Thermohydraulic performance of a novel curved serpentine coil

Abstract

Conventional coil designs, such as helical and flat serpentine (FS) coils, are commonly employed for heat transfer applications due to their higher heat transfer performance and compactness. In the last few decades, chaotic coil designs have attracted the attention of a few researchers due to their superior thermohydraulic performance. In this paper, we present a novel and simple chaotic coil design termed the curved serpentine (CS-θ) coil, which is a modified version of the conventional FS coil. The straight tubes of length L in the FS coil are bent as arcs of radius R1 and subtended angle θ (i.e., L = R1 × θ), which are interconnected with U-bends of radius R2. The laminar flow of water through the CS-θ coil is numerically investigated, and the peaks and valleys in the local Nusselt number and friction factor at various axial locations are explained with the help of velocity and temperature contours and secondary flow patterns. The chaotic nature of flow through these coils is explained with the help of streamlines and transverse flow vectors, transversal intersection of the trajectories, and the Lyapunov spectrum. The thermohydraulic performance (η) of this coil is found superior to conventional FS and helical coils. It is found that the CS-θ coils, in which the flow is fully developed just before entering the U-bend, can achieve the best thermohydraulic performance. We also propose generalized correlations for predicting the average Nusselt number and friction factor in the CS-θ coils with a maximum deviation of ±10% and ±7.5%, respectively.