Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Numerical Simulat ion of Nano Particles in a Fluidize d Bed
Afsin Gungor 1 *
1 Department of Mechanical Engineering, Nigde University, Nigde 51245, Turkey
Abstract-In this study, two dimensional numerical model is developed to simulate the hydrodynamic characteristics of nano particles such as the
solids fraction and bed pressure drop in a fluidized bed. The model results are compared with and validated against experimental data given in
the literature for the solids fraction in the bubble phase and emulsion phase, and for bed pressure drop as a function of superficial velocity.
Nano-particles of 1–100 nm in diameter provide unique
physical and chemical properties in numerous applications.
The processing and handling of the nano-particles are very
important in the applications. In this respect, the fluidization
of the nano-particles to provide good gas and solids mixing,
high mass and heat transfer efficiency, and continuous
processing, can make a process more efficient [1]. The
fluidization characteristics of nano-particles were investigated
by many scholars [2-4] from various aspects. According to
Geldart's classification [1], nano-particles are categorized in
Group C which is a category of particles that is hard to
fluidize due to strong cohesiveness or inter-particle forces.
However, many researchers [3-6] have found that a variety of
nano-particles displayed good fluidization similar to Group A
particles. Until now, two types of nano-particle fluidization,
termed agglomerate particulate fluidization (APF) and
agglomerate bubbling fluidization (ABF) [4, 6], have been
reported. Many researchers are attracted by the surprisingly
smooth and uniform fluidization characteristics of APF [3, 5,
6]. Wang et al. [5] reported the multi-staged agglomerate
(MSA) of some nano-powders and revealed that the formation
of a MSA structure is the key issue for good fluidization. The
formation of a MSA structure leads to the resulting significant
characteristics of these nano-powders, namely, extremely
loose structure and low density of the agglomerates, which
reduces the interparticle forces sharply. The reduction in the
inter-particle forces plays a crucial role in changing the
fluidization performance of the particles [7].
As nano-technology has brought about a new realm into
chemical engineering, a natural question arises: besides the
unique technologies and processes developed on nano-scales,
whether or not the legacy of our traditional engineering
practices could still be preserved or extended by miniaturizing
the macro-scale equipment and processes. Considering the
difficulties in conducting microscopic experiments and/or
measurements, proper simulation methods may well serve as
convenient and effective tools in seeking such possibilit ies [1].
From this point of view, in this study, two dimensional
numerical model is developed to simulate the hydrodynamic
characteristics of nano particles such as the solids fraction and
bed pressure drop in a fluidized bed. The model results are
compared with experimental data given in the literature for the
solids fraction in the bubble phase and emulsion phase, and for
bed pressure drop as a function of superficial velocity.
In the first step, simulation results are compared with
experimental results obtained from test unit (transparent
polymethylmethacrylate) of 5 cm in diameter and 1 m in
height for bed pressure drop as a function of superficial
velocity [8]. The particles are Aerosil R974 hydrophobic
silica. The primary particle size and particle density of the
powder were 12 nm and 2200 kg/m 3 respectively, with a bulk
density of 30 kg/m 3 .
In the second step, simulation results are compared with
experimental results obtained from test unit (transparent
polymethylmethacrylate) of 28 cm in diameter and 2 m in
height for the solids fraction in the bubble phase and emulsion
phase [7]. The particles are R972, a co mmon synthetic silicon
dioxide. The average primary particle size is 16 nm, the
particles have a primary density of 2560 kg/m
3 , but the bulk
density is unusually low and is 31.85 kg/m 3 . The fluidization
experiments are carried out at room temperature and ambient
pressure.
Pressure drop/Bed weight
per unit area (-)
0.9
0.6
0.3
Experiment
Model prediction
0
0 0.4 0.8 1.2 1.6 2
Superficial velocity (cm/s)
Figure 1. Comparison of model pressure drop predictions [8]
As shown in Figure 1, bed pressure drop increases with
superficial velocity. On the other hand, with the increase of
gas velocity, the pressure drop curves do not show a plateau as
a general coarse particle (either Group B or A) bed does.
Model pressure drop predictions are in good agreement with
experimental data [8].
The existence of a bubble phase and emulsion phase and the
difference in properties between the two phases such as the
solids fraction lead to the spatial inhomogeneity in the
bubbling and turbulent fluidization regimes. However, as a
result of this study, the fluidization in the NAFB is more
homogeneous not only on the scale of the macroscopic
phenomena but also on the scale of the micro-phase structure.
*Corresponding author: 1Tafsingungor@hotmail.com
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[2] D. Geldart, Powder Technol., 7, 285 (1973).
[3] W. Zhaolin, M. Kwauk and L. Hongzhong, Chem. Eng. Sci., 53
(3) 377 (1998).
[4] A.W. Pacek and A.W. Nienow, Powder Technol., 60, 145 (1990).
[5] Y.Wang, G.S. Gu, F.Wei and J.Wu, Powder Technol., 124, 152
(2002).
[6] C. Zhu, Q. Yu, R.N. Dave and R. Pfeffer, AIChE J., 51, 426
(2005).
[7] C. Huang, Y. Wang and F. Wei, Powder Technol., 182, 334
(2008).
[8] X.S. Wang, V. Palero, J. Soria and M.J. Rhodes, Chem. Eng. Sci.,
61, 5476 (2006).
6th Nanoscience and Nanotechnology Conference, zmir, 2010 318