Numerical study on heat transfer enhancement through a circular duct fitted with centre-trimmed twisted tape

Abstract

Twisted tape is a widely used technique for heat transfer enhancement. In the present study, the influences of centre-trimmed twisted tapes (CTTT) on heat transfer rate, friction factor and thermal enhancement efficiency were numerically investigated. The centre-trimmed twisted tapes were used as swirl flow generators inside the circular duct. Investigations were performed in the Reynolds number range of 100 - 5,000 with four different centre-cleared twin twisted tapes at twist ratio (TR) of H/W = 1.0, 2.0, 3.0 and 4.0. The governing equations are solved with a finite-volume-based numerical method. A three-dimensional non uniform grid was generated, in order to critically examine the flow and heat transfer. Results show that the centre-cleared twin twisted tape causes considerable enhancement of heat transfer when compared with plain twisted tape (TT). The enhancement over standard twisted tape increases with the increase of Reynolds number. The improved parameter is observed in the range of Reynolds number below 800 and also above Re 4000 for all TR, though the best performance is found at TR = 1.0 and 3.0