Thank You for your reply. I see that this book is available at both Amazon.Com and Barnes & Noble on the Internet. I have just receicved my copy of "Heat Transfer Calculations by Finite Differences" by G.M. Dusinberrre and using this book with the "Heat Transfer Handbook" by Roshenow et al, I think I can set up a spread sheet to do the calculations I need to do. The trick is in using a common time element as the materials change and varying the material thickness element for the different materials as a ration of the different material diffusivies. The book you recommended sounds like a good one to have in your library though. <br>Also, in circular coordinates with only radial variation, to use an arc angle of 1 radian. This makes the problem set up very easy.<br>Thanks Again<br><br>Don<br><A HREF="mailto:dleffingwell@snet.net">dleffingwell@snet.net</A>