Air at 10°c enters a 12-cm-diameter and 5-m-long pipe at a rate of 0.065 kg/s. the inner surface of the pipe has a roughness of 0.22 mm, and the pipe is nearly isothermal at 50°c. determine the rate of heat transfer to air using the nusselt number relation given by (a) eq. 8–66 and (b) eq. 8–71. evaluate air properties at a bulk mean temperature of 20°c. is this a good assumption?