Numerical and Experimental Studies on Heat Transfer Enhancement in a Circular Tube Inserted with Twisted Tape Inserts

Abstract

Numerical simulations and experiments are carried out in this paper to research about characteristics of heat transfer, frictional resistance and comprehensive performance of turbulent water flow (3000<Re<10,000) in a circular tube with twisted tape inserts. A new type of twisted tape is proposed and it shows excellent performance on heat transfer enhancement. Effects of three parameters including twist ratio (p/w=3, 4, 5), geometrical structure of alternation of clockwise and counterclockwise, existence of semicircular cuts are researched in simulations. The results show that lower twist ratio and the geometrical structure of alternation of clockwise and counterclockwise can enhance heat transfer while the existence of semicircular cuts can significantly reduce flow resistance. Experiments are conducted to validate the actual effect of the twisted tapes and the experimental results are basically consistent with the simulation results. Nusselt number and friction factor with the new type of twisted tape inserts are respectively 1.66-2.42 times and 4.36-4.97 times to that of plain tube while the maximum value of PEC (performance evaluation criteria) reaches 1.42 in experiments. The results of simulations and experiments indicate that the new type of twisted tape has a distinct advantage on heat transfer enhancement. Verification between simulations and experiments are carried out. The result shows that all deviations of corresponding values between simulations and experiments are within 15%, which reflects that the numerical predications are basically in agreement with the experiment results. Finally, a comparative analysis was carried out with the new type of twisted tape in this paper and the different twisted tapes in the previous research. The new type of twisted tape proposed in this paper has higher Nusselt number and friction coefficient.

The Effects of Circular Inserts on the Thermal and Flow Characteristics in a Horizontal Pipe Exchanger: A Numerical Investigation

“…One of the most considered approaches is dealing with the flow regime throughout the system and improving the heat transfer, enabling development of more compact systems, with a smaller room requirement for installation [4], reduced initial cost and lower payback time. In this area, studies involve numerical and experimental methods and mostly employ a circular single tube or pipe as the test section through which lies an insert (which are also called swirl/vortex generator or turbulator) to create turbulent flow [5][6][7][8][9][10][11][12][13]. Inserted into the pipes or tubes as blades [14], rods [15,16], rings [17,18], tapes [8,19], strips [8,20] or coils [21,22], tube inserts enhance heat transfer by providing increased flow mixing and thus creating turbulent flow induced by longitudinal vortices.…”