scholarly journals A numerical study of the natural convection of Al2O3-EG nanofluid in a square enclosure and impacts and a comparison of various viscosity and thermal conductivity models

2021 ◽  
Vol 5 (2) ◽  
pp. 247-259
Author(s):  
Neşe KEKLİKCİOĞLU ÇAKMAK ◽  
Hasan Hüseyin DURMAZUÇAR ◽  
Kerim YAPICI
Keyword(s):  
Thermal Conductivity ◽  
Natural Convection ◽  
Numerical Study ◽  
Square Enclosure ◽  
Conductivity Models

Comparative Analysis of Different Thermal Conductivity Models for Nanofluids in a Square Enclosure Under Natural Convection Conditions

2005 ◽  
Author(s):  
Sushant Anand ◽  
R. C. Arora
Keyword(s):  
Thermal Conductivity ◽  
Natural Convection ◽  
Maxwell Model ◽  
Theoretical Models ◽  
Abnormal Behavior ◽  
Square Enclosure ◽  
Nusselt Numbers ◽  
Bruggeman Model ◽  
The Comparative Study ◽  
Conductivity Models

Previous investigations have revealed that addition of nanoparticles dispersed in conventional fluids such as water or ethylene glycol result in a new class of coolant which has anomalously high thermal conductivity under stagnation conditions. Few theoretical models have been proposed to resolve this abnormal behavior of nanofluids. This study focuses on the comparative study of some of these models namely, Wasp’s model, Choi’s modified Maxwell model, Bruggeman model and Xue’s model for complex nanoparticles. Flow in a cavity has been considered with insulated horizontal walls and vertical walls at different uniform temperatures under Boussinesq’s approximation. Results obtained are presented in form of plots of streamlines, isotherms and Nusselt number. Steady state solutions have been obtained for natural convection in a square cavity partially filled with copper-water. Parameters considered are Grashof number (103 to 105) and particle concentration (φ = 0%–20%). The results validate the stand that nanofluids are better coolants under dynamic conditions than conventional fluids. The flow properties have been found to be dependent upon the choice of thermal conductivity models chosen. The flow patterns predicted by various models have been found to be in close agreement with each other; however substantial variance has been found to exist in Nusselt numbers predicted by these models.

Numerical Simulation of Heat Transfer in Laminar Natural Convection of Mixed Newtonian-Non-Newtonian and Pure Non-Newtonian Nanofluids in a Square Enclosure

2021 ◽  
pp. 1-44
Author(s):  
Ajay Vallabh ◽  
P.S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Base Fluid ◽  
Volume Fraction ◽  
Numerical Study ◽  
Transfer Model ◽  
Nanoparticle Concentration ◽  
Left Wall ◽  
Square Enclosure ◽  
First Case

Abstract This paper presents a steady-state heat transfer model for the natural convection of mixed Newtonian-Non-Newtonian (Alumina-Water) and pure Non-Newtonian (Alumina-0.5 wt% Carboxymethyl Cellulose (CMC)/Water) nanofluids in a square enclosure with adiabatic horizontal walls and isothermal vertical walls, the left wall being hot and the right wall cold. In the first case the nanofluid changes its Newtonian character to Non-Newtonian past 2.78% volume fraction of the nanoparticles. In the second case the base fluid itself is Non-Newtonian and the nanofluid behaves as a pure Non-Newtonian fluid. The power-law viscosity model has been adopted for the non-Newtonian nanofluids. A finite-difference based numerical study with the Stream function-Vorticity-Temperature formulation has been carried out. The homogeneous flow model has been used for modelling the nanofluids. The present results have been extensively validated with earlier works. In Case I the results indicate that Alumina-Water nanofluid shows 4% enhancement in heat transfer at 2.78% nanoparticle concentration. Following that there is a sharp decline in heat transfer with respect to that in base fluid for nanoparticle volume fractions equal to and greater than 3%. In Case II Alumina-CMC/Water nanofluid shows 17% deterioration in heat transfer with respect to that in base fluid at 1.5% nanoparticle concentration. An enhancement in heat transfer is observed for increase in hot wall temperature at a fixed volume fraction of nanoparticles, for both types of nanofluid.

scholarly journals Natural convection in a differentially heated enclosure with triangular roof

1970 ◽  
Vol 39 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Sumon Saha ◽  
Noman Hasan ◽  
Chowdhury Md Feroz
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Natural Convection ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Element Analysis ◽  
Left Wall ◽  
Square Enclosure

A numerical study has been carried out for laminar natural convection heat transfer within a two-dimensional modified square enclosure having a triangular roof. The vertical sidewalls are differentially heated considering a constant flux heat source strip is flush mounted with the left wall. The opposite wall is considered isothermal having a temperature of the surrounding fluid. The rest of the walls are adiabatic. Air is considered as the fluid inside the enclosure. The solution has been carried out on the basis of finite element analysis by a non-linear parametric solver to examine the heat transfer and fluid flow characteristics. Different heights of the triangular roof have been considered for the present analysis. Fluid flow fields and isotherm patterns and the average Nusselt number are presented for the Rayleigh numbers ranging from 103 to 106 in order to show the effects of these governing parameters. The average Nusselt number computed for the case of isoflux heating is also compared with the case of isothermal heating as available in the literature. The outcome of the present investigation shows that the convective phenomenon is greatly influenced by the inclined roof height. Keywords: Natural convection, triangular roof, Rayleigh number, isoflux heating. Doi:10.3329/jme.v39i1.1826 Journal of Mechanical Engineering, vol. ME39, No. 1, June 2008 1-7

Experimental and Numerical Investigation on Natural Convection Heat Transfer of TiO2–Water Nanofluids in a Square Enclosure

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Yanwei Hu ◽  
Yurong He ◽  
Shufu Wang ◽  
Qizhi Wang ◽  
H. Inaki Schlaberg
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Numerical Investigation ◽  
Convection Heat Transfer ◽  
Distribution Functions ◽  
Lattice Boltzmann Model ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Square Enclosure

An experimental and numerical investigation on natural convection heat transfer of TiO2–water nanofluids in a square enclosure was carried out for the present work. TiO2–water nanofluids with different nanoparticle mass fractions were prepared for the experiment and physical properties of the nanofluids including thermal conductivity and viscosity were measured. Results show that both thermal conductivity and viscosity increase when increasing the mass fraction of TiO2 nanoparticles. In addition, the thermal conductivity of nanofluids increases, while the viscosity of nanofluids decreases with increasing the temperature. Nusselt numbers under different Rayleigh numbers were obtained from experimental data. Experimental results show that natural convection heat transfer of nanofluids is no better than water and even worse when the Rayleigh number is low. Numerical studies are carried out by a Lattice Boltzmann model (LBM) coupling the density and the temperature distribution functions to simulate the convection heat transfer in the enclosure. The experimental and numerical results are compared with each other finding a good match in this investigation, and the results indicate that natural convection heat transfer of TiO2–water nanofluids is more sensitive to viscosity than to thermal conductivity.

NATURAL CONVECTION HEAT TRANSFER FROM A DISCRETE HEAT SOURCE COUPLED WITH CONDUCTION DOMINATED PHASE CHANGE

1998 ◽  
Vol 22 (3) ◽  
pp. 269-289
Author(s):  
M. Lacroix
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Steady State ◽  
Natural Convection ◽  
Thermal Diffusivity ◽  
Heat Source ◽  
Phase Change ◽  
Numerical Study ◽  
Thermal Conductivity Ratio ◽  
Discrete Heat Source

A numerical study has been conducted for the heat transfer from a discrete heat source by natural convection in air above coupled with conduction dominated melting of a phase change material (PCM) below via a wall of finite thermal diffusivity. Results indicate that the presence of a PCM layer underneath the wall significantly delays the temperature rise of the heat source. The time delay increases as the thermal diffusivity of the wail material decreases and as the thickness of the PCM layer increases. For high thermal conductivity wall materials [Formula: see text] the steady state heat source temperatures are similar and independent of the PCM layer. On the other hand, for [Formula: see text], the steady state temperatures are higher and dependent on the thickness of the PCM layer. A correlation is proposed in terms of the thickness of the PCM layer and the thermal conductivity ratio of the wall.

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