Heat Transfer CONDUCTION HEAT TRANSFER Q k  A_lm DT Dr k 2  p   L r_o r_i ln r_o r_i T_o T_i r_o r_i (2-8) Q 2  p   k  L(DT) ln(r_o /r_i) where: L     =   length of pipe (ft) r_i =   inside pipe radius (ft) r_o =   outside pipe radius (ft) Example: A stainless steel pipe with a length of 35 ft has an inner diameter of 0.92 ft and an outer diameter of 1.08 ft.   The temperature of the inner surface of the pipe is 122^oF and the temperature of the outer surface is 118^oF.   The thermal conductivity of the stainless steel is 108 Btu/hr-ft-^oF. Calculate the heat transfer rate through the pipe. Calculate the heat flux at the outer surface of the pipe. Solution: Q 2  p   k  L  (T_h T_c) ln(r_o/r_i) 6.28 108 Btu hr   ft   °F (35  ft)  (122°F 118°F) _ln0.54  ft 0.46  ft 5.92  x  10^5Btu hr Rev. 0 Page 13 HT-02