Numerical study of flow mixing and heat transfer in helical pipes, coiled flow inverters and a novel coiled configuration

Abstract Liquid mixing is compared in different helical configurations, i.e. straight coils, coiled flow inverters (CFI), and newly introduced coils (Coiled Flow Reversers, CFR). The considered ranges of Reynolds and Dean numbers are 10 ⩽ Re ⩽ 3,000 and 3 ⩽ De ⩽ 900, respectively. Two orientations for the liquids interface at the inlet were applied (parallel or perpendicular interface to the coil axis). The parallel interface leads to significantly higher mixing, due to an optimal alignment with Dean vortices. The use of CFI or CFR could reduce the strong influence of the inlet interface. For Re ⩾ 500, mixing in the CFR is best despite the strongly reduced residence time. When heat transfer is compared to the straight coil, the CFR shows about 5% increase in outlet temperature, compared to less than 4% increase in the CFI for Re ⩾ 1,000. Nevertheless, the CFR has a slightly higher pressure drop.