Saturated propane gas at 305 K is pumped to a tank at 5 m/s through a cast iron of 5 cm diameter and 10 m length. The pipe's surface is exposed to air at 280 K. Tip: The pipe is not smooth. a. Find the convective heat transfer coefficient. b. If 35,000 W of energy is required to be dissipated along its length, what must be the length of the pipe?