Heat transfer in the transitional flow regime inside smooth tubes with twisted tape inserts

Abstract

A higher heat transfer at relatively low energy cost in heat exchangers used in various engineering applications is essential towards achieving sustainable energy management in the industries. This is achievable by enhancing and operating heat exchangers in the transitional flow regime as compared with the laminar flow regime. The Nusselt number results of an experimental investigation on transition in a smooth tube equipped with twisted tape insert of twist ratio 5 are presented in this study. This experiment was performed under a constant heat flux boundary condition of 2 kW⁄m2, using water as working fluid over a range of 500 ≤ Re ≤ 11 000 and 3.9 ≤ Pr ≤ 6.7. In the enhanced tube transition from laminar to turbulent occurred at a range of Reynolds numbers of 750 to 2 082, while the transition in smooth tube commenced and ended at a Reynolds number of 2 700 and 3 187 respectively. The commencement of the transitional flow regime inside the tube with twisted tape insert was observed to be earlier as compared with smooth tube counterpart. The heat transfer coefficients with twisted tape insert tube are also higher than the one in smooth tube in the all the flow regimes. This investigation makes data available for both designers and researchers of heat exchangers. Particularly in the transitional flow regime, the heat transfer results are higher at low Reynolds numbers. This increase is very useful in the industries where higher heat transfer through heat exchangers at low energy consumption and cost are required.