Enhancement of Heat Transfer rate by Using Twisted Tapes in Tube in Tube Heat Exchanger

Impact of the twisted tape insertion on heat transfer and flow friction characteristics in a concentric double pipe heat exchanger have been studied through experimentally. In the experiments, the swirling flow was introduced by using twisted tape placed inside the inner test tube of the heat exchanger with different twist ratios, y = 5.0 and 7.0. The experimental results revealed that the increase in heat transfer rate of the twisted-tape inserts is found to be strongly effect by tape-induced swirl or vortex motion. Experimentation are carried out in three phase. In first phase, the air flow through the smooth circular duct and heat transfer characteristics are observed. In second phase, a GI Sheet twisted tapes with twist ratio of 7.0 are inserted inside the circular duct and the changes in characteristics are observed. These changes are occurred due the destruction of flow behaviour. In third phase, instead of tapes with twist ratio 5.0 is inserted. Heat transfer rate and heat transfer coefficient of both types are also compared to without twisted tapes. Over the range investigated, the maximum Nusselt numbers for using the enhancement devices with y = 5.0 and 7.0 are higher than that for the plain tube. In addition, the effects of the twisted tape on the heat transfer enhancement are also investigated.