Flow In Horizontal Channel Research Articles

Simulation of inertial behavior of dilute particle flow in horizontal channel with Eulerian method of velocity-reassociated quadrature-based method of moments

The velocity reassociated two-node quadrature-based method of moments (VR-QMOM) is a robust Eulerian method which is able to predict the crossing trajectory and surface bouncing phenomena for dilute particle flow. It is used here to predict the particle-laden flow in the dilute particle concentration in a horizontal channel. The multiphase simulation was carried out in the Eulerian-Eulerian two-phase model with VR-QMOM for the particle phase and for comparison with the more established Eulerian-Lagrangian two-phase flow method. The gas phase is simulated with RANS equations and discretised with second-order upwind spatial numerical schemes. Comparing the predicted particle flows obtained using the VR-QMOM and Eulerian-Lagrangian approaches, the conclusion can be made that the VR-QMOM can successfully predict bouncing multiphase flows with dilute particle phase. Both trajectory crossing and bouncing behavior and the trend with increasing particle size are reproduced. The two-node VR-QMOM is seen to be an alternative methodology for the prediction of dispersed particle flow problems.

Effect of low gravity on water removal inside proton exchange membrane fuel cells (PEMFCs) with different flow channel configurations

Practically investigate water removal and cell performance for PEMFCs under low gravity circumstance is an urgent task, especially as a promising power supply unit applied to space engineering. PEMFC with an in-situ optical flow field was used to explicate two-phase flow and water removal inside cathode flow field from terrestrial gravity to microgravity. The cell was tested in the vertical and horizontal flow channel orientations. A 3.6 s short-time micro-gravity circumstance was provided by National Microgravity Laboratory. Results show that gravitational level has an essential influence on gas-liquid two-phase flow characteristics for PEMFC with different configurations. The cell placed in different channel orientations also shows distinguished operating behavior because of the complicated impact of the changed gravity and configuration. Under the operating condition of a vertical flow channel orientation, accumulated water and droplets in terrestrial are pushed by oxygen flow to continuous removal toward the outlet of the fuel cell to alleviate water flooding, and the cell performance is slightly enhanced in a 3.6 s micro-gravity circumstance. Operating in a horizontal flow channel orientation, the generated water throughout the micro-gravity circumstance duration is not prone to move and flood flow channels in micro-gravity, meanwhile the cell performance is slightly deteriorated.

Flow Characterization of Milk Protein Foam Transport in Horizontal Channels

Foams are considered as highly complex phenomena and their complexity becomes more challenging when they start to flow. An experimental foaming system based on the milk protein foam was developed in order to investigate the foam flow characterization which enabled the foam transport through a horizontal channel. The article presents the macroscopic phenomena, mechanism and flow characterization of milk protein foam during mechanical transport. The protein foam quality was obtained by controlling the gas and liquid flowrate. The pressure gradient was measured as a function of the foam quality and the influence of the gas and liquid flowrate on the pressure drop was studied. The foam flow revealed a uniform profile within a pressure drop deviation of 600–850 Pam-1. The foam rheology was described by the well-known Moody chart for Newtonian fluids and the empirical power-law model. The corresponding friction factor and Reynolds number were obtained from the entire foam qualities exhibited a close agreement with the well-known equation for laminar flow of a single Newtonian fluid in a pipe ( ) with a constant value of 36.723 and an exponent of 1.034. Practical Applications The improvement of foam product qualities in food stuffs is undoubtedly a major concern for food producers. Because proteins are widely used foaming agents in food industry, a comprehensive knowledge of protein foam flow is required. The aim of this study was assigned to offer the first experimental results in terms of the milk protein foam flow dynamics, corresponding pressure gradient and related foam rheology in a horizontal channel flow in order to improve the manufacturing process.

Modeling and simulation of particle–wall adhesion of aerosol particles in particle-laden turbulent flows

The present study is concerned with the development of a computational model for predicting particle–wall adhesion (deposition) of aerosol particles in turbulent particle-laden flows. Particularly, the standard hard-sphere model is extended to include the adhesion during sticking or sliding particle–wall collisions. For both impact types the deposition condition of a particle on bounding walls is determined. The strategy of the proposed model is based on the momentum-based agglomeration model by Breuer and Almohammed (2015). The main advantage of the proposed model compared to the state-of-the-art in the literature is that the adhesive impulse is determined more reasonably taking the time intervals of the compression and the restitution phase into account. Furthermore, if the deposition condition is not satisfied, the treatment of the particle motion after the impact including adhesion depends on the particle–wall type (sticking or sliding). To examine the effect of the particle–wall adhesion, the developed model is first evaluated using simple test cases including oblique particle–wall collisions with friction. In the second step, the performance of the adhesion model is validated based on a horizontal turbulent channel flow against existing experimental data of Kvasnak et al. (1993) and numerical results by Fan and Ahmadi (1993)based on an energy-based deposition model. The predictions of the present model agree very well with the experiments and the numerical results chosen for the validation study as well as the empirical relation by Wood (1981). Third, the adhesion model is employed to investigate the influence of different simulation parameters (normal restitution coefficient for particle–wall collisions and particle diameter) on the particle–wall adhesion and deposition process in a vertical turbulent channel flow laden with a huge number of primary particles. The results show that the inclusion of the adhesion significantly reduces the number of particle–wall collisions, whereas the number of particle–particle collisions is only slightly reduced. Furthermore, the number of deposited particles is higher for small particles than for large particles, since the adhesive impulse is inversely proportional to the diameter of the primary particles. The proposed adhesion model is developed and tested in the context of large-eddy simulation, but it can also be applied in DNS or RANS predictions.

Influence of Inertial Particles on Turbulence Characteristics in Outer and Near Wall Flow as Revealed With High Resolution Particle Image Velocimetry

A fully developed turbulent particle-gas flow in a rectangular horizontal channel 100 × 10 × 4000 mm3 is disclosed with high spatial resolution two-dimensional (2D) particle image velocimetry (PIV). The objective is to increase the knowledge of the mechanisms behind alterations in turbulent characteristics when adding two sets of relatively large solid spherical particles with mean diameters of 525 and 755 μm and particle size distributions of 450–600 and 710–800 μm, respectively. Reynolds numbers are 4000 and 5600 and relatively high volume fraction of 5.4 × 10−4 and 8.0 × 10−4 are tested. Both the near wall turbulent boundary layer flow and outer core flow are considered. Results show that the carrier phase turbulent intensities increase with the volume fraction of the inertial particles. The overall mean flow velocity is affected when adding the particles but only to a minor extent. Near the wall, averaged velocity decreases while fluctuating velocity components increase when particles are added to the flow. Quadrant analysis shows the importance of sweep near the wall and ejection events in the region defined by y+ > 20. In conclusion, high inertia particles can enhance turbulence even at relatively low particle Reynolds number <90. In the near bottom wall region, particles tend to be a source of instability reflected as enhancement in rms values of the normal velocity component.

Statistics of inertial particle deviation from fluid particle trajectories in horizontal rough wall turbulent channel flow

Previous experimental, theoretical and numerical studies showed that in particle laden wall-bounded flows particles much heavier than the carrier flow preferentially accumulate in low-speed streaks. Depending on the inertia, the distribution of particles in turbulent flows is strongly influenced by the characteristics of the coherent turbulent structures which develop in the carrier flow field. In wall-bounded flows, these coherent structures, which control the turbulent regeneration cycles, are strongly affected by the roughness of the wall, which systematically modifies turbulent structures coherence and shape. Nevertheless, the effects of the roughness of the wall on the particle transport in two-phase turbulent flows has been still poorly investigated. The issue is discussed here by addressing direct numerical simulations (DNS) combined with Lagrangian particle tracking (LPT) with 6 particle sets of different inertia (St+=0.1,0.5,5,10,25,50). As observed in previous numerical studies devoted to the analysis of particle velocity statistics, in shear flows bounded by a smooth wall, particles lead the fluid near the wall and lag behind the fluid far away from the wall and particle inertia has a great impact on the difference between fluid seen and particle velocities. Here this issue is investigated in flows bounded by a rough wall, considering particles of different inertia, whose size is much smaller than the smallest flow scales (point-particle approach).

Steady and unsteady simulations for annular internal condensing flows, part II: Instability and flow regime transitions

ABSTRACTThe algorithm for the accurate and relevant numerical solution technique given in part I of this article is used to obtain the results for shear-driven annular condensing flows in horizontal channels—with or without transverse gravity. The unsteady wave simulation capability is used to implement a unique non-linear stability analysis. The steady and unsteady simulations’ results for millimeter scale (hydraulic diameter 4–8 mm), modest mass-flux (5–120 kg/m2/s), and refrigerant vapors (FC-72, R113, etc.) are used to mark the approximate location beyond which the annular regime typically transitions to a non-annular regime. These are used to develop correlations for local heat transfer coefficients and the approximate length that marks the transition from annular to non-annular regimes.

Stability of stratified two-phase flows in horizontal channels

Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems, the stratified flow with a smooth interface is stable only in confined zone of relatively low flow rates, which is in agreement with experiments, but is not predicted by long-wave analysis. Depending on the flow conditions, the critical perturbations can originate mainly at the interface (so-called “interfacial modes of instability”) or in the bulk of one of the phases (i.e., “shear modes”). The present analysis revealed that there is no definite correlation between the type of instability and the perturbation wavelength.

Two-phase flow patterns in horizontal rectangular minichannel

The two-phase flow in a short horizontal channel of rectangular cross-section of 1 × 19 mm 2 has been studied experimentally. Five conventional two-phase flow patterns have been detected (bubble, churn, stratified, annular and jet) and transitions between them have been determined. It is shown that a change in the width of the horizontal channels has a substantial effect on the boundaries between the flow regimes.

Convective Thermal Analysis of a Turbulent Flow in a Pipe with Two and Three Corrugated Baffles Arranged in Overlap

The present work is a numerical computation of steady turbulent forced convection flow and pressure drop characteristics in a two-dimensional horizontal rectangular cross section channel with isothermal walls and with two and three transverse waved baffles disposed overlapping in a channel. The fluid is considered as Newtonian, incompressible with constant properties. The governing equations are solved by the method of finite volume using the SIMPLE-algorithm, in two-dimensions with the k-e Realizable model to describe the turbulence phenomena. Air is the working fluid with the flow rate in terms of Reynolds numbers ranging from 5.000 to 20.000. The effects of baffle shape geometries as well as Reynolds numbers on the flow patterns and heat transfer performances are investigated. To understand the characteristics of thermal enhancements, the friction factors are also computed. The numerical results are validated with available flat rectangular-shaped baffle measured data and found to agree well with measurement. The computational results reveal essentially, that the shape of the baffles can alter substantially the flow and heat transfer characteristics. In general, an increase in the flow Reynolds number causes a substantial increase in the convective Nusselt number other than the pressure loss is also very important. The detailed knowledge on the flow and heat transfer distribution in this computation provides the basis for further optimization of shell-and-tube heat exchangers.

Two-phase flow patterns in short horizontal rectangular microchannels

The two-phase flow in a short horizontal channel of a rectangular cross-section with the height of 100–500 µm and width of 9–40 mm was studied experimentally. The use of the Schliren and fluorescent methods made it possible to reveal the flow of liquid in the channel and to determine its characteristics quantitatively. The features of the churn, jet and drop flow patterns were studied in details. Two particular regimes that can be distinguished represent formation of immobile drops on the channel walls because of the liquid film or liquid bridges breakage and appearance of mobile drops due to the two-phase flow instabilities. It is found out that formation of various two-phase flow patterns and transitions between them are determined by instabilities of the liquid–gas flow in the side parts of a channel. Frontal instability has been observed during the liquid–gas interaction in the region of liquid output from the nozzle. It is shown that a change in the height and width of the horizontal channels has a substantial effect on the boundaries between the flow regimes. One of the results is that the region of the churn regime increases significantly with decreasing thickness of the channel.

Ultrasonic pulse echography for bubbles traveling in the proximity of a wall

The behavior of a bubbly two-phase flow in the vicinity of a wall affects heat, mass, and momentum transfer; therefore, there is great interest in developing a quantitative technique to monitor this behavior. Herein we propose a new method based on ultrasound echo signal processing that it feasible for industrial applications where the boundary layer is modified by traveling bubbles. By introducing time-resolved direct waveform analysis at 100 MHz, we have succeeded in the spatio-temporal detection of bubble surfaces at echographic profiling frequencies in the range of 15–20 kHz. Unlike conventional approaches, which use short pulses, a relatively long pulse length is applied to allow ultrasound Doppler velocimetry in the liquid phase. Examination of the horizontal bubbly two-phase turbulent channel flows demonstrated the feasibility of this method; spatio-temporal echography of moving bubble surfaces is successfully achieved as the bubbles travel on length scales smaller than the spatial ultrasonic pulse length near the wall. The applicable range of parameters (e.g. bubble size and shape, and flow speed) was determined by 3D numerical analysis of the wave equation and its application to bubbles flowing beneath a flat-bottom model ship.

Study of gas-water flow in horizontal rectangular channels

The two-phase flow in the narrow short horizontal rectangular channels 1 millimeter in height was studied experimentally. The features of formation of the two-phase flow were studied in detail. It is shown that with an increase in the channel width, the region of the churn and bubble regimes increases, compressing the area of the jet flow. The areas of the annular and stratified flow patterns vary insignificantly.

Two-phase flow in short horizontal rectangular microchannels with a height of 300 μm

The two-phase flow in a narrow short horizontal channel with a rectangular cross section is studied experimentally. The channel has a width of 10, 20, or 30 mm and a height of 300 μm. The specifics of formation of such two-phase flows are investigated. It is demonstrated that the regions of bubble and churn flow regimes grow and constrain the region of jet flow as the channel gets wider. The boundaries of the regions of annular and stratified flow regimes remain almost unaltered.

Drag reduction promoted by repetitive bubble injection in turbulent channel flows

To promote the efficiency of frictional drag reduction using bubbles, we designed a novel bubble control method that involves repetitive injection of bubbles rather than the conventional continuous bubble injection approach. Even if the mean void fraction of bubbles to be injected into the turbulent boundary layer is set to be low, repetitive bubble injection (RBI) maintains the frictional drag reduction by generating bubble swarms. The enhanced drag reduction mechanism and the effectiveness of the RBI approach are investigated by studying wall shear stress and the velocity vector field in the liquid phase when measured in a turbulent horizontal channel flow. The bubble swarms generated by RBI consist of bubbles of various sizes with leading large air films, which have high reproducibility. The leading air films, which are a result of the concentrated void fraction, maintain a high drag reduction effect by air lubrication and by suppression of Reynolds shear stress events in the turbulent vortical structures beneath the bubble swarm. The latter effect of RBI in particular plays a significant role at higher Reynolds numbers. Based on the combination of these effects, we confirmed that RBI provides an extra drag reduction effect when compared with continuous bubble injection.

Effects of sedimenting particles on the turbulence structure in a horizontal channel flow

This work presents the results of experiments conducted in a horizontal channel to characterize low Reynolds number turbulent flows in the presence of small solid particles. The particle diameter relative to the integral length scale, dp/Λx, is approximately 0.02. Particles and fluid turbulence characteristics are measured for three average solid volume fractions of approximately ϕv = 2.0 × 10−4, 4.0 × 10−4, and 8.0 × 10−4 under conditions where the particle number density is evolving due to deposition. The results indicate that the mean slip between particles and the fluid is important only close to the wall. Away from the wall, the particles and unladen fluid mean velocities are similar. Differences between particles and the unladen fluid statistics are more pronounced in the wall-normal velocity fluctuations than the streamwise velocity fluctuations and Reynolds shear stress due to the stronger effect of the gravitational force in the wall-normal direction. The fluid turbulent intensities show no dependency on loading, but the peak Reynolds shear stress is significantly reduced. A quadrant decomposition of the Reynolds shear stress revealed a corresponding reduction in the ejections and sweeps for the laden flow in comparison with the unladen flow. Swirling strength and vorticity root-mean-square fluctuations decayed due to the damping effect of particles. The influence of particles on the turbulence structure was examined using two-point correlations of the velocity fluctuations and swirling strength, where it was demonstrated that the wall structures are attached eddies which are more extensive (much larger) in the particle-laden flow compared to the unladen flow.

Nonlinear Dynamics and Wall Touch-Up in Unstably Stratified Multilayer Flows in Horizontal Channels under the Action of Electric Fields

This study considers the nonlinear dynamics of stratified immiscible fluids when an electric field acts perpendicular to the direction of gravity. A particular setup is investigated in detail, namely, two stratified fluids inside a horizontal channel of infinite extent. The fluids are taken to be perfect dielectrics, and a constant horizontal field is imposed along the channel. The sharp interface separating the two fluids may or may not support surface tension, and the Rayleigh--Taylor instability is typically present when the heavier fluid is on top. A novel system of partial differential equations that describe the interfacial position and the leading order horizontal velocity in the fluid layers is studied analytically and computationally. The system is valid in the asymptotic limit of one layer being asymptotically thin compared to the second fluid layer, and as a result nonlocal electrostatic terms arise due to the multiscale nature of the physical setup. The initial value problem on spatially perio...

Features of two-phase flow in a rectangular microchannel with the height of 300 μm

The two-phase flow in a narrow short horizontal channel of rectangular cross section with the width of 10 mm and height of 300 μm was studied experimentally. The features of the jet regime were studied in detail. It is shown that an increase in superficial velocity of jet pulsation frequency increases, and the ratio of unwetted area of the upper channel wall to the wetted area of the upper channel wall decreases.

Analytical model for steady flow through a finite channel with one porous wall with arbitrary variable suction or injection

This paper presents an exact solution of two-dimensional laminar flow through a finite length channel with one porous wall. It improves upon previous solutions by (1) satisfying the no-slip boundary condition at the channel dead end, (2) adding a turbulent term to the porous wall boundary condition, (3) allowing for arbitrary variable suction or injection across the porous wall, and (4) model validation against new cryogenic liquid hydrogen and oxygen experimental data. Of particular interest in the current work is the modeling of cryogenic propellant flow through a porous liquid acquisition device (LAD) screen and channel inside a propellant tank. First, a detailed review of the literature is presented for previously attempted solutions to channel flow with one porous wall. Next, the governing equations, boundary conditions, and model assumptions are used to derive the analytical flow solution and present general model results for pressure and velocity fields within the channel. Then, the model solution is compared with horizontal LAD channel flow data in liquid oxygen as well as vertical LAD channel flow data in an inverted outflow configuration in liquid hydrogen. Model results are used to update the static cryogenic bubble point pressure model with a dynamic bubble point term which factors in enhanced convection and cooling at the screen during propellant outflow. Convective heat transfer at the LAD screen during outflow is also quantified by comparing model and data. The new analytical flow solution with the dynamic bubble point model is shown to compare well with available cryogenic experimental data.

Modelling of gas–solid turbulent channel flow with non-spherical particles with large Stokes numbers

This paper describes a complete framework to predict the behaviour of interacting non-spherical particles with large Stokes numbers in a turbulent flow. A summary of the rigid body dynamics of particles and particle collisions is presented in the framework of Quaternions. A particle-rough wall interaction model to describe the collisions between non-spherical particles and a rough wall is put forward as well. The framework is coupled with a DNS-LES approach to simulate the behaviour of horizontal turbulent channel flow with 5 differently shaped particles: a sphere, two types of ellipsoids, a disc, and a fibre. The drag and lift forces and the torque on the particles are computed from correlations which are derived using true DNS.The simulation results show that non-spherical particles tend to locally maximise the drag force, by aligning their longest axis perpendicular to the local flow direction. This phenomenon is further explained by performing resolved direct numerical simulations of an ellipsoid in a flow. These simulations show that the high pressure region on the acute sides of a non-spherical particle result in a torque if an axis of the non-spherical particle is not aligned with the flow. This torque is only zero if the axis of the particle is perpendicular to the local direction of the flow. Moreover, the particle is most stable when the longest axis is aligned perpendicular to the flow.The alignment of the longest axis of a non-spherical particle perpendicular to the local flow leads to non-spherical particles having a larger average velocity compared to spherical particles with the same equivalent diameter. It is also shown that disc-shaped particles flow in a more steady trajectory compared to elongated particles, such as elongated ellipsoids and fibres. This is related to the magnitude of the pressure gradient on the acute side of the non-spherical particles. Finally, it is shown that the effect of wall roughness affects non-spherical particles differently than spherical particles. Particularly, a collision of a non-spherical particle with a rough wall induces a significant amount of rotational energy, whereas a corresponding collision with a spherical particle results in mostly a change in translational motion.