ODE Temperature profile solution

[ptc-3948107]

I've having a bit of a problem using the rkfixed function (have tried Rkadapt and Odesolve and results in the same problem).

The ODE describes the temperature profile in a length of pipe cooling from the feed temperature to an ambient temperature. However, the rkfixed solution results in an unexpected exponential growth curve.

Luckily the function can actually be integrated by hand, plotting this gives the expected exponential decay.

Graph in the attached file shows the rkfixed result as T and the analytical solution as Tb.

Thanks

Cameron

[Fred_Kohlhepp · Accepted solution]

You've got your subtraction backwards.

[ptc-3948107]

Now that was kinda obvious. Although it does now raise more questions and doubt about the accuracy of the equation's source (published article).

Thanks

Cameron