Results and discussion
As the simulations are carried out
using numerical methods a convergence study is carried out to ascertain
the accuracy of the solution using four different meshes. The number of
grid elements in each of these meshes are 679, 1005, 1494 and 2212
corresponding to uniform grid sizes 18, 15, 12 and 10 mm respectively.
The simulations are carried out without application of EMS. The
temperature at 800 mm below the meniscus and 20 mm from the left wall is
taken as the parameter to check grid convergence. A plot (Figure 3) is
drawn with these temperatures against grid sizes for all these meshes
and it is almost flat in x-direction. Hence, it can be concluded that
grid convergence has been achieved with grid size 10 mm and this has
been used in all subsequent simulations.
[CHART]
Figure
3. Grid convergence
Further simulations are carried out by placing EMS as per the specified
positions to obtain the histories of velocity and liquid fraction of the
liquid metal solidifying in the mold.
The contours of magnitude of velocity along the length of the mold
without EMS and with different positions H- EMS and V-EMS are shown in
Figure 6 and Figure 7 respectively. The vectors indicate that the fluid
flow velocity is maximum at the location of EMS, in its respective
directions of application. The fluid is dispersed to form recirculation
loops above and below at the position of EMS at centre of the mold due
to the stirring effect. As the position of the EMS is lowered the
thickness of loops increases but is more confined to the center of the
mold. It is observed that the recirculation loops formed are more
defined for all the positions of the V-EMS. The decrease of thickness of
the loops and its confinement to the center because of lowering of EMS
position is not as significant as H-EMS. The maximum values of velocity
magnitude for H-EMS and V-EMS are given in the Table 2.