1000 resultados para aluminum tube
Resumo:
Variable cross-sectional area ducts are often used for attenuation at lower frequencies (of the order of firing frequency), whereas concentric tube resonators provide attenuation at relatively higher frequencies. In this paper, analysis of one dimensional control volume approach of conical concentric tube resonators is validated experimentally. The effects of mean flow and taper are investigated. The experimental setup is specially designed to measure the pressure transfer function in the form of Level Difference or Noise Reduction across the test muffler. It is shown that there is a reasonably good agreement between the predicted values of the Noise Reduction and the measured ones for incompressible mean flow as well as stationary medium. (C) 2011 Institute of Noise Control Engineering.
Resumo:
The influence of an eccentrically inserted catheter on the peristaltic pumping in a tube is investigated under long wavelength, low Reynolds number assumptions. The radially asymmetric deformation of the wall arising through an eccentrically inserted catheter is taken into consideration by choosing an appropriate bipolar coordinate system. The effect of the position and size of the catheter on pumping characteristics is studied. The best performance of pumping is noticed at a certain position of the catheter. The size of the catheter, when placed eccentrically, alters the pressure signature significantly inside the bolus, unlike the concentric case discussed by Lykoudis and Roos (1971). Further, the maximum pressure rise in one period of the peristaltic wave is observed to decrease with an increase in the eccentricity.
Resumo:
Peristaltic motion of two immiscible viscous incompressible fluids in a circular tube is studied in pumping and copumping ranges under long-wavelength and low-Reynolds-number assumptions. The effect of the peripheral-layer viscosity on the time-averaged flux and the mechanical efficiency is studied. The formation and growth of the trapping zone in the core and the peripheral layer are explained. It is observed that the bolus volume in the peripheral layer increases with an increase in the viscosity ratio. The limits of the time-averaged flux (Q) over bar for trapping in the core are obtained. The trapping observed in the peripheral layer decreases in size with an increase in (Q) over bar but never disappears. The development of the complete trapping of the core fluid by the peripheral-layer fluid with an increase in the time-averaged flux is demonstrated. The effect of peripheral-layer viscosity on the reflux layer is investigated. It is also observed that the reflux occurs in the entire pumping range for all viscosity ratios and it is absent in the entire range of copumping.
Resumo:
The stability of the Hagen-Poiseuille flow of a Newtonian fluid in a tube of radius R surrounded by an incompressible viscoelastic medium of radius R < r < HR is analysed in the high Reynolds number regime. The dimensionless numbers that affect the fluid flow are the Reynolds number Re = (rho VR/eta), the ratio of the viscosities of the wall and fluid eta(r) = (eta(s)/eta), the ratio of radii H and the dimensionless velocity Gamma = (rho V-2/G)(1/2). Here rho is the density of the fluid, G is the coefficient of elasticity of the wall and V is the maximum fluid velocity at the centre of the tube. In the high Reynolds number regime, an asymptotic expansion in the small parameter epsilon = (1/Re) is employed. In the leading approximation, the viscous effects are neglected and there is a balance between the inertial stresses in the fluid and the elastic stresses in the medium. There are multiple solutions for the leading-order growth rate s((0)), all of which are imaginary, indicating that the fluctuations are neutrally stable, since there is no viscous dissipation of energy or transfer of energy from the mean flow to the fluctuations due to the Reynolds stress. There is an O(epsilon(1/2)) correction to the growth rate, s((1)), due to the presence of a wall layer of thickness epsilon(1/2)R where the viscous stresses are O(epsilon(1/2)) smaller than the inertial stresses. An energy balance analysis indicates that the transfer of energy from the mean flow to the fluctuations due to the Reynolds stress in the wall layer is exactly cancelled by an opposite transfer of equal magnitude due to the deformation work done at the interface, and there is no net transfer from the mean flow to the fluctuations. Consequently, the fluctuations are stabilized by the viscous dissipation in the wall layer, and the real part of s(1) is negative. However, there are certain values of Gamma and wavenumber k where s((1)) = 0. At these points, the wall layer amplitude becomes zero because the tangential velocity boundary condition is identically satisfied by the inviscid flow solution. The real part of the O(epsilon) correction to the growth rate s((2)) turns out to be negative at these points, indicating a small stabilizing effect due to the dissipation in the bulk of the fluid and the wall material. It is found that the minimum value of s((2)) increases proportional to (H-1)(-2) for (H-1) much less than 1 (thickness of wall much less than the tube radius), and decreases proportional to H-4 for H much greater than 1. The damping rate for the inviscid modes is smaller than that for the viscous wall and centre modes in a rigid tube, which have been determined previously using a singular perturbation analysis. Therefore, these are the most unstable modes in the flow through a flexible tube
Resumo:
The stability of Hagen-Poiseuille flow of a Newtonian fluid of viscosity eta in a tube of radius R surrounded by a viscoelastic medium of elasticity G and viscosity eta(s) occupying the annulus R < r < HR is determined using a linear stability analysis. The inertia of the fluid and the medium are neglected, and the mass and momentum conservation equations for the fluid and wall are linear. The only coupling between the mean flow and fluctuations enters via an additional term in the boundary condition for the tangential velocity at the interface, due to the discontinuity in the strain rate in the mean flow at the surface. This additional term is responsible for destabilizing the surface when the mean velocity increases beyond a transition value, and the physical mechanism driving the instability is the transfer of energy from the mean flow to the fluctuations due to the work done by the mean flow at the interface. The transition velocity Gamma(t) for the presence of surface instabilities depends on the wavenumber k and three dimensionless parameters: the ratio of the solid and fluid viscosities eta(r) = (eta(s)/eta), the capillary number Lambda = (T/GR) and the ratio of radii H, where T is the surface tension of the interface. For eta(r) = 0 and Lambda = 0, the transition velocity Gamma(t) diverges in the limits k much less than 1 and k much greater than 1, and has a minimum for finite k. The qualitative behaviour of the transition velocity is the same for Lambda > 0 and eta(r) = 0, though there is an increase in Gamma(t) in the limit k much greater than 1. When the viscosity of the surface is non-zero (eta(r) > 0), however, there is a qualitative change in the Gamma(t) vs. k curves. For eta(r) < 1, the transition velocity Gamma(t) is finite only when k is greater than a minimum value k(min), while perturbations with wavenumber k < k(min) are stable even for Gamma--> infinity. For eta(r) > 1, Gamma(t) is finite only for k(min) < k < k(max), while perturbations with wavenumber k < k(min) or k > k(max) are stable in the limit Gamma--> infinity. As H decreases or eta(r) increases, the difference k(max)- k(min) decreases. At minimum value H = H-min, which is a function of eta(r), the difference k(max)-k(min) = 0, and for H < H-min, perturbations of all wavenumbers are stable even in the limit Gamma--> infinity. The calculations indicate that H-min shows a strong divergence proportional to exp (0.0832 eta(r)(2)) for eta(r) much greater than 1.
Resumo:
Flows with velocity profiles very different from the parabolic velocity profile can occur in the entrance region of a tube as well as in tubes with converging/diverging cross-sections. In this paper, asymptotic and numerical studies are undertaken to analyse the temporal stability of such 'non-parabolic' flows in a flexible tube in the limit of high Reynolds numbers. Two specific cases are considered: (i) developing flow in a flexible tube; (ii) flow in a slightly converging flexible tube. Though the mean velocity profile contains both axial and radial components, the flow is assumed to be locally parallel in the stability analysis. The fluid is Newtonian and incompressible, while the flexible wall is modelled as a viscoelastic solid. A high Reynolds number asymptotic analysis shows that the non-parabolic velocity profiles can become unstable in the inviscid limit. This inviscid instability is qualitatively different from that observed in previous studies on the stability of parabolic flow in a flexible tube, and from the instability of developing flow in a rigid tube. The results of the asymptotic analysis are extended numerically to the moderate Reynolds number regime. The numerical results reveal that the developing flow could be unstable at much lower Reynolds numbers than the parabolic flow, and hence this instability can be important in destabilizing the fluid flow through flexible tubes at moderate and high Reynolds number. For flow in a slightly converging tube, even small deviations from the parabolic profile are found to be sufficient for the present instability mechanism to be operative. The dominant non-parallel effects are incorporated using an asymptotic analysis, and this indicates that non-parallel effects do not significantly affect the neutral stability curves. The viscosity of the wall medium is found to have a stabilizing effect on this instability.
Resumo:
The oscillating flow and temperature field in an open tube subjected to cryogenic temperature at the cold end and ambient temperature at the hot end is studied numerically. The flow is driven by a time-wise sinusoidally varying pressure at the cold end. The conjugate problem takes into account the interaction of oscillatory flow with the heat conduction in the tube wall. The full set of compressible flow equations with axisymmetry assumption are solved with a pressure correction algorithm. Parametric studies are conducted with frequencies of 5-15 Hz, with one end maintained at 100 K and other end at 300 K. The flow and temperature distributions and the cooldown characteristics are obtained. The frequency and pressure amplitude have negligible effect on the time averaged Nusselt number. Pressure amplitude is an important factor determining the enthalpy flow through the solid wall. The frequency of operation has considerable effect on penetration of temperature into the tube. The density variation has strong influence on property profiles during cooldown. The present study is expected to be of interest in applications such as pulse tube refrigerators and other cryocoolers, where oscillatory flows occur in open tubes. (C) 2011 Elsevier Ltd. All rights reserved.
Resumo:
Nanoembedded lead-tin alloys in aluminum matrix were synthesized by rapid solidification processing. These melt-spun aluminum alloys were then investigated using XRD, EDX and TEM. The XRD study reveals that the melt-spun samples contain elemental aluminum, lead and tin. The TEM analysis shows that embedded particles in aluminium matrix have a distinct two-phase contrast of lead and tin. The lead and tin in these nanoalloys exhibit an orientation relationship with the matrix aluminum and with each other. DSC studies were conducted to reveal the melting and solidification characteristics of these embedded nanoalloys. DSC thermograms exhibit features of multiple solidification exotherms on thermal cycling, which can be attributed to sequential melting and solidification of lead and tin in the respective alloys.
Resumo:
Thermal decomposition of 1,2-dichloroethane (1,2-DCE) has been studied in the temperature range of 10501175 K behind reflected shock waves in a single pulse shock tube. The unimolecular elimination of HCl is found to be the major channel through which 1,2-DCE decomposes under these conditions. The rate constant for the unimolecular elimination of HCl from 1,2-dichloroethane is found to be 10(13.98+/-0.80) exp(-57.8+/-2.0/RT) s(-1), where the activation energy is given in kcal mol(-1) and is very close to that value for CH3CH2Cl (EC). Ab initio (HF and MP2) and DFT calculations have been carried out to find the activation barrier and the structure of the transition state for this reaction channel from both EC and 1,2-DCE. The preexponential factors calculated at various levels of theory (BF/6-311++G**, MP2/6-311++G**, and B3LYP/6-311++G**) are (approximate to10(15) s(-1)) significantly larger than the experimental results. If the torsional mode in the ground state is treated as free internal rotation the preexponential factors reduce significantly, giving excellent agreement with experimental values. The DFT results are in excellent (fortuitous?) agreement with the experimental value for activation energy for 1,2-DCE while the MP2 and HF results seem to overestimate the barrier. However, DFT results for EC is 4.5 kcal mol(-1) less than the previously reported experimental values. At all levels, theory predicts an increase in HCI elimination barrier on beta-Cl substitution on EC.
Resumo:
In order to obtain basic understanding of microstructure evolution in laser-surface-alloyed layers, aluminum was surface alloyed on a pure nickel substrate using a CO2 laser. By varying the laser scanning speed, the composition of the surface layers can be systematically varied. The Ni content in the layer increases with increase in scanning speed. Detailed cross-sectional transmission electron microscopic study reveals complexities in solidification behavior with increased nickel content. It is shown that ordered B2 phase forms over a wide range of composition with subsequent precipitation of Ni2Al, an ordered omega phase in the B2 matrix, during solid-state cooling. For nickel-rich alloys associated with higher laser scan speed, the fcc gamma phase is invariably the first phase to grow from the liquid with solute trapping. The phase reorders in the solid state to yield gamma' Ni3Al. The phase competes with beta AlNi, which forms massively from the liquid. The beta AlNi transforms martensitically to a 3R structure during cooling in solid state. The results can be rationalized in terms of a metastable phase diagram proposed earlier. However, the results are at variance with earlier studies of laser processing of nickel-rich alloys.
Resumo:
A new type of bearing alloy containing ultrafine sized tin and silicon dispersions in aluminum was designed using laser surface alloying and laser remelting techniques. The microstructures of these non-equilibrium processed alloys were studied in detail using scanning and transmission electron microscopy. The microstructures revealed three distinct morphologies of tin particles namely elongated particles co-existing with silicon, globular particles, and very fine particles. Our detailed analyses using cellular growth theories showed that the formation of these globular tin particles was due to the pinching off of the tin rich liquid in the inter-cellular space by the growth of aluminum secondary dendrite arms. Evidence of fine recrystallized aluminum grains at the top layer due to constrained solidification was shown. Thermal analyses suggested that melting of the spherical shaped tin particles was controlled by the binary aluminum-tin eutectic reaction, whereas non-spherical tin particles melted via the tin-silicon eutectic reaction.
Resumo:
A flow-induced instability in a tube with flexible walls is studied experimentally. Tubes of diameter 0.8 and 1.2 mm are cast in polydimethylsiloxane (PDMS) polymer gels, and the catalyst concentration in these gels is varied to obtain shear modulus in the range 17–550 kPa. A pressure drop between the inlet and outlet of the tube is used to drive fluid flow, and the friction factor $f$ is measured as a function of the Reynolds number $Re$. From these measurements, it is found that the laminar flow becomes unstable, and there is a transition to a more complicated flow profile, for Reynolds numbers as low as 500 for the softest gels used here. The nature of the $f$–$Re$ curves is also qualitatively different from that in the flow past rigid tubes; in contrast to the discontinuous increase in the friction factor at transition in a rigid tube, it is found that there is a continuous increase in the friction factor from the laminar value of $16\ensuremath{/} Re$ in a flexible tube. The onset of transition is also detected by a dye-stream method, where a stream of dye is injected into the centre of the tube. It is found that there is a continuous increase of the amplitude of perturbations at the onset of transition in a flexible tube, in contrast to the abrupt disruption of the dye stream at transition in a rigid tube. There are oscillations in the wall of the tube at the onset of transition, which is detected from the laser scattering off the walls of the tube. This indicates that the coupling between the fluid stresses and the elastic stresses in the wall results in an instability of the laminar flow.
Resumo:
The stability of the Hagen-Poiseuille flow of a Newtonian fluid in a tube of radius R surrounded by an incompressible viscoelastic medium of radius R < r < HR is analysed in the high Reynolds number regime. The dimensionless numbers that affect the fluid flow are the Reynolds number Re = (ρVR / η), the ratio of the viscosities of the wall and fluid ηr = (ηs/η), the ratio of radii H and the dimensionless velocity Γ = (ρV2/G)1/2. Here ρ is the density of the fluid, G is the coefficient of elasticity of the wall and Vis the maximum fluid velocity at the centre of the tube. In the high Reynolds number regime, an asymptotic expansion in the small parameter ε = (1/Re) is employed. In the leading approximation, the viscous effects are neglected and there is a balance between the inertial stresses in the fluid and the elastic stresses in the medium. There are multiple solutions for the leading-order growth rate do), all of which are imaginary, indicating that the fluctuations are neutrally stable, since there is no viscous dissipation of energy or transfer of energy from the mean flow to the fluctruations due to the Reynolds strees. There is an O(ε1/2) correction to the growth rate, s(1), due to the presence of a wall layer of thickness ε1/2R where the viscous stresses are O(ε1/2) smaller than the inertial stresses. An energy balance analysis indicates that the transfer of energy from the mean flow to the fluctuations due to the Reynolds stress in the wall layer is exactly cancelled by an opposite transfer of equal magnitude due to the deformation work done at the interface, and there is no net transfer from the mean flow to the fluctuations. Consequently, the fluctuations are stabilized by the viscous dissipation in the wall layer, and the real part of s(1) is negative. However, there are certain values of Γ and wavenumber k where s(l) = 0. At these points, the wail layer amplitude becomes zero because the tangential velocity boundary condition is identically satisfied by the inviscid flow solution. The real part of the O(ε) correction to the growth rate s(2) turns out to be negative at these points, indicating a small stabilizing effect due to the dissipation in the bulk of the fluid and the wall material. It is found that the minimum value of s(2) increases [is proportional to] (H − 1)−2 for (H − 1) [double less-than sign] 1 (thickness of wall much less than the tube radius), and decreases [is proportional to] (H−4 for H [dbl greater-than sign] 1. The damping rate for the inviscid modes is smaller than that for the viscous wall and centre modes in a rigid tube, which have been determined previously using a singular perturbation analysis. Therefore, these are the most unstable modes in the flow through a flexible tube.
Resumo:
We report the formation ω phase in the remelted layers during laser cladding and remelting of quasicrystal forming Al65Cu23.3Fe11.7 alloy on pure aluminum. The ω phase is absent in the clad layers. In the remelted layer, the phase nucleates at the periphery of the primary icosahedral phase particles. A large number of ω phase particles forms enveloping the icosahedral phase growing into aluminum rich melt, which solidify as α-Al solid solution. On the other side it develops an interface with aluminum. A detailed transmission electron microscopic analysis shows that ω phase exhibits orientation relationship with icosahedral phase. The composition analysis performed using energy dispersive x-ray analyzer suggests that this phase has composition higher aluminum than the icosahedral phase. The analysis of the available phase diagram information indicates that the present results represent large departure from equilibrium conditions. A possible scenario of the evolution of the ω phase has been suggested.
Resumo:
Internal haemorrhage, often leading to cardio-vascular arrest happens to be one of the prime sources of high fatality rates in mammals. We propose a simplistic model of fluid flow in our attempt to specify the location of the haemorrhagic spot, which, if located accurately, could possibly be operated leading to an instant cure. The model we employ for the purpose is basically fluid mechanical in origin and consists of a viscous fluid, pumped by a periodic force and flowing through an elastic tube. The analogy is with that of blood, pumped from the heart and flowing through an artery or vein. Our results, aided by graphical illustrations, match reasonably well with experimental observations.