Effect of Partition Wall on Natural Convection Heat Transfer in a Vertical Air Layer

2001 ◽  
Vol 123 (3) ◽  
pp. 441-449 ◽  
Author(s):  
Yoshiyuki Yamaguchi ◽  
Yutaka Asako
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Finite Thickness ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Ideal Boundary ◽  
Convection Heat ◽  
Total Heat Transfer ◽  
Partition Wall

Three-dimensional natural convection heat transfer characteristics in a vertical air layer partitioned into cubical enclosures by partition walls of finite thermal conductivity and finite thickness were obtained numerically. The air layer is differentially heated from each surface. In this work, the analyses were performed using finite thickness and finite conductivity of the partition wall for Ra=104 and 105, and for wide range of the thickness and the conductivity of the partition wall. The results were presented in the form of overall convection and total heat transfer coefficient. From the comparison of the results with the traditional ideal boundary conditions such as “conduction,” “adiabatic,” and “no-thickness,” the correlation of the heat transfer with the actual partition wall and the ideal boundary conditions were developed. After examinations of the results, it was shown that the proportion of the heat transfer quantity in the partition wall to the total heat transfer quantity from the hot wall is a function of a product of the thermal conductivity and the thickness of the partition wall.

Natural Convection Heat Transfer in a Vertical Air Layer Partitioned Into Cubical Enclosures of Finite Wall Thermal Conductivity and Thickness

1999 ◽  
Author(s):  
Y. Yamaguchi ◽  
Y. Asako
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Wall Thickness ◽  
Finite Thickness ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Wide Range

Abstract Three-dimensional natural convection heat transfer characteristics in a vertical air layer partitioned into cubical enclosures of finite wall thermal conductivity and finite thickness were obtained numerically. The outer surfaces of the enclosure are prescribed at different temperatures. These walls are often encountered in applications such as door panels and thermal insulation boards. The analyses were performed for finite wall thickness and conductivity, for Ra = 104 and 105 and for a wide range of wall thickness and thermal. The results were presented in form of temperature distributions and contour plots of Num and Qwall/Qtotal. From comparison of the results with ideal boundary conditions, a correlation for heat transfer for partitioned walls was developed. It was shown from the results that the ratio of heat transfer into the partition walls to the total heat transfer from the hot wall is a function of the product of wall thermal conductivity and thickness.

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 in Rectangular Cavity With Nanoparticle Enhanced Ionic Liquids (NEILs)

2012 ◽  
Author(s):  
Titan C. Paul ◽  
A. K. M. M. Morshed ◽  
Elise B. Fox ◽  
Ann E. Visser ◽  
Nicholas J. Bridges ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Ionic Liquid ◽  
Ionic Liquids ◽  
Natural Convection ◽  
Thermophysical Properties ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat

A systematic natural convection heat transfer experiment has been carried out of nanoparticle enhanced ionic liquids (NEILs) in rectangular enclosures (lengthxwidthxheight, 50×50×50mm and 50×50×75mm) heated from below condition. In the present experiment NEIL was made of N-butyl-N-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl} imide, ([C4mpyrr][NTf2]) ionic liquid with 0.5% (weight%) Al2O3 nanoparticles. In addition to characterize the natural convection behavior of NEIL, thermophysical properties such as thermal conductivity, heat capacity, and viscosity were also measured. The result shows that the thermal conductivity of NEIL enhanced ∼3% from the base ionic liquid (IL), heat capacity enhanced ∼12% over the measured temperature range. The natural convection experimental result shows consistent for two different enclosures based on the degrading natural convection heat transfer rate over the measured Rayleigh number range. Possible reasons of the degradation of natural convection heat transfer may be the relative change of the thermophysical properties of NEIL compare to the base ionic liquid.

Effect on Natural Convection Heat Transfer of Nanofluid in an Enclosure Due to Uncertainties of Viscosity and Thermal Conductivity

2007 ◽  
Author(s):  
C. J. Ho ◽  
M. W. Chen ◽  
Z. W. Li
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Dynamic Viscosity ◽  
Convection Heat Transfer ◽  
Alumina Nanoparticles ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Significant Difference ◽  
Effective Dynamic

In this study we aim to identify effects due to uncertainties in effective dynamic viscosity and thermal conductivity of nanofluid on laminar natural convection heat transfer in a square enclosure. Numerical simulations have been undertaken incorporating a homogeneous solid-liquid mixture formulation for the two-dimensional buoyancy-driven convection in the enclosure filled with alumina-water nanofluid. Two different formulas from the literature are each considered for the effective viscosity and thermal conductivity of the nanofluid. Simulations have been carried out for the pertinent parameters in the following ranges: the Rayleigh number, Raf = 103 ∼ 106 and the volumetric fraction of alumina nanoparticles, φ = 0 ∼ 4%. Significant difference in the effective dynamic viscosity enhancement of the nanofluid calculated from the two adopted formulas, other than that in the thermal conductivity enhancement, was found to play as a major factor, thereby leading to contradictory results concerning the heat transfer efficacy of using nanofluid in the enclosure.

Experimental Investigation of Natural Convection Heat Transfer of an Ionic Liquid in a Rectangular Enclosure Heated From Below

2011 ◽  
Author(s):  
Titan C. Paul ◽  
A. K. M. M. Morshed ◽  
Elise B. Fox ◽  
Ann Visser ◽  
Nicholas Bridges ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Ionic Liquid ◽  
Nusselt Number ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Temperature Range

This paper presents an experimental study of natural convection heat transfer for an Ionic Liquid. The experiments were performed for 1-butyl-2, 3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, ([C4mmim][NTf2]) at a Rayleigh number range of 1.13×107 to 7.7×107. In addition to determining the convective heat transfer coefficients, this study also included experimental determination of thermophysical properties of [C4mmim][NTf2] such as, density, viscosity, heat capacity, and thermal conductivity. The results show that the density of [C4mmim][NTf2] varies from 1.437–1.396 g/cm3 within the temperature range of 10–50°C, the thermal conductivity varies from 0.125–0.12 W/m.K between a temperature of 10 to 70°C, the heat capacity varies from 1.015 J/g.K–1.760 J/g.K within temperature range of 25–340°C and the viscosity varies from 243cP–18cP within temperature range 10–75°C. The results for density, thermal conductivity, heat capacity, and viscosity were in close agreement with the values in the literature. Measured dimensionless Nusselt number was observed to be higher for the ionic liquid than that of DI water. This is expected as Nusselt number is the ratio of heat transfer by convection to conduction and the ionic liquid has lower thermal conductivity (approximately 20% of DI water) than DI water.

scholarly journals Natural Convection Heat Transfer in Nanofluids: A Numerical Study

2008 ◽  
Author(s):  
W. Rashmi ◽  
A. F. Ismail ◽  
W. Asrar ◽  
M. Khalid ◽  
Y. Faridah
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Base Fluid ◽  
Volume Fraction ◽  
Coefficient Of Thermal Expansion ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat

Natural convection heat transfer in nanofluids has been investigated numerically using computational fluid dynamics (CFD) approach. Analytical models that describe molecular viscosity, density, specific heat, thermal conductivity and coefficient of thermal expansion have been considered in terms of volume fraction and size of nanoparticles, size of base fluid molecule and temperature. The uniform suspensions of different concentrations of Al2O3 in base fluid (water) are considered as nanofluids. Thermal conductivity of the nanofluids has been obtained by solving the governing equations in conjunction with Kinetic model and interfacial layer model using FLUNET 6.3. Numerical simulations have been carried out in a closed pipe for L/D = 1.0. The numerical values of k have also been compared with the experimental values available in the literature. Both the models gave similar predictions with experimentally compared values of k.

Effect of Wall Conduction on Natural Convection in an Enclosure With a Centered Heat Source

1995 ◽  
Vol 117 (4) ◽  
pp. 301-306 ◽  
Author(s):  
Yi-Hsiang Huang ◽  
Suresh K. Aggarwal
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Heat Source ◽  
Wall Thickness ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Primitive Form

This study presents a numerical investigation of the effects of wall conduction on laminar natural convection heat transfer in a two-dimensional rectangular enclosure. The heat transfer is driven by a constant-temperature heat source in the center of the enclosure. The time dependent governing equations in the primitive form are solved numerically by the use of a finite-volume method. The numerical algorithm is first validated by comparing our predictions with those of Kim and Viskanta for a square cavity surrounded by four conducting walls. A parametric study is then conducted to examine the effects of wall conduction on the natural convection heat transfer. The parameters include the Rayleigh number, wall thickness, wall thermal conductivity ratio and diffusivity ratio. In addition, the effects of varying thermal boundary conditions on the outside walls are reported. Results indicate that the qualitative features of natural convection heat transfer in the laminar range are not significantly altered by the inclusion of wall conduction. However, the quantitative results may be significantly modified by the wall conductance. In general, the wall conduction reduces the rate of heat dissipation from the enclosure. The average Nusselt number decreases as the wall thickness ratio is increased and/or the wall thermal conductivity is reduced. Results also indicate that it may be possible to define an effective Rayleigh number that includes the effects of wall thickness and conductivity.

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