Natural Convection Of Nanofluid Research Articles

Investigation of natural convection of magnetic nanofluid in an enclosure with a porous medium considering Brownian motion

In this work, magnetic nanofluid natural convection in the porous enclosure considering Brownian motion is studied numerically using Control Volume Finite Element Method (CVFEM). The effective viscosity and thermal conductivity of nanofluid are specified by Corcione correlation in which the impact of Brownian motion on the thermal conductivity is considered. The considered porous enclosure is heated from the inner circular side and it cooled from the outer circular side while two other walls are insulated. The impacts of various controlling parameters such as the Rayleigh number, Hartmann number, Darcy number and angle of magnetic field parameter are examined on the streamlines and isotherms. In addition, the average and local Nusselt numbers are obtained and presented via figures. The results state that the intensity of the convective flow has a direct relationship with the Rayleigh number and Darcy number while it has a reverse relationship with the Hartmann number and inclination angle of the magnetic field.

Numerical Investigation of the Effect of Baffle Inclination Angle on Nanofluid Natural Convection Heat Transfer in A Square Enclosure

The characteristics of the conjugate natural convection of (Al2O3-water) nanofluid inside differentially heated enclosure is numerically analyzed using COMSOL Multiphysics (5.3a). The enclosure consists of two vertical walls, the left wall has a thickness and maintain at a uniform hot temperature, while the opposite wall at cold temperature and the horizontal walls are isolated. A high thermal conductivity thin baffle has been added on the insulated bottom wall at a different inclination angles. The effect of the volume fractions of nanoparticles (f), Rayleigh number (Ra), solid wall thermal conductivity ratio (Kr), baffle incline angles (Ø) and the thickness of solid wall (D) on the isothermal lines, fluid flow patterns and the average Nusselt number (Nu) has been investigated. At low Rayleigh number (Ra=103 to 104) the Isothermal lines are parallel with the vertical wall which is characteristic of conduction heat transfer. on the other hand, when Rayleigh number increase to (Ra=106), the isotherms lines distribution in the inner fluid become parallel curves with the adiabatic horizontal walls of the enclosure and smooth in this case convection heat transfer becomes dominant. As the Rayleigh number further increases, the average Nusselt number enhance because of buoyancy force become stronger. In addition, the fluid flow within the space is affected by the presence of a fin attached to the lower wall that causes blockage and obstruction of flow near the hot wall, hence the recirculation cores become weak and effect on the buoyant force. The maximum value of the stream function can be noticed in case of nanofluid at (Ø=60), whereas they decrease when (Ø > 60), where the baffle obstruction causing decreases in flow movement. So that the left region temperature increases which cause reduction of the convective heat transfer by the inner fluid temperatures. This is an indication of enhancing of insulation. When the inclination angle increases (Ø >90), the baffle obstruction on flow and fluid resistance becomes smaller and the buoyancy strength increase, as a result, the heat transfer is increasing in this case. As a result of increasing the thermal conductivity from 1 to 10, an increase in the amount of heat transferred through the solid wall to the internal fluid have been noticed. This change can be seen in the isothermal lines, also, there was growth and an increase in the temperature gradient. The increasing of wall thickness from (D=0.1 to 0.4) leads to reduce the intensive heating through the solid wall as well as small heat transferred to the inner fluid. Therefore, it can be noticed that when the wall thickness increases the stream function decrease.

A simple homogeneous numerical solution for nanofluid natural convection in an enclosure with disconnected and conducting solid blocks

Following a series of discrepancies in the literature regarding the effects of nanoparticle concentration on the heat transfer rate, this paper proposes a simple homogeneous modeling for natural convection of nanofluids. The proposed modeling allows a custom choice of correlations for the nanofluid’s thermophysical properties, which proved to be very convenient in validations carried out for the case of natural convection inside a clear enclosure. The general heat transfer decreasing behavior for high concentrations of nanoparticles, previously observed in experimental and two-phase numerical works, was successfully represented. A very interesting and pioneer case study of laminar natural convection of nanofluids in a laterally heated enclosure with conductive solid blocks uniformly distributed within the enclosure was numerically investigated with the proposed modeling. To compute the nanofluids characteristics, Corcione’s correlations for thermal conductivity and dynamic viscosity for effective properties and generic correlations for density, specific heat and thermal expansion coefficient were employed. Therefore, it was possible to isolate the nanoparticle’s influence on the heat transfer rate, evaluated by the average Nusselt number. By isolating the nanoparticle’s parameters, the effects of diameter and material have been interpreted from the homogeneous solution. A parametric investigation was conducted by varying the number of blocks inside the enclosure and the effective Rayleigh number. A numerical correlation for the average Nusselt number was derived for a wide range of effective Rayleigh number and number of blocks. The model developed herein is suitable to other applications in which the total heat transfer rate needs to be computed.

Effect of inclination angle on natural convection of nanofluids in a U-shaped cavity

In this work, the natural convection in a U-shaped enclosure containing CuO–water nanofluid is studied numerically with a special emphasize on the influence of inclination angle. The three walls of the enclosure are at constant hot temperature while the walls of the rib of U-shaped profile are at constant cold temperature. The remaining walls of the U-shape are thermally insulated. The study is parametrically carried out to investigate the influence of aspect ratio (height of cold wall to the length of hot wall), volume fractions of the CuO nanofluid and inclination of the cavity on the velocity and temperature fields for Ra = 105 and Pr = 6.2. The study includes four different inclination angles of 0°, 45°, 90° and 135°, three different volume fractions of 0%, 1% and 3% and three different aspect ratios of 0.1, 0.3 and 0.5. The influence of considered parameters on the streamlines, isotherms and mean Nusselt numbers is discussed.

Examining of nanofluid natural convection heat transfer in a [formula omitted]-shaped enclosure including a rectangular hot obstacle using the lattice Boltzmann method

The present investigation is set to evaluate the nanofluid thermogravitational convection within a Γ-shaped enclosure that consists of a local heater by the lattice Boltzmann method (LBM). In this study the Rayleigh number (103–106), cavity’s aspect ratio (0.2–0.6), nanofluid solid volume fraction (0–0.05), height and location of the heater on the liquid circulation and heat transfer parameters examined with respect to the Γ-shaped enclosure. The study is innovated in nature as it combines the nanofluid and the hot obstacle within the same Γ-shaped enclosure. The results of the conducted analyses indicate that the mean Nusselt number would increase as the Rayleigh number and nanoparticles concentration increased. This resulted in a reduction in the enclosure aspect ratio and increment in the obstacle’s height. The thermal transmission rate is highly affected by the obstacle’s position. Also, it is found that, when the heater is situated on the left border, the mean Nusselt number would be maximized.

Koo–Kleinstreuer–Li correlation for simulation of nanofluid natural convection in hollow cavity in existence of magnetic field

The lattice Boltzmann method is used to study natural convection of a CuO/water nanofluid in a hollow cavity. The hollow walls are fixed at a uniform temperature, and the effect of an applied magnetic field is examined. The Koo–Kleinstreuer–Li model, which accounts for nanoparticle’s Brownian motion, is used to gain the nanofluid effective thermal conductivity and nanofluid viscosity. The mechanisms how the inclination angle of magnetic field, Hartmann number, Rayleigh number, hollow width and nanoparticle volume fraction affect the streamlines, isotherms and rate of heat transfer are also studied. The results show that the average Nusselt number is increased by incrementing the nanoparticle volume fraction, Ra, magnetic field inclination angle and hollow width, but decreased by the Ha. For L = 0.4, the value of Ra where the dominant mechanism of heat transfer is changed from conduction to convection is larger than 105. But for L = 0.48 or 0.56, the turning point of the dominant heat transfer mechanism is at Ra < 105. Besides, at L = 0.4 or 0.48, the average Nusselt numbers in hot walls are higher than those in cold wall, but the opposite trend is found at L = 0.56.

Nanoparticle transportation of CuO-H2O nanofluid in a porous semi annulus due to Lorentz forces

PurposeThe purpose of this paper is to research on CuO-water nanofluid Non-Darcy flow because of magnetic field. Porous cavity has circular heat source and filled with nanofluid. Lattice Boltzmann Method (LBM) has been used to simulate this problem.Design/methodology/approachIn this research, LBM has been applied as mesoscopic approach to simulate water-based nanofluid free convection. Koo–Kleinstreuer–Li model is used to consider Brownian motion impact on nanofluid properties. Impacts of Rayleigh number, Darcy number, nanofluid volume fraction and Hartmann number on heat transfer treatment are illustrated.FindingsIt is found that temperature gradient decreases with rise of while it enhances with augment of Ha. Darcy number can enhance the convective flow.Originality/valueThe originality of this work is to analyze the to investigate magnetic field impact on water based CuO-H2O nanofluid natural convection inside a porous cavity with elliptic heat source.

Natural convection of magnetic hybrid nanofluid inside a double-porous medium using two-equation energy model

Porous media and nanofluids can be used for heat transfer enhancement in different industrial sectors. Very often technical systems consist of several porous layers. At the same time, hybrid nanofluids can be more effective in comparison with a nanofluid including only one kind of nanoparticles. The present study deals with a numerical analysis of MHD hybrid nanofluid natural convection heat transfer within the T-shaped cavity heated from the bottom and cooled from the upper chamber walls. Two different porous layers form the considered enclosure. The viscosity of the nanofluid depends on the magnetic field intensity. Governing equations written in dimensionless primitive variables using the extended Darcy–Brinkman–Forchheimer model for the porous medium, single-phase nanofluid model and local thermally non-equilibrium model were solved by the finite element method. Wide-range governing parameters impacts were examined to define the development of nanofluid flow and heat transfer inside the enclosure. Heat transfer enhancement can be gained for low values of the solid-liquid interface convection parameter, magnetic field viscosity parameter and high values of the thermal conductivity ratio.

Entropy generation analysis of nanofluid natural convection in coaxial cylinders subjected to magnetic field

This paper concerns with the effect of a magnetic field on the entropy generation due to natural convection of Al2O3-water nanofluid flow between coaxial cylinders of aspect ratio H/D = 2. The inner and outer cylinders are maintained at hot and cold temperatures, respectively. The top and bottom walls are thermally insulated. The finite volume method was used to discretize the mathematical equations. The present results are compared with those found in the literature, which reveal a very good agreement. The influence of dimensionless parameters such as Hartmann number, Rayleigh number, solid volume fraction of nanoparticules, ?, and inclination angle of magnetic field on streamlines, isotherms contours, local entropy generation, mean Nusselt number, total entropy generation, St, and Bejan number is discussed. The results show that the local entropy generation are strongly influenced by the application of magnetic field. The increase in heat transfer and entropy generation by adding the nanoparticles to the base fluid depends on the magnetic field strength and direction.

Hybrid lattice Boltzmann/Taguchi optimization approach for magnetohydrodynamic nanofluid natural convection in a hemisphere cavity

In the present work, heat transfer optimization for natural convection with MHD flow in the hemisphere enclosure embedded with a vertical isothermal cylinder is investigated using Taguchi method. The simulations were planned based on Taguchi's L25 orthogonal array with each trial performed under different magnetic field, heat source aspect ratio and particle volume fraction of nanofluid. The thermal lattice Boltzmann based on D3Q19 methods was purposed to simulate the flow and thermal fields. Signal-to-noise ratios analyses were carried out in order to determine the effects of process parameters and optimal factor settings. The present results provide a good approximation for choosing effective parameters of designing the thermal system.

Effect of solid body aspect ratio on natural convection of nanofluid in a square cavity

The goal of this numerical study is to understand the free convection flow and transfer of heat in a differentially heated cavity having solid block in the centre. The coupled equations of momentum, mass and energy are governed the mathematical model. The governing equations are solved via utilizing the finite difference technique. The outcomes are performed for various combinations of aspect ratios of the solid block, nanoparticles volume fraction and Rayleigh numbers. The outcomes are shown in the form of isotherms, streamlines, and Nusselt numbers. It is concluded that the increment of average Nusselt number is detected when the nanoparticles volume fraction and Rayleigh number increase.

Magnetohydrodynamic Nanofluid Natural Convection in a Cavity under Thermal Radiation and Shape Factor of Nanoparticles Impacts: A Numerical Study Using CVFEM

In this study, the natural convection of a magnetohydrodynamic nanofluid in an enclosure under the effects of thermal radiation and the shape factor of nanoparticles was analyzed numerically using the control-volume-based finite element method (CVFEM). Columns, spheres, and lamina are examples of the nanoparticle shapes used in the investigation. The study of nanofluid flow and heat transfer was accomplished with an extensive range of nanofluid volume fractions, radiation parameters, Hartmann numbers, Rayleigh numbers, and nanoparticle shape factors. Also, the correlation between the average Nusselt number and the influencing parameters of the current study was determined. The findings demonstrate that laminar nanoparticles have a more notable impact on the average and local Nusselt numbers than the other nanoparticle shapes.

Lattice Boltzmann study of multi-walled carbon nanotube (MWCNT)-Fe3O4/water hybrid nanofluids natural convection heat transfer in a Π-shaped cavity equipped by hot obstacle

In the present paper, the effect of nanofluid and the hot obstacle in a Π-shaped cavity is investigated. Lattice Boltzmann method is used to simulate the fluid flow and heat transfer. The effects of the parameters such as the nanoparticle solid volume fraction, the Rayleigh number, aspect ratio of cavity and hot obstacle position on the flow pattern and heat transfer parameters are studied. The numerical results are compared with previous results for validation, and a good agreement obtained. It is found that the average Nusselt number is increased by increasing the nanoparticle solid volume fraction, the Rayleigh number and the aspect ratio of cavity. Moreover, the effect of Rayleigh number on the average Nusselt number at high Rayleigh numbers (105–106) is more pronounced than that at low Rayleigh numbers (103–104) due to the different heat transfer mechanisms. The position of the hot obstacle affects the heat transfer significantly. When the hot obstacle is located on the center, the heat transfer is more effective.

Numerical study of MHD nanofluid natural convection in a baffled U-shaped enclosure

In this study, nanofluid natural convection in a baffled U-shaped enclosure in the presence of a magnetic field is investigated. Lattice Boltzmann method (LBM) is used to study present problems. KKL (Koo-Kleinstreuer-Li) correlation is applied to calculate the effective thermal conductivity and viscosity of nanofluid. The effect of the Brownian motion on the effective thermal conductivity is considered in this correlation. The combination of the four topics (nanofluid, U-shaped enclosure, baffle, magnetic field) is the main novelty of the present study. Effect of Rayleigh number, Hartmann number, nanoparticle volume fraction and cavity aspect ratio on the flow field and heat transfer characteristics have been investigated. The results demonstrate that the average Nusselt number increases by increments of the Rayleigh number, nanoparticle solid volume fraction and aspect ratio. However, the rate of heat transfer is suppressed by the magnetic field. The effect of magnetic field on heat transfer is more significant at higher Rayleigh number and the effect of Ra on the average Nusselt number is more noteworthy at lower Ha. Besides, the effect of Rayleigh number on heat transfer enhancement becomes more significant at higher aspect ratio.

Effects of temperature-dependent properties on natural convection of power-law nanofluids in rectangular cavities with sinusoidal temperature distribution

In this paper, the effects of temperature-dependent properties on natural convection of nanofluids in rectangular cavities with sinusoidal temperature distribution are investigated in detail with lattice Boltzmann method. To improve the computational efficiency, all simulations are performed on the Graphics Processing Unit (GPU) using NVIDIA’s CUDA. The fluid in the enclosure is a water-based nanofluid containing Al2O3 nanoparticles. The effects of power-law index (0.5⩽n⩽1.5), thermal Rayleigh number (104⩽Raf⩽106), diameter of nanoparticle (25nm⩽ds⩽100nm), nanoparticle volume fraction (0.0⩽ϕ⩽0.04), temperature of the cooled sidewall (315K⩽Tc⩽335K), temperature difference between the sidewalls (10K⩽ΔT⩽50K), amplitude ratio (0.0⩽A⩽1.0), wave number (0.0⩽ω⩽6.0), phase deviation (0.0⩽θ⩽π) and aspect ratio (0.250⩽AR⩽4.00) on heat and fluid flows are investigated. The results reveal that there is an optimal volume fraction ϕopt at which the maximum heat transfer enhancement is obtained, and the value of ϕopt is found to increase slightly with decreasing the nanoparticle diameter, and to increase remarkably with increasing the temperature of Tc or ΔT. In addition, the average Nusselt number is generally decreased with increasing power-law index, while increased with increasing A and ω. Further, we found that the average Nusselt number behaves nonlinearly with the phase deviation parameter. Moreover, the present results also indicate that there is an optimal value of aspect ratio at which the impact of AR on heat transfer is the most pronounced.

The onset of nanofluid natural convection inside a porous layer with rough boundaries

Smooth boundaries guarantee the infinitely stable flow when the linear stability analysis is implemented. Hence, the study on rough boundaries is essential when the laminar-turbulent transition is being considered. Because of the importance of rough boundaries, the present paper concentrates on the analysis of the onset of nanofluid natural convection (Rayleigh-Bénard convection) in a porous layer between two rough solid walls. The nanofluid surrounded between these surfaces contains the influence of both Brownian motion and thermodiffusion (thermophoresis). The non-negligible roughness boundary conditions are modeled according to the Saffman interface condition. For this purpose, the roughness is analogized as a shallow saturated fluid porous media. The simulation is performed under the isothermal condition and the zero nanoparticle flux condition for both surfaces. Then the governing equations are transported to an eigenvalue problem, and they are solved by a numerical method. The results prove that boundaries roughness and porosity parameters have a stabilizing influence on the onset of convective heat transfer while nanoparticle-concentration Rayleigh number, thermophoresis parameter, modified nanoparticle-density increment, and Lewis number have the destabilizing effects on the onset of Rayleigh-Bénard convection. For example, by increasing the roughness parameter from zero (i.e., stress-free boundary condition) to 100 (i.e., rigid solid walls with no-sleep condition), the critical convection Rayleigh number and the critical wave number increase around 145% and 41%, respectively.

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.

Peristaltic pumping with double diffusive natural convective nanofluid in a lopsided channel with accounting thermophoresis and Brownian moment

In the current study, double-diffusive natural convective peristaltic flow of a nanofluid with induced magnetic field in an asymmetric porous channel is discussed. The five coupled equations are solved analytically using with new analytical techniques detail of which is given in solution section. The analytical solutions for pressure gradient and pressure rise, velocity profile, temperature, solutal concentration, and nanoparticle fraction are evaluated and presented through graphs.

Optimization and sensitivity analysis of magneto-hydrodynamic natural convection nanofluid flow inside a square enclosure using response surface methodology

This article studies buoyancy-driven natural convection of a nanofluid affected by a magnetic field within a square enclosure with an individual conductive pin fin. The effects of electromagnetic forces, thermal conductivity, and inclination angle of pin fin were investigated using non-dimensional parameters. An extensive sensitivity analysis was conducted seeking an optimal heat transfer setting. The novelty of this work lies in including different contributing factors in heat transfer analysis, rigorous analysis of design parameters, and comprehensive mathematical analysis of solution domain for optimization. Results showed that magnetic strength diminished the heat transfer efficacy, while higher relative thermal conductivity of pin fin improved it. Based on the problem settings, we also obtained the relative conductivity value in which the heat transfer is optimal. Higher sensitivity of heat transfer was, though, noticed for both magnetic strength and fin thermal conductivity in comparison to fin inclination angle. Further studies, specifically with realistic geometrical configurations and heat transfer settings, are urged to translate current findings to industrial applications.

Simulation of nanofluid natural convection in a U-shaped cavity equipped by a heating obstacle: Effect of cavity's aspect ratio

Abstract Research on nanofluid for heat transfer enhancement of thermal systems has received great attention owing to the lack of energy sources. In this study, fluid flow and natural convection heat transfer of Al2O3–Water or TiO2–water nanofluid inside a U-shaped cavity consist of a hot obstacle has been investigated numerically by lattice Boltzmann method (LBM). In this paper, different parameters are investigated such as Rayleigh number, the solid volume fraction of the nanoparticles, the U-shaped cavity's aspect ratio and heating obstacle's height on the flow field and heat transfer in the enclosure. The results showed that the Rayleigh number (Ra), cavity aspect ratio (AR) and obstacle's height can be affected on isotherms, streamlines and local and average Nusselt number. The average Nusselt number of the obstacle sides increased by increasing the Ra number and solid volume fraction of nanoparticles (ϕ) regardless the AR. In addition, by increasing the AR, the average Nusselt number increased. At low Ra, the effect of nanoparticles on increment of heat transfer for narrow cavities was more than wide ones.