Effect of curved and reverse curved cross sectional twisted tapes on heat transfer enhancement

Present study investigated the effects of the curved and reverse curved cross sectional twisted tapes on heat transfer enhancement in a circular pipe by means at computational fluid dynamics at Reynolds numbers ranging from 5800 to 31000. Twelve different geometries such as three curved and three reverse curved twisted tapes with two different twist ratios (3 and 4) were analysed. The diameter ratios of curved tape to pipe were changed as 1.761, 2.252, and 3.271. The diameter ratios of reverse curved tape to pipe were changed as 0.554, 0.647 and 0.872. The changes of the heat transfer, friction, and performance evaluation criteria were found out. Several concluding remarks are evaluated for the curved cross sectional twisted tapes. The Nusselt numbers are higher than the smooth pipe approximately in the region of 31 to 89 % for all curved twisted types. The highest Nusselt number is obtained at the highest Re for was around 112 and obtained from the C1TR3 model, which has the highest curve ratio and the lowest twist ratio. The maximum friction factor is obtained around 0.11 at lowest twisted ratio and Re. The curve ratio effect on friction is negligible. The friction factors are higher than the smooth pipe approximately 122 to 206%. The maximum performance evaluation factor is calculated around 1.3 at Reynolds number 5800 for C1TR3 and C1TR4 cases due to the best mixing and high swirl. Better performance evaluation factors are observed in the lower Reynolds number. Some of the important conclusions are evaluated for reverse curved cross sectional twisted tapes. The highest Nusselt number is calculated the lowest twist ratio and the highest curve ratio for the case R1TR3. The Nusselt number is higher than the smooth pipe approximately 0 to 85 %. The curve diameter is the less effective than twist ratio on the friction factor. The friction factor of reverse curved cross sectional twisted tapes is higher than the smooth pipe in the region of 124 to 238 %. The maximum value of PEC for the reverse curved cross sectional twisted tape is calculated around 1.22 at Reynolds number 5849 for R1TR3 and R1TR4.