Investigation into cavity flow natural convection for Al2O3-water nanofluids numerically. (original) (raw)
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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.
Numerical Study of Heat Transfer Performance of Homogenous Nanofluids under Natural Convection
The present study aims to identify heat transfer and flow characteristic due to buoyancy forces in a heated enclosure using nanofluid and their behaviors under natural convective heat transfer condition. In the present work nanofluids with water based containing Al 2 O 3 nanoparticle numerically investigated. Numerical works are done on the use of the stable nanofluids under natural convective heat transfer conditions. Process of heating is done in two different ways: in first process the heater mounted to the down wall and in second way it mounted to the left vertical wall with a finite length, also heated and cooled walls keep in a constant temperature. Our numerical simulation has been undertaken incorporating a homogenous solid-liquid mixture. In particular this study deals with Al 2 O 3 nanofluids with Newtonian behavior. Simulation have been carried out in the ranges Ra=10 3-10 6. Our volumetric fraction of nanoparticles was 1.3%. It was shown the Nusselt-Rayleigh number relation and then nanofluid Nu-Ra number diagrams based on found is plotted. Results showed an increasing in Nusselt-Rayleigh number at nanofluids diagrams as compared to Nusselt-Rayleigh relations of pure water. Increase in the average Nusselt number plays a significant role in heat transfer applications. Due to our numerical investigations vertical cavities with nanofluid were better than horizontal cavities. Also the cavities, which we used nanofluid, had better efficiency in natural convection numerical modeling for both horizontal and vertical fluid layer.
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 " .
Advances in Mechanical Engineering, 2010
The natural convection heat transfer characteristics of [Formula: see text] nanofluids comprised of 47 nm, [Formula: see text] and water, with volume fractions ranging from 0.5% through 6%, has been investigated through a set of experimental measurements. The temperature of the heated surface and the Nusselt number of different volume fractions of [Formula: see text] nanofluids natural convection tests clearly demonstrated a deviation from that of pure base fluids (distilled water). In the investigation, a deterioration of the natural convection heat transfer coefficient was observed with increases of the volume fraction of the nanoparticles in the nanofluids. The deterioration phenomenon was further investigated through a visualization study on a 850 nm diameter polystyrene particle/water suspension in a bottom heating rectangular enclosure. The influence of particle movements on the heat transfer and natural flow of the polystyrene particle/DI water suspension were filmed, and the...
Investigation of enhancement of heat transfer in natural convection utilizing of nanofluids
World Academy of Science, Engineering and Technology, International Journal of Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering, 2015
This paper analyses the heat transfer performance and fluid flow using different nanofluids in a square enclosure. The energy equation and Navier-Stokes equation are solved numerically using finite volume scheme. The effect of volume fraction concentration on the enhancement of heat transfer has been studied icorporating the Brownian motion; the influence of effective thermal conductivity on the enhancement was also investigated for a range of volume fraction concentration. The velocity profile for different Rayleigh number. Water-Cu, water AL2O3 and water-TiO2 were tested.
Advanced Powder Technology, 2015
The problem of natural convection boundary layer heat transfer of nanofluids is theoretically analyzed. Different aspects of nanoparticles, such as size, shape and constructive material, as well as the type of the base fluid and the working temperature, are examined. The drift-flux model of nanofluids, including the effects of Brownian motion, thermophoresis, and the local volume fraction of nanoparticles, is adopted to model the boundary layer heat and mass transfer of nanofluids. Following the state-of-theart, the thermo-physical properties are extracted from five different synthesized types of nanofluids. A new non-dimensional parameter, the enhancement ratio, indicating the ratio of the convective heat transfer coefficient of the nanofluid to the base fluid, is introduced. The effect of the nanoparticles on the enhancement of natural convective heat transfer of nanofluids is discussed. The main findings of this study are as follows: (i) the type of the nanoparticles and the base fluid are the most important parameters affecting the heat transfer of nanofluids; (ii) in some cases, the presence of nanoparticles in the base fluid deteriorates the heat transfer rate; and (iii) the rise of the working temperature reduces the efficiency of the nanofluid, which is a crucial issue in applications of nanofluids as coolants.
The effects of nanoparticles diameter and concentration on natural convection heat transfer of a nanofluid around a vertical cone embedded in a Darcy porous medium is theoretically investigated utilizing the drift-flux model. The thermal conductivity and the viscosity of the nanofluid are assumed as simultaneous functions of temperature and local volume fraction of nanoparticles using experimental correlations. In addition, the flux of nanoparticles on the surface of the cone is assumed to be zero. An efficient mathematical approach with a self-similar solution is utilized to theoretically analyze the boundary layer heat and mass transfer of an Al 2 O 3 -water nanofluid. The reduced system of ordinary differential equations are general and can be solved for any arbitrary functions of thermal conductivity and viscosity. The analysis of the nanofluid natural convection flow is accomplished for two cases of (i) T w > T 1 and (ii) T w < T 1 . The results show that using nanoparticles would not (would) enhance the heat transfer from the cone for the case of a cone with a hot surface (cold surface). A decrease in the size of nanoparticles or an increase in the volume fraction of nanoparticles causes a decline in the heat transfer rate from the cone when the cone surface is hot. Finally, a comparison between the non-homogenous model (drift-flux model) and the homogenous model of nanofluids is performed. The results demonstrate that the driftflux model tends to the homogeneous model as the size and volume fraction of nanoparticles increase.
Effect of Temperature and Nanoparticle Concentration on Free Convective Heat Transfer of Nanofluids
Energies
A theoretical analysis of the influence of temperature and nanoparticle concentration on free convection heat transfer from a horizontal tube immersed in an unbounded nanofluid was presented. The Nusselt (Nu) number and heat transfer coefficient were parameters of the intensity of the convective heat transfer. For free convection, the Nu number was a function of the Rayleigh (Ra) number and Prandtl (Pr) number. The Rayleigh (Ra) number and Prandtl (Pr) number were functions of the thermophysical properties of nanofluids. The thermophysical properties of nanofluids varied with temperature and nanoparticle concentration. Therefore, an analysis was conducted to evaluate the effects on the performance of nanofluids due to variations of thermal conductivity, viscosity, thermal expansion, density, and specific heat, which are functions of nanoparticle concentration and temperature. Water- and ethylene glycol (EG)-based nanofluids with dispersed alumina (Al2O3) nanoparticles at mass concen...
International Journal of Simulation Modelling, 2012
Numerical analysis is performed to examine the heat transfer enhancement of Au, Al 2 O 3 , Cu and TiO 2 water-based nanofluids. The analysis uses a two-dimensional enclosure under natural convection heat transfer conditions and has been carried out for the Rayleigh number range 10 3 ≤ Ra ≤ 10 5 , and for the nanoparticles' volume fraction range 0 ≤ φ ≤ 0,10. The governing equations were solved with the standard finite-volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. Highly accurate numerical results are presented in the form of average Nusselt number and heat transfer enhancement. The results indicate clearly that the average Nusselt number is an increasing function of both, Rayleigh number and volume fraction of nanoparticles. The results also indicate that heat transfer enhancement is possible using nanofluids in comparison to conventional fluids, resulting in the compactness of many industrial devices. However, low Rayleigh numbers show more enhancement compared to high Rayleigh numbers.