Influence of Torsion on the Laminar Flow and Convective Heat Transfer in Coiled Tubes Arranged in a Rectangular Pattern

A detailed numerical investigation has been undertaken to understand the intricacies of laminar forced flows with convective heat transfer inside coiled tubes of circular cross section. The coiled tubes consist of two straight parts and two bends which are arranged in a rectangular pattern. The laminar flows are characterized by three different Reynolds numbers: Re = 300, 700, and 1400. Computer simulations to calculate the laminar velocity and temperature fields were performed for four coiled tubes having different bend torsion ratios. Compared to the coiled tubes near the entrance of the first bend, the rotation experienced by the fluid motion due to torsion is less significant in the second bend. This behavior is attributable to the flow redevelopment in the upstream straight tube. The numerical results demonstrate a vigorous fluid rotation for flows possessing higher velocities whose magnitudes are given by Re = 700 and 1400. The flow path in the bend is representative of a typical flow near the entrance region of a helically coiled tube. The numerical predictions agree well with those results generated by numerical computations and experimental observations. Overall, the heat transfer coefficient decreases with increments in the bend torsion; this behavior is caused primarily by the weakening in the secondary flows.