Channel Of Rectangular Section Research Articles

Determination of pressure in a flat channel of a solar water heater when water is freezing

The article considers the problem of modeling a flat channel of a rectangular section of a solar water heater filled with water when it freezes to estimate the pressure in the channel. It is assumed that when water freezes, due to the density difference between the solid and liquid phases, the volume it occupies in the channel changes, and under the influence of the pressure difference between the external environment and the internal region, the channel walls are deformed. The theory of elastic cylindrical bending of a two-layer plate is used for modeling. Calculation relations are obtained for determining the pressure in the channel depending on the thickness of the freezing ice. An example of calculating the pressure in a channel of rectangular cross section when water freezes is given.

矩形截面通道中颗粒惯性聚集现象的力学成因

矩形截面通道中颗粒惯性聚集现象的力学成因

Influence of aspect ratio on vortex formation in X-junctions: Direct numerical simulations and eigenmode decomposition

We study numerically the appearance and number of axial vortices in the outlets of X-shaped junctions of two perpendicular channels of rectangular sections with facing inlets. We explore the effect of the aspect ratio of the cross section, AR, on the number of vortices created at the center of the junction. Direct numerical simulations (DNSs) performed for different values of the Reynolds number Re and AR demonstrate that vortices with their axis parallel to the outlets, referred to as axial vortices, appear above critical Reynolds numbers Rec. As AR increases from 1 to 11, the number of vortices observed increases from 1 to 4, independently of Re. For AR = 1, the single axial vortex induces an interpenetration of the inlet fluids in the whole section; instead, for larger AR’s for which more vortices appear, the two inlet fluids remain largely segregated in bands, except close to the vortices. The linear stability analysis demonstrates that only one leading eigenmode is unstable for a given set of values of AR and Re. This mode provides a simplified model of the flow field, reproducing its key features such as the number of vortices and their distance. Its determination with this method requires a much smaller computational load than the DNS. This approach is shown to allow one to determine quickly and precisely the critical Reynolds number Rec and the sensitivity function S, which characterizes the influence of variations of the base flow on the unstable one.

Vortex intensification of heat exchange in rectangular section channel by the rotating disk on its wall

Vortex intensification of heat exchange in rectangular section channel by the rotating disk on its wall

Effect of propagation speed on the quenching of methane, propane and ethylene premixed flames between parallel flat plates

This paper reports on an experimental investigation of the effect of flame speed on the quenching distance. In a rectangular section channel, the quenching distance of methane-air, propane-air and ethylene-air flames, arriving on the quenching element with different speeds, is investigated. The experiments are performed in a constant volume combustion chamber comprising two volumes separated by the quenching section. The quenching tests are performed at pressure close to atmospheric, with an initial temperature of the walls and flammable mixture of 293 K. Flame quenching is assessed from pressure measurements, while the apparent flame speed is determined from fast schlieren imaging. The results show a similar trend for the three fuels considered: the quenching distance for laminar propagating flames is about twice smaller than when the flow becomes turbulent, close to the entrance of the channel. In the case of laminar flames, the quenching distance is almost constant at 1.3–1.5 mm for the conditions considered, while for turbulent flames, depending on the fuel and equivalence ratio, the quenching distance is in the range 2–2.5 mm. Starting from the quenching theory, the results are analyzed and the effects of flame curvature and turbulence are discussed.

Heat Transfer in Air Flow Past a Bottom Channel Wall-Attached Diamond-Shaped Baffle – Using a CFD Technique

A computational analysis has been conducted to investigate turbulent flow and convective thermal transfer characteristics in a two-dimensional horizontal rectangular section channel with a hot lower wall-mounted diamond-shaped baffle. The calculations are based on the finite volume method, by means of Commercial Computational Fluid Dynamics software FLUENT, standard k-epsilon turbulence model with QUICK numerical scheme, and the SIMPLE discretization algorithm has been applied. The fluid flow and heat transfer characteristics, i.e., dynamic pressure coefficient, stream function, mean, axial, and transverse velocities, turbulent viscosity, temperature field, skin friction coefficients, local and average Nusselt numbers, and thermal enhancement factor are presented for flow Reynolds numbers based on the aeraulic diameter of the computational domain ranging from 12,000 to 32,000 at constant surface temperature condition along the upper and lower walls. Effect of the diamond configuration of the insulated baffle is studied numerically and the data obtained from this same baffle model are also compared with that of the simple flat rectangular baffle under similar operating conditions. Over the range under investigation, the improvements are found to be around 3.962 and 29.820 times higher than the smooth air channel with no baffle for heat thermal transfer and skin friction factor, respectively. The maximum TEF is around 1.292 at the highest Reynolds number value, Re = 32,000.

Numerical investigation on the forced laminar convection heat transfer of Al2O3-water nanofluid within a three-dimensional asymmetric heated channel

PurposeThe purpose of this paper is to carry out a numerical investigation to study laminar convection flow of Al2O3-water nanofluids within a three-dimensional rectangular section channel asymmetrically heated.Design/methodology/approachA three-dimensional model of the channel is designed and simulated by using Comsol Multiphysics. The finite elements method is used to perform the numerical simulation. A variety of cases are taken into account by considering Reynolds numbers ranging from 250 up to 1,000, concentration between 0 and 6 per cent, particle dimension of 20, 40 and 60 nm and inlet temperature equal to 293.15 and 320 K. A constant heat flux of 1,000 W/m2is imposed on the top surface of the channel.FindingsThe results demonstrate that nanofluids guarantee improved thermal performances with respect to the base fluid, as shown by the augmented Nusselt number. On the other hand, pressure drop shows a noticeable increase; therefore, an entropy generation analysis is developed to establish optimal conditions for the system under investigation.Originality/valueThe originality of this work consists in the analysis of a three-dimensional asymmetric heated channel with nanofluids in laminar convection. The present work would be beneficial to improve the design of devices with particular focus on solar thermal panel.

Numerical Analysis of Thermal and Aerodynamic Fields in a Channel with Cascaded Baffles

A computational fluid dynamic analysis of thermal and aerodynamic fields for an incompressible steady-state flow of a Newtonian fluid through a two-dimensional horizontal rectangular section channel with upper and lower wall-attached, vertical, staggered, transverse, cascaded rectangular-triangular (CRT), solid-type baffles is carried out in the present paper using the Commercial, Computational Fluid Dynamics, software FLUENT. The flow model is governed by the Reynolds averaged Navier-Stokes (RANS) equations with the SST k-ω turbulence model and the energy equation. The finite volume method (FVM) with the SIMPLE-discretization algorithm is applied for the solution of the problem. The computations are carried out in the turbulent regime for different Reynolds numbers. In this study, thermo-aeraulic fields, dimensionless axial profiles of velocity, skin friction coefficients, local and average heat transfer coefficients, and thermal enhancement factor were investigated, at constant surface temperature condition along the heated upper wall of the channel, for all the geometry under investigation and chosen for various stations. The impact of the cascaded rectangular-triangular geometry of the baffle on the thermal and dynamic behavior of air is shown and this in comparing the data of this obstacle type with those of the simple flat rectangular-shaped baffle. This CFD analysis can be a real application in the field of heat exchangers, solar air collectors, and electronic equipments.

Thermo-mechanical simulations for the comparison of heating channels geometries for composite material injection tools

To meet the expectations of the aeronautics and automotive manufacturers in terms of throughput, appearance quality and structural quality for high-performance composite injected parts, it is necessary to produce reactive and thermally efficient tools. The aim of this paper is to compare the thermal performance of a conventional mold with circular cross-section heating channels, resulting from the design rules published in the literature, and a mold with rectangular section channels for different heating channel positions. The thermal simulations carried out on the models were made at identical operating points, with the models based on the design rules of conventional molds with circular cross-section heating channels. It is important to note that this study was conducted taking into account the technological constraints related to pressure drops and pump use.

Visualization of a Flow in a Spherical Dimple Built in the Lower Wall of the Rectangular-Section Channel of a Water Tunnel and Numerical Identification of the Vortex-Jet Structures in It

Numerical and physical simulations of a laminar separation flow over a single spherical dimple built in the lower wall of the rectangular-section plane-parallel channel of a water tunnel were performed on the basis of the multiblock computational technologies realized in the VP2/3 package. The vortex mechanism of intensification of the heat-transfer processes in this dimple was analyzed with special emphasis on the identification of the vortex-jet structures self-generated in it.

Experimental Investigation of the Fluid Dynamics of a Finned Heat Sink under Operating Conditions

An experimental study has been made of the fluid dynamics performance of electronic equipment designed to cool a heat sink in the form of a finned duct. The apparatus consists of a channel of rectangular section containing the finned duct. A forced airflow is driven by three fans placed in parallel in the inlet and in the outlet sections of the channel. In order to investigate a full range of flow rates, different sets of fans were used in the inlet section. Measurements were made of static pressures at different channel positions by pressure taps connected to a micro manometer, and of the flow rate by a Venturi meter. The experimental working conditions of the active fans were consistent with the manufacturers’ characteristic curves. Values of the local friction coefficient compared well with published correlations. The experimental working points agreed very well with the theoretical curve of the pressure drop and the hydraulic diameter was demonstrated to be of the appropriate size for this fluid dynamics problem.

NUMERICAL AND EXPERIMENTAL STUDY OF DAM-BREAK FLOOD PROPAGATION AND ITS IMPLICATION TO SEDIMENT EROSION

Regarding the hydrodynamics, within the past two decades it has become popular in numerical modeling of free-surface flow to adopt a Reynolds-averaged Navier-Stokes approach, where the volume of fluid (VOF) method is utilized to track the evolution of free-surface. However, this robust numerical model has not been widely applied to the study of sediment transport processes. In this study, we shall extend the numerical model to simulate suspended sediment transport and study the erosion pattern during the initial stage of the dam break flow. We also conducted a series of experiments in a horizontal channel of rectangular section and recorded the snap shots of surface profiles of a dam- break wave during the initial stage of dam-break. Measured data is utilized here to study the hydrodynamics and to validate the numerical model.

The role of etched silicon channels on the pore ordering of mesoporous silica: The importance of film thickness on providing highly orientated and defect-free thin films

If mesoporous thin films (MTFs) are to be utilised in device applications it is important that we produce films which not only possess a single pore direction across large substrate areas (in the range of microns) but are also relatively defect free. In this paper we report the use of confining architectures in the form of topographically patterned rectangular section channels etched into native silicon substrates to promote ordering of the mesopores. We discuss the effects of the channels on films with different thicknesses. The film thickness is shown to be a critical parameter in defining highly orientated and defect-free films and the data demonstrate that it is possible to achieve a single mesoporous silica domain across macroscopic dimensions with thin film thicknesses of approximately 200 nm but that critically pore order can be lost in ultra thin and thicker films produced by these methods.

Numeric and experimental analysis of the turbulent flow through a channel with baffle plates

The present work presents the numeric and experimental analysis of the turbulent flow of air inside a channel of rectangular section, containing two rectangular baffle plates. This is an important problem in the scope of heat exchangers where the characterization of the flow, pressure distribution, as well as the existence and the extension of possible recirculations need to be identified. The differential equations that describe the flow were integrated by the Finite Volumes Method, in two dimensions, employing the Fluent software with the k-e model to describe the turbulence. The mesh is structured, with rectangular volumes. Several boundary conditions were explored, being the more realistic results obtained by prescribing the inlet velocity field and atmospheric pressure at the exit. The obtained results are compared with experimental data, being analyzed and commented the deviations. The velocity field was measured with a hot wire anemometer, and the pressure field with an electronic manometer. The largest variations in the pressure and velocity fields occur in the regions near to the deflectors, as expected.

Modeling of ultrafiltration: Predictions of concentration polarization effects

This paper essentially deals with modeling of the concentration polarization effects on solute separation in ultrafiltration. Laminar tangential flow in a rectangular section channel is considered. The concentration polarization phenomenon in ultrafiltration has been studied by different authors who used different approaches for the finite-difference discretization of the mass transport differential equation. Two of those approaches are examined in detail. It is shown how numerical convergence can be reached, with a small number of increments, when an appropriate choice of the discretized mass transport equation is done. It is also shown why erroneous results have been obtained even with a large number of increments. Parametric studies show a strong influence of the true separation and of the permeation velocity on the separation profile along the tangential flow channel. A comparison between a finite-difference solution and an analytical solution for the mass transport differential equation is presented. Good agreement between the two methods is shown for the limiting case of high separation.

Characteristics of Turbulent Flow and Mass Transfer in Divergent Channels of Rectangular Section

The characteristics of turbulent flow and mass transfer in divergent channels of rectangular cross-section were experinlentally investigated and the typical effects of main flow and the secondary flow on mass transfer were discussed. Sherwood number Shx, could be suitably expressed by Reynolds number Rex, and acceleration parameter K. Sherwood numbers Shx, in the entrance region of mass concentration were proportional to Rex, 0.83 for every diver-gent angle in the present experiment. The velocity profiles in the upper region were recognized as a composite structure consisting of those for the inner and outer layers. but it was difficult to predict the velocity profiles in the lower region with the plane jet profile.

Dispersion in Meandering Channels of Rectangular Section

Dispersion in Meandering Channels of Rectangular Section

Characteristics of Turbulent Flow and Mass Transfer in Divergent Channels of Rectangular Section

The characteristics of turbulent flow and mass transfer in divergent channels of rectangular section were experimentally investigated and the typical effects of main flow and the secondary flow on mass transfer were also discussed. Sherwood number Shx1 could successfully be expressed by Reynolds number Rex1 and acceleration parameter K. Sherwood numbers S__(hx1) in the entrance region of concentration were proportional to R__(ex1)0.83 for any divergent angle, which changed more intensively than R__(ex1)0.8 for the straight channel. The velocity profiles above the axis of divergent channels were recognized as a composite structure consisting of those in the inner and outer layers, but it was difficult to predict the velocity profiles below the axis by those of the plane jet.

Characteristics of Turbulent Flow in Divergent Channels of Rectangular Section

Characteristics of Turbulent Flow in Divergent Channels of Rectangular Section

Difference schemes for elliptic equations with special boundary conditions

On the boundary S of the rectangle a linear combination of the derivative of the unknown function along the inward normal to S, the second derivative along the tangent to the boundary and the values of the unknown function on S are specified. Problems of this type occur, for example, in magnetohydrodynamics [ll in the flow of a conducting fluid with velocity u (x1, x,1 in a magnetic field B in a channel of rectangular section. It is assumed that the walls of the channel are conducting only on segments of finite length. Then we obtain for the potential u in the rectangle G a boundary value problem with boundary conditions of the type indicated above on two opposite sides of the rectangle and u F 0 on the other two sides. In the rectangle itself Au = -f, f = f(v, B). In section 1 we consider the boundary value problem for an elliptic selfconjugate equation which includes the problem of the potential. In section 2 we consider the problem for Poisson’s equation in the rectangle G. On all the sides of the rectangle we specify the boundary conditions