rkfixed help very much needed

[Burnzy]

Hello all,

I am currently working on a project that involves heavy use of Mathcad and I am quite the Mathcad newbie. For context, I am trying to find 6 unknown temperatures that are involved in various radiation and convection equations. I feel I am just about done but getting rkfixed to work is causing me such strife. It says " D cannot be used here" when trying to use the rkfixed function and I have made so many changes but none seem to work. Attached is my problem, the rkfixed is at the very bottom. The excel attachment is necessary to run the program as well. Help would be very much appreciated.

Sincerely,

Mathcad Newbie

[LucMeekes]

Is there any potential that this is related to:

https://community.ptc.com/t5/PTC-Mathcad-Questions/Rkfixed-Solver/td-p/491245

?

Luc

[Burnzy]

Ah yes, that must be one of my peers. It appears we have the same issue and doing what you suggested in his post resulted in the same outcome of equal results.

[LucMeekes]

I'm limited to Express, which means I can't evaluate everything. (Symbolics and programming does not work, also rkfixed() is off limits for me). But I have one observation to start with:

Your function Nu(t) leaves one condition unaccounted for, when Re.h(t)>10^7.

It may help to define the outcome for  that situation.

Success!
Luc

[Burnzy]

Thanks for the assistance, sadly that did not help. I feel I'm on the verge of cracking the code soon though.