A Bakelite coating is to be used with a 10-mm-diameter conducting rod, whose surface is maintained at 200°C by passage of an electrical current. The rod is in a fluid at 25°C, and the convection coefficient is 140 W/m2 ∙ K. What is the critical radius associated with the coating? What is the heat transfer rate per unit length for the bare rod and for the rod with a coating of Bakelite that corresponds to the critical radius? How much Bakelite should be added to reduce the heat transfer associated with the bare rod by 25%?