of the control sample. [ABSTRACT FROM AUTHOR]

Controlling and manipulating liquid jets are of great interest in practical and scientific aspects. In the present work effects of transverse uniform electric field on behaviour of liquid jet, streaming downward due to the gravity, is experimentally investigated in details by performing a precise image processing of the extracted high speed video frames. In the experiments, by altering liquid flow rate and applied electric field strength, authors have tried to study the interplay of electrical and hydrodynamic forces which are indeed the main factors acting on the jet behaviour e.g. deflection, rhythmic motion, breakup mechanism and satellite droplets formation. Major aim of this study is to manipulate liquid jet so as to attain uniformly sized droplets by removing satellite droplets which has potential applications in various industrial and laboratorial units. This procedure was performed by applying dielectrophoretic force to the water jet as a polar liquid. Furthermore the droplets and also satellites behaviour, influenced by transverse electric field, have been investigated thoroughly. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a novel method for preparing metal powder with the aid of electrohydrodynamic (EHD) force is introduced. A pneumatic based atomization apparatus was constructed for this study. Solder melt jet is injected from a 250μm ID nozzle onto a viscous medium (transformer oil). As a result of jet impingement and penetration into the oil, the melt jet disintegrates into micro-sized droplets and ligaments by a combination of the natural jet breakup phenomenon and EHD atomization. Due to the presence of electrostatic forces, the disintegrated droplets and ligaments repel each other and therefore particle coalescence and agglomeration is minimized in this method. The breakup was captured with a high speed camera. The morphology and structure of the obtained powders were investigated using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), respectively. Morphology of the particles was controlled by varying the oil temperature and the EHD voltage. Structure investigations show that a decrease in particle size leads to an increase in interior microstrain. Also, interior microstrain increases by decreasing the oil temperature. The main advantage of the developed method is to produce fine powder with controlled characteristics such as size, size distribution, morphology and structure. [ABSTRACT FROM AUTHOR]