Numerical Simulation Of Mixed Convection Research Articles

Effect of the position of the hot source on mixed convection in a rectangular cavity

This work presents a study by numerical simulation of mixed convection in a rectangular cavity with a sinusoidal temperature imposed on the right vertical wall while the other wall on the left is kept at a cold temperature. The upper and lower walls are thermally insulated, the inlet and outlet ports are respectively located on the hot wall to the bottom and on the top to the left. The enclosure represents a practical system such as an air-cooled electronic device, the heat source represents a radiator or an electronic component located in three different positions towards the left side at the bottom, the center and towards the right side at the top in such an enclosure. All calculations are made for a range of Richardson number from 0 to 10 and Reynolds numbers from 50 to 200. The influence of Richardson number, the position of the heat source and the influence of amplitude and phase deviation of the temperature imposed on the Nusselt number on the hot surface is studied. The results are presented in the form of streamlines and isotherms graphs as well as the variation in maximum temperature and mean Nusselt number under different conditions. The numerical resolution of the governing equations is obtained using the software of Multiphysics Comsol based on the finite element method.

Numerical simulation of mixed convection in a lid-driven trapezoidal cavity with flexible bottom wall and filled with a hybrid nanofluid

Numerical simulation of mixed convection in a lid-driven trapezoidal cavity with flexible bottom wall and filled with a hybrid nanofluid

Numerical simulation of mixed convection in a two-sided lid-driven square cavity with four inner cylinders based on diamond arrays

The hydrodynamics and thermal characteristics due to mixed convection in a vertical two-sided lid-driven differentially square cavity containing four hot cylinders in a diamond array are investigated by the lattice Boltzmann equation model. The moving walls of the cavity are cold while the others are adiabatic. The flow in the cavity is driven by both the temperature difference and the moving vertical walls. The influence of different flow governing parameters, including the direction of the moving walls (the left wall moves up and the right wall moves down (Case I), both the left and right walls are moving upward (Case II), both the left and right walls are moving downwards (Case III)), the distance between neighboring cylinders [Formula: see text] ([Formula: see text]), and the Richardson number [Formula: see text] ([Formula: see text]) on the fluid flow and heat transfer are investigated with the Reynolds number in the range of [Formula: see text], the Grashof number of [Formula: see text] and the Prandtl number of [Formula: see text]. Flow and thermal performances in the cavity are analyzed in detail by considering the streamlines and isotherms profiles, the average Nusselt number, as well as the total Nusselt number. It is found that the heat transfer efficiency is highest when [Formula: see text] for the cases of the walls moving in the opposite direction. When the walls move in the same directions, the heat transfer efficiency obtained by [Formula: see text] is maximum among the considered values of [Formula: see text]. On the other hand, compared with the cases of [Formula: see text] and [Formula: see text], the cylinder positions corresponding to the largest and the smallest Nusselt numbers are very sensitive to the moving direction of the walls for [Formula: see text]. Moreover, the results also show that in terms of the value of Nusselt number and the stability the case of both walls moving downwards works well. Besides, the effect of the distance between neighboring cylinders is also discussed, it is found that increasing or decreasing the spacing between cylinders could enhance heat transfer to different degrees for the range of [Formula: see text] number considered. Finally, the empirical relationships among [Formula: see text], [Formula: see text], and the spacing between the cylinders ([Formula: see text]) are given, and predictive results match with the computed values very well.

A computational study on mixed convection with surface radiation in a channel in presence of discrete heat sources and vortex generator based on RSM

Numerical simulation of mixed convection and surface radiation in a horizontal rectangular channel with five discrete heat sources protruded from the bottom wall has been carried out. Air is considered as working fluid and flow to be laminar, steady, and incompressible. The parameters varied are Reynolds number (Re) = 100–750, the spanwise position of vortex generator (VG) x/H = 1.8, 2.8, 3.8 4.8 and 5.8, the pitchwise position of VG, y/H = 0.5, 0.6 and 0.7 and emissivity of the heat source, ec = 0.1–0.9, while emissivity of the VG and channel walls is fixed as 0.9. The governing equations are solved based on SIMPLE algorithm using ANSYS 16.2. The results show that the Reynolds number, the position of vortex (spanwise and pitchwise), and emissivity of heat source have significant effects on heat transfer. It is also noticed that the maximum non-dimensional temperature (θmax) is 47.81% with VG at Re = 250 with change in emissivity of the heat sources from 0.1 to 0.9. Finally, a correlation has been developed for average non-dimensional temperature (θavg) using response surface methodology.

Numerical simulation of mixed convection of a nanofluid in a circular pipe with different numerical models

In this paper, we present a numerical study of laminar mixed convection of a nanofluid in a pipe and compare the results to experimental measurements. Mechanisms that control the behavior of nanoparticles in the base fluid and the fluid motion are not very well known. Thus, it is important to know, which mathematical model describes the nanofluid best. For this study, we used two numerical models, that are based on the Euler–Euler modelling of multiphase flow. The comparison of results has shown that none of the numerical models could accurately model the flow of a nanofluid. Hence, to better model the nanofluid flow, we varied the nanoparticle concentration distribution at the inlet. The results show that the temperature field in the fluid and in the pipe depends strongly on the nanoarticle concentration distribution.

Numerical simulation of mixed convection in a square cavity using Direct Meshless Local Petrov-Galerkin (DMLPG) method.

This paper present the extension of the Direct Meshless Petrov-Galerkin (DMLPG) for solving mixed convection heat transfer in a square cavity for the flow up to Reynolds number up to Re 400 and Grashof number Gr = 100. The semi algebraic forms of the governing equations are solved using fractional step method. The numerical results of the DMLPG method are in good agreement with the conventional numerical results in the literature. Based on the numerical results it is shown that The DMLPG is very promising in dealing with the fluid flow and heat transfer problem.

Direct numerical simulation of mixed convection of a liquid metal in the vertical rectangular channel

In the present work, mixed convection was studied using the direct numerical simulation (DNS) method for the upward flow of a liquid metal (Pr = 0.025) in a vertical rectangular heated channel. The Reynolds number (Re) varied from 104 to 2·104. The criterion for the appearance of thermogravitational convection, as well as the characteristic of the intensity of its influence, was the Grashof number (Gr), which varied in the range from 0 to 4·109. A significant and ambiguous effect of free convection on hydrodynamics and heat transfer, which depends on the ratio Gr/Re2 and the Prandtl number, is obtained.

Mixed convection in superposed nanofluid and porous layers in square enclosure with inner rotating cylinder

In this study, numerical simulation of mixed convection in a partitioned square cavity having CuO-Water nanofluid and superposed porous medium with an adiabatic rotating cylinder is performed. The bottom horizontal wall of the cavity is heated and the top horizontal wall is cooled while the remaining vertical walls are insulated. An adiabatic rotating cylinder is located at the center of the square cavity. Galerkin weighted residual finite element method is utilized to solve the governing equations of the system. The influence of Rayleigh number (between 103 and 106), angular rotational velocity of the cylinder (between 0 and 6000), solid volume fraction of the nanoparticle (between 0 % and 0.05 %), Darcy number (between 10−5 and 10−2) and three different vertical locations of the cylinder on the fluid flow and heat transfer characteristics are numerically investigated in detail for three different cylinder sizes. It is observed that the averaged heat transfer enhances as the value of Rayleigh number, angular rotational speed of the cylinder, nanoparticle volume fraction and Darcy number increase. The effect of the angular rotational speed of the cylinder on the averaged heat transfer enhancement is more pronounced for large cylinder size and 432.55% of averaged enhancement is achieved for Ω=6000 compared to motionless cylinder case at Ω=0 using cylinder sizes of R=0.3. The averaged heat transfer enhances almost linearly with nanoparticle volume fraction for different cylinder sizes and adding solid nanoparticles to the base fluid is favorable for the locations when high values of local Nusselt number is observed. Local and averaged Nusselt number enhance as the cylinder approaches to the upper wall of the cavity.

Numerical Investigation of Mixed Convection Fluid Flow, Heat Transfer and Entropy Generation in Triangular Enclosure Filled with a Nanofluid

In this paper, mixed convection fluid flow, heat transfer and entropy generation inside a triangular enclosure filled with CuO-water nanofluid with variable properties are investigated numerically. The inclined walls of enclosure are maintained at a constant temperature Tc. The moving bottom wall is kept at a constant temperature Th, which Th>Tc.The numerical simulation of mixed convection is carried out using a computer program (FORTRAN language) based on finite volume method and SIMPLER algorithm. This study is performed over a range of nanoparticle volume fractions(0-0.02-0.04) Richardson numbers(0.01, 0.1, 1, 10, 100), and angles of inclined walls(15 0 , 30 0 , 45 0 , 60 0 , 75 0 ) and a fixed Grashof number (Gr=10 4 ).In all investigated aspect ratios and Richardson numbers, average Nusselt number increased by enhancement of volume fraction till 0.02, but it is approximately constant by adding more nanoparticles till 0.04.It is also observed that in all aspect ratios and Richardson numbers, the variation of total entropy generation by enhancement of volume fraction is similar to Nusselt number.

Numerical simulation of mixed convection in vertical concentric cylinders

We conduct numerical simulation of mixed convection in a gap between rotating hot inner cylinder and stationary cold outer cylinder to investigate flow regimes at various intensities of rotational speed and buoyancy in terms of Reynolds number and Grashof number. For the current study, a projection method with explicit Adams-Bashforth and implicit Crank-Nicolson schemes was adopted. Flows with various Reynolds numbers are investigated at fixed Grashof number, and flow pattern is examined through streamlines and iso-surfaces of helicity. Phase plots constructed by velocity components, Nusselt number and torque reveal the transition between different flow regimes. With Grashof number less than 3000, the flow go through a sequence of axisymmetric, spiral and Taylor-Couette flow as Reynolds number increases, while the flow with Grashof number 4000 shows complex pattern including quasi-periodic flows and chaos in a wide range of Reynolds number. Transition to chaos is investigated using the budget analysis of centrifugal and buoyant forces, indicating that competition between the two driving forces causes chaos.

Study of the Mixed Convection in a Horizontal Channel Heated from below

In this work, a contribution to the modeling and numerical simulation of mixed convection in a horizontal channel heated from below is presented. The lattice Boltzmann model with double thermal populations (TLBM) is used with the D2Q9 model for the dynamic field and D2Q5 for the thermal field. A comparison of the results obtained by the lattice Boltzmann model with those of the literature is presented for an area stretching ratio B = H / L = 20, a Reynolds number Re = 10, Rayleigh Ra = 104 and Peclet number Pe = 20/3. The streamlines and isotherms are presented for different periods of flow.

Numerical simulation of mixed convection of the nanofluid in heat exchangers using a Buongiorno model

A numerical study of mixed convection heat transfer of nanofluid (Al2O3–water) in a lid driven cavity flow is carried out by using a Buongiorno model. Several pairs of heater and cooler (HACs) with isothermal walls of Th and Tc (Th>Tc) are located inside the cavity. Two-dimensional Navier–Stokes, energy and volume fraction equations are solved using the finite volume method. The effects of Brownian and thermophoresis diffusion, which cause non-homogeneity, are considered. The effects of volume fraction (0≤φ≤0.05) and nanoparticles' diameter (25nm≤dp≤145nm) with the location, orientation and number of HACs on flow structure and heat transfer rate are examined in different Richardson numbers (0.01≤Ri≤100).The simulation results indicate that there is an optimal volume fraction of the nano-particles at each Richardson number for which the maximum heat transfer rate can be obtained. Moreover, it is found that for a constant surface area of the HAC at the entire range of Richardson number, the rate of heat transfer is increased by changing the orientation of the HAC from horizontal to vertical. Results also indicate that at low Ri, the distribution of the solid particles remains almost uniform.

Mixed convection in an inclined lid-driven cavity with non-uniform heating on both sidewalls

The present work reports a numerical simulation of mixed convection in an inclined square cavity. The vertical sidewalls are assumed to have a nonuniform temperature distribution. The finite volume method is used to solve dimensionless governing equations. Simulations are performed for different Richardson numbers, amplitude ratios, phase deviations, and cavity inclination angles. The results are presented graphically. The mean heat transfer significantly increases in the buoyancy-dominated mode on increasing cavity inclination angle if both walls have identical heating and cooling zones.

Numerical simulation of mixed convection in a porous medium filled with water/Al2 O3 nanofluid

AbstractThe present work encloses the application of a Brinkman–extended Darcy model in a problem concerning mixed convection ina lid–driven porous cavity using nanofluids. The transport equations are solved numerically by the finite volume method on a co–located grid arrangement using the Quadratic Upstream Interpolation for Convective Kinematics (QUICK) scheme. The effects of governing parameters, namely, Grashof number (Gr), Darcy number (Da), and solid volume fraction $(\chi )$, on the streamlines and the isotherms are studied. The present results are validated by favorable comparisons with previously published results and are in good agreement with them. The present numerical results show that the addition of nanoparticles to a base fluid has produced an augmentation of the heat transfer coefficient and it is found to increase significantly with an increase of the particle volume concentration. It is observed from the results that at the higher value of the Grashof number (Gr = 104 ), the average Nusselt number increases with an increase in the Darcy number for a constant solid volume fraction. The detailed results are reported by means of streamlines, isotherms, and Nusselt numbers. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21029

A 3D numerical simulation of mixed convection of a magnetic nanofluid in the presence of non-uniform magnetic field in a vertical tube using two phase mixture model

In this paper, results of applying a non-uniform magnetic field on a ferrofluid (kerosene and 4 vol% Fe 3O 4 ) flow in a vertical tube have been reported. The hydrodynamics and thermal behavior of the flow are investigated numerically using the two phase mixture model and the control volume technique. Two positive and negative magnetic field gradients have been examined. Based on the obtained results the Nusselt number can be controlled externally using the magnetic field with different intensity and gradients. It is concluded that the magnetic field with negative gradient acts similar to Buoyancy force and augments the Nusselt number, while the magnetic field with positive gradient decreases it. Also with the negative gradient of the magnetic field, pumping power increases and vice versa for the positive gradient case.

An experimental and numerical simulation of mixed convection in large baffled rectangular chambers

The effects of mixed convection within large baffled chambers for both ‘aided’ and ‘opposed’ buoyant forces are investigated. Experimental and numerical results are compared for the momentum boundary layer thickness and temperature distribution within the chamber. Two- and three-dimensional transient laminar numerical models are formulated using a fully implicit finite-difference scheme. The inlet and wall temperatures are held constant while maintaining a uniform inlet velocity. Two tiers of four (two per tier) horizontal baffles are located axisymmetrically about the vertical axis with the inlet at the top and exhaust at the base of the chamber. The difference between the inlet and wall temperatures ranges between −1.0 and 3.3°C with a Prandtl number, Pr = 0.7, inlet Reynolds number. Re = 32 and 235, and inlet Rayleigh number, Ra = 0–6.8 × 10 7. It is concluded that the flow is predominantly buoyant and asymmetric in nature. The development of the flow is sensitive to small variations in the temperature difference between the inlet and wall.