Draw the thermal resistance network for this problem and write the equations for evaluating the conduction and convection resistances. Determine mathematically a relation for the critical radius racer by equating the total resistance.

This value is larger than the radius of the plastics cover, the critical radius of insulation of the plastic cover. Therefore, increasing the thickness of the plastics cover, will improve the transfer of the outer surface 6.25m.

Determine mathematically a relation for the critical radius RC by equating the total resistance dR_total/dr = 0.

d. Determine the critical radius of insulation r_acer from the graph and compare the result with the calculated value.

By the Graph we know that Q = 80