Consider heat transfer from an insulated copper pipe carrying hot water, at Tw=60 C, to the surrounding air at Tair 20 C. The dimensions of the pipe are: ID=25 mm. OD = 28 mm. The ID of the insulation is 28 mm; OD = 38 mm. The thermal conductivity of the insulation is k_ins-0.1 W/m-K. The heat transfer coefficients are given: h_w=600 W/m2-K and k_air- 12 W/m2-K. Ignore radiation heat transfer. Calculate the rate of heat transfer per m. a) Model the insulation as a plate having thickness 8 =(OD-ID)/2 = 38-28)/2 = 5 mm. This approach will provide a simple approximate solution. b) Using cylindrical geometry. The cylindrical resistance of insulation is Reyt = In(r/r) 2mLk In(Outer radius/Inner radius) 2X (Length) x (Thermal conductivity) (3-39)