4.2-1. Mean Thermal Conductivity in a Cylinder. Prove that if the thermal conductivity varies linearly with temperature as in Eq. (4.1-11), the proper mean value km to use in the cylindrical equation is given by Eq.(4.23) as in a slab. 3) A 2.5-mm-diameter electrical wire at 60C is covered by 3 -mm-thick plastic insulation (k=0.17 W/mK). The wire is exposed to a medium at 50C, with a convection heat transfer coefficient of 22W/m2K. (a) Determine the rate of heat transfer ( 15 points). (b) Determine the heat transfer rate if the thickness of this plastic insulation doubles ( 10 points)