Numerical investigation of rectangular-cut twisted tape insert on performance improvement of heat exchangers

A numerical analysis has been performed to investigate the flow structure and thermal hydraulic performance of turbulent flow through circular tube equipped with twisted tapes with different cut shapes. The geometries of cuts are rectangular with different cut ratios 0.25 < b/w < 0.75 and 0.25 < c/w < 1 for two different sets of cuts (single-cut and double-cut). Three dimensional simulations are validated by experimental data available in literature. The governing equations of turbulent flow are solved by using (RNG) k-epsilon for Reynolds number from 5000 to 16000. Due to swirl flow, the effect of two regions, including near wall region and core region on heat transfer and pressure drop are discussed. Presence of rectangular-cut twisted tape (RCT) leads to better mixing of fluid and centrifugal force near the wall, which has significant effect on heat transfer and friction factor at this region. The results show that both of heat transfer and pressure drop are dependent on the cut ratio. The thermal performance value for the case of single-cut twisted tape with b/w = 0.75 and c/w = 0.5 is about 1.2-1.64.