Identical Cross-sectional Area Research Articles

Computational investigation of highly heated homogeneous subsonic turbulent jets issuing from plane and circular nozzles

In this paper, dynamic and thermal aspects of highly heated subsonic plane and circular jets flowing into a weak co-flow stream are numerically investigated. The two studied nozzle exit shapes have identical cross-sectional area and so equal equivalent diameter. Simulations are performed using the second order Reynolds Stress Model (RSM). The concordance between code predictions and experimental results is reasonably good. The centerline evolutions of velocity and temperature field are analyzed. It is shown that the mean centerline velocity and temperature decays are more rapid, the fluctuating quantities grow faster and the momentum and thermal half-widths are higher for the plane jet than for the circular jet. Moreover, higher values of entropy generation rate and Merit number correspond to non-circular jet. These results show that the breakdown of the axisymmetry at the exit of the jet together with heating the homogeneous jet enhance the mixing and the entrainment rates between the jet and its surrounding.

Finite element analysis of beam with different loading condition

Abstract This examination researches the diversion and the stressful appropriation in a length, thin cantilever beam or bar light emission rectangular cross section segment made of straight versatile the material behavior and mechanical properties that are homogeneous mixture. The redirections of a beam are basically a modeling of 3D issue. A flexible extending one way is joined by a pressure in opposite ways. This undertaking, structural and dynamic examination is a cycle to decide the stress, strain and distortion. Shaking qualities of a formation or a machine segment while it is being planned. It was gotten a significant choice to give an accommodating commitment in understanding control of numerous vibration wonders which experienced practically speaking. In present work we thought about the pressure and regular recurrence for various material have identical cross sectional area of the shafts are T, I and C shaft. The beam is planned and dissected in ANSYS 14.0 software. The beam shaft is fixed toward one side is vibrate to acquire the normal recurrence, modal shape in addition to redirection by the various segments and equipment.

Can the shape influence entropy generation for thermal convection of identical fluid mass with identical heating? A finite element introspection

PurposeThis paper aims to investigate the role of shapes of containers (nine different containers) on entropy generation minimization involving identical cross-sectional area (1 sq. unit) in the presence of identical heating (isothermal). The nine containers are categorized into three classes based on their geometric similarities (Class 1: square, tilted square and parallelogram; Class 2: trapezoidal type 1, trapezoidal type 2 and triangular; Class 3: convex, concave and curved triangular).Design/methodology/approachGalerkin finite element method is used to solve the governing equations for a representative fluid (engine oil: Pr = 155) at Ra = 103–105. In addition, finite element method is used to solve the streamfunction equation and evaluate the entropy generation terms (Sψ and Sθ). Average Nusselt number () and average dimensionless spatial temperature () are also evaluated via the finite element basis sets.FindingsBased on larger , larger and optimal Stotal values, containers from each class are preferred as follows: Class 1: parallelogrammic and square, Class 2: trapezoidal type 1 and Class 3: convex (larger , optimum Stotal) and concave (larger ). Containers with curved walls lead to enhance the thermal performance or efficiency of convection processes.Practical implicationsComparison of entropy generation, intensity of thermal mixing () and average heat transfer rate give a clear picture for choosing the appropriate containers for processing of fluids at various ranges of Ra. The results based on this study may be useful to select a container (belonging to a specific class or containers with curved or plane walls), which can give optimal thermal performance from the given heat input, thereby leading to energy savings.Originality/valueThis study depicts that entropy generation associated with the convection process can be reduced via altering the shapes of containers to improve the thermal performance or efficiency for processing of identical mass with identical heat input. The comparative study of nine containers elucidates that the values of local maxima of Sψ (Sψ,max), Sθ (Sθ,max) and magnitude of Stotal vary with change in shapes of the containers (Classes 1–3) at fixed Pr and Ra. Such a comparative study based on entropy generation minimization on optimal heating during convection of fluid is yet to appear in the literature. The outcome of this study depicts that containers with curved walls are instrumental to optimize entropy generation with reasonable thermal processing rates.

Effects of nanopore geometry on confined water flow: A view of lattice Boltzmann simulation

Water flow in nanoscale channel is demonstrated to be affected by the robust water-wall interactions, including that the flow significantly deviates from the conventional continuum flow. As suggested in different results of experimental observation and simulation in recent literature, nanopores exhibit higher/lower-than-expected flow capacity. Most existing studies are limited to simple geometry that displays a circular cross-section. However, the flow dynamics of water in noncircular pores significantly deviates from the Hagen–Poiseuille flow equation adopted in circular pores that exhibit different contact angles and dimensions. In this study, molecular interactions between water and the solid inner wall are substituted into the formulations of the Lattice Boltzmann method to simulate the flow dynamics in nanopores that exhibit different cross-sectional shapes and wettability. The results show that, under identical cross-sectional area injection pressure, the circular nanopore exhibits the maximum flow capacity. In terms of a circular cross-sectional shape, the constant density lines are also circular and concentric. For angular cross-sectional shape, the constant density lines do not comply with the cross-sectional shape, and the density varies significantly at the corner. The effects of geometry and density distribution of different contact angles are elucidated. An empirical formula under different geometry and wettability has been established, which is of high significance in modeling water flow in various engineering nano-systems such as shale matrix, membrane, and aquaporins.

Open-Channel Capillary Trees and Capillary Pumping.

Velocity of capillary flow in closed or open channels decreases as the flow proceeds down the length of the channel, varying as the inverse of the square root of time or as the inverse of travel distance. In order to increase the flow rate-and extend the duration of the flow-capillary pumps have been designed by mimicking the pumping principle of paper or cotton fibers. These designs provide a larger volume available for the wicking of the liquids. In microsystems for biotechnology, different designs have been developed based on experimental observation. In the present paper, the mechanisms at the basis of capillary pumping are investigated using a theoretical model for the flow in an open-channel "capillary tree" (i.e., an ensemble of channels with bifurcations mimicking the shape of a tree). The model is checked against experiments. Rules for obtaining better designs of capillary pumps are proposed; specifically, we find (1) when using a capillary tree with identical channel cross-sectional areas throughout, it is possible to maintain nearly constant flow rates throughout the channel network, (2) flow rate can be increased at each branch point of a capillary tree by slightly decreasing the areas of the channel cross section and decreasing the channel lengths at each level of ramification within the tree, and (3) higher order branching (trifurcations vs bifurcations) amplify the flow rate effect. This work lays the foundation for increasing the flow rate in open microfluidic channels driven by capillary flow; we expect this to have broad impact across open microfluidics for biological and chemical applications such as cell culture, sample preparation, separations, and on-chip reactions.

Finite element (GFEM) simulations on the effect of microwave heating for lossy dielectric samples with various shapes (circle, square and triangle)

Purpose This paper aims to investigate the thermal performance involving larger heating rate, targeted heating, heating with least non-uniformity of the spatial distribution of temperature and larger penetration of heating within samples vs shapes of samples (circle, square and triangular). Design/methodology/approach Galerkin finite element method (GFEM) with adaptive meshing in a composite domain (free space and sample) is used in an in-house computer code. The finite element meshing is done in a composite domain involving triangle embedded within a semicircular hypothetical domain. The comparison of heating pattern is done for various shapes of samples involving identical cross-sectional area. Test cases reveal that triangular samples can induce larger penetration of heat and multiple heating fronts. A representative material (beef) with high dielectric loss corresponding to larger microwave power or heat absorption in contrast to low lossy samples is considered for the current study. The average power absorption within lossy samples has been computed using the spatial distribution and finite element basis sets. Four regimes have been selected based on various local maxima of the average power for detailed investigation. These regimes are selected based on thin, thick and intermediate limits of the sample size corresponding to the constant area of cross section, Ac involving circle or square or triangle. Findings The thin sample limit (Regime 1) corresponds to samples with spatially invariant power absorption, whereas power absorption attenuates from exposed to unexposed faces for thick samples (Regime 4). In Regimes 2 and 3, the average power absorption non-monotonically varies with sample size or area of cross section (Ac) and a few maxima of average power occur for fixed values of Ac involving various shapes. The spatial characteristics of power and temperature have been critically analyzed for all cross sections at each regime for lossy samples. Triangular samples are found to exhibit occurrence of multiple heating fronts for large samples (Regimes 3 and 4). Practical implications Length scales of samples of various shapes (circle, square and triangle) can be represented via Regimes 1-4. Regime 1 exhibits the identical heating rate for lateral and radial irradiations for any shapes of lossy samples. Regime 2 depicts that a larger heating rate with larger temperature non-uniformity can occur for square and triangular-Type 1 lossy sample during lateral irradiation. Regime 3 depicts that the penetration of heat at the core is larger for triangular samples compared to circle or square samples for lateral or radial irradiation. Regime 4 depicts that the penetration of heat is still larger for triangular samples compared to circular or square samples. Regimes 3 and 4 depict the occurrence of multiple heating fronts in triangular samples. In general, current analysis recommends the triangular samples which is also associated with larger values of temperature variation within samples. Originality/value GFEM with generalized mesh generation for all geometries has been implemented. The dielectric samples of any shape are surrounded by the circular shaped air medium. The unified mesh generation within the sample connected with circular air medium has been demonstrated. The algorithm also demonstrates the implementation of various complex boundary conditions in residuals. The numerical results compare the heating patterns for all geometries involving identical areas. The thermal characteristics are shown with a few generalized trends on enhanced heating or targeted heating. The circle or square or triangle (Type 1 or Type 2) can be selected based on specific heating objectives for length scales within various regimes.

Comparison of Efficiency of Conventional Shaped Circular and Elliptical Shaped Combustor

There have been concerted efforts towards improving the fuel efficiency of the jet engines in the past, with an aim of reducing the incomplete combustion. The process of combustion in a jet engine takes place in the combustor. A study was conducted for enhancement of air-fuel mixing process by computational analysis of an elliptically shaped combustor for a gas turbine engine. The results of computational analysis of an elliptical shape combustor were compared with a circular shape combustor used in gas turbine engines with a identical cross sectional area. The comparison of the computationally derived parameters of the two combustors i.e. temperature, pressure, and velocity are studied and analyzed. The study intends towards the comparison of the combustion efficiencies of the circular and elliptically shaped combustors. The combustion efficency of elliptical chamber is found to be 98.72% at the same time it was observed 56.26% in case of circular type combustor.

Remnant Woven Bone and Calcified Cartilage in Mouse Bone: Differences between Ages/Sex and Effects on Bone Strength.

IntroductionMouse models are used frequently to study effects of bone diseases and genetic determinates of bone strength. Murine bones have an intracortical band of woven bone that is not present in human bones. This band is not obvious under brightfield imaging and not typically analyzed. Due to the band’s morphology and location it has been theorized to be remnant bone from early in life. Furthermore, lamellar and woven bone are well known to have differing mechanical strengths. The purpose of this study was to determine (i) if the band is from early life and (ii) if the woven bone or calcified cartilage contained within the band affect whole bone strength.Woven Bone Origin StudiesIn twelve to fourteen week old mice, doxycycline was used to label bone formed prior to 3 weeks old. Doxycycline labeling and woven bone patterns on contralateral femora matched well and encompassed an almost identical cross-sectional area. Also, we highlight for the first time in mice the presence of calcified cartilage exclusively within the band. However, calcified cartilage could not be identified on high resolution cone-beam microCT scans when examined visually or by thresholding methods.Mechanical Strength StudiesSubsequently, three-point bending was used to analyze the effects of woven bone and calcified cartilage on whole bone mechanics in a cohort of male and female six and 13 week old Balb/C mice. Three-point bending outcomes were correlated with structural and compositional measures using multivariate linear regression. Woven bone composed a higher percent of young bones than older bones. However, calcified cartilage in older bones was twice that of younger bones, which was similar when normalized by area. Area and/or tissue mineral density accounted for >75% of variation for most strength outcomes. Percent calcified cartilage added significant predictive power to maximal force and bending stress. Calcified cartilage and woven bone could have more influence in genetic models where calcified cartilage percent is double our highest value.

Resistance to venous flow: A mathematical description and implications for compartment syndromes.

The object of this work was to describe resistance to flow within a vein in a closed compartment. A vein is mathematically modeled as a collapsible cylinder with fixed perimeter exposed to extraluminal hydrostatic pressure within a closed compartment of the body. The principle of minimization of energy is used to determine the cross-sectional area and resistance to flow through such a cylinder in various states of collapse. A mathematical expression for the cross-sectional area of a partially collapsed tube is derived. Resistance to flow is calculated within the tube in various states of collapse and compared with the resistance to flow in an annular tube of identical cross-sectional area. Resistance increases very rapidly in the first 5% of collapse and remains greater than that in an annular vessel of identical cross-sectional area through all further collapse. Resistance to flow closely follows a logarithmic gain as the tube undergoes collapse from extraluminal pressure until opposite sides of the vein make contact. Within a closed compartment in which there is rising pressure, resistance to flow through a vein is predicted to increase as a logarithmic function of the vein's cross-sectional area. This rapid rise in resistance and hence decline in flow are consistent with the position that in compartment syndromes of all anatomic locations, the venous contribution to resistance of flow is of paramount importance to the pathophysiology.

Theoretical study on an integrated two-stage cascaded thermoelectric module operating with dual power sources

This paper presents an integrated two-stage cascaded thermoelectric module (TTEM) operating with dual power source. The integrated TTEM contains two stages of thermocouples with identical semiconductor cross-sectional area but different leg lengths. An analytical model for the TTEM is developed, and the influences of the key parameters are theoretically investigated. The obtained results indicate that optimum two stage currents combination can maximize both the cooling capacity and coefficient of performance (COP). Furthermore, the leg length allocation ratio for the two stages affects the maximum cooling capacity significantly. Larger leg length proportion of the colder stage may effectively contribute to the improvement in maximum cooling capacity. In addition, there exists an optimum leg length allocation ratio to obtain the corresponding optimum COP when the two stage currents are set to achieve the maximum cooling capacity of the TTEM. However, the total leg length has no effect on the corresponding optimum COP.

Pinch-off of non-axisymmetric vortex rings

AbstractThe formation and pinch-off of non-axisymmetric vortex rings is considered experimentally. Vortex rings are generated using a non-circular piston–cylinder arrangement, and the resulting velocity fields are measured using digital particle image velocimetry. Three different nozzle geometries are considered: an elliptical nozzle with an aspect ratio of two, an elliptical nozzle with an aspect ratio of four and an oval nozzle constructed from tangent circular arcs. The formation of vortices from the three nozzles is analysed by means of the vorticity and circulation, as well as by investigation of the Lagrangian coherent structures in the flow. The results indicate that, in all three nozzles, the maximum circulation the vortex can attain is determined by the equivalent diameter of the nozzle: the diameter of a circular nozzle of identical cross-sectional area. In addition, the time at which the vortex rings pinch off is found to be constant along the nozzle contours, and independent of relative variations in the local curvature. A formation number for this class of vortex rings is defined based on the equivalent diameter of the nozzle, and the formation number for vortex rings of the three geometries considered is found to lie in the range of 3–4. The implications of the relative shape and local curvature independence of the formation number on the study and modelling of naturally occurring vortex rings such as those that appear in biological flows is discussed.

The effects that changes in the diaphragm aperture have on the resulting shock tube flow

In a conventional shock tube, the driver and the driven sections have similar (if not identical) cross-sectional area and the diaphragm opened area, upon rupturing, is practically equal to the tube cross-sectional area. Such geometry results in generating a well-formed shock wave in the tube’s driven section. The present experimental work checks the effects that changes in the diaphragm ruptured area have on the generated shock and rarefaction waves. Experiments were conducted in an 80 mm by 80 mm cross section shock tube generating incident shock waves having Mach numbers within the range from 1.06 to 1.25. In each run, pressure histories were recorded along the driven and the driver sections of the shock tube. The recorded pressures reveal that progressive reduction in the diaphragm open space resulted in a weaker shock and both longer time and distance until the compression waves generated close to the diaphragm coalesces into a shock wave. In addition, reducing the open space of the diaphragm resulted in a significant slow down in the high pressure reduction prevailing in the driver section.

Permeability effects of single groin on flow characteristics

The results of an experimental study on the flow characteristics around a groin structure of various geometries and permeabilities are presented. The impermeable rectangular, the permeable pile, and the triangular-shaped groins are considered. The velocity fields were observed using large-scale particle image velocimetry, whereas the maximum velocities were measured using an acoustic Doppler velocimeter. An increased velocity at the groin tip and a broad range of the recirculation zones were observed for the impermeable rectangular groin. For the permeable pile groin, the velocity at the groin tip, the vortex strength, and the scale of the recirculation zone tended to decrease as the openings between the piles increased. Also, the triangular-shaped groin formed narrower and longer recirculation zones compared with the permeable pile groin of identical cross-sectional flow area. These quantitative findings on the flow patterns for groins of various geometries and permeabilities are practically important to design and evaluate their performance in field applications.

The effect of geometrical parameters on the discharge capacity of meandering compound channels

A number of methods and formulae has been proposed in the literature to estimate the discharge capacity of compound channels. When the main channel has a meandering pattern, a reduction in the conveyance capacity for a given stage is observed, which is due to the energy dissipations caused by the development of strong secondary currents and to the decrease of the main channel bed slope with respect to the valley bed slope. The discharges in meandering compound channels are usually assessed applying, with some adjustments, the same methods used in the straight compound channels. Specifically, the sinuosity of the main channel is frequently introduced to account for its meandering pattern, although some methods use different geometric parameters. In this paper the stage—discharge curves for several compound channels having identical cross-sectional area, roughness and bed slope but different planimetric patterns are numerically calculated and compared, in order to identify which geometric parameter should be efficaciously used in empirical formulae to account for meandering patterns. The simulations are carried out using a 3D finite-volume model that solves the RANS equations using a k - ε turbulence model. The numerical code is validated against experimental data collected in both straight and meandering compound channels. The numerical results show that the sinuosity is the main parameter to be accounted for in empirical formulae to assess the conveyance capacity of meandering compound channels. Comparison of the stage—discharge curves in the meandering compound channels with that obtained in a straight channel having identical cross-sectional area clearly shows the reduction of discharge due to the presence of bends in the main channel. The effect of other geometric parameters, such as the meander-belt width and the mean curvature radius, results very weak.

Experimental Demonstration of Electromagnetic Tunneling Through an Epsilon-Near-Zero Metamaterial at Microwave Frequencies

Silveirinha and Engheta have recently proposed that electromagnetic waves can tunnel through a material with an electric permittivity (epsilon) near zero (ENZ). An ENZ material of arbitrary geometry can thus serve as a perfect coupler between incoming and outgoing waveguides with identical cross-sectional area, so long as one dimension of the ENZ is electrically small. In this Letter we present an experimental demonstration of microwave tunneling between two planar waveguides separated by a thin ENZ channel. The ENZ channel consists of a planar waveguide in which complementary split ring resonators are patterned on the lower surface. A tunneling passband is found in transmission measurements, while a two-dimensional spatial map of the electric field distribution reveals a uniform phase variation across the channel--both measurements in agreement with theory and numerical simulations.

Three-dimensional distribution of spin-polarized current inside(Cu∕Co)pillar structures

We present a formalism determining spin-polarized current and electrochemical potential inside arbitrary electric circuit within diffusive regime for parallel/antiparallel magnetic states. When arbitrary nano-structure is expressed by 3-dimensional (3D) electric circuit, we can determine 3D spin-polarized current and electrochemical potential distributions inside it. We apply this technique to (Cu/Co) pillar structures, where pillar is terminated either by infinitely large Cu layer, or by Cu wire with identical cross-sectional area as pillar itself. We found that infinitely large Cu layers work as a strong spin-scatterers, increasing magnitude of spin-polarized current inside the pillar twice and reducing spin accumulation nearly to zero. As most experimentally studied pillar structures are terminated by such a infinitely large layers, we propose modification of standard Valet-Fert formalism to simply include influence of such infinitely large layers.

Direct vascular actions of methyclothiazide in remodeled mesenteric arteries from hypertensive patients

In vitro experiments were designed to assess the inhibitory effect of the thiazide diuretic methyclothiazide (MCTZ) on contractile responses to norepinephrine (NE) of mesenteric rings from hypertensive patients and normotensive controls. Arteries were taken from portions of mesocolon from 24 patients: 13 hypertensives and 11 normotensives. Changes in the tension of mesenteric ring preparations were measured isometrically. Histologic studies showed that the arteries from hypertensive patients exhibited 1) a greater media thickness-to-lumen diameter ratio, 2) a smaller lumen diameter, and 3) identical media cross-sectional area as those of normotensive controls. At the physiologic level, the hypertensive and normotensive arteries display similar contractile responses to KCl and NE. Furthermore, our results indicate that MCTZ induces concentration-dependent inhibition of the vasoconstrictor responses to NE. This study provides evidence that hypertension is associated with the remodeling of the human mesenteric artery and that MCTZ is as efficient in inhibiting the contractile response induced by NE on hypertensive than on normotensive arteries.

A Novel Cross-Flow Cascade Packed Column Design and Simulation

This paper develops a novel cross-flow cascade packed column. The column has a smaller width of packing in the direction of the gas flow and a bigger area for gas flow compared with a conventional cross-flow device with identical column diameter, stage height, and cross-sectional area for the irrigating liquid flows. The performance comparisons of the novel cross-flow cascade packed column with a countercurrent packed column for stripping ethanol from water indicate that the gas-phase pressure drop per theoretical stage in the novel cross-flow column is significantly lower than that in a countercurrent packed column operation under identical conditions. A methodology is developed for modeling the novel nine-stage cross-flow cascade packed column by using the number of transfer unit technique. This method is demonstrated by experimental data on ethanol-water.

An improved flow evaluation scheme in orifices of different aspect ratios

An accurate and reliable method of regurgitant flow calculation is currently unavailable. The goal of this study was to define a new general method of flow calculation for orifices of different aspect ratios. The success of the method relies on matching the imaged flow field distribution obtained by color flow mapping (CFM) to a three-dimensional (3D) numerical flow field distribution of known geometry. The flow field in three orifices of identical cross-sectional area with aspect ratios of 1 (circular), 2 and 4 (elliptical) was evaluated by: (a) CFM, (b) 3D echocardiographic imaging, and (c) 3D finite element modeling (FEM). The orifice shape and size were accurately estimated by 3D echocardiographic imaging. FEM showed that the normalized centerline velocity profile of the flow field depends on the orifice aspect ratio. CFM provided a good description of the centerline profile for each case. For a given distance from the orifice center, the equivelocity contour surface area increases with increasing aspect ratio. A simple flow calculation scheme was developed to calculate regurgitant flow independent of orifice shape. This improved method showed better results than previous studies and may prove to be advantageous when analyzing in vivo flow fields with complex geometries.

Entrainment into two-dimensional and axisymmetric turbulent gravity currents

Entrainment of ambient fluid into both two-dimensional and axisymmetric gravity currents is investigated experimentally using a novel neutralization technique. The technique involves the titrative neutralization of an alkaline gravity current which intrudes into and entrains an acidic ambient, and is visualized using a pH indicator solution. Using this technique, we can determine quantitative results for the amount of dilution in the head of the current. The head of the current is able to entrain ambient fluid both by shear instabilities on the current/ambient interface and by over-riding (relatively light) ambient fluid. Guided by our experimental observations, we present two slightly different theoretical models to determine the entrainment into the head of the current as a function of distance from the source for the instantaneous release of a constant volume of fluid in a two-dimensional geometry. By dimensional analysis, we determine from both models that the dimensionless entrainment or dilution ratio, E, defined as the ratio of the volumes of ambient and original fluid in the head, is independent of the initial reduced gravity of the current; and this result is confirmed by our experiments in Boussinesq situations. Our theoretical evaluation of E in terms of the initial cross-sectional area of the current agrees very well with our experimental measurements on the incorporation of an entrainment coefficient α, evaluated experimentally to be 0.063 ± 0.003. We also obtain experimental results for constant-volume gravity currents moving over horizontal surfaces of varying roughness. A particularly surprising result from all the experiments, which is reflected in the theoretical models, is that the head remains essentially unmixed – the entrainment is negligible – in the slumping phase. Thus the heads of gravity currents with identical initial cross-sectional areas but different initial aspect ratios (lock lengths) will begin to be diluted by ambient fluid at different positions and hence propagate at different rates. A range of similar results is determined, both theoretically and experimentally, for the instantaneous release of a fixed volume of (heavy) fluid in an axisymmetric geometry. By contrast, the results of our experiments with gravity currents fed by a constant flux exhibit markedly different entrainment dynamics due to the continual replenishment of the fluid in the head by the constant input of undiluted fluid from the tail.