After reading some more literature it turns out that the interface conductance should be sorted out by the simulation by just including the two conductivities and allowing the heat flow between them. However, I am getting a lineseach failure again. When I use a smaller file size mesh my code works however when a larger mesh is used i get the linesearch failure.
The code which works is the single_vol. The redefined_vol file is exactly the same but with the mesh filename changed.
http://www.mediafire.com/file/9suv03rt4odr870/single_vol.mesh/file http://www.mediafire.com/file/bkmi2hw4uugqeoa/single_vol.py/file http://www.mediafire.com/file/3n1tna5nn1n6gre/redefined_vol.py/file http://www.mediafire.com/file/jmdu6j6jwek0had/redefined_vol.mesh/file