where M is the number of the tubes in the confined enclosure. In
the present paper, the lattice Boltzmann method (LBM) was
adopted. The LBM is based on microscopic models and macroscopic
kinetic equations for fluids. The kinetic nature of LBM enables it
very suitable for fluid systems involving microscopic interactions.
Recently, the LBM method has been developed to a stage that can
simulate successfully various heat and mass transfer problems with
complex configuration, multiphase fluids, and even turbulent fluids
[3]. The double distribution function LBGK D2Q9 model (Fig. 2) was
used to simulate the velocity and temperature, and the force term
treated in momentum equation was the same as in our previous
work. [4]
In order to have more information nearby the tubes and save
computer memory, a multi block method was employed. The fine
block area covers the two tubes while the coarse block surrounds
the fine block. The fine and coarse blocks have a common narrow
belt area covered by both blocks, where the two size blocks are for
information exchange. Therefore, there is at least one mesh of
coarse block that be covered by fine blocks. The details about the
multi block method can be referred to the work by Yu et al. [5] and
Filippova and Hänel [6]. The computational domain can be divided
into two or more blocks which are connected through an overlaying
mesh area. If the ratio of lattice space between the two blocks is
defined as m ¼ Dxc/Dxf.
The particle distribution functions for the coarse and fine mesh
after collision step are,