ODESOLVE too few equations

Forum|Forum|12 years ago
March 31, 2014
2 replies
3376 views

Hi all,

This is my first post here on the PTC Community. I have a question regarding an ordinary differential equation solver.

I just simply do not understand why it can not solve the equations with the constraints provided.

I did not miss any initial conditions.

The document is about a membrane distiller, where the temperature is variable along the length of the membrane. The change of length is stated as x where the temperature becomes a function of x. Also the mass flow and flux will be a function of the length of the membrane since the mass flow at the seawater section loses mass that goes to the demiwater section.

The literature references for this problem are these:

https://www.dropbox.com/s/na4xr1ko7jgzvm2/Modelling%20heat%20and%20mass%20transfers%20in%20DCMD%20using%20compressible%20membranes.pdf

http://web.mit.edu/seawater/Seawater_Property_Tables.pdf

Can someone take a look at it? If you need more information, just ask me.

Thanks in advance, Rowan

1_MD-Still-mcdx.zip

Other

F

Fred_Kohlhepp

23-Emerald I

I think you're too complex!

You really have only three functions to solve: T_sw, T_dw, and phi. (phi_sw = -phi_dw, and H and J are combinations of the other three.

Try recasting the problem for those three, see how you do.

R

rguerrero

Author

1-Visitor

It do sounds like a problem where it would terminate the calculation. Though my second task is to plot the functions J_m(x), phi_sw(x), phi_dw(x), T_sw(x), T_dw(x), Psat_dw(T_dw(x)) and Psat_sw(T_sw(x)).

Would it still be possible to plot these since these are not solved in the odesolver?

After deleting the combinations out of the odesolver, it comes up with a new error:

"dae%_initial%_condition%_error"

If I rewrite the inital conditions of all functions like in the .mcdx file, but keep the odesolver like in the image above, the problem persists.

F

Fred_Kohlhepp

23-Emerald I

Took a closer look:

You have two functions Psw(T) and Pdw(T) that aren't defined, and you need them defined. You need to write your equations in T and phi, remove the J's and H's.