The presence of nanoparticles in buoyancy-driven flows affects the thermophysical properties of the fluid and consequently alters the rate of heat transfer. The focus of this paper is to estimate the range of volume fractions that results in maximum thermal enhancement in buoyancy-driven nanofluids. In this study, a two-dimensional rectangular enclosure with isothermal vertical walls and adiabatic horizontal surface is filled with 27nm Al2O3 - H2O nanofluid. The volume fraction is varied between 0 to 12%. Results shows that for small volume fraction, 0.2≤Φ≤2%, the presence of the nanoparticles does not impede the free convective heat transfer, rather it augments the rate of heat transfer. However, for large volume fraction, Φ>2%, the convective heat transfer coefficient declines due to reduction in the Rayleigh number but the rate of thermal diffusion is enhanced.

1.
Nnanna, A. G. A., T. Fistrovich, J. Malinski, and S. U. S. Choi, 2004, “Thermal Transport Phenomena in Buoyancy-Driven Nanofluids, Part I,” Proceedings of the ASME Int. Mechanical Engineering Congress and Exposition, No IMECE 2004-62059
2.
Nnanna, A. G. A., Routhu Manohar, 2005, “Thermal Transport Phenomena in Buoyancy-Driven Nanofluids, Part II,” Proceedings of the ASME Summer Heat Transfer Conference, No SHTC 2005-72782
3.
Xue
Qing-Zhong
,
2003
, “
Model for Effective Thermal Conductivity of nanofluids
,”
Physics Letters A
, Vol.
307
, pp.
313
317
.
4.
Wang
X.
,
Xu
X.
, and
Choi
U. S.
,
1999
, “
Thermal Conductivity of Nanoparticle-Fluid mixture
,”
Journal of Thermophysics and Heat Transfer
, Vol.
13
, No.
4
, pp.
474
480
.
5.
Eastman
J. A.
,
Choi
U. S.
,
Li
S.
,
Soyez
G.
,
Thompson
L. J.
, and
Melfi
Di
,
1999
, “
Novel Thermal Properties of NanoStructured Materials
,”
Materials Science Forum
, Vol.
312–314
, pp.
629
634
.
6.
Xuan
Y.
,
Li
Q.
, and
Hu
W.
,
2003
, “
Aggregation Structure and thermal Conductivity of nanofluids
,”
AIChE Journal
, Vol.
49
, No.
4
, pp.
1038
1043
.
7.
Wang
Bu-Xuan
,
Zhou
Le-Ping
, and
Peng
Xiao-Feng
,
2003
, “
A Fractal Model for Predicting the Effective Thermal Conductivity of Liquid with Suspension of Nanoparticles
,”
International Journal of Heat and Mass Transfer
, Vol.
46
, pp.
2665
2672
.
8.
Masuda
H.
,
Ebata
A.
,
Teramae
K.
, and
Hishinuma
N.
,
1993
, “
Alteration of Thermal Conductivity and Viscosity of Liquid by Dispersing Ultra-Fine Particles (Dispersion γ-Al2O3, SiO2, and TiO2 Ultra-Fine Particles)
,”
Netsu Bussei (Japan)
, Vol.
7
, No.
4
, pp.
227
233
.
9.
Xuan
Y.
, and
Li
Q.
,
2000
, “
Heat Transfer Enhancement of Nanofluids
,”
International Journal of Heat and Fluid Flow
, Vol.
21
, pp.
58
64
.
10.
Pak
B. C.
, and
Cho
Y. I.
,
1998
, “
Hydrodynamic and Heat Transfer Study of dispersed Fluids with Submicron Metallic Oxide particles
,”
Experimental Heat Transfer
, Vol.
11
, No.
2
, pp.
151
170
.
11.
Khanafer K., Vafai K., and Lightstone M., 2003, “Buoyancy-Driven Heat Transfer Enhancement in a Two-Dimensional Enclosure Utilizing Nanofluids,” International Journal of Heat and Mass Transfer, pp. 1–15.
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