External Cylinder Research Articles

Numerical simulation and performance improvement of a multi-polar concentric Halbach cylindrical magnet for magnetic refrigeration

Multi-polar concentric Halbach cylinders of magnets could generate the magnetic field varying considerably in the annular gaps, thus were applied in the rotary magnetic refrigerators. In the current investigation, a six-polar concentric Halbach cylinder is developed based on the ideal concentric one by the numerical simulation with COMSOL Multiphysics. Cylinder radii are optimized and magnet material profiles are adjusted for a better overall performance (Λcool). Moreover, the segmentation on the concentric cylinder is conducted for an easy fabrication, and the edge effect of finite-length device is studied. With the present investigation, it is found that a larger external radius of external cylinder facilitates a larger flux density in the high field region (|B|¯high), while Λcool could be worse. Meanwhile, with the removal of magnet materials enclosed by the equipotential lines of magnetic vector potential, the magnetic flux density in low field region (|B|¯low) drops from 0.271 to 0.0136T, and Λcool rises from 1.36 to 1.85T0.7. Moreover, a proper segmentation would not degrade the difference between |B|¯high and |B|¯low, on the contrary, Λcool rises by about 20.2% due to magnet materials lack for efficiency replaced by soft irons. Finally, current 3D simulation indicates the edge effect on Λcool could be trivial.

Considerations regarding the stress relieving in a special product

The special product has a steel bearing structure located inside the shoulders and it is fitted with a steel cylinder loaded by an internal pressure pi. The value of the maximum internal pressure is high, at limit being equal to the allowable stress (σa = pi), where pi = 3000 MPa. The uniform stresses decrease if there is an external pressure applied on the cylinder. Therefore, it must be produced external pressure in order to reduce the stress ctmax., in other words to achieve a relieving operation. The external diameter of the internal tube is larger than the internal diameter of the external tube. In the normal temperature conditions these two cylinders cannot be assembled. After it is heated up, expanded cylinder is mounted on the internal cylinder and after the quenching, on the contact surface it appears a relieving pressure p. We are interested in computing the parameters of this technological procedure, for the classic way of relieving, namely by heating up the external cylinder. After processing by cutting, radius R2 of the internal tube is greater than δ = 0.05 mm radius R2 of the external tube. After cooling, the two tubes have a common radius R2, which will have an average value between the values they had before the assembling process. This is why the external tube has to suffer a thermal expansion, the internal tube suffering a compression, so that the two displacements summed, measured perpendicular to the contact surface, have a value of δ = 0.05 mm. After the relieving operation, on the contact surface between the two tubes will be produces a contact pressure, p. In the paper we study the effect of the relieving pressure p, onto the stresses if there would be not relieving and the variation of stresses considering relieving of both the internal tube and the external tube. The highest values of the stresses are those on the internal face of the bearing. If calculations are in accordance with the third failure theory it results that the maximum tangential stresses are the highest values. The values of normal and shear stress influence the phenomenon of relieving in the bearing because high internal pressures inside the bearing may break the internal tube leading to collapse of the structure.

Development of a system of natural gas storage governed by simultaneous processes of adsorption–desorption

A system for natural gas storage was developed where energy effects involved in adsorption and desorption were combined through two concentric cylinders containing equal masses of activated carbon. The storage operating cycle was performed using methane feeding (compression/adsorption) in the internal cylinder, while simultaneously methane discharging (decompression/desorption) in the external cylinder. The charge and discharge operations were evaluated using the barometric technique at 298 K under storage pressures of 10, 30 and 60 bar, with flow rates of 1.14 × 10−3, 5.13 × 10−3 and 9.09 × 10−3 m3/min. The coaxial storage system provided faster pressure and temperature evolution toward equilibrium. A 50 % increase in the mass of gas stored under 60 bar was obtained when compared with the single storage tank.

A Luting Technique for Passive Fit of Implant-Supported Fixed Dentures.

Several factors contribute to distortion of implant prostheses during fabrication and could prevent passive, accurate adaptation between implants and implant frameworks. The misfit between implants and restorative components may be significant and possibly lead to biologic or mechanical complications. The aim of this article is to describe a laboratory luting technique used to lute implant cylinders to metal frameworks in implant prostheses. This technique provides accurate, passive fits. According to this technique, titanium implant cylinders provided with corresponding external castable cylinders are used. Implant cylinders are screwed into the analogs in the master cast while the castable cylinders on top are splinted together using castable resin to realize a castable resin pattern. After casting, the framework is adjusted and cemented to the titanium cylinders on the master cast. Due to its ease and quickness of use and clinical efficiencies, this technique is deemed particularly useful in immediate loading rehabilitations.

Numerical simulation of natural convection between a decentered triangular heating cylinder and a square outer cylinder filled with a pure fluid or a nanofluid using the lattice Boltzmann method

Natural convection around a decentered triangular cylinder placed in a square cylinder is studied numerically using the lattice-Boltzmann method. The study is conducted for pure water and water–silver nanofluid. The inner heating triangular cylinder is maintained at a constant and uniform temperature while the vertical/(horizontal) sides of the external cylinder are cooled at constant temperature/(considered adiabatic). The numerical analysis is carried out for three decentered positions of the triangular block toward the left side of the outer square cylinder; these are Left-Bottom (LB), Left-Middle (LM) and Left-Top (LT). The other parameters governing the problem are the Rayleigh number (103≤Ra≤107), the Prandtl number of the pure water (Pr=7) and the volume fraction of nanoparticles (0≤φ≤0.1). The effective thermal conductivity and viscosity of nanofluids are calculated using Maxwell–Garnetts (MG) and Brinkman models, respectively. The results obtained show that fluid flow and heat transfer characteristics are highly affected by the heating cylinder position. The increase of nanoparticles volume fraction has a positive impact on the average Nusselt number for all considered positions of the heating block. Results of the block's positions on the vertical centerline of the outer cylinder are also presented and discussed for comparison purposes. In dominating natural convection regime, it is found out that the bottom/(top) position of the block becomes the most/(least) favorable to heat transfer.

Оценка конструктивного совершенства систем принудительного охлаждения синхронных электромагнитных машин ударного действия

Impact synchronous electromagnetic machines forced cooling systems constructions have been classified and estimated. The first group of electromagnetic machines cooling systems include impact node external ventilation ones where heat is dissipated only from the magnetic core external cylinder surface. The second group involves cooling systems with internal airflow paths having independent air inlet and outlet through holes in poles. The third group includes cooling systems with coaxial channels in windings. If multilayer winding separate sections have the same thickness, their balancing cooling is provided by airflow rate in particular ventilation channels in proportion to dissipated power. Hence temperature difference between heated layers in the winding space can be two times and more reduced. The fourth group includes cooling systems with channels radial configuration to increase windings total cooling surface area, reduce airflow resistance and provide more balanced heating of both windings. External forced airflow cooling systems are specified with heat flow range related to winding cooling surface area and specific winding active volume thermal load. Forced air cooling is proved to permit additional electromagnetic impact load, increasing impact energy or frequency at permissible heating. Ventilation unit power to support electromagnetic impact machine duty cycle about 100% can be 25% of power consumed by the impact node.

Estudio del Comportamiento I vs. V de la Descarga Luminiscente de Baja Presión en Corriente Continua y Corriente Continua Pulsante en un Reactor Tipo Calorímetro

<p>Al generar una descarga luminiscente con corriente continua o corriente continua pulsada en diferentes<br />atmósferas gaseosas, ésta se puede caracterizar por el color o por el comportamiento de la curva de I vs. V donde, para cada una de las atmósferas se pueden presentar los tipos de régimen de la descarga luminiscente, que son: descarga luminiscente subnormal, descarga luminiscente normal y descarga luminiscente anormal. En este trabajo se generaron estos tipos de descargas en un reactor cilíndrico concéntrico cuyo electrodo interno hace las veces de cátodo, y el externo, de ánodo. Entre los dos electrodos fue generada la descarga luminiscente de baja presión, utilizando diferentes atmósferas gaseosas (aire, argón e hidrógeno). Las descargas fueron estudiadas a varias presiones, entre 1 torr y 6 torr, y también a diferentes corrientes, entre 200 mA y 500 mA, con incremento de 50 mA en los regímenes de corriente continua y corriente continua pulsada. Las características de dichas descargas fueron analizadas a través de sus curvas I vs. V.</p><p><br /><strong>Palabras clave:</strong> Curvas I vs. V, Descarga luminiscente subnormal, Descarga luminiscente normal, Descarga luminiscente anormal.</p><p> </p>

A Multi-Zone Model of the Combustion Process in an Si Engine as an External Cylinder of the Gt-Power Simulation Tool

Shrnutí Příspěvek představuje obecnou proceduru týkající se implementace uživatelského modelu jako externího válce simulačního nástroje GT-Power. Konkrétně, vyvinutý vícezónový model vysokotlaké části termodynamického cyklu čtyřdobého spalovacího motoru je zde použit jako přizpůsobený simulační kód pro zajištění výpočtů souvisejících s chemickou transformací spalování, přestupem tepla a odpovídajícími stavovými veličinami. Jsou zde prezentovány vybrané technické podrobnosti a výsledky tohoto propojení

The stability of a thin water layer over a rotating disk revisited

The flow driven by a rotating disk of a thin fluid layer in a fixed cylindrical casing is studied by direct numerical simulation and experimental flow visualizations. The characteristics of the flow are first briefly discussed but the focus of this work is to understand the transition to the primary instability. The primary bifurcation is 3D and appears as spectacular sharp-cornered polygonal patterns located along the shroud. The stability diagram is established experimentally in a (Re, G plane, where G is the aspect ratio of the cavity and Re the rotational Reynolds number and confirmed numerically. The number of vortices scales well with the Ekman number based on the water depth, which confirms the existence of a Stewartson layer along the external cylinder. The critical mixed Reynolds number is found to be constant as in other rotating flows involving a shear-layer instability. Hysteresis cycles are observed highlighting the importance of the spin-up and spin-down processes. In some particular cases, a crossflow instability appears under the form of high azimuthal wave number spiral patterns, similar to those observed in a rotor-stator cavity with throughflow and coexists with the polygons. The DNS calculations confirm the experimental results under the flat free surface hypothesis.

Sinusoidal geometry effects on heat transfer and environment in a cylindrical configuration

Several heat transfer expressions have been developed for the local and average Nusselt numbers in a vertical cylindrical configuration to reduce heat losses around a device. Three cases are considered: first, the two cylinders are stationary, second, the inner cylinder rotates about the vertical axis and the outer cylinder is kept stationary and third, the cylinders walls make the object of the two sinusoidal protuberances. One protuberance on the inner cylinder (external surface) and the other one on the external cylinder (internal surface). Numerical solutions are obtained for laminar natural and mixed convection using the control volume method in the case of uniform heating and uniform wall temperature. The obtained heat correlations provide a basis for estimating transfer rates for Newtonian fluids. These are obtained for restricted ranges of conditions and are compared with representative theoretical and experimental expressions.

Strong nonlinear focusing of light in nonlinearly controlled electromagnetic active metamaterial field concentrators

The idea of nonlinear ‘transformation optics-inspired’ [–] electromagnetic cylindrical field concentrators has been taken up in a preliminary manner in a number of conference reports [–]. Such a concentrator includes both external linear region with a dielectric constant increased towards the centre and internal region with nonlinearity characterized by constant coefficients. Then, in the process of farther investigations we realized the following factors considered neither in [–] nor in the recent paper []: saturation of nonlinearity, nonlinear losses, linear gain, numerical convergence, when nonlinear effect becomes very strong and formation of ‘hotspots’ starts. It is clearly demonstrated here that such a strongly nonlinear process starts when the nonlinear amplitude of any incident beam(s) exceeds some ‘threshold’ value. Moreover, it is shown that the formation of hotspots may start as the result of any of the following processes: an increase of the input amplitude, increasing the linear amplification in the central nonlinear region, decreasing the nonlinear losses, a decrease in the saturation of the nonlinearity. Therefore, a tendency to a formation of ‘hotspots’ is a rather universal feature of the strongly nonlinear behaviour of the ‘nonlinear resonator’ system, while at the same time the system is not sensitive to the ‘prehistory’ of approaching nonlinear threshold intensity (amplitude). The new proposed method includes a full-wave nonlinear solution analysis (in the nonlinear region), a new form of complex geometric optics (in the linear inhomogeneous external cylinder), and new boundary conditions, matching both solutions. The observed nonlinear phenomena will have a positive impact upon socially and environmentally important devices of the future. Although a graded-index concentrator is used here, it is a direct outcome of transformation optics. Numerical evaluations show that for known materials these nonlinear effects could be readily achieved.

A numerical approach to solve an inverse problem in lubrication theory

In this paper we consider a numerical approach to reach the equilibrium position of a journal bearing with radial loading. The system consists of an external cylinder surrounding a rotating shaft. The problem is modelled by the hydrodynamic Reynolds equation with a cavitation model of Elrod–Adams. Both equations are coupled to Newton’s second law which describes the position of the shaft. The problem is considered as an inverse problem where the coefficient of the equation is unknown. The numerical approach to solve the inverse problem is based on a trust-region algorithm along with the finite element method. The Heaviside function in the Elrod–Adams equation is approximated by a third order Hermite polynomial. The trust-region algorithm for solving the inverse problem showed another way of solution, different from the ones that exist at this moment.

Inverse Problem of Failure Mechanics for a Drawing Die Strengthened with a Holder

A plane problem of failure mechanics is considered for concentrically integrated cylinders. It is assumed that the drawing die (internal cylinder) is negative allowance strengthened by means of external cylinder (holder), and near the surface of the drawing die there are N arbitrarily located rectilinear cracks of length 2lk (k=1,2,...,N). Theoretical analysis on definition the negative allowance providing minimization of failure parameters (stress intensity factors) of drawing die was carried out on minimax criterion. A simplified method for minimization the failure parameters of a hard alloy drawing die was separately considered.

Influence of Rotating Speed Ratio on the Annular Turbulent Flow between Two Rotating Cylinders

Rotating flows represent a very interesting area for researchers and industry for their extensive use in industrial and domestic machinery and especially for their great energy potential, annular flows are an example that draws the attention of researchers in recent years. The best design and optimization of these devices require knowledge of thermal, mechanical and hydrodynamic characteristics of flows circulating in these devices. An example of hydrodynamic parameters is the speed of rotation of the moving walls. This work is to study numerically the influence of the rotating speed ratio Γ of the two moving cylinders on the mean and especially on the turbulent quantities of the turbulent flow in the annular space. The numerical simulation is based on one-point statistical modeling using a low Reynolds number second-order full stress transport closure (RSM model), simulation code is not a black box but a completely transparent code where we can intervene at any step of the calculation. We have varied Γ from -1.0 to 1.0 while maintaining always the external cylinder with same speed Ω. The results show that the turbulence structure, profiles of mean velocities and the nature of the boundary layers of the mobile walls depend enormously on the ratio of speeds. The level of turbulence measured by the kinetic energy of turbulence and the Reynolds stresses shows well that the ratio Γ is an interesting parameter to exploit turbulence in this kind of annular flows.

Taylor-Couette flow control using the outer cylinder cross-section variation strategy

A numerical study of a controlled flow evolving in a Taylor-Couette system is presented in this paper. The study is devoted to investigate the effect of the outer cylinder cross-section variation on the flow behavior. It is aimed to make assessment of the flow response in terms of the criticality of the early transitional flow regimes and the accompanying flow topology alterations. The numerical simulations are carried out on the Fluent software package for a three-dimensional incompressible flow. The basic system is characterized by a height H = 200 mm, a ratio of the inner to the outer cylinders radii η = 0.9, an aspect ratio corresponding to the cylinders height reported to the gap length Г = 40 and a ratio of the gap to the radius of the inner cylinder δ = 0.1. The numerical deformation of the outer cylinder is executed using the dynamic mesh program according to a predefined function implemented in a homemade program as an UDF (user defined function). It is established that the first instability mode of transition is retarded from Ta c1 = 41.33, corresponding to the first Taylor number critical value, to Ta c1 = 70 when the deforming amplitude is equal to 15% the external cylinder diameter value. This flow relaminarization process is accompanied by substantial modifications in the flow behavior and configuration.

The Couette problem for a Kelvin–Voigt medium

An analog of the classical Couette problem for the motion of an incompressible viscoelastic Kelvin–Voigt medium in a gap between two coaxial cylinders is considered. The external cylinder is fixed, whereas the internal cylinder is rotating either forcedly with a constant velocity or inertially. The unique solvability is proved in both cases. An analogy between the propagation of acoustic cylindrical waves in a viscous gas and transversal waves in a Kelvin–Voigt medium moving along circular trajectories is discussed. The asymptotic behavior of solutions is also studied. It is shown that the limit regime can be monotone or oscillatory in dependence on the parameters of the problem. Bibliography: 11 titles. Illustrations: 2 figures.

In Situ Explosive Detection Using a Miniature Plasma Ion Source and a Portable Mass Spectrometer

A small low-temperature plasma (LTP) ionization probe was coupled to a portable mass spectrometer for the rapid detection of trace explosives on surfaces. Using only a small diaphragm pump to supply ambient air to the LTP source, 100 ng each of pentaerythritol tetranitrate (PETN), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and 2,4,6-trinitrophenylmethylnitramine (Tetryl) were detectable on glass in under 1 minute. The main ion signal from these molecules (M) is the [M + NO3]− species. While much optimization remains, it is believed that this miniature LTP source will remove the need for external gas cylinders and additional heating for in situ explosives detection using portable mass spectrometers.

DEVELOPMENT OF A NEW SEMI-ACTIVE FRICTION DAMPER USING PIEZOELECTRIC TECHNOLOGY FOR THE ANTI-SEISMIC CONTROL OF CIVIL STRUCTURES

This work presents a new semi-active friction damper, based on the piezoelectric technology, for the anti-seismic control of a civil structure. The device has been conceived and designed at D.I.A.S. (Department of Aerospace En­gineering) of University Federico II of Naples. It belongs to the family of the semi-active technologies of structural control for a civil structure. Damper is based on an external cylinder and an internal hollow piston that slips in­side the cylinder. Device presents an original conceptual lay-out, developed at D.I.A.S and it is independent by any scheme, available in literature.

Stresses in rotating heterogeneous viscoelastic composite cylinders with variable thickness

An analytical solution is presented for the rotation problem of a two-layer composite elastic cylinder under a plane strain assumption. The external cylinder has variable-thickness formulation, and is made of a heterogeneous orthotropic material. It contains a fiber-reinforced viscoelastic homogeneous isotropic solid core of uniform thickness. The thickness and elastic properties of the external cylinder are taken as power functions of the radial direction. By the boundary and continuity conditions, the radial displacement and stresses for the rotating composite cylinder are determined. The effective moduli and Illyushin’s approximation methods are used to obtain the viscoelastic solution to the problem. The effects of heterogeneity, thickness variation, constitutive, time parameters on the radial displacement, and stresses are investigated.

An efficient micromixer based on multidirectional vortices due to baffles and channel curvature.

An efficient planar micromixer based on multidirectional vortices in a curved channel with radial baffles is proposed and examined in this work. The curvature of the microchannel and the radial baffles induce vortices in different directions. The multidirectional vortices and the converging-diverging flow caused by the baffles contribute together to the enhancement of mixing. The micromixer is fabricated with polydimethylsiloxane by a single planar microlithography process and the mixing behaviors are observed by a confocal spectral microscope imaging system to validate the simulation obtained by a commercial code. The simulation and experimental results are in reasonable agreement. The concentration distributions and flow patterns obtained reveal the following trends. (i) The mixing efficiency of the basic C-shaped micromixer with the first baffle attached to the internal cylinder and the second attached to the external cylinder is better than that of the C-shaped micromixer with inverted arrangement of baffles. (ii) When the radius of the curved channel and the width of the passage between the baffle and the cylindrical wall are small enough and the Reynolds number (Re) is large enough, an extra separation vortex develops in the downstream of the second baffle. This phenomenon is one of the reasons of trend (i). (iii) A micromixer consisting of a few basic C-shaped micromixers connected by straight channels may generate a high degree of mixing for the case with a large Re.