Exercise -1 

Consider the design of a cylindrical electric resistance furnace. The heating coil should have maximum temperature at steady state when the power supply is 750 watts. The outer diameter of a ceramic tube on which heating coil is to be wound is 0.08m. The insulation is fireclay inside and asbestos magnesia outside. Asbestos- magnesia can sustain a maximum temperature of  .Determine the thickness of the two insulation layers when the total insulation thickness is minimum. Length of furnace is 0.7m.
Given: outer shell temperature    and . Assumeof total power is lost from both ends.