Two-dimensional Horizontal Channel Research Articles

Numerical Investigation of Convective Heat Transfer and Fluid Flow Past a Three Square Cylinders Controlled by a Partition in Channel

This document presents a research article on the control of fluid flow around three heated square cylinders placed side by side in a 2D horizontal channel using a flat plate. The objective of this research is to examine the effect of the position, length and height of a flat plate on fluid flow and heat transfer. For this purpose, numerical simulations are performed by using the Boltzmann double relaxation time multiple network method (DMRT-LBM). The MRT-D2Q9 and MRT-D2Q5 models are used to treat the flow and temperature fields respectively. In contrast to several existing investigations in the literature in this domain which study the passive control of the flow using a horizontal or vertical plate around a single cylinder, this work presents a numerical study on the effect of the position, length and height of a flat plate (horizontal and vertical) on three heated square cylinders on the flow and temperature fields. First, the effect of the position and length of the horizontal flat plate is examined. This study shows that the implementation of a flat plate of length Lp = 4D at a position g=3 behind the central cylinder reduces the amplitude of the Von Karman Street and allows large and regular heat exchange. Thus, in the second part, the effect of the position and height of the vertical flat plate is studied. The results obtained show that the implementation of a flat plate of height h=2D at a position g=3 behind the central cylinder improves the thermal exchange between the incoming fluid and the heated cylinders. This numerical work could lead to the prediction of the cooling of the electronic components: The cooling of the obstacles is all the better when the control plate is arranged at g = 3 and its height h = 2D in the case of the vertical plate or its length Lp equal to 4D in the case where the plate is implemented horizontally

Combined Heat and Mass Transfer of Fluid Flowing through Horizontal Channel by Turbulent Forced Convection

In the present paper, we report a numerical study of dynamic and thermal behavior of the incompressible turbulent air flow by forced convection in a two-dimensional horizontal channel. This one contains the complicated form of the deflector which has been studied by varying the inclination angle from φ = 40°, φ = 55° to φ = 65°. The baffles are mounted on lower and upper walls of the channel. The walls are maintained at a constant temperature (375 K), the inlet velocity of air is Uint = 7.8 m/s, and the Reynolds number Re = 8.73 × 104. A specifically developed numerical model was based on the finite-volume method to solve the coupled governing equations and the SIMPLE (Semi Implicit Method for Pressure Linked Equation) algorithm for the treatment of velocity-pressure coupling. For Pr = 0.71, the results obtained show that (i) the streamlines and isotherms are strongly affected by the inclinations angles at Re = 8.73 × 104, (ii) the friction coefficient near the baffles increases under the angle exchange effect, and (iii) for a constant Re, the local Nusselt number at the walls of the channel varies with increasing the inclination angle of the deflector. Furthermore, the deflectors are generally used to change the direction of the structure of flow and also to increase the turbulence levels. We can conclude that the contribution of inclined baffles improves the increase of heat and mass transfer in which the Nusselt number at a certain angle increases noticeably.

Baffle orientation and geometry effects on turbulent heat transfer of a constant property incompressible fluid flow inside a rectangular channel

Purpose A computational fluid dynamics (CFD) analysis has been carried out on the aerodynamic and thermal behavior of an incompressible Newtonian fluid having a constant property and flowing turbulently through a two-dimensional horizontal high-performance heat transfer channel with a rectangular cross section. The top surface of the channel was kept at a constant temperature, while it was made sure to maintain the adiabatic condition of the bottom surface. Two obstacles, with different shapes, i.e. flat rectangular and V-shaped, were inserted into the channel; they were fixed to the top and bottom surfaces of the channel in a periodically staggered manner to force vortices to improve the mixing and consequently the heat transfer. The first fin-type obstacle is placed on the heated top channel surface, and the second baffle-type one is placed on the insulated bottom surface. Five different obstacle situations were considered in this study, which are referred as cases FF (flat fin and flat baffle), FVD (flat fin and V-downstream baffle), FVU (flat fin and V-upstream baffle), VVD (V-downstream fin and V-downstream baffle) and VVU (V-Upstream fin and V-upstream baffle). Design/methodology/approach The flow model is governed by Reynolds-averaged Navier–Stokes equations with the k-epsilon turbulence model and the energy equation. These governing equations are discretized by the finite volume method, in two dimensions, using the commercial CFD software FLUENT software with the Semi Implicit Method for Pressure Linked Equations (SIMPLE) algorithm for handling the pressure-velocity coupling. Air is the test fluid with the flow rate in terms of Reynolds numbers ranging from 12,000 to 32,000. Findings Important deformations and large recirculation regions were observed in the flow field. A vortex causes a rotary motion inside the flow field, which enhances the mixing by bringing the packets of fluid from the near-wall region of the channel to the bulk and the other way around. The largest value of the axial variations of the Nusselt number and skin friction coefficient is found in the region facing the baffle, while the smallest value is in the region near the fin, for all cases. The thermal enhancement factor (TEF) was also introduced and discussed to assess the performance of the channel for various obstacle situations. It is found that the TEF values are 1.273-1.368, 1.377-1.573, 1.444-1.833, 1.398-1.565 and 1.348-1.592 for FF, FVD, FVU, VVD and VVU respectively, depending on the Re values. In all cases, the TEF was found to be much larger than unity; its maximum value was around 1.833 for FVU at the highest Reynolds number. Therefore, the FVU may be considered as the best geometrical configuration when using the obstacles to improve the heat transfer efficiency inside the channel. Originality/value This study can be a real application in the field of shell-and-tube heat exchangers and flat plate solar air collectors.

Analysis for Various Effects of Relaxation Time and Wall Properties on Compressible Maxwellian Peristaltic Slip Flow

Abstract The present study is related to indicating the several effects of the relaxation time, dynamic behaviour of wall properties and slip conditions at the boundaries on the peristaltic locomotion of viscous non-Newtonian Maxwell fluid flow through a two-dimensional (2D) horizontal flexible sinusoidal wave-shaped channel. An approximated theoretical model is constructed. The solution of the governing equations is developed using the perturbation method. Small amplitude ratio “ratio between amplitude of the wave and half channel width” for the wavy transport is considered for describing the velocity and pressure distributions. Different factors of wall features such as damping force coefficient, wall tension parameter, wall bending coefficient and spring stiffness factor in addition to various flow parameters such as the compressibility factor, Reynolds number, slip coefficient and also the main parameter of interest relaxation time are involved in the mathematical calculations and discussed through graphical representation. Graphs for mean axial velocity, perturbation function and velocity at the wall distributions using the previous coefficients are plotted and then discussed in detail. Results indicate that wall properties, compressibility factor and relaxation time in the presence of peristaltic transport have a significant effect on velocity distributions. The damping factor, wall tension, slip parameter and relaxation time are reducing the mean axial velocity and raising the reversal flow but, the wall elasticity factor enhances the mean axial velocity. Also, the liquid compressibility has a strong effect on the dynamics of the flow.

Effect of wall-mounted V-baffle position in a turbulent flow through a channel

PurposeThe purpose of this paper is to carry out a numerical study on the dynamic and thermal behavior of a fluid with a constant property and flowing turbulently through a two-dimensional horizontal rectangular channel. The upper surface was put in a constant temperature condition, while the lower one was thermally insulated. Two transverse, solid-type obstacles, having different shapes, i.e. flat rectangular and V-shaped, were inserted into the channel and fixed to the top and bottom walls of the channel, in a periodically staggered manner to force vortices to improve the mixing, and consequently the heat transfer. The flat rectangular obstacle was put in the first position and was placed on the hot top wall of the channel. However, the second V-shaped obstacle was placed on the insulated bottom wall, at an attack angle of 45°; its position was varied to find the optimum configuration for optimal heat transfer.Design/methodology/approachThe fluid is considered Newtonian, incompressible with constant properties. The Reynolds averaged Navier–Stokes equations, along with the standard k-epsilon turbulence model and the energy equation, are used to control the channel flow model. The finite volume method is used to integrate all the equations in two-dimensions; the commercial CFD software FLUENT along with the SIMPLE-algorithm is used for pressure-velocity coupling. Various values of the Reynolds number and obstacle spacing were selected to perform the numerical runs, using air as the working medium.FindingsThe channel containing the flat fin and the 45° V-shaped baffle with a large Reynolds number gave higher heat transfer and friction loss than the one with a smaller Reynolds number. Also, short separation distances between obstacles provided higher values of the ratios Nu/Nu0 and f/f0 and a larger thermal enhancement factor (TEF) than do larger distances.Originality/valueThis is an original work, as it uses a novel method for the improvement of heat transfer in completely new flow geometry.

Lattice Boltzmann simulation of nanofluid natural convection heat transfer in a channel with a sinusoidal obstacle

The aim of this work is to conduct numerical study of fluid flow and natural convection heat transfer by utilizing the nanofluid in a two-dimensional horizontal channel consisting of a sinusoidal obstacle by lattice Boltzmann method (LBM). The fluid in the channel is a water-based nanofluid containing Cuo nanoparticles. Thermal conductivity and nanofluid’s viscosity are calculated by Patel and Brinkman models, respectively. A wide range of parameters such as the Reynolds number ([Formula: see text]–400) and the solid volume fraction ranging ([Formula: see text]–0.05) at different non-dimensional amplitude of the wavy wall of the sinusoidal obstacle ([Formula: see text]–20) on the streamlines and temperature contours are investigated in the present study. In addition, the local and average Nusselt numbers are illustrated on lower wall of the channel. The sensitivity to the resolution and representation of the sinusoidal obstacle’s shape on flow field and heat transfer by LBM simulations are the main interest and innovation of this study. The results showed that increasing the solid volume fraction [Formula: see text] and Reynolds number Re leads to increase the average Nusselt numbers. The maximum average Nusselt number occurs when the Reynolds number and solid volume fraction are maximum and amplitude of the wavy wall is minimum. Also, by decreasing the [Formula: see text], the vortex shedding forms up at higher Reynolds number in the wake region downstream of the obstacle.

Constant Property Newtonian Fluid Flow and Heat Transfer overCascaded Fins

Turbulent flow and heat transfer characteristics were studied and analyzed numerically for a constant property Newtonian fluid flowing through a two-dimensional horizontal rectangular cross section channel with staggered, transverse cascaded rectangular-triangular fins (CRTFs) and a constant temperature along both walls. The governing equations based on model used to describe the turbulence phenomenon, are solved by the finite volume method using the SIMPLEC-algorithm. Computations were carried out in the fully-developed regime for different Reynolds numbers, and geometric locations. In particular, velocity and temperature fields, skin friction coefficient, and local and average Nusselt numbers were obtained. This study can be a real application in the field of heat exchangers and air plane solar collectors.

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.

Numerical study of biofluid flow over a backward-facing step: The hydro-thermal behavior in the presence of magnetic field effects

In this paper, the results of adding nanoparticles and applying non-uniform magnetic fields on a biofluid (blood) flow through a two-dimensional horizontal channel with a step are reported. Two magnetic fields with positive and negative gradients were applied. The control volume technique and two-phase mixture model in the numerical approach have been used to illustrate the hydro-thermal behavior of flow. Simulation results reveal that nanoparticles can significantly increase the Nusselt number and wall shear stress. Also, the wall shear stress, Nu, and recirculation length in the presence of a magnetic field with different gradients can be externally controlled. Based on the results, the negative gradient magnetic field increases wall shear stress and Nu in the affected region, unlike the positive gradient.

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.

Numerical Simulation of Non-Darcy Forced Convection through a Channel with Nonuniform Heat Flux in an Open Cavity Using Nanofluid

This article aims to numerically investigate forced convection heat transfer phenomena in a two-dimensional horizontal channel having an open cavity with porous medium. A nonuniform heat flux is considered to be located on the bottom surface of the cavity. Three different heating modes are considered at this wall. The rest of the surfaces are taken to be perfectly adiabatic. The physical domain is filled with water based nanofluid containing TiO2 naparticles. The fluid enters from left and exits from right with initial velocity U i and temperature T i . Governing equations are discretized using the penalty finite element method. The simulation is carried out for a range of Prandtl number Pr(=5.2–12.2) and solid volume fraction φ (=0%–15%). Results are presented in the form of streamlines, isothermal lines, local and average Nusselt number, average temperature of the fluid, horizontal and vertical velocities at mid-height of the channel, and mean velocity field for various Pr and φ. It is found that increasing Pr and φ cause the enhancement of the heat transfer rate.

Numerical Simulation of Fluid Flow Past an Oscillating Triangular Cylinder in a Channel

The structure of laminar incompressible flow in a two-dimensional horizontal channel past a triangular cylinder undergoing vertical oscillating motion is simulated using the finite element method. The oscillating motion is carried out for a fixed Reynolds number equal to 100 and dimensionless oscillating amplitudes of 0.125, 0.25, 0.5, and 1, while the dimensionless forced oscillation frequencies are chosen from St/4 to 4 St, where St is the natural Strouhal number of a stationary triangular cylinder. The arbitrary Lagrangian–Eulerian kinematics is utilized to simulate the oscillating motion. The present problem is first solved for a stationary triangular cylinder to obtain the natural Strouhal number. Then, the fluid dynamics for an oscillating triangular cylinder are solved in terms of instantaneous drag and lift, mean of drag, and root mean square (RMS) of lift coefficients. Detailed illustrations of flow streamlines and vortices contours are presented. The results indicate that when the oscillating frequency is equal to the natural Strouhal number of the stationary cylinder, the RMS of lift coefficient reaches its maximum and the oscillating amplitude has no effect at high oscillating frequency.

A numerical study of laminar and transitional mixed convection flow over a backward-facing step

This work focuses on the study of the transition from steady to chaotic behavior in mixed convection flow over a backward-facing step. Direct numerical simulations are performed in a two-dimensional horizontal channel of expansion ratio ER = 2 at step level. The effects of the temperature difference between the heated bottom wall and the inflow temperature are investigated by keeping constant the Richardson number at 1. The covered range of Grashof and Reynolds numbers is respectively 3.31 × 10 4 ⩽ Gr ⩽ 2.72 × 10 5 and 182.03 ⩽ Re ⩽ 521.34. The thermal and dynamical instabilities which cause the onset of unsteady flow are described in detail. A spectral and phase portrait analysis of the temperature time series allows us to observe that the transition from steady to chaotic flow occurs by period-doubling bifurcations.

Numerical prediction of flow and heat transfer of power-law fluids in a plane channel with a built-in heated square cylinder

Structure of unsteady laminar flow and heat transfer of power-law fluids in two-dimensional horizontal plane channel with a built-in heated square cylinder is studied numerically. The governing equations are solved using a control volume finite element method (CVFEM) adapted to the staggered grid. Computations are performed over a range of Reynolds and Richardson numbers from Re = 20 to 200 and from Ri = 0 to 8, respectively at fixed Prandtl number Pr = 50 and blockage ratio value β′ = 1/8. Three different values of the power-law index ( n = 0.5, 1 and 1.4) are considered in this study to show its effect on the value of the critical Reynolds number defining the transition between two different flow regimes (symmetrical and periodic flows), the variations of Strouhal number, drag and lift coefficients and the heat transfer from the square cylinder as function of Reynolds number. Heat transfer correlations are obtained through forced convection. A discussion about the buoyancy effect on the flow pattern and the heat transfer for different power-law index is also presented.

Mixed convection air cooling of protruding heat sources mounted in a horizontal channel

A numerical study of laminar mixed-convection heat transfer to air from two identical protruding heat sources, which simulate electronic components, located in a two-dimensional horizontal channel, is presented in this paper. The finite volume method and the SIMPLER algorithm are used to solve the conservation equations of mass, momentum, and energy for mixed convection. Results show that the heat transfer increases remarkably for Pr = 0.71 and 5 ≤ Re ≤ 30. It was also found that the increase of separation distance, the height and the width of the components has a considerable enhancement of the heat removal rate from the components, and therefore, on the improvement of the heat transfer inside the channel.

A numerical study of mixed convection in a horizontal channel with a discrete heat source in an open cavity

This article aims to numerically investigate mixed convection heat transfer in a two-dimensional horizontal channel with an open cavity. A discrete heat source is considered to be located on one of the walls of the cavity. Three different heating modes are considered which relate to the location of the heat source on three different walls (left, right and bottom) of the cavity. The analysis is carried out for a range of Richardson numbers and cavity aspect ratios. The results show that there are noticeable differences among the three heating modes. When the heat source is located on the right wall, the cavity with an aspect ratio of two has the highest heat transfer rate compared to other cavity heating modes. Moreover, when the heat source is located on the bottom wall, the flow field in the cavity with an aspect ratio of two experiences a fluctuating behaviour for Richardson number of 10. The results also show that at a fixed value of Richardson number, all three different heating modes show noticeable improvements in the heat transfer mechanism as the cavity aspect ratio increases.

Simulation of mixed convection in a channel partially filled with porous media

We present a numerical study for mixed convection in a two-dimensional horizontal plan channel containing both fluid and porous layers, heated by a constant flux on the top surfaces. The finite volume method and the iterative SIMPLER algorithm are used. The thermal field, streamlines and local Nusselt numbers are analysed for a wide range of the Darcy numbers (1 < Da < 10-5), and for different values of the thermal conductivity ratio, Rk. The results identify the limit of mixed convection and the effect of porous media characteristics (permeability, conductivity) on flow structure and heat transfer.

Steady natural convection in a horizontal channel containing heated rectangular blocks periodically mounted on its lower wall

In this paper, we perform a numerical investigation of laminar steady natural convection flows in a twodimensional horizontal channel containing heating rectangular blocks, periodically mounted on its lower wall. The blocks are heated at a constant temperature, T 0 and connected with adiabatic surfaces. The upper wall of the channel is maintained at a cold temperature T 0 . The parameters governing the problem are the Rayleigh number (10 2 6 Ra 6 2 · 10 6 ), the geometric parameter C (0.25 6 C = l 0 /H 0 6 0.75) and the relative height of the blocks (1/8 6 B = h 0 /H 0 6 1/2). The effect of the computational domain choice on the multiplicity of solutions is also investigated. The results obtained using air (Pr = 0.72) as the working fluid show that the parameters B and C have a significant effect on the fluid flow and temperature fields. The symmetry of the flow is not always maintained although the boundary conditions for this problem are symmetrical, and the difference between two multiple solutions in terms of heat transfer may reach 34% for a given set of the governing parameters. � 2005 Elsevier Ltd. All rights reserved.

Effect of Heat Flux Ratio on Two-Dimensional Horizontal Channel Flow

Numerical analysis is performed to investigate thermal fluid-flow transport phenomena in channel under asymmetrical heat flux from both side walls. Emphasis is placed on an effect of heat-flux ratio from both sides on the velocity and thermal fields. The low-Reynolds-number k-e turbulence model and the two-equation heat-transfer model are employed to determine turbulent viscosity and thermal eddy diffusivity, respectively. It is found that 1) under strong heating from both walls, laminarization, that is, a substantial deterioration in heat-transfer performance, occurs as in the circular tube flow case; 2) during the laminarization process, both the velocity and temperature gradients in the vicinity of the heated walls decrease along the flow, resulting in a substantial attenuation in both the turbulent kinetic energy and the temperature variance over the entire channel cross section; and 3) in contrast, laminarization is suppressed in the presence of one-side heating because turbulent kinetic energy is produced in the vicinity of the other insulated wall. Therefore, an occurrence of laminarization in the channel is affected by the ratio of heat flux from both side walls.

Channel flow past bluff-body: outlet boundary condition, vortex shedding and effects of buoyancy

Structure of laminar flow and heat transfer, in a two-dimensional horizontal plane channel differentially heated, with a built-in triangular prism is investigated from the numerical solutions of complete Navier–Stokes and energy equations. Results are obtained for Reynolds and Grashof numbers ranging respectively from 30 to 200 and from 0 to 1.5 × 104 at Pr=0.71. In forced convection, results are specially presented to show how the vortex shedding at downstream affects the upstream. Also, two correlations giving the Strouhal and the averaged Nusselt numbers as functions of the Reynolds number are proposed. In mixed convection, the superposition of Von Karman street and convective cells is discussed.