Oil at 158C is to be heated by saturated steam at 1 atm in a double-pipe heat exchanger to a temperature of 258C. cen98187_ch08_p473-532.indd 530 17/02/14 9:57 AM 531 CHAPTER 8 The inner and outer diameters of the annular space are 3 cm and 5 cm, respectively, and oil enters with a mean velocity of 0.8 m/s. The inner tube may be assumed to be isothermal at 1008C, and the outer tube is well insulated. Assuming fully developed flow for oil, determine the tube length required to heat the oil to the indicated temperature. In reality, will you need a shorter or longer tube