The experimental thermal and hydraulic performance analyses for the location of perforations and dimples on the twisted tapes in twisted tape inserted tube

Experimental heat transfer enhancement investigation is carried out by using various twisted tape inserted tube configurations under turbulent flow conditions. Constant heat flux is applied on the outer wall of the test tube. The working fluid is selected as water. The twisted tapes having twist ratio (y/w) of 5.88 are modified with perforations (PTTE) and dimples (DTTE) at the edge of the twisted tape. The ratio of the distances between the perforations/dimples (p) to the twist length (y), i.e. pitch ratio (p/y), are selected as 0.25, 0.50 and 1.00. The results show that using twisted tapes lead to increase thermal performance when compared to the smooth tube. The DTTEs promise more heat transfer performance rather than the PTTEs, while the PTTEs gives less friction loss penalty than the DTTEs. Overall results are given as performance evaluation criteria and the highest PEC value is obtained as 1.57 for DTTE_p/y = 0.25 type twisted tape insert used case at Reynolds number of 6367. In addition, the paper includes a comparative evaluation in terms of the heat transfer and the hydraulic performance about the perforations/dimples at the edge or centre of the twisted tape.