Study on shell side heat transport enhancement of double tube heat exchangers by twisted oval tubes

The shell side heat transport enhancement characteristics of double tube heat exchangers composed of twisted oval tubes alone and twisted oval tubes coupled with circular tubes is investigated numerically in the range of Reynolds number from 2700 to 22,000. The effects of the aspect ratio, twist pitch length, twisting direction and ratio of inner tube diameter to outer tube diameter on shell side convection heat transfer and hydraulic resistance performance are also explored. The rotational motions caused by the twisted oval tubes realize the occurrence of secondary flow and spiral flow which destroys the boundary layer and intensifies the shell side heat transport of double tube heat exchangers composed of twisted oval tubes. Simultaneously reducing the twist pitch length and increasing the inner tube aspect ratio can significantly improve the shell side comprehensive heat transport performance. Case 10 with the largest inner tube aspect ratio and the smallest twist pitch length shows the highest comprehensive heat transport performance. The comprehensive heat transport performance can be increased by 24.0- 39.0% by the application of twisted oval tubes as inner tubes. The leftward and rightward twisting directions of inner twisted oval tubes have the same effect on the shell side heat transport intensification.