a small doubt with the 'patching method'
 

Hello.

I´ve been working in the cooling of an iron cube in a molten salt bath, and by advice from someone here, I used the patching method to put the two volumes at different temperatures.

The problem is that the two volumes don´t interact at all if I don´t specify boundary conditions (which I don´t want to impose to see how the cooling develops). So, am I doing something wrong, or it can´t be done without specifying boundary conditions?

Thanks in advandce