Flow In Horizontal Channel Research Articles

Structural impact of kerosene-Al2O3 nanoliquid on MHD Poiseuille flow with variable thermal conductivity: Application of cooling process

The fuel of rocket engine can improve the cooling process of chamber and nozzle walls by means of Kerosene−alumina nanoliquid. In particular this investigation is devoted to explore the credible potential use of kerosene-Al2O3 nano-liquid for thrust chamber regenerative cooling in semi-cryogenic rocket engine due to its enhanced thermal properties. Mixed convection boundary layer plane Poiseuille flow in horizontal channel under the variable thermal conductivity and inclined magnetic field are taken into account. The spherical shaped Alumina (Al2O3) nano-size particles with volume fraction (0.01, 0.02, 0.03 and 0.04) are suspended in kerosene oil carrier liquid. The governing flow problem consists of nonlinear coupled differential equations is tackled by analytical technique. Influence of various evolving pertinent parameters is examined graphically. The role of physical parameters of contemporary interest like Eckert number, Grashof number, thermal radiation, heat source/sink, Nusselt number and Skin-friction are numerically investigated and presented in tabular form. Convergence of obtained series solutions has been deliberated by “h” and the square error norm 2 curves are also presented in each case.

Stochastic modelling for capturing the behaviour of irregular-shaped non-spherical particles in confined turbulent flows

For calculating dispersed particle-laden flows in confined systems, the well-known Euler/Lagrange approach is most suitable. Lagrangian tracking of non-spherical particles with certain shapes is mostly performed by additionally solving for the orientation of particles in the flow and using resistance coefficients (i.e. drag, lift and torque) which depend on this orientation. For that in many cases theoretical results for Stokes flow around such particles are used. In practical situations where very often irregular shaped non-spherical particles are transported in a flow, such an approach cannot be adopted since the particles have mostly a statistical distribution of shape and hence it is difficult to define a major and minor axis of the particles. The novel approach developed here is based on a statistical treatment of the fluid forces and moments acting on irregular-shaped particles as well as the wall collision process in order to mimic their stochastic behaviour. The required probability distribution functions (PDF's) for the resistance coefficients were derived by applying direct numerical simulations (DNS) based on the Lattice-Boltzmann method (LBM). The PDF's for the wall normal and parallel restitution ratios were developed based on an experimental analysis of the wall collision of irregular-shaped particles using stereoscopic high-speed imaging. Preliminary Euler/Lagrange calculations applying these statistical models were conducted for a horizontal channel flow laden with irregular-shaped particles and compared to measurements. The results revealed that the calculation of the particle phase assuming the standard models for spherical particles yields completely wrong cross-stream profiles of particle mass flux, an under-prediction of the stream-wise particle mean velocity and an over-prediction of the associated fluctuating component. The stochastic models for the flow resistance coefficients and the wall collision process on the other hand provided much better agreement with the measurements.

Visualization of motion of bubble cluster in horizontal channel flow by moving camera

Visualization of motion of bubble cluster in horizontal channel flow by moving camera

The effect of mixed convection on the thermal field of horizontal channel flow

An experimental study was conducted to investigate the thermal field of low-speed flow of moistair in a horizontal rectangular duct, uniformly heated from below (Poiseuille–Benard flow). Averaged temperature fields were measured in vertical mid-plane using thermocouples. The buoyancy-induced secondary flow is interacting with forced Poiseuille flow which leads to complex flow behaviour with flow reversal along the top surface. Two types of bottom boundary conditions were examined: aluminium plate (only heat transfer) and water film (simultaneous heat and mass transfer) heated to the same temperature. Presence of mass transfer causes stronger transient behaviour above the bottom surface and enhancing of heat transfer, but the overall character of the thermal field remains the same as in case of heat transfer only.

Hydrodynamic investigation of slurry flows in horizontal narrow rectangular channels

Hydrodynamic investigation of slurry flows in horizontal narrow rectangular channels

Numerical simulation of external inertia and compressibility effects on the dynamic instabilities of two-phase boiling flows in horizontal parallel channels

Density wave oscillations and pressure drop oscillations are investigated numerically in two horizontal parallel channels using lumped parameter model assuming a homogeneous two-phase flow model. In this study the effects of external parameters, such as fluid inertia and compressible gases on the stability margins and transient behaviors of parallel channels system are analyzed. The results show, that the fluid inertia and compressible gases have high impact on the stability margins of two parallel channels; in fact, increasing the inlet inertia and outlet compressibility will increase the system stability while increasing the outlet inertia and inlet compressibility decrease its stability.

Mechanism of water inrush driven by grouting and control measures—a case study of Chensilou mine, China

Water inrush into coal mines from aquifers underlying coal seams often causes serious casualties and economic losses. The key to preventing the disaster is to discover a water inrush mechanism suitable for specific geological and hydrogeological conditions and apply reasonable control measures. A case of the Chensilou mine is studied in this paper. Complex geological and hydrogeological conditions, such as 12 aquifers in the floor and small distance between coal seam and aquifer, make the mining face in the synclinal basin have a great risk of water inrush. In addition, as an important way to prevent the disaster, grouting will aggravate the risk of water inrush from the floor. The slurry will drive groundwater in the limestone aquifers L8, even L7 and L6 along the horizontal (fracture zone in L11~L8) and vertical (Fs1 ~Fd1) water flow channel into the mining face and synclinal basin. A new water inrush mechanism driven by grouting is formed. In order to prevent this disaster, based on statistical law of hole deviation, the relative error of vertical depth and the angle between the borehole and the rock formation are obtained. Finally, an improved grouting method is proposed, which is useful to ensure the safe production of coal mine and reduce the cost of grouting.

Viscoplastic fluid displacement flows in horizontal channels: Numerical simulations

We study numerically isoviscous displacement flows of a Bingham fluid by a Newtonian fluid in a horizontal plane channel. We consider a heavy-light displacement flow with a laminar imposed flow. We analyze the flow from various perspectives, using the three dimensionless parameters that largely describe the flow: the Bingham number (Bn), the densimetric Froude number (Fr) and the Reynolds number (Re). In particular, we are able to categorize three classes for the main flow regimes, viz., center-type and slump-type, no-back-flow and temporary-back-flow, and stable and unstable displacements, for which we also quantify their transition boundaries versus the aforementioned dimensionless numbers. We show that the appearance of unstable flows can eventually lead to a number of different flow patterns, such as sinusoidal shaped wave and periodic-detachment forms. In addition, we study in depth an interesting feature exclusively associated to viscoplastic fluid displacements, i.e., the formation of static residual layers on the upper/lower walls of the channel. We also study the evolution of the key displacement flow features, i.e., the trailing and leading fronts, and classify certain secondary flow features related to the leading front, such as plug-like, inertial tip, semi-detached and fully-detached fronts. Finally, we quantify the velocity of the leading front at long times.

Effect of inertia and compressibility on the pressure drop oscillations of two-phase boiling flows in horizontal parallel channels

In this study, a mathematical model is developed to study Pressure drop oscillations (PDOs) in two horizontal parallel channels using lumped parameter model assuming a homogeneous two-phase flow model. This model investigates the effect of external parameters, such as fluid inertia and compressible gases, on the stability margins of PDOs. Results show that the fluid inertia and compressible gases have high impact on the stability margins of two parallel channels; in fact, increasing the inlet inertia and outlet compressibility increases system stability, while increasing the outlet inertia and inlet compressibility decreases system stability. Thus, increasing the sub-cooling number and inlet resistance coefficient improves stability behavior.

Observational study on the fine structure and dynamics of a solar jet. I. Energy build-up process around a satellite spot

Abstract We report on a solar jet phenomenon associated with successive flares on 2014 November 10. These explosive events were involved with the satellite spots’ emergence around a δ-type sunspot in the decaying active region NOAA 12205. The data for this jet were provided by the Solar Dynamics Observatory, the X-Ray Telescope aboard Hinode, and the Interface Region Imaging Spectrograph and Domeless Solar Telescope at Hida Observatory, Kyoto University. These abundant data enabled us to present this series of papers to discuss the entire process of the observed phenomena, including the energy storage, event trigger, and energy release. In this paper, we focus on the energy build-up and trigger phases, by analyzing the photospheric horizontal flow field around the active region by an optical flow method. The analysis shows the following results: (1) The observed explosive phenomena involved three satellite spots, the magnetic fluxes of which successively reconnected with their pre-existing ambient fields; (2) All of these satellite spots emerged in the moat region of a pivotal δ-type sunspot, especially near its convergent boundary with the neighboring supergranules or moat regions of adjacent sunspots; (3) Around the jet ejection site, the positive polarities of the satellite spot and adjacent emerging flux encountered the global magnetic field with a negative polarity in the moat region of the pivotal δ-type sunspot, and thus the polarity inversion line was formed along the convergent boundary of the photospheric horizontal flow channels.

Surfactant and gravity dependent instability of two-layer Couette flows and its nonlinear saturation

A horizontal channel flow of two immiscible fluid layers with different densities, viscosities and thicknesses, subject to vertical gravitational forces and with an insoluble surfactant monolayer present at the interface, is investigated. The base Couette flow is driven by the uniform horizontal motion of the channel walls. Linear and nonlinear stages of the (inertialess) surfactant and gravity dependent long-wave instability are studied using the lubrication approximation, which leads to a system of coupled nonlinear evolution equations for the interface and surfactant disturbances. The (inertialess) instability is a combined result of the surfactant action characterized by the Marangoni number $Ma$ and the gravitational effect corresponding to the Bond number $Bo$ that ranges from $-\infty$ to $\infty$. The other parameters are the top-to-bottom thickness ratio $n$, which is restricted to $n\geqslant 1$ by a reference frame choice, the top-to-bottom viscosity ratio $m$ and the base shear rate $s$. The linear stability is determined by an eigenvalue problem for the normal modes, where the complex eigenvalues (determining growth rates and phase velocities) and eigenfunctions (the amplitudes of disturbances of the interface, surfactant, velocities and pressures) are found analytically by using the smallness of the wavenumber. For each wavenumber, there are two active normal modes, called the surfactant and the robust modes. The robust mode is unstable when $Bo/Ma$ falls below a certain value dependent on $m$ and $n$. The surfactant branch has instability for $m<1$, and any $Bo$, although the range of unstable wavenumbers decreases as the stabilizing effect of gravity represented by $Bo$ increases. Thus, for certain parametric ranges, even arbitrarily strong gravity cannot completely stabilize the flow. The correlations of vorticity-thickness phase differences with instability, present when gravitational effects are neglected, are found to break down when gravity is important. The physical mechanisms of instability for the two modes are explained with vorticity playing no role in them. This is in marked contrast to the dynamical role of vorticity in the mechanism of the well-known Yih instability due to effects of inertia, and is contrary to some earlier literature. Unlike the semi-infinite case that we previously studied, a small-amplitude saturation of the surfactant instability is possible in the absence of gravity. For certain $(m,n)$-ranges, the interface deflection is governed by a decoupled Kuramoto–Sivashinsky equation, which provides a source term for a linear convection–diffusion equation governing the surfactant concentration. When the diffusion term is negligible, this surfactant equation has an analytic solution which is consistent with the full numerics. Just like the interface, the surfactant wave is chaotic, but the ratio of the two waves turns out to be constant.

On the Validity of Boussinesq Approximation in Variable Property Turbulent Mixed Convection Channel Flows

ABSTRACTThe present study investigates the effects of fluid thermo-physical property variations on fully developed turbulent mixed convection flow in vertical and horizontal parallel plate channels where walls are kept at different temperatures. The main attention is paid to the validity of the Boussinesq approximation when the temperature differences are enhanced. Reynolds number based on the channel half-width and friction velocity is assumed to be 150. The governing equations are solved utilizing the large eddy simulation and the low Mach number approach on a finite-volume basis. Dealing with the sub-grid scale stress tensor and the heat flux vector, the dynamic Smagorinsky model is used. All the numerical simulations are carried out by developing a solver in OpenFOAM. The present results display that an increase in the walls' temperature difference, applying the Boussinesq approximation and neglecting the dependency of thermal conductivity and dynamic viscosity on temperature, can result in relatively large errors. Deviations of up to 33% and 45% in the prediction of friction coefficient and Nusselt number, respectively, are shown. This is true for both vertical and horizontal configurations.

Large eddy simulation of microbubble transport in a turbulent horizontal channel flow

Liquid-gas multiphase flows occur in many engineering and environmental applications, with the former ranging from the flow of oil and gas in pipelines, of steam and water in nuclear reactors and steam generators, and the evaporation and condensation of refrigerants in refrigeration and air conditioning equipment. In this paper, the dispersion and interaction between microbubbles and turbulence in a horizontal channel flow is investigated using a two-way coupled Eulerian–Lagrangian approach based on large eddy simulation. The microbubbles are considered to be spherical and non-deformable, and are represented by a Lagrangian bubble tracking technique, with the bubbles subject to drag, gravity, buoyancy, shear lift, added mass and pressure gradient forces. Dynamic calibration of a Smagorinsky-type sub-grid scale (SGS) closure is employed to account for the unresolved stresses, whilst a stochastic Markov method is used to describe the effect of the SGS velocity fluctuations on bubble dispersion. Channel flows of water at two shear Reynolds numbers, Reτ=150 and 590, and three different bubble diameters, db=100, 220 and 330µm, are simulated. The results show acceptable agreement with DNS predictions of single- and two-phase flows, with the low density microbubbles migrating towards the upper channel wall with time under the influence of buoyancy, and segregating in the upper half of the channel, with this effect increasing with bubble diameter. The accumulated bubbles near the upper wall modify the liquid velocity field, with the mean velocity profile becoming asymmetric as a consequence and with slight modification of the turbulent stresses. At higher mean velocity and turbulence levels, the buoyancy effect is reduced due to more effective turbulent dispersion of the microbubbles, leading to reduced bubble migration towards the upper channel wall.

Solid sediment transport in turbulent channel flow over irregular rough boundaries

The presence of a loading of dispersed particles in a turbulent flow affects the dynamics of the carrier flow field which, in turn, drives grains movement. The focus of the paper is on the analysis of the coupling effects between near-bed turbulence structures and the dynamics of dispersed suspended solid particles in wall-bounded turbulent multiphase flows. We consider turbulent horizontal channel flows bounded by rough boundaries. The friction Reynolds number of the unladen flow is Reτ=180 and the dispersed phase spans one order of magnitude of particle diameter. To analyze sedimentation and suspended phase transport, we adopt concepts and modeling ideas derived from the Euler-Lagrange approach, using Direct Numerical Simulations (DNS) for the carrier phase coupled with Lagrangian Particle Tracking (LPT) for the dispersed phase. The analysis takes into account fluid-particle interaction (two-way coupling) in the frame of the Particle-Source-In-Cell (PSIC) method. The effect of the wall’s roughness is taken into account modeling the elastic rebound of particles onto it, instead of using a virtual rebound model.

Direct Numerical Simulation on Turbulent Transportation and Thermophoretic Deposition of Micron-Sized Particles in Rectangle Channel

The turbulent transportation and thermophoretic deposition of micron-sized particles ranging from 1-20 μm are studied by direct numerical simulation of a horizontal turbulent rectangular channel flow in this paper. Present research on thermophoretic deposition mainly focused on the sub-micron particles, whereas the particle size usually exceeds this range during radioaerosol monitoring. If a coolant leakage takes place in the primary loop, there will be a huge temperature gradient between the air and the wall, which leads to thermophoretic deposition. A temperature gradient of 1700 K/m is set between the hot and cold walls. Simulation results show that thermophoresis plays an important role in aerosol deposition which depends on particle size. It is found that deposition of 1 μm particles on the cold wall is almost 15 times more than that on the hot wall. With the increasing of particle size, the difference of thermophoretic deposition between the two walls decreases. In this paper, 10% particles per second are deposited by thermophoresis, which concludes that thermophoretic deposition should be considered and adjusted according to particle size during aerosol transportation where large temperature gradient exists.

Математическое моделирование течений с испарением в двухслойной системе с теплоизолированной верхней границей

The problem of two-layer flow in an infinite horizontal channel with solid impermeable walls is studied. The upper boundary of the system is considered to be thermally insulated, and the longitudinal gradient of the temperature on the lower boundary is given. The lower layer is filled with a liquid that evaporates through the thermocapillary interface; the upper layer is a gas–vapor mixture. Stationary flows induced by action of gas flow in the upper layer and longitudinal temperature gradient are studied. The thermodiffusion and diffusive thermal conductivity effects are taken into account in the gas–vapor mixture. The mathematical model is based on the Boussinesq approximation of the Navier–Stokes equations, and the diffusion equation also holds for the upper layer. The exact solutions of a special type are constructed, where only the longitudinal velocity differs from zero and depends on the transverse coordinate, and the temperature and the vapor concentration are linearly dependent on the longitudinal coordinate. Evaporation of the liquid is taken into consideration using the mass balance and heat transfer conditions. Velocity and temperature profiles for liquid-gas systems such as ethanol-airand HFE7100-nitrogenare presented. The phenomenon of return flows near the interface is investigated. DOI 10.14258/izvasu(2017)4-16

Periodically fully developed laminar flow and heat transfer in a two-dimensional horizontal channel with staggered fins

The 2-D periodically fully developed laminar forced convection fluid flow and heat transfer characteristics in a horizontal channel with staggered fins are investigated numerically under constant wall heat flux boundary condition. Study is performed using ANSYS Fluent 6.3.26 which uses finite volume method. Air (Pr @ 0.7) and Freon-12 (Pr @ 3.5) are used as working fluids. Effects of Reynolds number, Prandtl number, fin height, and distances between two fins on heat transfer and friction factor are examined. Results are given in the form of non-dimensional average Nusselt number and average Darcy friction factor as a function of Reynolds number for different fin distances and Prandtl numbers. The velocity and temperature profiles are also obtained. It is seen that as the fin distance increases, behavior approaches the finless channel, as expected. Also, thermal enhancement factors are given graphically for working fluids. It is seen that heat transfer dominates the friction as both the distance between two fins and Prandtl number increase. It is also seen that fins having blockage ratio of 0.10 in 2-D periodically fully developed laminar flow is not advantageous in comparison to smooth channel without fins.

Visualization of behavior of single bubble in horizontal turbulent channel flow

Visualization of behavior of single bubble in horizontal turbulent channel flow

Deposition of particles in liquid flows in horizontal straight channels

A flow in a horizontal channel is an important method for the transport of materials, products and/or waste gases/liquids. The deposition of particles in a horizontal channel may clog the flow path. The purpose of this paper is to extend the use of a developed Eulerian deposition model to liquid flows in horizontal straight channels to predict the particle deposition rate. For a horizontal pipe, the deposition rates may differ greatly along a cross section, due to the influences of gravity and buoyancy. The current deposition model is first applied to air flows to enable a comparison with available experimental data. Then, the model is applied to liquid flows in horizontal straight pipes. The effects of gravity, buoyancy, water flow rates, wall roughness, particle size and temperature difference in the near-wall boundary layer on the deposition rate have been studied and explained. The results show that the deposition rates of particles increase with an increased flow rate. The gravity separation has a large influence on the deposition of large particle at high and low parts of the horizontal pipe in some flows. Moreover, both the wall roughness and thermophoresis have a significant influence on the deposition rate of small particles. In addition, the roughness also shows an important influence on the large particle deposition at the top of the investigated pipe, due to that a large value of roughness can make the deposition location somewhat far away from the wall, where a stronger turbophoresis exists. The intensity of the turbophoresis relative to the gravity separation before a particle is reaching the deposition location is important for the large particle deposition when the gravity separation play a negative role on the deposition rate.

Experimental and numerical investigations on the direct contact condensation phenomenon in horizontal flow channels and its implications in nuclear safety

Abstract The complex direct contact condensation phenomenon is investigated in horizontal flow channels both experimentally and numerically with special emphasis on its implications on safety assessment studies. Under certain conditions direct contact condensation can act as the driving force for the water hammer phenomenon with potentially local devastating results, thus posing a threat to the integrity of the affected NPP components. New experimental results of in-depth analysis of the direct contact condensation phenomena obtained in Kaunas at the Lithuanian Energy Institute will be presented. The German system code ATHLET employing for the calculation of the heat transfer coefficient a mechanistic model accounting for two different eddy length scales, combined with the interfacial area transport equation will be assessed against condensation induced water hammer experimental data from the integral thermal-hydraulic experimental facility PMK-2, located at the KFKI Atomic Energy Research Institute in Budapest Hungary.