EXPERIMENTAL STUDY ON CAVITY FLOW NATURAL CONVECTION IN A POROUS MEDIUM, SATURATED WITH AN Al2O3 60%EG-40%WATER NANOFLUID (original) (raw)
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Natural convection is convection where the fluid motion is driven by buoyancy forces. Porous media and nanofluids have an impact on the heat transfer capabilities of thermal systems. The present experimental study is part of ongoing research and lies at the intersection of buoyancy driven flow in a cavity, porous mediums and nanofluids. The nanofluid consists of Al 2 O 3 nanoparticles in the base fluid of 60% ethy-lene glycol (EG) and 40% water. A Rayleigh number range of 6 × 10 3 < Ra * < 1.6 × 10 4 , for a volume fraction of 0.2% nanoparticles. The porous medium used is glass spheres of 16mm. In this research the effective viscosity of the nanofluid was determined experimentally while the effective thermal conductivity was available in the literature. The results showed that heat transfer is affected by both the porous medium and the nanofluid. The results show that the heat transfer in the case of porous media with nanofluid is more than the case of pure base fluid. However, more experimentation for a wider range of Rayleigh numbers will be a part of future works of this ongoing research.
Natural convection enhancement in a porous cavity with Al 2 O 3 -Ethylene glycol/water nanofluids
The natural convection heat transfer of a differentially heated cavity filled with porous material and saturated with nanofluid is studied. The nanofluid used in the present study contains 60% Ethylene glycol, 40% DI-water and 30 nm size Al 2 O 3 nanoparticles. The volume concentration of nanofluid used is in the range of 0.05% 6 / 6 0.4%. The range of Rayleigh number in the present study is 1.2 Â 10 8 6 Ra 6 4 Â 10 8 for clear cavity and 3 Â 10 3 6 Ra 6 1.3 Â 10 4 for the porous cavity. Viscosity of the nanofluid is also measured at volume concentration of 0.05% and found one available model works for the calculations. In order to explain the heat transfer behaviour of the present system, heat transferred by both clear and porous cavity, heat transfer coefficients of both hot and cold wall, as well as Nusselt number variation with concentrations of nanofluids are presented. It is found that the performance of porous cavity filled with a nanofluid volume concentration of 0.05% is enhanced while the other concentrations of nanofluids deteriorate the performance. At a volume concentration of 0.05%, the heat transfer capability of porous cavity is enhanced to a maximum of 10% compared to the base fluids.
Review of convection heat transfer and fluid flow in porous media with nanofluid
Renewable and Sustainable Energy Reviews, 2015
There are two advantages of using porous media. First, its dissipation area is greater than the conventional fins that enhances the heat convection. Second is the irregular motion of the fluid flow around the individual beads which mixes the fluid more effectively. Nanofluids result from the mixtures of base fluid with nanoparticles having dimensions of (1-100) nm, with very high thermal conductivities; as a result, it would be the best convection heat transfer by using two applications together: porous media and nanofluids. This article aims to summarize the published articles in respect to porosity, permeability (K) and inertia coefficient (C f ) and effective thermal conductivity (k eff ) for porous media, also on the thermophysical properties of nanofluid and the studies on convection heat transfer in porous media with nanofluid.
Experimental investigation on cavity flow natural convection of Al 2 O 3 –water nanofluids
Thermo-physical properties of nanofluids have attracted the attention of researchers more than the heat transfer characteristic of nanofluids. On the other hand, contradictory results were reported on the thermal-fluid behaviour of nanofluids numerically and experimentally in the open literature. In addition to that, experimental natural convection has been investigated less than others. In this paper, characteristic and stability of Al 2 O 3 –water nanofluid (d = 30 nm) has been analyzed by using Malvern Zetasizer, Zeta potential, and UV–visible spectrosco-py. The natural convection of Al 2 O 3 –water nanofluids (formulated with single-step method) was experimentally studied in detail for volume fractions of 0, 0.05, 0.1, 0.2, 0.4 and 0.6% in a rectangular cavity, heated differentially on two opposite vertical walls for Rayleigh number (Ra) range 3.49 × 10 8 to 1.05 × 10 9. The viscosity of the Al 2 O 3 –water nanofluids are also measured experimentally in a temperature range between 15 °C and 50 °C and effect of temperature and volume fraction on viscosity have investigated. Detailed study on the influence of nanoparticle concentration on natural convection heat transfer coefficient was performed. It was found that increasing concentration of nanoparticles improves heat transfer coefficient up to an optimum value of 15% enhancement , at 0.1% volume fraction, then further increasing of concentration of the nanoparticles deteriorates natural convection heat transfer coefficient. This research also supports the idea of " for nanofluids with thermal conductivity more than the base fluids, there may exist an optimum concentration which maximizes the heat transfer in an exact condition as natural convection, laminar forced convection or turbulence forced convection " .
Heat and Mass Transfer Characteristics of Al2O3-Water and Ag-Water NanofluidThrough Porous Media.pdf
In this article, we have presented a numerical solution to the MHD heat and mass transfer flow of a nanofluid through porous media over a vertical cone with heat generation/absorption, thermal radiation, and chemical reaction. Though we have different varieties of nanofluids, we have considered Al 2 O 3 -water and Ag-water based nanofluids (with volume fraction 1% and 4%) in this problem. The transformed conservation equations for the nanofluid are solved numerically subject to the boundary conditions using an efficient, extensively validated, variational finite element analysis. The numerical code is validated with previous studies. The influence of important nondimensional parameters, namely, nanoparticle volume fraction (φ), Prandtl number (Pr), magnetic parameter (M), mixed convection (Ra), buoyancy ratio (Nr), and space-dependent (A), temperature-dependent (B), thermal radiation (R), and chemical reaction (Cr) on velocity, temperature, and nanoparticle concentration fields as well as the skin-friction coefficient, Nusselt number, and Sherwood number are examined in detail and the results are shown graphically and in tabular form to illustrate the physical importance of the problem. Thermal conductivity enhancement of suspensions containing nanosized alumina particles, J. Appl. Phys., vol. 91, pp. 4568-4572, 2002.
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In this study, the natural convection heat transfer of variable properties Al 2 O 3-EG-water nanofluid in a differentially heated rectangular cavity has been investigated numerically. The governing equations, for a Newtonian fluid, have been solved numerically with a finite volume approach. The influences of the pertinent parameters such as Ra in the range of 10 3-10 7 and volume fraction of nanoparticles from 0 to 0.04 on heat transfer characteristics have been studied. The results verified by making overall comparison with some existing experimental results have shown that for Ra=10 3 , for which conduction heat transfer is dominant, the average Nusselt number increases as volume fraction of nanoparticles increases, but for higher Ra numbers in contradiction with the constant properties cases it decreases. This reduction, which is associated with increased viscosity, is more severe at Ra of 10 4 compared to higher Ra numbers such that the least deterioration in heat transfer occurs for Ra=10 7. This is due to the fact that as Ra increases, the Brownian motion enhances; thus conductivity improves and becomes more important than viscosity increase. An scale analysis, performed to clarify the contradictory reports in the literature on the natural convection heat transfer enhancement or deterioration of nanofluids, showed that different kinds of evaluating the base fluid Rayleigh number has led to such a difference.
Investigation into cavity flow natural convection for Al2O3-water nanofluids numerically.
Numerical simulations have been carried out on natural convection heat transfer in a rectangular cavity. The effect of distilled water-Al 2 O 3 nanofluid on heat transfer in a rectangular cavity heated vertically on sidewalls is analysed. The effective properties of distilled water-Al 2 O 3 nanofluid were calculated from the correlations obtained from literature. The simulation was carried under different volume fraction concentration of nanoparticles as well as different correlations for effective properties of Al 2 O 3-water nanofluid. The results indicate that in general adding Al 2 O 3 nanoparticles into pure water improves its heat transfer performance; however, there is an optimum nanoparticle volume fraction which maximises the heat transfer rate for each condition. It is investigated and discussed the influence of uncertainty of available correlations for effective properties of distilled water-Al 2 O 3 nanofluid. The effects of aspect ratios of the cavity on heat transfer were also analysed. The influence of pertinent parameters such as Rayleigh number and Nusselt number on the heat transfer characteristics of natural convection is also investigated. INTRODUCTION The poor physical properties of the conventional heat transfer fluids such as water, ethylene glycol and mineral oils, are the major problems in improving the performance of engineering equipment. The conventional heat transfer fluids have a limitation to the effectiveness of heat removal from the systems whose temperature control relies on natural convection. The effective thermal conductivity of the conventional heat transfer fluids can be improved by suspending nano-sized solid particles into them which enhances the heat transfer characteristics of the base fluid. These particles are called nanoparticles and the resultant mixture is named nanofluid. Therefore, a nanofluid is a suspension of ultrafine particles in a conventional (base) fluid which enhances the heat transfer characteristics of the base fluid. Free or natural convection is convection caused by temperature difference within the fluid. Natural convection heat transfer in enclosures is preferred in several situations by heat
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.
A B S T R A C T Cavity design is an important aspect in thermal systems, and proper cavity design saves plenty of energy as losses are minimised through better design. In this work, the influence that the Aspect Ratio (AR) of a rectangular cavity filled with nanofluids has on the natural convection process is studied experimentally. Three different cavities with the AR of 1, 2 and 4 are fabricated, and the heat transfer performance is studied using two different fluids namely de-ionised water and Al 2 O 3 /Water nanofluids. It is found that the AR of the cavity has a significant effect on the heat transfer coefficient and Nusselt number. More importantly, the optimum nanofluid concentration for maximum heat transfer varies with the AR of the cavity. It also found that the Rayleigh number has a strong effect on the Nusselt number as well as nanofluid buoyancy.