Tube Of Constant Cross Section Research Articles

On the effect of boundary vibration on mucus mobilization

In this study, we investigate the mobilization of mucus in a cylindrical tube of constant cross-section subjected to a Small Amplitude Oscillatory Shear (SAOS) assuming the viscoelastic behavior of mucus is governed by the Oldroyd-B constitutive equation. The Laplace transform method was adopted to derive expressions for the velocity profile, average velocity, instantaneous flowrate and mean flowrate (i.e., mobilization) of the mucus within the tube. Additionally, a 2D finite element model (FEM) was developed using COMSOL Multiphysics software to verify the accuracy of the derived analytical solution considering both a Newtonian and an Oldroyd-B fluid. Furthermore, sensitivity studies were performed to evaluate the influence of the vibration frequency, vibration amplitude, mean relaxation time, and zero-shear viscosity on mucus mobilization. Results prove that the analytical and numerical results are within acceptable error tolerance and thus in excellent agreement. Besides, the parametric studies indicate a 48%, 57%, and 343% improvement in mucus mobilization when the mean relaxation time, vibration amplitude, and vibration frequency, respectively were each increased by a factor of 6 from the assumed nominal values. Conversely, the mucus mobilization decreased by 25% when the zero-shear viscosity was increased by a factor of 6 from the assumed reference value. In general, this study confirms that mucus mobilization in a tube can be improved by increasing the magnitude of vibration amplitude and vibration frequency. Similarly, the larger the magnitude of mucus mean relaxation time the better the mucus mobilization when the tube is subjected to boundary vibrations. Finally, mucus mobilization decreases as the magnitude of mucus viscosity increases.

РАЗРАБОТКА КОНЦЕПЦИИ ДВУХФАЗНОЙ СИСТЕМЫ ТЕПЛООТВОДА СПУТНИКА

For spacecraft (SC) with power unit capacity more than 4 ... 6 kW promising construction of thermal control system (TCS) based on two-phase mechanically pumped loops (2PMPL). The development of 2PMPL has been carried out quite intensively since the early '80s. However, so far there are no examples of practical implementation of such high-power systems. One of the main reasons mentioned is the novelty of the system, and insufficient study of its operation in space conditions, which adds risks. The most important component of such systems is a heat rejection subsystem (HRS), whose task is to reject heat from the coolant and radiate it into space. In its turn, HRS is also a system, the design of which requires using a system approach, considering various aspects of its operation. HRS includes a heat-hydraulic network and a radiation heat exchanger (RHE). The key elements of the HRS are condensers (CC), quite new devices for space technology. This paper presents an algorithm for the design and optimization of the heat rejection subsystem (HRS) of a satellite two-phase thermal control system. The methodology of engineering synthesis of complex technical systems and informal procedures for multi-criteria optimization of elements and subsystems at various stages of HRS design is repeatedly used. t is shown that optimization should be carried out both at the level of elements and subsystems, and at the level of the whole thermal control system. As a result of the study, the HRS design is proposed, which uses condensers in the form of smooth steel tubes of constant cross-section and their series-parallel connection scheme in the hydraulic network. Main advantages of the design: traditional for single-phase loops elements are used; operation of elements and subsystems in zero gravity conditions is predictable and allows complete testing on the ground without mandatory flight experiment; the system is operable at high saturation pressures (temperatures) (on ammonia - up to 85℃).

Surface Pressure Measurements in a Model Helical Coil Steam Generator Using Pressure Sensitive Paint

Helical coil steam generators (HCSGs) are tube and shell heat exchangers under investigation due to their future in nuclear power applications. A model of an HCSG with a transverse pitch ratio of 2.98 and changing lateral pitch ratio was created to study the pressure on the surface of the tubes under low Reynolds number flow. Pressure-sensitive paint was applied to rods of an outer bundle of the test section, and instantaneous and average pressure fields were analyzed for Reynolds numbers 4000 and 6000. A comparative study showed that the pressures along the rods had nonlinear behavior. Previous studies suggested a relationship between tube bundle characteristics and the lateral pitch ratio in heat exchanger designs. Since the transverse pitch ratio is constant, the lateral pitch ratio defines the tube bundle cross section as either staggered or inline depending on the cross-section location. Averaged pressure distributions were compared to lateral pitch ratios at respective locations. The pressure distributions along the staggered cross-section portion of the test section were found to exhibit a linear behavior across the heat exchanger body. While this study focuses on average surface pressure measurements, the differences between the same lateral pitch ratio and surface pressure show disagreement with previous studies focused on constant cross-section tube bundles. Flow phenomena within tube bundles, such as vortex shedding, are suspected to be the cause of this discrepancy but a transient analysis is necessary to determine its source.

Effect of a time dependent stenosis on flow of a second order fluid through constricted tube with velocity slip at wall using integral method

The effect of time dependent axially symmetric constriction in a tube of constant cross section through which a non Newtonian fluid is flowing steadily is modeled and the analysis was made using integral approach The present article is stationed on second order fluid model The study is made applicable for mild constriction by using an order of magnitude analysis The effect of different parameters non Newtonian characteristics Reynolds number and time looming in the model on velocity distribution wall shear stress separation and reattachment and pressure gradient are reviewed graphically It is observed that Reynolds number gives a mechanism to oversight the attachment and de attachment data Constricted tube Non Newtonian fluids Time dependent stenosis Slip velocity Shear stress

Resonant oscillations in open axisymmetric tubes

We study the behaviour of the isentropic flow of a gas in both a straight tube of constant cross section and a cone, open at one end and forced at or near resonance at the other. A continuous transition between these configurations is provided through the introduction of a geometric parameter k associated with the opening angle of the cone where the tube corresponds to \(k=0\). The primary objective is to find long-time resonant and near-resonant approximate solutions for the open tube, i.e. \(k\rightarrow 0\). Detailed analysis for both the tube and cone in the limit of small forcing \((O(\varepsilon ^{3}))\) is carried out, where \(\varepsilon ^{3}\) is the Mach number of the forcing function and the resulting flow has Mach number \(O(\varepsilon )\). The resulting approximate solutions are compared with full numerical simulations. Interesting distinctions between the cone and the tube emerge. Depending on the damping and detuning, the responses for the tube are continuous and of \(O(\varepsilon )\). In the case of the cone, the resonant response involves an amplification of the fundamental resonant mode, usually called the dominant first-mode approximation. However, higher modes must be included for the tube to account for the nonlinear generation of higher-order resonances. Bridging these distinct solution behaviours is a transition layer of \(O(\varepsilon ^{2})\) in k. It is found that an appropriately truncated set of modes provides the requisite modal approximation, again comparing well to numerical simulations.

Experimental study of spontaneous ignition and non-premixed turbulent combustion behavior following pressurized hydrogen release through a tube with local enlargement

Pressure records, flame detection and high-speed photography are used to study the spontaneous ignition and non-premixed turbulent combustion behavior following high-pressure hydrogen release through a cylindrical tube with local enlargement into the semi-enclosed space. The study shows that the leading shock wave is partly reflected when it impacts on the vertical walls in the local enlargement section. The pressure behind the reflected shock wave has a significant increase compared with that behind the leading shock. Moreover, the leading shock wave speed decreases firstly and then increases as it passes through the enlargement. It is found that the presence of the local enlargement structure can significantly facilitate the occurrence of spontaneous ignition. The minimum storage pressure of spontaneous ignition is only 1.98 MPa in the tube with local enlargement, which is lower than that in a constant cross-section tube. The possible positions of initial ignition inside the tube and the delay times of ignition for different burst pressures are obtained. After the hydrogen flame comes out from the tube, a ball of flame is formed around the tube outlet and propagates outward. Then, the noticeable non-premixed turbulent combustion of hydrogen occurs in the semi-enclosed space, which leads to the increase of the pressure in the chamber. Twice peaks of overpressure are observed successively and the second pressure peak has a lower intensity compared with the first peak value. Moreover, the maximum overpressure of non-premixed turbulent combustion increases with the release pressure.

Transient motion of finite amplitude standing waves in acoustic resonators

Extraordinarily high maximum-to-minimum gas pressure ratios appear in an oscillating closed resonator at its resonance frequency for certain resonator shapes. Using a quasi-one-dimensional model based on the compressible Navier–Stokes equations and a finite volume method, we investigate the transient motion of a fluid inside oscillating axisymmetric tubes, from the quiescent condition to the periodic steady motion. We find that the amplitude of the fast oscillations in pressure increases monotonically to the value of its steady state for a cylindrical tube of constant cross-section, while the amplitude undergoes a spiral toward the final steady state value for conical or horn-cone resonators. We discuss the effects of fluid properties on the transient motions. In addition, we compare our numerical results with available experimental results and find good agreement. In particular, for horn-cone resonators driven by large amplitude force, we find a secondary lower peak in pressure waveform within one period of oscillation at the small end of the cavity, matching the findings of the existing experimental result.

Effect of surface roughness on wettability and displacement curvature in tubes of uniform cross-section

A fundamental problem in interpretation of the capillary properties of porous media is the effect of the interaction of wetting properties and pore geometry on interface curvature. Contact angles provide a fundamental measure of wetting. However, circumstances under which contact angles are reproducible and unambiguous are limited. Contact angles commonly exhibit hysteresis between advancing and receding conditions. The origin of the contact angle hysteresis may be related to either chemical or geometric properties or a combination of both. Small scale geometric features, such as surface roughness, can have a dominant effect on the effective contact angles at the three phase lines of contact and determine the local interface curvature. In this paper, the effect of roughness on the effective contact angle is studied by applying the MS–P (Mayer and Stowe, and Princen) method of computing interface curvatures, for the first time, to geometric models of surface roughness that include small scale periodic variation and retained fluid in grooves along the walls of tubes of constant cross section. The method provides a consistent account of interface behavior for wetting regimes commonly identified with Wenzel or Cassie and Baxter. The theoretical results are also shown to be consistent with experimental results on the wetting behavior of combinations of roughened polymeric tubes and pure liquids that give a range of well-defined intrinsic contact angles.

Adaptive Concepts for Herschel–Quincke Waveguides

The enhancement of Herschel–Quincke (HQ) waveguides to incorporate adaptive capabilities is investigated. Passive HQ waveguides are known to provide noise attenuation in pipes and ducts at selective narrow frequency bands associated with their resonances. The approach to achieve adaptation is to produce a frequency shift in these resonances to allow targeting incoming tonal noise of variable frequency. The frequency shift is obtained by placing a variable cross-section constriction along the interior of the waveguide. Two adaptive devices are considered. The first consists of a ball with fixed diameter that can be axially displaced inside the waveguide. Then, the frequency tuning is obtained as a function of the ball position. The second device consists of a diaphragm at fixed axial location which can be deformed to obtain a variable cross section. In this case, the frequency shift is obtained as a function of the diaphragm deflection. The internal acoustic dynamics of the two devices are investigated both analytically and experimentally. The created constriction inside the HQ waveguide is modeled as a series of constant cross-section tube elements with small finite area jump between adjacent pieces. The model is validated by comparing the predicted dynamics with experimental data from an extended impedance tube setup based on the two-microphone technique. Finally, attenuation predictions on a one-dimensional pipe are presented in order to illustrate the performance of the proposed adaptive HQ waveguides.

Levitating spherical particle in a slightly tapered tube at low Reynolds numbers: Application to the low-flow rate rotameters

In this study, a theoretical framework is developed to predict the equilibrium conditions of a non-neutrally buoyant sphere placed in a vertical conical tube as encountered in liquid rotameters. The analysis presented herein is applicable for a sphere heavier than the surrounding fluid, situated on the axis of a slightly tapered tube. The sphere is subject to the laminar flow conditions with the Reynolds numbers ranging between the Stokes type regimes up to values corresponding to slightly inertial regimes. In this work, we assume that the aperture angle of the tube is small and that the drag force is mainly due to the dissipation located in the gap between the tube and the sphere. Under these conditions, it is possible to consider the tube as locally cylindrical and we can use the results previously obtained for the correction factor of the Stokes force on a sphere subject to a Poiseuille flow in a tube of constant cross-section. We obtain an equation relating the flow rate to the vertical position of the sphere in the tube and the validity of this analysis is demonstrated by applying it to a commercially available rotameter. The present study provides a simple but sound theoretical method to calibrate such flowmeters.

Centrifugal separation in tube and disc geometries: experiments and theoretical models

The centrifugal separation of particles or droplets in dispersions is important in a variety of applications, e.g. mineral processing, water and waste water treatment, multistep processing of nanomaterials and biotechnology. Despite numerous studies in the past, separation processes of concentrated dispersions driven by gravity or centrifugal forces are not yet completely understood. Centrifuges can be subdivided into two categories: (1) centrifuges operating with tubes of constant cross section and (2) centrifuges operating with disc or cylinder rotors whose cross-sectional area changes with distance along the axis of rotation. This paper investigates the sedimentation process in centrifuges of these two categories experimentally and theoretically. Based on models for the separation of polydisperse dispersions in centrifugal field numerical calculations were carried out including the conversion of the time dependent concentrations profiles into light transmission profiles. The changes in the dispersion concentration profiles during the sedimentation process were monitored in situ by space- and time-resolved NIR light extinction profiles (STEP-Technology) obtained by multisample analytical centrifugation. Cells having constant and increasing cross sections were used. Results show that the velocity of the boundary between supernatant and dispersion as well as the alteration of the concentration measured radially in the centre of the cells do not depend on the geometry of the cells within the experimental errors. The sediment height in cells with increasing cross section is smaller compared to cells with constant cross section. The simulated sedimentation process is in good agreement with measured data for diluted and concentrated silica suspensions. Based on these results the sedimentation processes in disc or cylinder process centrifuges can be predicted from laboratory tests using analytical centrifugation.

MATHEMATICAL MODELING OF BLOOD FLOW THROUGH STENOSED TUBE

In the present study, blood flow in a stenosed tube is modeled. Blood is assumed to be represented by couple stress fluid. The growth projects into the lumen of the artery and blood flow is disturbed; thus, a potential coupling develops between the growth and the blood flow through the artery. An analysis of the effect of an axially symmetric growth into the lumen of a tube of constant cross-section through which a Newtonian fluid is steadily flowing is presented. The importance of the effect of slip velocity in stenosed tube is highlighted.

Comparison of Detonation Processes in a Variable Cross Section Chamber and a Simple Tube

The detonation processes occurring in a variable cross section detonation chamber are compared with that occurring in a simple, constant cross section tube. The variable cross section chamber is made up of a large tube and two small identical tubes connected on each side through frustums. The simple tube has the same diameter as the small tubes of the variable cross section chamber and the same total length as the entire variable section chamber. Both channels are closed at the left end and opened at the right. A two-dimensional, time-accurate, finite volume-based method is used to perform the computations. A five-species, two-step global hydrogen‐air reaction mechanism is used. The study showed complex wave phenomena in the variable cross section chamber that have an impact on thrust and specific impulse.

Nonlinear resonant oscillations in closed tubes of variable cross-section

An axisymmetric tube with a variable cross-sectional area, closed at both ends, containing a polytropic gas is oscillated parallel to its axis at or near a resonant frequency. The resonant gas oscillations in an equivalent tube of constant cross-section contain shocks. We show how cone, horn and bulb resonators produce shockless periodic outputs. The output consists of a dominant fundamental mode, where its amplitude and detuning are connected by a cubic equation – the amplitude–frequency relation. For the same gas, a cone resonator exhibits a hardening behaviour, while a bulb resonator may exhibit a hardening or softening behaviour. These theoretical results agree qualitatively with available experimental results and are the basis for resonant macrosonic synthesis (RMS).

Study of the Mechanisms of Flame Acceleration in a Tube of Constant Cross Section

Flame propagation in a tube of constant cross section with ignition at the closed end and propagation toward the open end was studied experimentally, in propane-air, ethylene-air and acetylene-air mixtures. The flame trajectory displays an oscillatory behaviour which can be correlated to pressure records. The overall phenomenon is highly dependent on the mixture composition and the tube length.

A Time-Domain Method for the Determination of Unsteady Pressure with a Tube of Constant Cross-Section

In this paper a new method for the determination of unsteady pressure with a tubing system is shown. The conventional methods try either to optimize the frequency behaviour of the tubing system by implementing restrictors or instantaneous jumps in the cross-sectional area or to correct the measurement by using the transfer function of the tubing system. The new method presented here simply uses a tube with constant, circular cross-section and solves the governing fluid-mechanic equations in the time-domain by numerically propagating in the direction of the spatial axis.

The equal channel angular extrusion process for materials processing

By the forcing of a bar of metal through a square tube of constant cross section that contains a sharp corner, simple shear is produced in the bar. Repeating the process several times results in a very large amount of strain. This paper describes the application of this technique to processing aluminum alloys for submicrometer grain size, deforming copper niobium alloy to increase the strength and extruding gamma titanium aluminide. The application of this process to materials for specific purposes is also discussed.

Bound states in twisting tubes.

The wave equation subject to Dirichlet boundary conditions has a bound state in an infinite tube of constant cross section in any number of dimensions, provided that the tube is not exactly straight. We prove this result, develop Green's-function methods to find the energy eigenvalue, and solve some simple cases. We discuss the implications for quantum systems and electromagnetic waveguides.

Vortex breakdown as a fundamental element of vortex dynamics

This paper presents an extension of an earlier analysis on vortex breakdown in tubes of constant cross section by Keller et al. (1985) to axisymmetric vortex flows in tubes with varying cross-sectional area. A broad investigation into the properties of steady axisymmetric vortex flows is given, insofar as they can be represented by perfect-fluid theory and simple extensions of it. It is argued that the basic physics of such flows, including vortex breakdown phenomena, can be explained with the help of the relatively simple theoretical concepts proposed. Numerical results are presented which show complete flow fields of loss-free transitions in diffusers.

Flux tubes in lattice gauge theory.

A (2+1)-dimensional SU(2) lattice gauge theory in the Hamiltonian formalism is studied. The wave function has the form of a sum of separable terms whose structure ensures the presence of two static color charges (quarks). Each plaquettelike degree of freedom moves in a ``potential'' determined by all other degrees of freedom. The system generates a flux tube of constant cross section between the quarks. The string tension and energy distribution on links and plaquettes within the flux tube are computed down to g=0.5 (\ensuremath{\beta}=16). The tube grows fatter and weaker as g is reduced.