Comparative analysis of single and two-phase models for CFD studies of nanofluid heat transfer (original) (raw)
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International Communications in Heat and Mass Transfer, 2012
In this article, forced convection heat transfer with laminar and developed flow for water-Al 2 O 3 nanofluid inside a circular tube under constant heat flux from the wall was numerically investigated using computational fluid dynamics method. Both single and two-phase models are accomplished for either constant or temperature dependent properties. For this study nanofluids with size particles equal to 100 nm and particle concentrations of 1 and 4 wt% were used. It is observed that the nanoparticles when dispersed in base fluid such as water enhance the convective heat transfer coefficient. The Nusselt number and heat transfer coefficient of nanofluids were obtained for different nanoparticle concentrations and various Reynolds numbers. Heat transfer was enhanced by increasing the concentration of nanoparticles in nanofluid and Reynolds number. Also, a correlation based on the dimensionless numbers was obtained for the prediction the Nusselt number. The modeling results showed that the predicted values were in very good agreement with reference experimental data.
Thermal Science, 2014
In this article, the laminar mixed convection of Al 2 O 3 -Water nanofluid flow in a horizontal flat tube has been numerically simulated. The two-phase mixture model has been employed to solve the nanofluid flow, and constant heat flux has been considered as the wall boundary condition. The effects of different and important parameters such as the Reynolds number (Re), Grashof number (Gr), nanoparticles volume fraction ( ) and nanoparticle diameter (d p ) on the thermal and hydrodynamic performances of nanofluid flow have been analyzed. The results of numerical simulation were compared with similar existing data and good agreement is observed between them. It will be demonstrated that the Nusselt number (Nu) and the friction factor (C f ) are different for each of the upper, lower, left and right walls of the flat tube. The increase of Re, Gr and and the reduction of d p lead to the increase of Nu. Similarly, the increase of Re and results in the increase of C f . Therefore, the best way to increase the amount of heat transfer in flat tubes using nanofluids is to increase the Gr and reduce the d p .
CFD studies on natural convection heat transfer of Al2O3-water nanofluids
Heat and Mass Transfer, 2011
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2007
In this work, an experimental investigation was carried out to study a laminar mixed convection flow and heat transfer of Al2O3-water nanofluid inside a horizontal tube submitted to a uniform wall heat flux at its outer surface. Measured data were collected for the following ranges of the governing parameters: the Reynolds number between 170 and 630, the Grashof number between 1.5 10 and 9.2 10 and the Prandtl number between 7 and 7.42. Results have shown that the experimental heat transfer coefficient remains nearly constant with an increase of particle volume concentration from 0 to 2%. However, we have observed a slight decrease of the Nusselt number with an increase of the particle volume fraction from 0 to 2%. Key-Words: Heat transfer, Laminar flow, Mixed convection, Natural and forced convection, Nanofluid, Al2O3-Water mixture, Alumina nanoparticles, Experimental study.
Engineering Journal, 2017
Forced convective heat transfer and wall characteristics of nanofluid flow containing Al2O3 nanoparticles and water inside a miniature tube is studied numerically by means of computational fluid dynamic (CFD) code. Problem is solved by employing finite volume approach using both single-phase (homogeneous) and dispersion models. In both models, constant and temperature-dependent thermophysical properties are used and results are compared to available experimental and theoretical literatures. It can be seen as the Reynolds number increases, the Nusselt number improves, too. However, it is accompanied by higher wall shear stress. Moreover, in the case of temperature-dependent properties, lower values for shear stress were obtained. In comparison with experimental data and available theoretical correlations, dispersion model in both temperature-dependent and constant properties shows a desirable compatibility. On the other hand, single-phase model in constant thermophysical properties underestimates the amount of convective heat transfer. Furthermore, it can be observed at wall, by increasing the particles volume concentration, not only wall temperature decreases also, rate of thermal enhancement decreases slightly.
Nanoscale Research Letters, 2011
In this article, laminar flow-forced convective heat transfer of Al2O3/water nanofluid in a triangular duct under constant wall temperature condition is investigated numerically. In this investigation, the effects of parameters, such as nanoparticles diameter, concentration, and Reynolds number on the enhancement of nanofluids heat transfer is studied. Besides, the comparison between nanofluid and pure fluid heat transfer is achieved in
Ain Shams Engineering Journal, 2015
In this study, the flow field and heat transfer of Al 2 O 3 -water nanofluid turbulent forced convection in a tube are investigated. The surface of the tube is hot (T h = 310 K). Simulations are carried out for constant water Prandtl number of 6.13, Reynolds numbers from 10,000, 20,000, 30,000 to 100,000, nanoparticles volume fractions of 0, 0.001, 0.1, 0.2, 0.4 and nanoparticles' diameter of 25, 33, 75, and 100 nm. The finite volume method and SIMPLE algorithm are utilized to solve the governing equations numerically. The numerical results showed that with enhancing Reynolds numbers, average Nusselt number increases. The variations of the average Nusselt number relative to volume fractions are not uniform. For all of the considered volume fractions, by increasing the Reynolds number the skin friction factor decreases and with increasing volume fractions and Reynolds number the pressure drop increases.
Energy, 2014
The present paper analyzes the turbulent convection of Al 2 O 3 -water nanofluid inside a circular section tube subjected to constant wall temperature. The analysis is developed numerically by using the mixture model, which has been proved to be a convenient method to simulate nanofluids behavior. The numerical model is successfully validated by means of analytical equations and experimental correlations. The study is focused on the analysis of the performance of Al 2 O 3 -water nanofluid within the considered device. Performance indicators based on the first and second law of thermodynamics are taken into account and analyzed. At the increase of nanofluid concentration, the Nusselt number increases, but entropy generation and pumping power also increase, therefore the penalties overcome the benefits.
Simulation of Laminar Convection Flow of AL2O3-WATER Nanofluid in an Asymmetric Heated Channel
2017
The present paper proposes a two dimensional analysis of the laminar convection flow of water-Al 2 O 3 nanofluid inside a rectangular section channel with non-symmetric boundary conditions. In particular, a constant heat flux is applied on the top surface of the channel and an adiabatic condition on the bottom one. This situation is typical of many devices, such as solar collector, which receives thermal radiation from the top surface with objective to heat a working fluid, water-Al 2 O 3 in the present case, and which are insulated on the bottom one in order to limit energy waste. Numerical simulations are developed by using the commercial software COMSOL, which employs finite element methods approach to solve the conservation equations, moreover thermal dependent properties are considered in the simulations The analysis is conducted for Re numbers ranging between 500-1000, concentration between 0%-6% and dimension of particles between 20-60 nm. An increase of Nu is observed at the increase of the concentration, as well as a substantial increment of the pressure losses.
In this study, forced convection heat transfer of nanoliquids is done using both single-phase and mixture-phase models and the results are compared with experimental results. The governing equations of the study here are discretized using the finite volume method. Hybrid differencing scheme is used to calculate the face values of the control volumes. A code is written using SIMPLER algorithm and then solved using the MATLAB engine. The mixture-phase model studied here, considers two slip mechanisms between nanoparticle and base-fluid, namely Brownian diffusion and thermophoresis. Al 2 O 3-water nanofluid is used for the study of nanofluid and the study shows significant increase in convective heat transfer coefficient while the mixture-phase model demonstrates slightly lower values than the single-phase model. The study is done with various nanoparticle concentrations and Reynolds numbers. With increasing particle concentration and Reynolds number, the convective heat transfer coefficient increases and as well as the shear stress. For low concentrations of the nanoparticle, Nusselt number is slightly lower than the base fluid and as the concentration increases, the Nusselt number also rises higher than the base fluid.