Search

In the present study, natural convection heat transfer is investigated in a porous cavity filled with Cu/water nanofluid and equipped with horizontal fins. Optimization and sensitivity analysis of the fin's geometry, porous medium and nanofluid properties to maximize heat transfer rate is the aim of this work. To achieve this purpose, a design space is created by input parameters which include length, number of fins, distance between fins, porosity, Darcy number and volumetric fraction of the nanoparticles. Several tools have been used to implement optimization methods including the Taguchi method (TM) for design points generation, sensitivity analysis of design variables by using signal-to-noise ratio (SNR) and analysis of variance (ANOVA), response surface method (RSM) for interpolation and regression by using nonparametric regression, and genetic algorithm (GA) for finding optimum design point. The double multi-relaxation time lattice Boltzmann method (MRT-LBM) is used to analyze and simulate the flow field and heat transfer in each design point. The results show that the optimal configuration leads to an average Nusselt number of 5.56. This optimal configuration is at the length of fins L/2, the number of fins 2, the distance between fins L/12, porosity 0.8, Darcy number 0.1, and the volumetric fraction of the nanoparticles 0.02. By using the SNR results, the Darcy number and the number of fins have the most and the least effect in maximizing the average Nusselt number, respectively. The ANOVA results and global sensitivity analysis (GSA) findings further validated this conclusion. [ABSTRACT FROM AUTHOR]

New numerical approach has been selected for simulating magnetic force and radiation influences on alumina transportation within a permeable medium. To enhance characteristics of working fluid, we choose Al2O3–water with various shapes of nanoparticles. Various amounts of radiation, magnetic force and buoyancy have been considered to show their impacts on nanoparticles transportation. Brownian motion influences on working fluid thermal conductivity and viscosity were involved. Outcomes prove that convection decreases with augment of magnetic forces. Considering radiation can increase Nusselt number. [ABSTRACT FROM AUTHOR]

Abstract In this study, a three-dimensional mesoscopic simulation of magneto hydrodynamics (MHD) natural convection in a cubic cavity has been studied by new means of the Lattice Boltzmann method with double Multi-Relaxation-Time (MRT) model. In order to solve the momentum and energy equations, two different populations with various lattices have been used. This paper has been conducted for specific values of the Grashof number (Gr = 2 × 1 0 3 _ 2 × 1 0 5) and Hartmann number (Ha=0–100), while the Prandtl number is fixed at Pr = 0. 73. The results are presented in the form of average and local Nusselt number and contours of temperature and velocity at different planes of the cavity. It was found that the double MRT-LBM method is an appropriate approach to solve the studied case. The present results also show that the increase of the Hartmann number causes the heat transfer to drop considerably. Also, the effect of Hartmann number increases by enhancing the Grashof number, as the reduction of average Nusselt number is 12% for Gr = 2 × 1 0 3 and 71% for Gr = 2 × 1 0 5 when Hartmann number increases from 0 to 100. In contrast with Hartmann number, increasing of Grashof number raises heat transfer rate and the average Nusselt number increases by more than three times by enhancing the Grashof number from 2 × 1 0 3 to 2 × 1 0 5. Highlights • Double MRT LBM method has been developed for three-dimensional MHD flow. • Average Nusselt number drops 71% when the Hartmann number rises from 0 to 100 for Gr = 2 × 1 0 5. • Average Nusselt number enhances 330% when Grashof number alters from 2 × 1 0 3 to 2 × 1 0 5. [ABSTRACT FROM AUTHOR]

In this study, the lattice Boltzmann method is used in order to investigate the natural convection in a cavity with linearly heated wall(s). The bottom wall is heated uniformly and the vertical wall(s) are heated linearly, whereas the top wall is insulated. Investigation has been conducted for Rayleigh numbers of 103 to 105, while Prandtl number is varied from 0.7 to 10. The effects of an increase in Rayleigh number and Prandtl number on streamlines, isotherm counters, local Nusselt number and average Nusselt number are depicted. It has been observed that the average Nusselt number at the bottom wall augments with an increase in Prandtl number. [ABSTRACT FROM AUTHOR]

In this article, Lattice Boltzmann simulation of turbulent natural convection with large-eddy simulations (LES) in a square cavity, which is filled by water/copper nanofluid, has been investigated. The present results are validated by the consequences of an experimental research at Pr = 0.71 and Ra = 1.58 × 109. Calculations are performed for high Rayleigh numbers (Ra = 107–109), low volume fractions of nanoparticles (0 ≤ ϕ ≤ 0.06), and three aspect ratios (A = 0.5, 1, and 2). In this investigation, we present that large-eddy turbulent nanofluid flow is modeled by the Lattice Boltzmann method (LBM) with a clear and simple statement. Effects of nanopartcles are displayed on streamlines, isotherm counters, local Nusselt number, and average Nusselt number. The average Nusselt number enhances with the augmentation of the nanoparticles volume fractions in the base fluid for multifarious aspect ratios and the Rayleigh numbers. Heat transfer declines with the increase in the aspect ratios in the base fluid, but the effects of nanopaticles are dissimilar for various aspect ratios at different Rayleigh numbers. [ABSTRACT FROM PUBLISHER]

This study deals with the analysis of the interacting influences of Lorentz force and bleeding on the hydrothermal behaviors of magnetohydrodynamic (MHD) nanofluid flow and entropy generation in a trapezoidal recess. This trapezoidal recess is created by two inclined steps in a horizontal channel. The Lorentz force is appeared due to the existence of a magnetic field in the flow domain. The Brownian motion influences on the effective characteristics of CuO -water nanofluid are considered to have more accuracy. The effects of bleeding coefficients (−0.005 ≤ V w ≤ + 0.005), Hartmann number (0 ≤ Ha ≤ 60) and concentration of solid nanoparticles (0 ≤ ϕ ≤ 0.04) on the flow characteristics, heat transfer and flow irreversibility rates are investigated. The results show that the trends and values of friction coefficient, Nusselt number and entropy generation number can be different at the various magnitudes of Ha and V w , whereas the ϕ parameter only increases the values of them. These differences are related to the variations of streamlines contours against the Ha , V w and ϕ parameters. [ABSTRACT FROM AUTHOR]

Abstract: Natural convection in enclosures using water/SiO2 nanofluid is simulated with Lattice Boltzmann method (LBM). This investigation compared with other numerical methods and found to be in excellent agreement. This study has been carried out for the pertinent parameters in the following ranges: the Rayleigh number of base fluid, Ra =103–105, the volumetric fraction of nanoparticles between 0 and 4% and aspect ratio (A) of the enclosure between 0.5 and 2. The thermal conductivity of nanofluids is obtained on basis of experimental data. The comparisons show that the average Nusselt number increases with volume fraction for the whole range of Rayleigh numbers and aspect ratios. Also the effect of nanoparticles on heat transfer augments as the enclosure aspect ratio increases. [Copyright &y& Elsevier]