The preferred lengths of tubes for heat exchangers are: 6 ft. (1.83 m), 8 ft (2.44 m),12 ft (3.66 m), 16 ft (4.88 m) 20 ft (6.10 m), 24 ft (7.32 m). For a given surface area,the use of longer tubes will reduce the shell diameter; which will generally result in alower cost exchanger, particularly for high shell pressures. The optimum tube length toshell diameter will usually fall within the range of 5 to 10.Can someone please explain what the last sentence means exactly?? how can i use the tube length to estimate the shell diameter?
According to this rule you divide the tube length by the shell diameter and it should result should be between 5 and 10. Example: Using a tube lenght of 24 ft and a diameter of 3 feet, the result would be 24/3 = 8. That would satisfy this rule. This type of rule is good for getting started but you need to also take into account other factors such as desired fluid velocities and pressure drop to make a final design. Likewise a very high pressure shell side requirement would normally drive you to a small diameter to reduce the wall thickness of the shell. A water cooled exchanger for a high pressure process is a example of this type of application. You want the water on the tube side for cleaning purposes and you want to keep the water velocity in a certain range.
