Page 361 - Process Modelling and Simulation With Finite Element Methods

348 Process Modelling and Simulation with Finite Element Methods

constraint on the inlet (bnd 1 of geom2). There is a coupled boundary constraint
of the Dirichlet type, which requires treatment with a weak boundary constraint.

Multiphysics AddEdit Modes
Select “Weak boundary constraint”
Mode WCC and variable name lmu>>
Apply/OK
Back in the FEMLAB GUI main window, select Boundary Mode and
Boundary Settings for mode wcl.
__s Boundary Mode and Boundary Settings (wcc)
Select domain 1, check active in this
subdomain, type ‘c’ into the constraint
variable entry box

Repeating the two solver steps - fast elliptic and time dependent - yields for
instance Figure 9.12, a cross plot at position x=OS for all times, clearly showing
the passage of a c=l slug being displaced by a c=O diffusive-convective front.

Concentration at position x=0.5

07

01- A

Time
Figure 9.12 Concentration at a fixed point x=0.5 in the outlet geometry over time

There are clearly many more variations on this theme that can be made.
Coupling variables and extended multiphysics enable the connections to be made
for entire microfluidic switching networks, if patiently constructed.
Electrokinetic microchannel flows have a rich texture of physicochemical
coupling for which this chapter has only touched the surface, hinting at the
power of control available through combined pressure and voltage application.