Discussion Forum

Hello All,

I am trying to simulate a dialysis with recirculation of both dialysate and permeate. In order to do that, I started with the dialysis example that the Comsol provides us.
I made some minor changes that I am going to explain. First I introduced a model coupling in the outlet of the dialysate and the permeate. I did that with the Average operater. Then I defined the concentration in the inflow of the dialysate and permeate as the average concentration in the respective outlets using the mensioned Averaged operater.
Next I did some stationary studies changing some parameters and I realized that a small change in the particional coefficient ''K'' has a drastic effect in the concentrations at the stationary state. I don't think this should be the case, because the total mass of contaminant should be constant, since I am recirculating everything. But when I decrease the value of K, the concentration in the dialysate, the permeate and inside the membrane decreases.
I also tryed to use the Boudary Similarity operater. The concentrations in the stationary state got lightly different compared with the first operater and the drastic effect of changing the value of K was still present.

Finnaly my questions are:
Why does the concentration in the stationary state is different with different model coupling?
What is the better model compling to use in this case?
And why does the particion coefficient have this big effect?
The mass conservation of the contaminant should not be expected?

You can find attached the simulation with the changes I made.

Thank you in advance and any help will be very appreciated.
Ricardo