Numerical Study of Variable Pitch Twisted Tape Inserts in Laminar Flow Through Circular Tubes

Abstract

Abstract. This study introduces a variable pitch twisted tape insert aimed at improving the understanding of laminar flow and heat transfer in circular tubes under uniform wall temperature conditions. To provide a fair basis for comparison with the conventional design, the overall average twist ratio of the proposed insert was maintained equivalent to that of the constant pitch twisted tape. Nine different configurations are examined, which include both constant and variable pitches, with four distinct pitch patterns—low-to-high (LH), high-to-low (HL), repeatedly low-to-high (RLH), and repeatedly high-to-low (RHL) twist ratios and two pitch variations (0.5 and 1). The present three-dimensional simulations are validated with available theoretical correlations and previously reported numerical data. Variable pitch inserts exhibit improved heat transfer relative to constant pitch inserts, and there is only a minor increase in the pressure drop. At low and high Reynolds numbers (Re), the RLH-1 configuration achieved better performance, whereas the LH-0.5 configuration performed best at moderate Re. Introducing a variable pitch design into the twisted tape inserts results in up to 9% increase in the average Nusselt number (Nuavg) over the constant pitch insert. The configuration achieves its best performance at Re=2000, emphasizing its capability for improving efficient laminar heat transfer.