Water is heated from 15 to 65°C in a steam-heated horizontal 50-mm-ID tube. The steam temperature is 120°C. The average Reynolds number of the water is 45. The individual coefficient of the water is controlling. By what percentage would natural convection increase the total rate of heat transfer over that predicted for purely faminar flow? Compare your answer with the increase indicated in Example 12.4.

Example 12.4

Air at 1 atm pressure is passed through a horizontal 2-in. (51-mm) Schedule 40 steam-jacketed steel pipe at a velocity of 1.5 ft/s (0.457 m/s) and an inlet temperature of 68°F (20°C). The pipe wall temperature is 220°F (104.4°C). If the outlet air temperature is to be 188°F (86.7°C), how long must the heated section be?