Numerical study of variable pitch twisted tape inserts in laminar flow through circular tubes

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- LH, HL, RLH and RHL and two pitch variations (0.5 and 1). The three-dimensional simulations are validated against theoretical correlations and published numerical data. Variable pitch inserts demonstrate improved heat transfer rates relative to constant pitch designs, with only a minor increase in flow resistance. At low and high Reynolds numbers (Re), the RLH-1 configuration demonstrates superior performance, whereas the LH-0.5 configuration is most effective at moderate Re. Introducing a variable pitch into the twisted tape design results in up to 9% increase in the average Nusselt number (Nuavg) over the constant pitch case. The configuration achieves its best performance at Re = 2000, underscoring its capability for efficient laminar heat transfer improvement.