Possible to use solver to break excel model?

So i'm trying to break a model of a PDE (heat conduction across a steel bar) and wondered if I could break the model. The model starts to become unstable when a value (lambda) becomes greater than 0.5. The value of lambda depends both on delta(x) and delta(t). Now I know I can use solver to find a nominal value of either delta(x) or delta(t) that will satisfy the value of lambda being 0.5 but my question is "is there a way to find where a function of delta(x) and delta(t) that takes lambda over 0.5 but also to find the exact value where it starts to produce negative values in the cells that contain the temperature of the steel bar at given values of delta(x) and delta(t)

Didn't really know how to word that well, so i've naturally attached a copy of the file.

Have you tested solver? Because when I did test the model set up on sheet1 solver told me "The problem is to large for solver to handle" so the excel version is not up to this.

The alternative is to download the free trial version from "FrontlineSolvers" the makers of solver.

http://www.solver.com/

this will give you a testing periode of 15 days of their most advanced models.

Alf

Yeah, same thing when I ran it. I'm on Mac and the solver Pro has been discontinued I believe so I might just need to try it on Windows when I get a chance, thanks for your help.

You are welcome.

Alf