Investigation of Nanofluid Natural Convection Heat Transfer in Open Ended L-shaped Cavities utilizing LBM (original) (raw)
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2020
In this numerical study, natural convection of Cu–water nanofluid in a cavity submitted to different heating modes on its vertical walls is analyzed. Maxwell-Garnetts (MG) and Brinkman models have been utilized for calculating the effective thermal conductivity and dynamic viscosity of nanofluid, respectively. Influences of Rayleigh number (<em>Ra</em> = 10<sup>3</sup>−10<sup>6</sup>), nanoparticle volume concentration (<em>f</em> = 0-0.04) and Hartmann number (<em>Ha</em> = 0-90) on the flow and heat transfer characteristics have been examined. The results indicate that the Hartmann number influences the heat transfer at <em>Ra</em> = 10<sup>6</sup> more than other Raleigh numbers, as the least effect is observed at <em>Ra</em> = 10<sup>3</sup>. Moreover, the results show that the solid volume fraction has a significant influence on heat transfer, depending on the value of Ha...
Journal of the Taiwan Institute of Chemical Engineers, 2018
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 Al 2 O 3-Water or TiO 2-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.
Enhancement of Heat Transfer in a Cavity Filled with Cu-water Nanofluid
This paper summarizes a numerical study of natural convection in a square cavity with a corner heater filled with water based nanofluid (water with Cunanoparticles). Finite volume method is used for solving momentum and energy equations in the form of stream function-vorticity. One wall of the enclosure is isothermal but its temperature is colder than that of heaters while the remaining walls are adiabatic. Calculations were performed for Rayleigh number (10 3 ≤ Ra≤ 10 6); dimensionless lengths of heater in x and y directions (0.25 H≤ H x ≤ 0. 5 H, 0.25 H ≤ H y ≤ 0.5 H) and volume fraction of nanoparticles (0 ≤ φ ≤ 0.1). The results indicate that dimensionless lengths of heater are an important parameter affecting the flow pattern and temperature field. Nusselt number increases with increasing both the Rayleigh number. It is also observed that at a given Rayleigh number and definite dimensionless lengths of heaters, the average Nusselt number increases linearly with the increase in the solid volume fraction of nanofluid.
Thermal Science, 2016
In this paper, a new approach is used for numerical analysis of the sole effects of nanoparticles volume fraction of Cu-water nanofluid on laminar mixed and natural convection heat transfer in a 2-D cavity. Horizontal walls are insulated and fixed, and vertical walls are maintained at constant temperature. Vertical walls are considered for both fixed and moving conditions. Some researchers have studied flow and heat transfer of nanofluid in a lid-driven cavity, keeping fixed both Richardson and Grashof numbers. They found that by the increase of nanoparticles volume fraction, Nusselt number increases, then from this result they concluded the total heat transfer increases from the walls. It is shown that total heat transfer obtained from the Nusselt number by the mentioned approach results from not only the nanoparticles volume fraction increase but also temperature difference and walls velocity increases. Thus, this approach is not appropriate to study the sole effects of nanoparticles volume fractions on the mixed convection heat transfer. Using the new approach, it is shown that in order to have specific heat transfer rate from the walls, base fluid (water) needs less power for moving the wall than Cu-nanofluid. Therefore, the usage of Cu-water nanofluid is not recommended to increase mixed convection heat transfer in a lid-driven cavity. Moreover, using this new approach, it is shown that the increase of nanoparticles volume fraction reduces natural convection heat transfer, which is contradictory to the previous studies. Thus, its usage is not recommended for this case as well.
Intensification of Heat Transfer in Cavity Partially Heated and Filled with Nanofluid (Cu-Water)
International Letters of Chemistry, Physics and Astronomy, 2015
Natural convection in a rectangular cavity with aspect ratio (Ax), partially heated and filled with a nanofluid (Cu-Water) has been studied numerically. Two heat sources with length (B) are placed on the opposite vertical walls; the remainder of the walls is maintained adiabatic while the horizontal walls are brought to a cold temperature. The equations governing the flow are solved using a finite volume home code using a multigrid technique. Among the parameters governing the flow, a detailed study on the effects of the aspect ratio (Ax) and the length of the source (B) on flow and heat transfer rate is given. The results are shown in terms of streamlines and isotherms. It was found that the transfer of heat significantly increases with the aspect ratio (Ax) and the length of the source (B). A correlation expressing the Nusselt number as a function of (Ax) and d is established.
Emerald Publishing Limited, 2020
Purpose-This study aims to apply the lattice Boltzmann method to investigate the natural convection flows utilizing nanofluids in a semicircular cavity. The fluid in the cavity is a water-based nanofluid containing Al 2 O 3 or Cu nanoparticles. Design/methodology/approach-The study has been carried out for the Rayleigh numbers from 104 to 106 and the solid volume fraction from 0 to 0.05. The effective thermal conductivity and viscosity of nanofluid are calculated by the models of Chon and Brinkman, respectively. The effects of solid volume fraction on hydrodynamic and thermal characteristics are investigated and discussed. The averaged and local Nusselt numbers, streamlines, temperature contours for different values of solid volume fraction and Rayleigh number are illustrated. Findings-The results indicate that more solid volume fraction corresponds to more averaged Nusselt number for both types of nanofluids. It is also found that the effects of solid volume fraction of Cu are stronger than those of Al 2 O 3. Originality/value-Numerical study of natural convection of nanofluid in a semi-circular cavity with lattice Boltzmann method in the presence of water-based nanofluid containing Al 2 O 3 or Cu nanoparticles.
Journal of Thermal Analysis and Calorimetry
The unsteady physics of laminar mixed convection in a lid-driven enclosure filled with Cu–water nanofluid is numerically investigated. The top wall moves with constant velocity or with a temporally sinusoidal function, while the other walls are fixed. The horizontal top and bottom walls are, respectively, held at the low and high temperatures, and the vertical walls are assumed to be adiabatic. The governing equations along with the boundary conditions are solved through D2Q9 fluid flow and D2Q5 thermal lattice Boltzmann network. The effects of Richardson number and volume fractions of nanoparticles on the fluid flow and heat transfer are investigated. For the first time in the literature, the current study considers the mechanical power required for moving the top wall of the enclosure under various conditions. This reveals that the power demand increases if the enclosure is filled with a nanofluid in comparison with that with a pure fluid. Keeping a constant heat transfer rate, th...
International Journal of Heat and Fluid Flow, 2010
This paper analyzes the heat transfer and fluid flow of natural convection in a cavity filled with Al 2 O 3 / water nanofluid that operates under differentially heated walls. The Navier-Stokes and energy equations are solved numerically, coupling Xu's model for calculating the effective thermal conductivity and Jang's model for determining the effective dynamic viscosity, with the slip mechanism in nanofluids. The heat transfer rates are examined for parameters of non-uniform nanoparticle size, mean nanoparticle diameter, nanoparticle volume fraction, Prandtl number, and Grashof number. Enhanced and mitigated heat transfer effects due to the presence of nanoparticles are identified and highlighted. Based on these insights, we determine the impact of fluid temperature on the heat transfer of nanofluids. Decreasing the Prandtl number results in amplifying the effects of nanoparticles due to increased effective thermal diffusivity. The results highlight the range where the heat transfer uncertainties can be affected by the size of the nanoparticles.
Applied Thermal Engineering, 2011
Purpose-This paper aims to study the natural convection of a nanofluid inside a cavity which contains obstacles using lattice Boltzmann method (LBM). The results have focused mainly on various parameters such as number and aspect ratio of roughness elements and different nanoparticle volume fraction. The isotherms and streamlines are presented to describe the hydrodynamics and thermal behaviors of the nanofluid flow throughout the enclosure. Design/methodology/approach-The methodology of this paper consists of mathematical model, statement of the problem, nanofluid thermophysical properties, lattice Boltzmann method, LBM for fluid flow, LBM for heat transfer, numerical strategy, boundary conditions, Nusselt (Nu) number calculation, code validation and grid independence. Findings-Natural convection heat transfers of a nanofluid inside cavities with and without rough elements have been studied. Lattice Boltzmann technique has been used as numerical approach. The results showed that at higher Rayleigh number (Ra = 10 6), there are denser streamlines near the left (source) and right wall (sink) which results in better cooling and enhances convective heat rejection to the heat sink. After a distinctive aspect ratio of rough elements (A = 0.1), change in streamline pattern which arises from increasing of aspect ratio does not have an important effect on isotherms. Results indicate that for lower Rayleigh number (Ra = 10 3), no variation in average Nu is observed with increasing in number of roughness, while for higher one (Ra = 10 6) average Nu decreases from N = 0 (smooth cavity) up to N = 4 and then remains constant (N = 6). Originality/value-Currently, no argumentative and comprehensive extraction can be concluded without fully understanding the role of different arrangement of roughness. Some geometrical parameters such as aspect ratio, number and position of rough elements have been considered. Also, the effect of nanoparticle concentration was studied at different Ra number. Briefly, using LBM, this paper aims to investigate the natural convection of a nanofluid flow on the thermal and hydrodynamics parameters in the presence of rough element with various arrangements.
International Journal of Numerical Methods for Heat & Fluid Flow, 2014
Purpose -The purpose of this paper is to study the effects of natural convection heat transfer in a cold outer circular enclosure containing a hot inner elliptic circular cylinder. The fluid in the enclosure is Cu-water nanofluid. The main emphasis is to find the numerical treatment for the said mathematical model. The effects of Rayleigh number, inclined angle of elliptic inner cylinder, effective of thermal conductivity and viscosity of nanofluid, volume fraction of nanoparticles on the flow and heat transfer characteristics have been examined. Design/methodology/approach -A very effective and higher order numerical scheme Control Volume-based Finite Element Method (CVFEM) is used to solve the resulting coupled equations. The numerical investigation is carried out for different governing parameters namely; the Rayleigh number, nanoparticle volume fraction and inclined angle of elliptic inner cylinder. The effective thermal conductivity and viscosity of nanofluid are calculated using the Maxwell-Garnetts (MG) and Brinkman models, respectively. Findings -The results reveal that Nusselt number increases with an increase of nanoparticle volume fraction, Rayleigh numbers and inclination angle. Also it can be found that increasing Rayleigh number leads to a decrease in heat transfer enhancement. For high Rayleigh number the minimum heat transfer enhancement ratio occurs at. Originality/value -To the best of the authors' knowledge, no such analysis is available in the literature which can describe the natural convection heat transfer in a nanofluid filled enclosure with elliptic inner cylinder by means of CVFEM.