CFD investigation of the impacts of variation in geometry of twisted tape on heat transfer and flow characteristics of water in tubes

In this research paper, the influence of variations in geometry of tape insert on thermal performance and flow characteristics of water inside tubes is investigated by means of computational fluid dynamics (CFD). The tape considered is alternate-axis triangular cut twisted tape. The perimeter of the cuts on the tape, the pitch of the tape and the width of the tape were varied. Turbulent flow is considered and uniform heat flux is imposed on the walls of the tubes. The RNG turbulence model is selected for the simulations and RANS equations are applied to render the Navier-Stokes equations tractable. The findings of the investigations indicated that the thermal performance of all the tubes fitted with twisted tape is better than that of the tube without twisted tape, and also that the performance is influenced by the geometry of the twisted tape. In particular, the thermal performance diminishes as the tape pitch increases but it is augmented by an increase in the size of the cuts on the tape and an increase in the width of the tape

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

Experimental&nbsp;heat transfer enhancement&nbsp;investigation is carried out by using various twisted tape inserted tube configurations under turbulent flow conditions.&nbsp;Constant heat flux&nbsp;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&nbsp;friction loss&nbsp;penalty than the DTTEs. Overall results are given as performance evaluation criteria and the highest&nbsp;PEC&nbsp;value is obtained as 1.57 for DTTE_p/y&nbsp;=&nbsp;0.25 type twisted tape insert used case at&nbsp;Reynolds number&nbsp;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.</p