Performance evaluation of horizontal straight tube equipped with twisted tape turbulator, with air–water two-phase flow as working fluid

Abstract

In this study, the effect of combination of twisted tape turbulator and air injection on heat transfer augmentation is studied. The air injection as the active method and the twisted tape turbulator as the passive method were used simultaneously to increase the heat transfer rate. The rate of air flow as like to pitch of twisted tape tabulator was considered as the variants. Six different air flow rates were considered in this study which provides a superficial gas Re number range of 147.07–882.30. Also the superficial liquid Re number had the range of 2400–6000. For the twisted tape, three different twisted tapes with twist ratio (λ) of 11.66, 6.66 and 5 were considered to check the effect of twist ratio on the thermo-hydraulic properties of the considered tube. A horizontal copper-made tube was considered as the test section which was under constant heat flux. In order to better understanding the flow structure, the flow structure was captured via a Canon SX540 camera. Flow patterns, heat transfer coefficient, pressure loss and C.B.R (cost per benefit ratio) were the variants that were probed in the present paper. It was found that the presence of the twisted tape turbulator could significantly affect the flow structure of the two-phase flow. The flow maps presented that by the decrement of twisted tape pitch the transition of slug flow to bubbly flow occurs very soon. Also, by the decrement of twisted pitch a swirling bubbly flow was observed in the horizontal tube. The maximum increment in the Nusselt number and pressure loss was about 35% and 81%, respectively. Also, it was revealed that for the water superficial Re number of more than 2400 with the decrement of pitch of twisted tape turbulator, the amount of C.B.R factor decreases.