Comments on ‘Lattice Boltzmann simulation of alumina-water nanofluid in a square cavity’ by Yurong He, Cong Qi, Yanwei Hu, Bin Qin, Fengchen Li and Yulong Ding
Nanoscale Research Letters
Comments on 'Lattice Boltzmann simulation of alumina-water nanofluid in a square cavity' by Yurong He, Cong Qi, Yanwei Hu, Bin Qin, Fengchen Li and Yulong Ding
Nor Azwadi Che Sidik 0
Arman Safdari 0
0 Faculty of Mechanical Engineering , Universiti Teknologi Malaysia, UTM Skudai, Johor 81310 , Malaysia
This work presents some comments concerning the paper entitled 'Lattice Boltzmann simulation of alumina-water nanofluid in a square cavity' by Yurong He, Cong Qi, Yanwei Hu, Bin Qin, Fengchen Li and Yulong Ding which was published in Nanoscale Research Letters in 2011. The comments are related to the numerical parameters and the computed results of average Nusselt number.
Lattice Boltzmann; Nanofluid; Volume fraction; Nusselt number
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Background
The authors of ‘Lattice Boltzmann simulation of
alumina-water nanofluid in a square cavity’ [1] have used
the conventional lattice Boltzmann scheme to analyse
the heat transfer and flow characteristics of Al2O3-water
nanofluid in a square cavity. They described the
numerical methodology which implemented the
doublepopulation lattice Boltzmann scheme to predict both
flow and thermal fields. In this paper, few comments on
the numerical parameters and the computed results will
be highlighted, followed by a conclusion and list of
references.
Numerical parameter
The authors have carried out a grid independence test
using three grid sizes of 1922, 2562 and 3002 to predict
the average Nusselt number at Ra = 8 × 105 and 0% of
volume fraction (page 5 of 8). The authors have chosen
the 2562 grid size and claimed that this grid size gave a
grid-independent solution. Since 0% of the volume
fraction has been chosen, the condition can be referred as
natural convection of pure water in an enclosure [2-5].
However, the rest of the predictions involved a more
critical condition, such as the Rayleigh number being
greater than 106 with a 5% of volume fraction of Al2O3.
Thus, it is extremely difficult to rely on the grid size that
resulted from the grid independence test at such mild
condition. In addition, the obtained average Nusselt
number at a grid size of 2562 deviates about 4.5% from
the benchmark results. Therefore, it can be concluded
that this grid size is not suitable and can lead to wrong
results as will be discussed in the ‘Numerical results’
section.
Numerical results
The authors have stated that as the volume fraction is
increased, the fluid becomes more viscous and the
velocity of the flow in the enclosure decreases (page 7 of 8).
At this point, the authors ignored the fact that the
presence of nanoparticles stimulates the flow that resulted
from high-energy transport through the flow associated
with the irregular motion of nanoparticles [6-8]. This
behaviour leads the thermal boundary layer to become
thinner and the Nusselt number to increase [9]. Even
though the authors have claimed that the Nusselt
number decreases as the volume fraction increases, which
was demonstrated in figure six of the said article, their
results however are still questionable since they have
been computed using inappropriate grid sizes.
Discussion
The present commentary aimed at providing an
indepth discussion on the numerical methodology
described in the work of He et al. [1]. The contribution
of the present work is in correcting a number of
mistakes made in an attempt to predict the heat and flow
characteristics of nanofluids in enclosure.
Conclusion
We recommend that the authors perform code
validation by comparing with the well-known benchmark
solution. We also suggest that the authors conduct a grid
independence test on the most critical condition of their
research case in order to comprehend the effect of grid
size on the numerical solution.
Acknowledgments
This research is financially supported by the Ministry of Higher Education of
Malaysia through Fundamental Research Grant Scheme, FRGS Vot no. 4F114.
1. He Y , Qi C , Hu Y , Qin B , Li F , Ding Y : Lattice Boltzmann simulation of alumina-water nanofluid in a square cavity . Nanoscale Res Lett 2011 , 6 : 184 - 191 .
2. Munir FA , Nor Azwadi NAC , Ibrahim NIN : Numerical simulation of natural convection in inclined square cavity . J Appl Sci 2011 , 11 : 373 - 378 .
3. Fakhreddine SO , Rachid B : Heterogeneous nanofluids: natural convection heat transfer enhancement . Nanoscale Res Lett 2011 , 6 : 222 - 232 .
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8. Saeed ZH , Seyyed H (...truncated)