Page 169 - Process Modelling and Simulation With Finite Element Methods

156 Process Modelling and Simulation with Finite Element Methods

the Boundary menu and select boundary settings

Boundary Mode
0 Set up boundary 1 Dirichlet h=l; r=l; (fixed cl=l)
Set up bnd 2,3,5,6,7 Neumann q=O; g=O
0
Apply/OK
Now pull down the Subdomain menu and select Subdomain settings.

Subdomain Mode
Select domains 1&2
Use the multiphysics pull down menu to select the IC NS mode
Use the Init Tab to set up u(tO)=tanku(x,y); v(tO)=tankv(x,y);
p(tO)=tankp(x,y 1
Apply/OK
Select cl mode
Set coefficients c=l;a=O;f=O;da=l;a=(O,O);~=(u,v),~(O,O)

Now choose the stationary nonlinear solver and click on the solve button. Do
not be surprised to find rapid convergence to a uniform concentration field and
the same flow field as in Figure 4.1 1.

Component 3: Buoyancy effects of solutal mass transport
Save the FEMLAB model as tank-nscl.mat. Now pull down the Subdomain
menu and select Subdomain settings.

Subdomain Mode (ns)
Select domains 1&2
0 Set Fy=-0.25*cl (Rayleigh number Ra=25)
Apply/OK
Now choose the stationary nonlinear solver and click on the solve button.
Again, do not be surprised that the steady state is a uniform profile, again with
the driven cavity velocity field. Next try the time dependent solver with output
times 0:O.l: 1 .O. The final concentration profile (Figure 4.13) just shows
continual spreading of the concentration front, but no hint of a stratification
forming (see Figure 4.12). The animation of the time series for the velocity
vectors is suitably unenlightening - visually it never changes from the driven
cavity vector field of Figure 4.1 1.