Question: a 1 kw commercial electric heating rod 8 mm in...
A 1 kW commercial electric heating rod, 8 mm in diameter and 0.3
m long, is to be used in a highly corrosive gaseous environment.
Therefore, it must be covered by a cylindrical sheath of fireclay.
The gas flows by at 120◦C, and h is 230 W/m2K outside the sheath.
The surface of the heating rod cannot exceed 800◦C. Determine the
maximum allowable sheath thickness and find the outer tem- perature
of the fireclay. (Hint: Use the heat flow and temperature boundary
conditions with thermal resistances in series.)