Numerical Investigation Of Mixed Convection Research Articles

Numerical investigation of mixed convection inside a three-dimensional l-shaped cavity filled with hybrid-nanofluids in the presence of a heating block

Numerical investigation of mixed convection inside a three-dimensional l-shaped cavity filled with hybrid-nanofluids in the presence of a heating block

Mixed convection in turbulent particle-laden channel flow at Re τ = 180

A numerical investigation of mixed convection in a turbulent particle-laden channel flow is presented. Using Eulerian-Lagrangian Direct Numerical Simulations (DNSs) within the point-particle approach, the interaction between wall turbulence, particle inertia and thermal inertia, and buoyancy in the two-way coupling regime has been studied. The flow dynamics is controlled by the friction Reynolds number, Richardson number, particle Stokes and thermal Stokes numbers, and the Prandtl number. The effects of particle inertia and buoyancy on fluid and particle statistics are shown for a friction Reynolds number of 180, Stokes numbers ranging from 0.6 to 120, Richardson numbers ranging from 2.72 × 10−4 to 27.2 at a single Prandtl number, 0.71. The results indicate that the effect of particle inertia is significant on particle statistics, but not as pronounced on fluid statistics at the relatively low volume fraction considered. Particle inertia modulates the overall heat flux in a non-monotonic way.

Numerical study on the mixed convection with nanofluids in vertical channel asymmetrically heated

Mixed convection heat transfer in cavities is of great interest in many industrial applications, such as the development of crystals, the thermal control of electronic components, the nuclear reactors and various manufacturing processes. Components are generally located on the wall of a channel, that can be also tilted and their thermal control is carried out by the fluid flow. They can be schematized as thermal sources on vertical boards and the heat flux is removed by natural or mixed convection. As to the mixed convection, the interaction between the buoyancy forces and the external flow plays a significant role in the thermal design of systems. When natural convection is not strong enough to remove heat flux, mixed convection is adoptedIn particular, mixed convection due to moving surfaces is very important is these applications. Mixed convection because of buoyancy and motion of one of the channel walls has received little research attention and few guidelines are available for choosing the best performing channel configuration. Moreover, to optimize the transfer through natural convection, it is possible to modify the geometric parameters of the component, thus maximizing the convective heat transfer coefficient. If this is not possible or if one chooses to keep the geometry of the component unchanged for design choices, a possible alternative is the use of nanofluids. The properties of nanofluids exhibit a behaviour ranging between the properties of the base fluid and the properties of the nanoparticles. However, the addition of nanoparticles in the working fluid is considered to enhance the thermal behaviour of the base fluid. In this study a numerical investigation of mixed convection in nanofluids due to the interaction between a buoyancy flow and a moving plate induced flow in a vertical channel is carried out. The moving plate has a constant velocity and moves in the same direction with respect to the buoyancy force. The channel principal walls are heated with uniform heat flux. The numerical analysis is obtained by means of the commercial code Fluent. The effects of the different wall heat fluxes and moving plate velocities are investigated and results in terms of the channel wall and moving plate temperatures and Nusselt numbers are given.

Numerical investigation of mixed convection of non‐Newtonian fluid in a vented square cavity with fixed baffle

AbstractThis paper numerically investigates mixed convective heat transfer in a vented square cavity incorporated with a baffle that is subjected to external non‐Newtonian fluids (NNFs). Adiabatic conditions are imposed on the top and bottom walls, while cold temperature conditions are applied to the right and left solid boundaries. Heated NNF enters the cavity through the inlet and goes out through the outlet at three different locations, and it passes on a vertical baffle fixed at the base placed at different lengths. To examine the impact of the inlet and outlet positions, three different shapes of the outlet port located on the right wall and the inlet port on the left bottom wall were investigated. The impacts of Reynolds number (Re) of 100 ≤ Re ≤ 1000, Richardson number (Ri) of 0.1 ≤ Ri ≤ 3, power law index (n) of 0.6 ≤ n ≤ 1.4, length of baffle (Lb) of 0.2 ≤ Lb ≤ 0.6 and the outlet hole positions (S) of on the thermal and flow distributions in the cavity are taken into consideration in this paper. The results demonstrated that the flow's intensity and heat transfer increase with improvement in the Re and n at any baffle length. When the Ri increased from 0.1 to 3, increased by 23.3% at , and 13.8% at . Also, the Ri increment results in the augmentation of the average heat transfer.

Numerical investigation of mixed convection through an infrared-suppression (IRS) device

The flow through an infrared-suppression (IRS) device, installed on a warship, is often subject to various thermal regimes, including forced, natural, and mixed convection. When the ship becomes stationary/idle in the middle of a sea or in a port, mixed convection flow through the IRS device becomes noteworthy. In this paper, we numerically investigate the thermo-fluid characteristics through a cylindrical IRS device in mixed convection regime. Computations are performed for turbulent flow mixed convection with Richardson number in the range 0.1 ≤ Ri ≤ 10 to analyze the entrainment ratio (ER), flow field, and temperature variations in the IRS device. For a parametric study, dimensionless parameters such as nozzle-exit temperature, diameter ratio, nozzle protrusion, and funnel overlap are varied over the range of 1.91 ≤ T* ≤ 2.577, 1.05 ≤ DR ≤ 1.25, −1.5 ≤ NP ≤ 1.5, and − 22% ≤ OL ≤ 22% respectively. Temperature-dependent fluid properties are considered to obtain accurate results at higher temperature scales. The computed ER fairly agrees with the benchmark experimental results. With increase in Ri, the ER rises, whereas the actual mass suction diminishes. The centerline plume temperature at the exit of the IRS device is around 0.53 times the nozzle-exit temperature for Ri = 10, whereas it is almost identical at Ri = 0.1. The optimal Ri (=0.75) is obtained based on the maximum cooling efficiency. Finally, an empirical correlation for the ER is developed as a function of the above pertinent parameters.

Numerical investigation of mixed convection from rectangular cylinders subjected to upper cross flow

Unsteady combined natural and forced convection heat transfer from a rectangular cylinder subjected to upward cross flow is investigated numerically. The working fluids are air (Pr = 0.7) and water (Pr = 7), and the flow is laminar. The governing flow and energy equations are solved using a fractional step finite-difference scheme. The effects of the cylinder aspect ratio (a = L/D), Reynolds and Richardson numbers on the flow and heat transfer characteristics are investigated. Numerical simulations were carried out for the cylinders with aspect ratios of a = 0.5, 1, and 2, while the Richardson and Reynolds numbers varied between 0 to 10, and 100 to 200, respectively. The mean drag, mean rms lift coefficients, as well as the Strouhal number and the mean Nusselt number were computed for each simulation to determine the quantitative effects on flow and heat transfer. Steady flow is observed for Pr = 0.7, Ri = 0.5, and a = 0.5 or for Re ≥ 150 and Ri ≥ 1. For Ri = 10 and Re = 200, the flow becomes unsteady in the downstream region and trigger vortex street formation for a = 0.5, 1, and 2. Decreasing the aspect ratio, as well as increasing Reynolds number, increases the heat transfer from the cylinder. The rms lift coefficient decreases sharply at Ri < 1 for Pr = 0.7, Ri < 2 for Pr = 7 due to vortex breakdown. Further increase in the Richardson leads to a slight increase in rms lift coefficient except for Re = 200 where the sharp increase is observed due to triggered vortex formation again. For air, the increase in the mean Nusselt number in Ri = 10 case with respect to the forced convection case (Ri = 0) was 54–65% and 80–98%, respectively, for a = 0.5 and 2, while these values for water were realized as 50–68% and 53–63%, respectively. Using the computed data and nonlinear regression, the mean Nusselt number and the drag coefficients were developed.

Numerical investigation of mixed convection and entropy production of nanofluid flow in a corrugated channel using a two‐phase mixture model

AbstractThe two‐dimensional mixed convection in a horizontal sinusoidal corrugated channel (CC) is investigated. The two‐phase mixture model (2PMM) is implemented in Ansys Fluent software to simulate the nanofluid (NF) flow. The mathematical formulation of the 2PMM shows the limitation of the single‐phase mixture model linked to the absence of the slip particle‐fluid velocity and, consequently, the parameters that depend on this factor, particularly the diffusion and the drag coefficients. The laminar mixed convection regime is studied, where the NF copper–water is considered under a uniform temperature wall. The simulation results agree with three published works on mixed laminar convection and forced laminar convection in horizontal CC. The effects of nanoparticles volume fraction (ϕ), Richardson number (Ri), wavelength (λ), and wave amplitude (α) are investigated. The results showed that for a mixed flow, the improvement of heat transfer in a horizontal CC could essentially be obtained for a low Ri, where for a given λ, the submits an apparent increase with the increase of λ, that is, for Ri = 0.05 (λ = 3, α = 0.3, ϕ = 3%), the enhancement is 29.7% for and 128.5% for average entropy production compared to the smooth channel. The effect of ϕ on or is weakly dependent on Ri. The use of a Cu–water NF with a volume fraction of 5% (α = 0.2, λ = 2) leads to an increase in the of 17.6% for Ri = 0.05 and 16.4% for Ri = 10 compared to conventional water fluid.

Mixed convection heat transfer in a lid-driven enclosure with a double-pipe heat exchanger

The numerical investigation of mixed convection in a heat exchanger with double-pipe, where the upper lid is given a constant velocity, is presented in this paper. The governing equations, as well as the boundary conditions, define the physical problem. The boundary conditions and governing equations are translated into non-dimensional form and solved by means of a finite-element methodology based on the Galerkin weighted residual. The investigation is conducted for three different governing parameters; namely, Prandtl number (Pr), Richardson number (Ri) and Reynolds number (Re). The outcomes are presented in terms of streamlines, isotherms and average heat transfer rate. Computations are done for a range of Ri (0.01 ≤ Ri ≤ 10), Re (50 ≤ Re ≤ 500), and Pr (1 ≤ Pr ≤ 10) for different dimensionless time (τ = 0.1, 0.5, 1). It is found that the influence of Ri on streamlines, isothermal lines, and heat transfer rate is significant and the maximum heat transfer is gained when values of Ri and Re are higher and Pr is lower. It is also found that the flow strength increases substantially with time and multiple vortices emerge as the convection rate increases.

Numerical investigation of mixed convection in an anchor-stirred tank filled with an Al2O3-water nanofluid

Numerical investigation of mixed convection in an anchor-stirred tank filled with an Al2O3-water nanofluid

Numerical investigation of mixed convection of nanofluid flow in oblique rectangular microchannels with nanofluid jet injection

Numerical investigation of mixed convection of nanofluid flow in oblique rectangular microchannels with nanofluid jet injection

Numerical investigation of mixed convection of nanofluid flow in a trapezoidal channel with different aspect ratios in the presence of porous medium

In this study, a numerical investigation of mixed convection of nanofluid flow in a trapezoidal channel with two different aspect ratios of 0.3 and 0.5 with the presence of porous media is investigated. The present study was based on Ri = 0.1, 1, and 10 and used water-Al2O3 nanofluid in ϕ= 0–3% as the working fluid. Also, metal foam made of aluminum alloy in Darcy numbers 10−2, 10−3, and 10−4 is used for the porous medium, and the thermal equilibrium model is used to simulate the porous medium. The finite volume method and the single-phase model are applied. Nusselt number diagrams for different porous heights are obtained in different Darcy and Richardson numbers for the lower and upper walls of the channel. The results show that with the decrease in Richardson number, the local and NuAveincreases. In addition, a fully filled channel with a porous medium does not yield satisfactory results for the lower wall, but the results are desirable for the upper wall. The highest heat transfer occurs in the 90% porous height range. Aspect ratio of 0.3 predicts more heat transfer than aspect ratio of 0.5. As the height of the porous medium increases, the NuAve goes through an upward-downward trend, with two heights of 10% and 90% of the turning points in this upward and downward trend. As the percentage of porous height increases, the Darcy number changes on the heat transfer rate exhibit unique behaviors.

Numerical Investigation of the nanofluid mixed convection on two layers enclosure with rotating cylinder: High Darcy Number Effects

The present study, numerically investigated of mixed convection in a square enclosure with two layers, with Al2O3–water nanofluid (upper layer) and nano-porous medium (lower layer) with an adiabatic rotating circular cylinder at the center of the enclosure. The top and bottom walls are assumed adiabatic, while the left sidewall is heated, and the right sidewall kept cooled. Numerically, COMSOL code based on the Galerkin finite element method used for solved the dimensionless governing equations. The non-dimensional parameters that used in this study are: Rayleigh number (Ra) ranged from 103 up to 106, Darcy number (Da) equal to 10−3, the angular rotational velocity (Ω) ranged (0 and 6000), the solid volume fraction (ɸ=0.06), and the inner circular cylinder radius as (R = 0.2). The results showed that when Rayleigh numbers increase, a noticeable increase in the flow intensity and the steep temperature gradient, while the values increase when the cylinder rotates. The value of the local Nusselt number was high in the upper half of the cavity. The effect of the cylinder rotates is greater on the value of the local Nusselt number when using the low Rayleigh Numbers.

Mixed Convection of a Bingham Fluid in Differentially Heated Square Enclosure with Partitions

This paper reports a two-dimensional numerical investigation of mixed convection inside a liddriven square enclosure, completely filled with a non-Newtonian fluid obeying the Bingham model, having two rectangular adiabatic partitions mounted in different dispositions. Due to the problem’ complexity, the latter is solved using finite volume method when the SIMPLER algorithm is adopted for the pressure-velocity coupling. In order to investigate the yield stress effects on flow field and heat transport, we maintain the Richardson number (Gr/Re2) as 0.01, 1 and 10, respectively, which generates a good simulation of forced, mixed and natural convection dominated flow. The Prandtl and Grashof numbers are fixed at 50 and 104, respectively, while the Bingham number covers the range from 0 to 30. The validity of the computing code was ascertained by comparing our results with the numerical ones already available in the literature and that for both cases: Newtonian and non-Newtonian fluid. The phenomenon is analyzed through the streamlines, the isotherms and the Nusselt numbers with special attention to the partitions’ arrangement and its size. It is found that all parameters related to the geometrical dimensions of the partitions play a crucial role on the temperature distribution, flow field and heat transfer enhancement. For all values of the Bingham number, the mean Nusselt number is found as an increasing function of the decrease Richardson number. Thus, the heat transfer improves.

Numerical investigation of mixed convection in a lid-driven triangular cavity with a circular cylinder using ANN modeling

Numerical investigation of mixed convection in a lid-driven triangular cavity with a circular cylinder using ANN modeling

Effect of moving walls on heat transfer and entropy generation in a nanofluid-filled enclosure

In this work, a numerical investigation of mixed convection has been carried out in a two-sided lid-driven enclosure filled with copper–water nanofluid. Three different cases have been discussed depending on the direction of moving vertical walls to analyze the behavior of fluid flow and heat transfer in nanofluid. The buoyancy effects are incorporated using two discrete heat sources placed on the bottom wall maintaining a fixed distance from both the side walls. The stationary part of the bottom wall is kept insulated while other walls are maintained at constant low temperature. A two-dimensional computational visualization technique has been employed to demonstrate the main findings of the presented work. The effect of higher nanoparticle volume fraction (up to 20%) with variations of Reynolds number and Richardson number is studied to find the rate of heat transfer. The results are presented using streamlines, isotherms, and energy flux vectors. The thermodynamic optimization of the system is analyzed by using Nusselt number and entropy generation.

Numerical study of assisting and opposing mixed convective nanofluid flows in an inclined circular pipe

A numerical investigation of mixed convection is carried out to study the heat transfer and fluid flow characteristics in an inclined circular pipe using the finite volume method. The pipe has L/D of 500 and it was subjected to a uniform heat flux boundary condition. Four types of nanofluids (Al2O3, CuO, SiO2, and TiO2 with H2O) with nanoparticles concentration in the range of 0≤φ≤5% and nanoparticles diameter in the range of 20≤dp≤60nm were used. The pipe inclination angle was in the range of 30∘≤θ≤75∘ using assisting and opposing flow. The influences of Reynolds number in the range of 100≤Re≤2000, and Grashof numbers in the range of 6.3×102≤Gr≤8.37×103 were examined. It is found that the velocity and wall shear stress are increased as Re number increases, while the surface temperature decreases. There is no significant effect of increasing Gr number on thermal and flow fields. The velocity and wall shear stress are increased and the surface temperature is decreased as φ and dp are decreased. It is concluded that the surface temperature is increased as the pipe inclination angle increases from the horizontal position (θ=0°) to the inclined position (θ=75°). In addition, it is inferred that the heat transfer is enhanced using SiO2 nanofluid compared with other nanofluids types. Furtheremore, it is enhanced using assisting flow compared to opposing flow.

Numerical investigation of mixed convection of Bingham fluids in cylindrical enclosures with heated rotating top wall

The steady-state laminar mixed convection of yield stress fluids obeying the Bingham model in a cylindrical enclosure with a heated rotating top cover has been numerically analysed based on axisymmetric incompressible flow simulations. Yield stress effects on heat and momentum transport have been investigated for an aspect ratio (height/radius) of unity (i.e. AR=1) for a range of different values of nominal Prandtl, Richardson and Reynolds numbers given by 10⩽Pr⩽500, 0⩽Ri⩽1 and 100⩽Re⩽3000. The mean Nusselt number Nu‾ has been found to decrease sharply with increasing Bingham number Bn, but subsequently Nu‾ approaches asymptotically to a value of unity, which is indicative of conduction-driven transport. It has also been found that Nu‾ increases with increasing values of Prandtl and Reynolds numbers for both Newtonian (i.e. Bn=0) and Bingham fluids. In contrast, Nu‾ decreases with increasing Ri for both Newtonian and Bingham fluids for small values of Bingham number, whereas Nu‾ remains insensitive to the variation of Ri for large values of Bingham number. The variation of torque coefficient CT, which gives a quantitative measure of power consumption, has also been investigated. The torque coefficient CT has been found to increase with increasing Bn whereas it decreases with increasing Re. It has also been found that CT decreases slightly with increasing Ri for small values of Bn, whereas it becomes insensitive to the variation of Ri for large Bingham numbers. For the fully forced convection (Ri=0) case, Pr does not have a significant influence on CT. However, in the case of mixed convection CT increases with increasing Pr. The simulation data has been used in conjunction with a detailed scaling analysis to propose a correlation for Nu‾ for the range of Re,Ri and Pr considered here.

Mixed convection due to rotating cylinder in an internally heated and flexible walled cavity filled with SiO2–water nanofluids: Effect of nanoparticle shape

In this study, numerical investigation of mixed convection in a square cavity filled with SiO2 nanofluid and volumetric heat generation is performed under the effect of an inner rotating cylinder and a flexible side wall. The top wall of the cavity is kept at constant cold temperature while the bottom wall is at hot temperature and the other walls of the cavity and the cylinder surface are assumed to be adiabatic. The finite element method is utilized to solve the governing equations. The Arbitrary Lagrangian–Eulerian method is used to describe the fluid motion with the flexible wall of the cavity in the fluid–structure interaction model. The effects of external Rayleigh number (between 103 and 5×105), internal Rayleigh number (between 104 and 106), Young's modulus of the flexible wall (between 5×102 and 106), angular rotational speed of the cylinder (between −2000 and 2000) and nanoparticle volume fraction (between 0 and 0.03) on the fluid flow and heat transfer are numerically studied for different solid nanoparticle shapes (spherical, cylindrical, brick and blade). It is observed that as the value of external Rayleigh number increases, internal Rayleigh number and elastic modulus of the flexible wall decrease, the local and averaged heat transfer enhances. The averaged heat transfer enhances with cylinder rotation in both directions for all nanoparticle types. Among all nanoparticle shapes, cylindrical ones show the best performance and spherical ones show the worst performance for heat transfer enhancement.

Numerical Study on Mixed Convection and Entropy Generation of a Nanofluid in a Lid-Driven Square Enclosure

A numerical investigation of mixed convection due to a copper–water nanofluid in an enclosure is presented. The mixed convection is governed by moving the upper lid of the enclosure and imposing a vertical temperature gradient. The transport equations for fluid and heat are modeled by using the Boussinesq approximation. A modified form of the control volume based SIMPLET algorithm is used for the solution of the transport equations. The fluid flow and heat transfer characteristics are studied for a wide range of Reynolds number and Grashof number so as to have the Richardson number greater or less than 1. The nanoparticle volume fraction is considered up to 20%. Heat flow patterns are analyzed through the energy flux vector. The rate of enhancement in heat transfer due to the addition of nanoparticles is analyzed. The entropy generation and Bejan number are evaluated to demonstrate the thermodynamic optimization of the mixed convection. We have obtained the enhancement rate in heat transfer and entropy generation in nanofluid for a wide range of parameter values.

Numerical investigation and reduced order model of mixed convection at a backward facing step with a rotating cylinder subjected to nanofluid

In the present study, numerical investigation of mixed convection at a backward facing step with a rotating cylinder subjected to nanofluid is conducted and a reduced order model of the system is obtained by using the proper orthogonal decomposition method. The governing equations are solved with a finite element based commercial solver. The effects of various pertinent parameters, Reynolds number, cylinder angular velocity and nanofluid volume fraction on the fluid flow and heat transfer characteristics are numerically studied. It is observed that flow field and thermal patterns change for different parameters and heat transfer enhancement is obtained for some combinations of parameters. Length averaged Nusselt number plots indicate that there is almost a linear increase in the heat transfer enhancement with increasing Reynolds number and nanoparticle volume fraction. Heat transfer enhancement is obtained for cylinder angular velocities of Ω=-4.5 and Ω=1.5. A reduced order model of the system with proper orthogonal decomposition method is obtained and it provides accurate results when compared to high fidelity CFD model of the system.