Thermohydraulic performance of twisted circular tube (TCT) retrofitted with twisted strip (TS) insert

Augmentation of heat transfer plays a crucial role in energy-saving options in modern thermal systems. These enhancement methods are passive with no external power source, and another is an active method where an external energy source is essential. The passive methods are more popular and the best energy-saving option, making the system more effective and efficient. The recent advancement in passive methods is a compound method consisting of alterations in the fluid containers and obstructions in fluid passages. In the prevailing study, the round tube is formed in the profile of a twisted tube, within which a twisted strip is placed. The twisted tube causes a reduction in the temperature and velocity gradients near the tube surface due to the twisting motion of the fluid at that region, whereas the central core portion of the fluid interacts thoroughly with the heated surface due to the presence of the twisted strip at the central portion of the twisted tube. This modified flow system enhanced heat transfer using air as a fluid in turbulent flow circumstances for Reynolds numbers ranging from 2500 to 17000. The present study indicates that the average improvement ratio, Nu_e/Nu_p, and average friction factor ratio, f_e/f_p, are 1.25–3.9 and 2.0–12.0, respectively, compared with the plain tube at the same flow rate conditions.