Coaxial Cones Research Articles

Static profiles of capillary surfaces in the annular space between two coaxial cones under microgravity

Static profiles of capillary surfaces in the annular space between two coaxial cones under microgravity

Modulation of coaxial cone-jet instability in active co-flow focusing

The breakup of coaxial cone-jet interfaces to compound droplets in axisymmetric co-flow focusing (CFF) upon actuation is studied through numerical simulations. Due to the coupling effect of double interfaces, the response behaviours of coaxial cone-jet flow to actuation are more complex than those of a single-layered interface structure. Particularly, the coaxial jet presents totally different response modes between weak and strong interface coupling situations. In this work, the phase diagrams of response modes for coaxial jet breakup are depicted, considering the effect of perturbation frequency, amplitude and liquid flow rates. In particular, the breakup of a coaxial jet can be synchronized with actuation within a frequency range containing the natural breakup frequency, resulting in uniform compound droplets with a single core inside the shell, and the size of droplets can be adjusted by frequency. As the perturbation frequency exceeds the upper critical value, the external perturbation is unable to dominate the jet breakup, while below the lower critical frequency, the jet breaks up with multiple droplets generated in one period. The perturbation amplitude mainly affects the jet breakup length and also leads to the transition between different response modes. The coaxial cone upstream of the orifice can act as a buffer layer, regulating the perturbation amplitude of the coaxial jet downstream. The degree of buffering effect is affected by the perturbation frequency and amplitude. As the perturbation amplitude approaches unity, the decrease of perturbation frequency leads to the intermittent jet behaviour from the cone tip with a vibrating manner of the coaxial cone. Based on the linear instability analysis on the simplified single jet models for weak-coupled and strong-coupled jets, scaling analyses are carried out, which predict the jet breakup length and the natural frequency and critical frequency for the synchronized breakup. Finally, a strong pulse is added on the perturbation to produce compound droplets with a controllable number of cores. The present work provides valuable guidance for the practical application of on-demand compound droplet generation through active CFF.

A novel method to measure small antennas using a wideband coaxial cone TEM cell

AbstractThis paper presents a novel method to measure physically small antennas using a coaxial cone transverse electromagnetic wave (TEM) cell. Due to the ultra‐wideband, large electric field strength, and high dynamic range characteristics, coaxial cone provides a reliable environment to measure parameters such as gain and antenna factor of small antennas. The frequency could cover 200 MHz–40 GHz. To investigate the suitability of the coaxial cone TEM cell to measure antenna, measurements for a wideband small antenna and a horn antenna are carried out. And the validity of this method is verified through comparison of the obtained results, the measurement uncertainty is evaluated. Compared to an anechoic chamber, the space, cost, and time requirements are reduced drastically. Accordingly, this method could be a more effective alternative way to conventional methods such as the three antennas method and the two antennas method using anechoic chambers.

Photographic studies of the normal impact of hard spheres on fused silica generating hertzian cones

Colour high-speed photographic framing sequences of the normal impact of 2 mm diameter tungsten carbide spheres on a block of fused silica at 150 m s−1 were taken at 1 × 106 frames per second. The initiation and growth of the resulting two coaxial cone cracks, which formed within 0.1 µs of the initial projectile contact, were followed. The innermost cone crack of a semi included angle of 32° travelled at a velocity of (2270± 100) m s−1 which is close to the theoretical maximum crack velocity of 2180 m s−1 in fused silica. Importantly, the semi included angle of the cone crack was about a half of the angle of the cone crack produced by quasi-static loading. A suggested explanation, based on the localized decrease of the target's Poisson's ratio due to the high impact loading rate, has been proposed and examples are given which support this suggestion.

Coupling Characteristics of Powder and Laser of Coaxial Cone Nozzle for Laser Direct Metal Deposition: Numerical Simulation and Experimental Study.

Laser direct metal deposition (LDMD) enables not only the preparation of high-performance coatings on the surfaces of low-property materials but also the three-dimensional direct manufacturing and re-manufacturing of parts. In the LDMD process, the spatial coupling characteristics of the powder flow and the laser beam are the key factors affecting the forming quality of the cladding layer. Based on the gas-solid two-phase flow theory, a numerical model of coaxial powder feeding was established by CFD. The powder flow characteristics of the lower part of the nozzle, the powder particle motion trajectory, and the optical-powder spatial coupling morphology and law were studied, and the relationship between the powder flow morphology, laser beam, and powder utilization was explored. On this basis, the law between the optical-powder coupling characteristics and the geometric characteristics of the cladding layer is discussed in conjunction with LDMD experiments. The results show that the powder concentration scalar located in the focal plane of the laser beam can be used to visualize the optical-powder coupling morphology. When the powder feeding speed exceeds the loading capacity of the carrier gas flow, the powder concentration in the center of the spot and the powder utilization rate decrease. When the carrier gas flow rate is 4.0 L/min and the powder feeding rate is 4.0 g/min, the best utilization rate achieved is 81.4%. In addition, the H (height) of the cladding layer is more sensitive to changes in the powder concentration than the W (width). These findings provide new ideas for nozzle structure design and the optimization of LDMD parameters.

Experimental and numerical investigations on characteristics of coaxial liquid cone in coflow focusing

This work examines the interfacial instability and flow patterns of the liquid cone in capillary co-flow focusing. The flow field of the outermost driving flow is estimated with the potential flow model, and the startup process of the coaxial cone is analyzed. The effect of various parameters on the cone instability is studied. Moreover, the flow field inside the cone is visualized through the particle tracing method and numerical simulation, showing that flow rates have a significant impact on the size of the recirculation flow.

Interfacial instability and transition of jetting and dripping modes in a co-flow focusing process

The breakup dynamics of coaxial liquid interfaces into compound droplets in a co-flow focusing process is studied systematically. In experiments, the jetting and dripping modes downstream the focusing orifice are identified within the parametric regime where a coaxial liquid cone can be established steadily, and the phase diagram is plotted under different flow rates of inner, outer, and driving liquids. The force balance for the jet interface is analyzed numerically to explore the critical conditions for the jetting-dripping transition. It is found that the instability of the inner interface is much easier to trigger the modes transition, and the transition criterion is decided by the balance of inertia force, shear stress, and interfacial tension at the local inner jet. The linear spatiotemporal instability analysis is further carried out to study the convective and absolute instabilities of the coaxial jets. The effects of main process parameters on jet instability are accessed, and the boundary between the absolute/convective instabilities is further compared with the experimental and numerical results, which achieves good agreement. Finally, the energy budget analysis of the instability of coaxial liquid jets is performed to provide more understanding of physical mechanisms for the mode transition.

Alternating current coaxial electrospray for micro-encapsulation

The present study examines the potential of low-frequency (< 1 kHz) alternating current (AC) electric field actuation for micro-encapsulation using coaxial electrospray. Ethanol, olive oil and glycerol fluid combinations have been used as working fluid. The amplitude of actuation has been varied in the range of 5.4–7.2 kV. Dye visualization of the Taylor cone and high-speed visualization of electrospray have been carried out. Confocal microscopy has been used to characterize the capsules structure. Current measurement has been used to quantify the net charge content of the capsules. The residual current carried by droplets is lower for AC actuation compared to that of DC actuation. DC actuation shows straight generatrix of Taylor cone while AC actuation shows cusp shape. Difference in charge accumulation on the interface of the core and shell liquid for the DC and AC actuation and the resulting Maxwell stress influence the curvature of Taylor cone. Bi-orthogonal decomposition is used to characterize the stability of the electrospray process. The cone jet is more stable at a higher frequency of AC actuation compared to low-frequency actuation. The minimum potential required for stable cone jet formation is lower for AC actuation compared to that of DC actuation. The Taylor cone length and cone angle are a function of actuation waveform, flow rates through the coaxial nozzle and actuation amplitude. The present study demonstrates that square wave AC actuation can successfully generate stable coaxial cone jet and capsules.

An all-dielectric 3D Luneburg lens constructed by common-vertex coaxial circular cones

An all-dielectric broadband 3D Luneburg lens has been designed and manufactured in our study, which is constructed by common-vertex coaxial circular cones. A prototype of the lens is fabricated using 3D printing technology. The far field of the, present lens is highly directive, incident waves are focused with highly concentration, and its operating frequency spans from 5 GHz to 20 GHz. It is also found that two highly directional beams are generated while two independent converged sources feed simultaneously at the edge of the lens. The intersection angle with the center of the lens is 90°, which indicates that the lens is an efficient double input-double output device.

Annular flow dynamic characteristics of two inverse coaxial rotational cones

Dye liquid visualization and PIV experiments were conducted to reveal the influence of the Reynolds number (Re) and the presence of an end plate at the upper boundary on the annular flow dynamics characteristics of coaxial cones. The key flow information, such as the vorticity and velocity distributions, time-averaged flow field, and Reynolds stresses, were obtained by processing the velocity field. The Taylor vortex dynamics mechanism was studied based on the quantitative evaluation of the periodic vortex transformations. The experimental results showed that there was upward flow in the annulus at very low Reynolds numbers (Re = 107 and 160), and the annular flow transitioned from an upward to a downward pattern as Re (Re ≥ 214) increased. The first vortex was always separated by a negative vortex, B2, generated in the top right corner for Re = 214–642. A counterclockwise vortex under the free water surface always formed because the centrifugal force dominated at the water level, and there was always a fixed clockwise vortex under the upper cap because the dynamic pressure dominated at the non-slip wall surface for Re = 214–1925. The dominant convex outward or concave inward flow reflected the dominant motive source force. The total Reynolds stress increased with the increase in Re, and the magnitudes of the stresses were in the following order: radial normal stress > axial normal stress > shear stress.

Проецирование коническими винтовыми линиями с постоянным шагом

This paper’s purpose is investigation of non-traditional projection systems and their projecting surfaces, the choice of such congruence parameters for conical helical lines, which allow cover the whole complex of requirements to the surface, obtained by projecting of an arbitrary flat or spatial line with congruence beams, as well as the use of computer graphics in surface visualization. In the paper has been presented an example of analytical interpretation for an image of curvilinear projection by conical helical lines with constant pitch, and a congruence example for conical helical lines located on coaxial cones with a common vertex and a variable angle of generatrix inclination to an axis. Have been investigated properties and defined parameters of the congruence helical line passing through a space arbitrary point which is not belonging to an axis. An approach for construction of spiral surfaces, which frame consists of beams projecting an arbitrary line. A form generation of surfaces by analytical methods and their visualization by means of computer graphics is one of applied geometry’s urgent problems in connection with the use of such methods in automated systems for scientific research, design, and manufacture on equipment with computer numerical control. The leading research method for this problem is the general analytical theory for surfaces’ applied form generation developed by Professor I.A. Skidan and formed a unique apparatus, based on mathematical support of computing technologies for design and creation of objects with complex forms. On examples of visualization for projecting surfaces by means of computer graphics it is possible to show applicability of analytical models in computer technologies for scientific researches, design and manufacturing.

Projecting by conical screw lines with constant step

The relevance of the study: The formation of surfaces by analytical methods and their visualization using computer graphics is one of the topical problems of applied geometry. Purpose of the study is to investigate non-traditional projection systems, to select congruence parameters of conical helical lines that cover the entire complex of surface requirements, obtained by projecting with conic rays an arbitrary flat or spatial line and using computer graphics in visualization of the surface. Methods of research: The general analytical theory of applied surface molding, developed by prof. Skidan I A and a single unit, which is based on the mathematical support of computer technologies for designing and creating objects of complex shape. Results of the research: An example of an analytical interpretation of the image of curvilinear projection by conical screw lines of a constant step and an example of congruence of conical screw lines, located on coaxial cones with a common vertex and a variable angle of inclination of the generator to the axis. The properties are investigated, the parameters of the helical line of the congruence, passing through an arbitrary point of space that does not belong to the axis, are determined. A method is proposed for constructing spiral surfaces, the framework of which consists of rays projecting an arbitrary line.

Modeling of ferrofluid-based microvalves in the magnetic field created by a current-carrying wire

The paper deals with a ferrofluid-based valve which can open and close the channel formed by two coaxial cones and a cylinder in the magnetic field of a straight current-carrying wire. Numerical modeling of the ferrofluid valve behaviour for different values of ferrofluid volume, pressure drop and current in the wire is done when the ferrofluid wets surrounding solid boundaries. It is shown that the presence of limiting cones allows the ferrofluid valve to sustain a pressure drop at high enough currents. The maximum pressure drop and the needed current can be obtained for each possible ferrofluid volume.

Laminar-turbulent transition regimes in the conical Taylor-Couette flow system

The present work is intended to experimentally study the Taylor-Couette flow between coaxial cones. The inner cone is rotated and the outer cone is maintained fixed. Both cones have the same apex angle Φ =12°, giving a constant annular gap δ =0.12. The height of the fluid column is H=155 mm. The working fluid is assumed as Newtonian and has constant properties (as density and viscosity) within the range of the required experimental conditions. By means of visualization techniques, the critical thresholds related to the onset of various instabilities have been obtained and the corresponding flow modes have been identified. Using images processing, spatio-temporal diagrams have also been calculated, showing the characteristics (wavelength, drift velocity) of the downward helical motion. The results obtained for these transition regimes are compared to those of Wimmer et al. [1-3].

Experimental Investigation of the Free Surface Effect on the Conical Taylor-Couette Flow System

The aim of this work is to highlight the critical thresholds corresponding to the onset of different instabilities considered in the flow between two vertical coaxial cones with and without free surface. The inner cone is rotating and the outer one is maintained at rest. Both cones have the same apex angle Φ =12° giving a constant annular gap δ =d/R1max. The height of the fluid column is H=155mm and It can be progressively decreased for each studied case of the flow system. Two kinds of configurations are studied, small and large gap. The working fluid is assumed as Newtonian and having constant properties like density and viscosity within the range of the required experimental conditions. By means of visualization technique of the flow we have been able to show the different transition modes occurring in the conical flow system according to the aspect ratio and then the induced action of the free surface which introduces a delay in the onset of different instability modes. The obtained results in term of features and stability of the flow are compared to those of Wimmer and Noui-Mehidi.

On the shielding of sound from a source near one or two coaxial cones

The shielding of the sound from a source near a cone or two coaxial circular cones is addressed by an exact analytical method, considering free spherical waves satisfying a rigid or impedance boundary condition on the wall of the cone(s); the boundary condition is applied for impedance proportional to the distance from the vertex. The exact solution involves the eigenvalues of the problem that are generally real or complex (not integers), and coincide with the degree of the associated Legendre functions and order of the spherical Bessel functions which specify respectively the latitudinal and radial dependencies of the wave field. These eigenfunctions or ‘conical wave harmonics’ can be chosen in more than one way, e.g. (a) as standing wave modes which are finite at the vertex of the cone(s), but do not satisfy a radiation condition at infinity; (b) as propagating waves satisfying a radiation condition at infinity, and generally singular at the vertex of the cone(s). The method of calculation of eigenvalues and eigenfunctions is presented both for a single cone and two coaxial cones with the same vertex, and arbitrary aperture(s). The method specifies the eigenvalues, and the corresponding radial, azimuthal and latitudinal eigenfunctions. An asymptotic formula is obtained for the eigenvalues which gives reasonable good agreement with the exact results. The eigenvalues and eigenfunctions appear with suitable amplitudes in the Green function representing a monopole source near the vertex of the cone(s). The acoustic field is plotted also for a longitudinal and a transverse dipole and mixed quadrupole source near the vertex.

Temperature rise in a verging annular die

Abstract Plastic pipes, tubes or catheters are extruded by pressure-driven flows through annular dies. Whereas die lands are straight, the section connecting the die land to the extruder either converges or diverges, converging when the product is smaller than the extruder barrel, and diverging when larger. In this paper, we carefully consider the converging or diverging connecting flows, in spherical coordinates, for the most common configuration: the Newtonian pressure-driven flow through the annulus between two coapical coaxial cones. We derive the exact analytical solution for the velocity profile, and then use this to arrive at the exact analytical solution for the temperature rise caused by viscous heating. We care about this rise because it often governs maximum throughput, since pipe makers must protect the melt from thermal degradation. We find that both the velocity profile, and the temperature profile, peak over the same conical surface and this surface is nearer the inner die wall. We also provide analytical expressions for the nonlinear pressure profile and the die cooling requirement. We find that this cooling requirement is always higher on the inner cone.

Perfectly rigid plastic flow in the thin gap between two approaching coaxial cones

A boundary value problem devoted to the inertialess axisymmetric flow of a perfectly rigid plastic incompressible material in the gap between two approaching coaxial cones is asymptotically analyzed. The ratio of the distance between the conical surfaces to the length of the generatrix is considered as a small geometric parameter. The coefficients at several leading terms in the expansions of velocities and stresses are found analytically using the method of asymptotic integration. The subdomains where an asymptotic behavior is not observed are determined.

On-demand generation of propagation-invariant photons with orbital angular momentum

We study the generation of propagation invariant photons with orbital angular momentum by spontaneous parametric down conversion (SPDC) using a Bessel-Gauss pump beam. The angular and conditional angular spectra are calculated for an uniaxial crystal optimized for type I SPDC with standard Gaussian pump beams. It is shown that, as the mean value of the magnitude of the transverse wave vector of the pump beam increases, the emission cone is deformed into two non coaxial cones that touch each other along a line determined by the orientation of the optical axis of the nonlinear crystal. At this location, the conditional spectrum becomes maximal for a pair of photons, one of which is best described by a Gaussian-like photon with a very small transverse wave vector, and the othera Bessel-Gauss photon with a distribution of transverse wave vectors similar in amplitude to that of the incident pump beam. A detailed analysis is then performed of the angular momentum content of SPDC photons by the evaluation of the corresponding transition amplitudes. As a result, we obtain conditions for the generation of heralded single photons which are approximately propagation invariant and have orbital angular momentum. A discussion is given about the difficulties in the interpretation of the results in terms of conservation of optical orbital angular momentum along the vector normal to the crystal surface. The angular spectra and the conditional angular spectra are successfully compared with available experimental data recently reported in the literature.

Bomb calorimetry as a bulk characterization tool for carbon nanostructures

Multiwalled carbon nanotubes (MWCNTs) consisting of coaxial graphene cylinders (cylindrical MWCNTs), cones (herringbone MWCNTs) or carbon fibers were combusted in an isothermal bomb calorimeter. Their standard enthalpies of formation were determined to be 16.56±2.76kJmol−1(C – per carbon mol) for carbon fibers, 21.70±1.32kJmol−1(C) for herringbone MWCNTs and 8.60±0.52kJmol−1(C) for cylindrical ones. All materials were characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, thermogravimetry, and elemental analysis. A linear correlation between the standard enthalpies of formation and D/G and G′/G Raman bands ratio (D – band is centered at 1350cm−1, G – 1585cm−1, G′ – 2700cm−1) demonstrates the applicability of bomb calorimetry for characterization of the “defectiveness” of the bulk carbon material in the sense Raman spectroscopy is widely used nowadays. Also, we show that the calorimetry may be used to estimate the oxygen content in the bulk carbon nanomaterials, as there is a linear correlation between the oxygen content (both total content and in carboxyl groups separately) and the standard enthalpies of formation for herringbone nanotubes oxidized by nitric acid.