Dialysis machine simulation

[Amr95]

Hi everyone,

I am trying to simulate a part of dialysis machine flow diagram. The idea of the program is to have the dialysate flow rate and the electrical conductivity of the flowrates as controllers and based on the values of the electrical conductivity and the dialysate flowrate, the values of the flowrates of the concentrates forming the dialysate flowrate should change and as a a result the rotational speed of the pumps should be changed.
My problem here is that all parameters are depending on each other, so if I want to enter a value for the dialysate flowrate, it should change the flowrates of the concentrates and water, subsquently the conductivity and the rotational speed of the pumps AND if I change the value of the electrical conductivity it would change all the other parameters. So how could I implement that in the program? I thought about using the case structures and make the value of the dialysate flowrate the controller and the value of the conductivity the indicator in once case and in the other case I do the opposite.
I would be thankful for your tips. I added a pdf of a sketch I made to make it easier for you to follow my words 

[Bob_Schor]

Here are some undefined terms: 

• Concentrate 1, Concentrate 2, Dialysate.  What, precisely, are these?  Are the items in C1 identical (but different concentrations) to C2 and to D?
• Are the two Conductivity Sensors measuring the same thing?  [It goes to the question is C1 = C2, except for concentration].
• Can we assume (as seems reasonable) that the mixing chamber is perfect, and that solvent in incompressible?  This means that the flow (of solution) out = Flow 1 + Flow 2.
• How is "Dialysate Flow Rate" determined?  Why is it not "Flow 1 + Flow 2"?  [I assume the modifier "Dialysate" has some hidden meaning.

Bob Schor

[Amr95]

Concentrate 1 is a bicarbonate solution that gets mixed with water in a mixing chamber and then with conductivity sensor the conductivity of the water+bicarbonate solution is measured and then the concentrate 2 " acid concentrate" is added to water+bicarbonate solution and another conductivity sensor is going to measure the conductivity of the Dialysate " Dialysate= water+concentrate1+concentrate 2". 
The flowrate of water, C1 and C2 have certain proportions and the sum of the flowrates of those 3 other solutions gives us the flowrate of the Dialysate.

so let's say that D = 30%water+ 60%C1+ 10%C2.

I have technical data of how the values of the electrical conductivity and dialysate flowrate should be or in which range of values they should be. So the way I am doing my program is that I just take reference values from those technical data and try to get a relationship between the different values. So I know that the pump has a volume of 220microliter and a flowrate calculated from the above formulae "D = 30%water+ 60%C1+ 10%C2

" so I just calculated the rotational speed manually and then saw what is percentage of the rotational speed from the conductivity value and then made it a fixed relation. So for example the rotational speed is 40% from the value of the conductivity.
so that's how I thought about implementing this part of the machine in Labview, by just doing relationships between the different parameters. But as I said all parameters are depending on each other and I cannot see how I could have the conductivity and the Dialysate flowrate as controls in the same program unless I made different cases using the case structures. But I am not sure if that's the best way to do it.
I added the program with what I did so far but the program is not doing what I want as the flowrates of the other concentrates doesn't change when I change the Dialysate flowrate( I know why but I can't find a solution) and all the parameters are determined by the values I set for the conductivity.

[Bob_Schor]

This is still confusing, incomplete, and "wrong" (or at least not consistent with the picture you showed of the process).

• You now have 3 components, not two, being mixed:  water (amount not specified), bicarbonate solution (C1), and "acid" solution (C2).  Is there another pump, W (for Water)?
• In describing the pump, you mention its volume, which seems (to me) to be irrelevant for this problem.
• The role of the sensors is unclear, as they have no effect (apparently) on the "rate of dialysate".  Of course, they play a critical role on the composition of the dialysate. 
• Your figure shows pumps C1 and C2 operating "in parallel", so the total flowrate is simply their sum.  If there's a third pump, W, also in parallel, then the flow rate is C1 + C2 + W.

I'm tempted to stop commenting here, as either "I just don't get it", or "You just don't understand what you are doing, and I'm just getting in the way, trying to help".  I don't think your real problem is LabVIEW, but being able to clearly formulate the question you want to solve by making a software "model" so that you can ... make a software "model" that has some relevance to the physical world.

If this is part of a class (as seems likely), I recommend you contact your instructor and discuss this with her or him -- they are most likely to set you on a more productive track.

Bob Schor