Duct Of Rectangular Cross-section Research Articles

Computation of three-dimensional incompressible flows using high-order weighted essentially non-oscillatory finite-difference lattice Boltzmann method

In the present work, an accurate and robust solution methodology based on the high-order weighted essentially non-oscillatory (WENO) finite-difference lattice Boltzmann method (LBM) in the three-dimensional generalized curvilinear coordinates is presented and applied for simulating the three-dimensional incompressible flows over complicated configurations with curved boundaries. Here, the incompressible form of the lattice Boltzmann equation in three dimensions is considered and the discretization of the spatial derivative terms is performed with the fifth-order WENO finite-difference method and the temporal derivative term is discretized with the fourth-order Runge–Kutta scheme to ensure the accuracy and stability of the solution method for both the steady and unsteady problems. The three-dimensional lattice Boltzmann equation applied here is based on a nineteen discrete velocity model for transforming the microscopic properties to the macroscopic ones. To assess the accuracy and robustness of the present three-dimensional high-order finite-difference LBM solver, different incompressible flow benchmarks and practical test cases are studied that are the cavity flow, the Beltrami flow, the flow in the curved ducts of rectangular cross sections, and the flow over a sphere for different flow conditions. The decay of the homogeneous isotropic turbulence is also computed to examine the suitability of the present solution method to be applied as the direct numerical simulation of turbulent flows. It is demonstrated that the solution methodology presented based on the high-order WENO finite-difference LBM in the three-dimensional generalized curvilinear coordinate can be used for accurately and effectively computing the three-dimensional practical incompressible flow problems.

Time-resolved measurement of acoustic density fluctuations using a phase-shifting Mach-Zehnder interferometer.

Phase-shifting interferometry is one of the optical measurement techniques that improves accuracy and resolution by incorporating a controlled phase shift into conventional optical interferometry. In this study, a four-step phase-shifting interferometer is developed to measure the spatiotemporal distribution of acoustic density oscillations of the gas next to a rigid plate. The experimental apparatus consists of a polarizing Mach-Zehnder interferometer with a polarization camera capable of capturing four polarization directions in one shot image and it is used to measure the magnitude and the phase of density fluctuations through a duct of rectangular cross section connected to a loudspeaker. The results are compared with the well-established thermoacoustic theory describing the thermal coupling between acoustic oscillations and rigid boundaries, and the results show a very good agreement for various ratios of the (frequency-dependent) thermal boundary layer thickness to the plate spacing. This measurement technique could be advantageously employed to analyze more complex heat transfer processes involving the coupling of acoustic oscillations with rigid boundaries.

Evaluation of 1D Models for Particle Transport with Wall Migration in Ducts of Rectangular Cross Section

Approximate 1D models of particle transport in ducts that make use of an exponential displacement kernel to describe the effect of wall migration are evaluated for ducts of rectangular cross section. The studied models are based on the use of either one or two basis functions to approximate the transverse and azimuthal dependencies of the angular flux in the duct. Thermal-neutron reflection and transmission probabilities resulting from Monte Carlo simulations carried out with the MCNP and PHITS codes for iron, concrete and graphite ducts are used as reference solutions. It is concluded that the model built on two basis functions performs well (deviations typically < 10% in magnitude) for iron, the material for which absorption is most important, but less so for the scattering-dominated materials concrete and graphite. It is also concluded that changes in the energy distribution of the incident source have their strongest influence on the results for iron ducts.

Heat transfer augmentation through rectangular cross section duct with one corrugated surface: An experimental and numerical study

One of the techniques utilized to enhance the heat transfer rate within air ducts is creating turbulence inducing designs. In this work, turbulent air flow through a rectangular cross-sectional duct with one corrugated surface was experimentally and numerically investigated. Hydraulic and thermal behaviors of the system were evaluated at different Reynolds numbers. A test rig was constructed to experimentally investigate the performance. Also, a two-dimensional computational fluid dynamics simulation was performed using k-ε model to simulate fluid flow within the duct. The model was validated against previous results as well as the experimental results from this research. The computational and experimental findings were in reasonable agreement with a maximum error of less than 10%. The results showed that the existence of the corrugated surface considerably enhanced the heat transfer rate in all the studied cases, while slightly increasing the pressure drop. Consequently, a parametric study was performed to investigate the effect of different design parameters on the performance. The best performance was observed at a rib height to width ratio of 0.2, and groove length to width ratio of three, with a thermal enhancement factor of about 1.5. an empirical relation between Nusselt number and Reynolds number was established using the obtained results with a relative error value less than 8%. The study proved the value of using a corrugated surface as a means to increase heat transfer rate within rectangular air ducts.

Effects of anisotropy on the transition to absolute instability in a porous medium heated from below

The emerging instability of a forced throughflow in a fluid saturated horizontal porous duct of rectangular cross section is investigated. The duct is heated from below by assuming the horizontal boundaries to be at different temperatures. Both the horizontal and the vertical boundaries are impermeable and the basic flow is parallel to such boundaries. The porous medium is anisotropic with different permeabilities in the vertical and horizontal directions. The effect of anisotropy on the onset of buoyancy-driven modal instability and absolute instability is analyzed. The parametric conditions leading to the instability of the basic flow are determined by employing an analytical dispersion relation. The different permeabilities in the vertical and horizontal directions turn out to play opposite roles in the onset of modal instability and in the transition to absolute instability. It is shown that an increasing vertical permeability has a destabilizing effect, while an increasing horizontal permeability has a stabilizing effect.

Convective fluid flow and heat transfer in a vertical rectangular duct containing a horizontal porous medium and fluid layer

PurposeThe purpose of this paper is to investigate thermally and hydrodynamically fully developed convection in a duct of rectangular cross-section containing a porous medium and fluid layer.Design/methodology/approachThe Darcy–Brinkman–Forchheimer flow model is adopted. A finite difference method of second-order accuracy with the Southwell-over-relaxation method is deployed to solve the non-dimensional momentum and energy conservation equations under physically robust boundary conditions.FindingsIt is found that the presence of porous structure and different immiscible fluids exert a significant impact on controlling the flow. Graphical results for the influence of the governing parameters i.e. Grashof number, Darcy number, porous media inertia parameter, Brinkman number and ratios of viscosities, thermal expansion and thermal conductivity parameters on the velocity and temperature fields are presented. The volumetric flow rate, skin friction and rate of heat transfer at the left and right walls of the duct are also provided in tabular form. The numerical solutions obtained are validated with the published study and excellent agreement is attained.Originality/valueTo the author’s best knowledge this study original in developing the numerical code using FORTRAN to assess the fluid properties for immiscible fluids. The study is relevant to geothermal energy systems, thermal insulation systems, resin flow modeling for liquid composite molding processes and hybrid solar collectors.

Algebraic model of turbulent flow in ducts of rectangular cross-section with rounded corners

Of increasing importance are nowadays ducts of rectangular cross-section with large-radius rounded corners. They are used for large air flow rates at low pressure levels — typically for air flow distribution in buildings ventilation and heating systems. Paper develops an analytic model of turbulent flows in these ducts. It makes possible in particular evaluation of velocity profiles – and volume flow rates as a function of duct cross-section shapes. The model was validated by comparing the solutions with full-scale duct laboratory measurements.

Experimental Investigation of Heat Transfer Enhancement Using Straight Flat Baffles

Heat transfer augmentation finds its significance in many uses such as air conditioning, heat exchanger and refrigeration structures. On heat transfer augmentation many researchers conducted experimental and numerical to develop various techniques and methods. Heat transfer enhancement techniques are used to nurture the heat transfer rate without disturbing the complete performance of the system. The energy transport is considered enhanced if the flow is agitated and mixed well. This is the fundamental principle in the development of enhancement techniques that generate swirl flows. Nowadays, baffle inserts have widely been applied for improving the convective heat transfer in various applications due to their effectiveness, low cost and easy setting up. In this experiment an array of straight flat baffles was mounted transversely to the direction of air flow in a rectangular cross-sectioned duct and experiment was conducted for different Reynolds numbers. It is proposed to conduct the investigation to evaluate the influence of the presence of straight flat baffles on the flow path. It is observed experimentally that the straight flat baffles influence greater rate of heat transfer than that of the channel without baffles. The flow visualization for various Reynolds numbers also reports the significance of the presence of straight flat baffles in transverse directional flow.

Buoyancy-driven exchange flows in inclined ducts

Buoyancy-driven exchange flows arise in the natural and built environment wherever bodies of fluids at different densities are connected by a narrow constriction. In this paper we study these flows in the laboratory using the canonical stratified inclined duct experiment, which sustains an exchange flow in an inclined duct of rectangular cross-section over long time periods (Meyer & Linden, J. Fluid Mech., vol. 753, 2014). We study the behaviour of these sustained stratified shear flows by focusing on three dependent variables of particular interest: the qualitative flow regime (laminar, wavy, intermittently turbulent, or fully turbulent), the mass flux (net transport of buoyancy between reservoirs), and the interfacial thickness (thickness of the layer of intermediate density between the two counter-flowing layers). Dimensional analysis reveals five non-dimensional independent input parameters: the duct aspect ratios in the longitudinal direction $A$ and spanwise direction $B$, the tilt angle $\theta$, the Reynolds number $Re$ (based on the initial buoyancy difference driving the flow), and the Prandtl number $Pr$ (we consider both salt and temperature stratifications). After reviewing the literature and open questions on the scaling of regimes, mass flux, and interfacial thickness with $A,B,\theta,Re,Pr$, we present the first extensive, unified set of experimental data where we varied systematically all five input parameters and measured all three output variables with the same methodology. Our results in the $(\theta,Re)$ plane for five sets of $(A,B,Pr)$ reveal a variety of scaling laws, and a non-trivial dependence of all three variables on all five parameters, in addition to a sixth elusive parameter. We further develop three classes of candidate models to explain the observed scaling laws: ...

Experimental Study of Forced- Convection from Horizontal Rectangular Fins Array into Air Duct

In this work, an experimental study has been done to expect the heat characteristics and performance of the forced-convection from a heated horizontal rectangular fins array to air inside a rectangular cross-section duct. Three several configurations of rectangular fins array have been employed. One configuration without notches and perforations (solid) and two configurations with combination of rectangular-notches and circular-perforations for two various area removal percentages from fins namely 18% notches-9% perforations and 9% notches-18% perforations are utilized. The rectangular fins dimensions and fins number are kept constant. The fins array is heated electrically from the base plate with five different magnitudes of power-inputs. Five several air flow velocity into a duct are utilized. The influence of fin geometry, air flow velocity, Reynolds number and the surface heat flux on the heat-performance of forced heat convection have been simulated and studied experimentally. The experimental data indicates that the combination of 18% rectangular-notched and 9% circular-perforated rectangular fins array gave best forced heat performance in terms of average heat transfer coefficient about (25% - 45%) and (7% - 20%) compared than solid and 9% notches with18% perforations fins array respectively. Five empirical correlations to predict the average Nusselt number for the 18% notches with 9% perforations rectangular fins array at wide range of surface heat flux are deduced. The present data are compared with previous works and a good closeness in behavior is noticed.

An Investigation of Natural Convection of Air Flow through A Vertical Duct with Rectangular Cross-Section Heated from A Singled-Side.

An experimental investigation is made to study the effect of different parameters affecting the process of natural air flowing through vertical ducts. The experimental setup has been designed and installed in the Air Conditioning Laboratory, Faculty of Engineering, Mansoura University. The test rig is consisted of mainly of rectangular cross-section duct of 25 cm width with different heights and gap thicknesses. The air gap thickness ranges from 3 to 20 cm while the height is ranged from 50 to 200 cm. All duct sides are well insulated with one side heated under heat flux density ranges from 191.04 to 440.75 ⁄ . Experimental results are plotted to indicate the relation between air volume flow rate through the vertical duct and different parameters discussed, namely, gap thickness, duct height and heat flux density. Based on measured results the air volume flow rate increases with increasing both heat flux density and duct height. It is concluded also that, the air volume flow rate increases with increasing the gap thickness until it reaches maximum values, namely at gap thickness of 10 cm and then decreases with further increase in gap thickness. The results of the present study could be useful in the design and application of buoyancy-assisted natural ventilation systems.

Particle image velocimetry as a teaching with technology resource in oscillatory laminar fluid flow

A harmonically driven oscillatory fully developed laminar flow through a rectangular cross-sectioned duct is analytically and experimentally studied. Experimental data is gathered at low cost with a relatively easy to implement, non-commercial, do-it-yourself (DIY) particle image velocimetry (PIV) system, which is proposed here as a flexible pedagogic resource for use in physics/engineering fluid mechanics undergraduate or graduate level education. As a DIY system, its components can be generic and/or open source based, making it useful in developing countries as well. An analytical model was developed, solved, and compared to the experimental data while the key features of the oscillatory flow were recognised and reciprocally represented by theory and experiments. This validated the proposed system as a low-cost alternative to the commercially available systems and it also confirmed it as a viable pedagogical resource. Consequently, the activities described could be straightforwardly implemented into undergraduate/graduate fluid mechanics pedagogical contexts, such as lecture aids, course projects, and laboratory practices. The proposed DIY-PIV system constitutes a teaching with technology pedagogical resource on fluid mechanics physics/engineering education that is also able to function as a limited/auxiliary or even state of the art research tool, according to the budget and the objectives.

Laminar flow of Newtonian liquids in ducts of rectangular cross-section a model for both physics and mathematics

In this paper, we considered the laminar fully developed flow, of a Newtonian fluid, inducts of rectangular cross-section. Poisson’s partial differential equation Saint-Venant solution was used, to calculate Poiseuille number values whatever is rectangles aspect ratio. From these results, we considered limit cases of square duct and plane Poiseuille flow (infinite parallel plates). We showed there exists a rectangle equivalent to a circular cross-section for energy dissipation through viscous friction. Finally, we gave some mathematical consequences of this approach for odd integers zeta function calculations and Catalan’s constant.

Vibroacoustic study of a point-constrained plate mounted in a duct

The vibroacoustic study of the interaction of sound with a point-constrained, simply-supported square plate is considered in this paper. The plate is mounted flush on one of the walls of an infinite duct of rectangular cross section and is backed by a cavity. The plate response and the acoustic field is predicted by solving the coupled governing equations using modal expansion with the relevant eigenmodes of the plate dynamics and acoustic fields in the duct and cavity. By varying the location of the point constraint, the frequency characteristics of the transmission loss in the duct can be tuned. The point constraint can also alter the amplitude and spectral characteristics of the plate's response. Interestingly, some new peaks are observed in the response because of the excitation of unsymmetric modes which are otherwise dormant. Mode-localization phenomenon, which is the localization of vibration in specific regions of the plate, is observed for selected constrained points.

Dean instability and secondary flow structure in curved rectangular ducts

The pressure driven, fully developed turbulent flow of incompressible viscous fluid (water) in 120° curved ducts of rectangular cross-section is investigated experimentally and numerically. Three different types of curved duct (A-CL, B-SL and C-IL) with continuously varying curvature conform to blade profile as the inner and outer curvature walls to simplify and guide the impeller design of pumps. After validating the numerical method against Particle Image Velocimetry (PIV) measurements, the flow development in the ducts is analyzed in detail by Computational Fluid Dynamics (CFD) for a wide range of Reynolds numbers (Re = 2.4 × 104–1.4 × 105) and aspect ratios (Ar > 1.0, =1.0 and <1.0). The results clearly depict the existence of multiple Dean vortices along the duct: while the axial velocity profile is more related to an inner Dean vortex (called split base vortex), the wall pressure is more influenced by the Dean vortex attached to the inner curvature wall (called ICW Dean vortex). The induced multiple Dean vortices and the secondary flow patterns in the duct cannot be faithfully predicted by using traditional techniques. Therefore, a new criterion based on the vortex core velocities is proposed. With this approach, the effects of Re, Cr and Ar on the Dean instabilities in curved ducts are carefully studied. Decreasing Re promotes the generation of Dean vortices closer to the duct inlet, a trend that is as opposed to laminar flow. In addition, a new pair of vortices called entrainment Dean vortex occurs near the outlet of the curved duct with Ar = 1.0, which has not been previously reported in the literature.

Buoyancy effects in vertical rectangular duct with coplanar magnetic field and single sided heat load

In some DEMO blanket designs liquid metal flows in vertical ducts of rectangular cross-section between ceramic breeder units providing their cooling. Heat exchange in these conditions is governed by the influence of magnetic field (coplanar) and by buoyancy effects that depend on the flow orientation to the gravity vector (downward and upward flow). Magnetohydrodynamic and heat transfer of liquid metal in vertical rectangular ducts is not well researched. Experimental study of buoyancy effects in rectangular duct with coplanar magnetic field for one-sided heat load and downward and upward flowsis presented in this paper. The detail research with has been done on mercury MHD close loop with using of the probe technique allow to discover several advantageous and disadvantageous effects. The intensive impact of buoyancy force has been observed in a few regime of downward flow which has been laminarized by magnetic field. Due to the development in the flow of the secondary large-scale vortices heat transfer improved and the temperature fluctuations of the abnormally high intensity have been fixed. On the contrary, in the upward flow the buoyancy force stabilized the flow which lead to decreasing of the turbulence heat transfer ratio and, consequently, deterioration of heat transfer.

Application of 1D Models to Particle Transport in a Duct of Rectangular Cross Section

ABSTRACTThe approximate 1D model for particle transport in ducts that is based on the use of two basis functions to represent the transverse and azimuthal-angle dependencies of the angular flux is applied to the case of a duct of rectangular cross section. Isotropic particle incidence is considered. Numerical results obtained for the reflection and transmission probabilities from the 1D models with one and two basis functions are compared with Monte Carlo results for the full 3D problem. It is shown that the 1D model with two basis functions performs very well for ducts of rectangular cross section, displaying deviations of less than 3% with respect to Monte Carlo, in general. Two exceptions in the general behavior of this model are very short ducts, for which deviations in the reflection probability of up to 9% in magnitude were encountered, and long ducts with strongly absorbing walls, for which the deviations in the transmission probability reached about 8% in magnitude.

Turbulent drag reduction by polymer additives in parallel-shear flows

In this study, we experimentally investigate the turbulent drag-reduction (DR) mechanism in flow through ducts of circular, rectangular and square cross-sections using two grades of polyacrylamide in aqueous solution having different molecular weights and various semidilute concentrations. Specifically, we explore the relationship between drag reduction and fluid elasticity, purposely exploiting the mechanical degradation of polymer molecules to vary their rheological properties. We also obtain time-resolved velocity data for various DR levels using particle image velocimetry and laser Doppler velocimetry. Elasticity is quantified via relaxation times determined from uniaxial extensional flow using a capillary breakup apparatus. A plot of DR against Weissenberg number ($Wi$) is found to approximately collapse the data, with the onset of DR occurring at $Wi\approx 0.5$ and the maximum drag-reduction asymptote being approached for $Wi\gtrsim 5$. Thus quantitative predictions of DR in a range of shear flows can be made from a single measurable material property of a polymer solution, at least for this particular flexible linear polymer.

Three-dimensional flow analysis of Carreau fluid model induced by peristaltic wave in the presence of magnetic field

This work investigates the impact of magnetohydrodynamics (MHD) on a non-Newtonian peristaltic flow of Carreau fluid in a uniform duct of rectangular cross section. An applied magnetic field is considered whereas the induced magnetic field is taken to be zero here due to small magnetic Reynolds number. Non-Newtonian fluid model is impossible to describe with the help of single constitutive relationship among strain and stress rate. These kinds of constitutive equations give a very complicated mathematical models and thus, mathematicians, physicist, modelers and computer scientist face multiple kinds of problems during the development of numerical and analytical methods. Generally, non-Newtonian fluids are classified into three categories such as the rate type, differential type, and integral type. Carreau fluid model is one of them. The governing nonlinear equations are studied under the considerations of long wavelength and the inertial forces have been ignored. Flow is examined in a wave frame of reference with the velocity of the wave. Such types of flow with magnetic effect are beneficial in drug delivery systems and also helpful to control the flow. Further in microfluidics, magnetohydrodynamics helps to produce a nonpulsating and stable flow in a design of complex microchannel. Analytical solutions of nonlinear partial differential equations are obtained by employing a perturbation method with the combination of eigenfunction expansion method. Numerical computation has been successfully used in order to analyze the pumping characteristic of the flow. Peristaltic pumping is also an engrossing mechanism in a human body that helps to propagate various kinds of biological fluids in different parts of a human body. Velocity behavior is analyzed and presented in both two and three-dimensional profile. Contours are also drawn with the help of streamlines against various involved parameters. Particularly, the obtained results are presented graphically to explore the impact of all the sundry parameters for velocity, pressure gradient, and pressure rise. An excellent comparison is also presented with previously published data to validate the current methodology and results. This problem has multiple numbers of applications in different fields of biomedical engineering including the three-dimensional fluid flow under the influence of elastic waves, blood flow dynamics in a living body.

A Recollection with Respect to Flow Induced Crystallization in Polymer Melt Processing

Abstract A review is given of the work in the field of flow induced crystallization in polymer melts, as has been carried out during the last twenty five years mostly in Linz. A concise discussion of some results of a recent monograph is given. In this connection polymer melt rheology provides insights into the differences of information, as provided by shear and extensional flow. These differences show up with increased degrees of deformation. One finds four important pictures in this report: An electron micrograph of the crystalline structure in a cross-section perpendicular to the previous flow direction. No branching is found of the tracks, which are lines of intersection with the plane of the cross-section. A ring-shaped sample of polypropylene is shown, which fits into a newly developed apparatus. Because of the large radius secondary flow is avoided. A picture, which was obtained already a long time ago, shows that the relaxation of flow induced structures occurs with polypropylene only at temperatures between 210 and 190°C. Below the latter temperature no relaxation of crystalline structures occurs. The sharp boundary between a highly oriented zone near the duct wall and the spherulitic structure in the interior of samples, which have been extruded through ducts of rectangular cross-section, can readily be explained.