tubular furnace design

Jason

Want to simulate a resistively-heated furnace. Its outside is insulator and inside the a quartz tube. Need to find 1) furnace power, 2) insulator thickness, by meeting the requirement of 1) the required temp profile/level inside the tube; 2) the temp at the outside wall of insulator below certain value.

Questions how to set the boundary for the furnace, including 1) wall facing inside to tube 2) wall-shadow of above facing outside toward insulator 3) outside wall of insulator

or should I use two solid zones: one for heating element and one for insulator.

By the way, can I use a single wall (just a edge rather a face in meshing, i.e. no thickness in meshing) to represent a thin structure inside the reactor. Then use the wall thickness setting in boundary condition setting.

Thanks so much for your help.