Numerical Investigation of Heat Transfer Enhancement in Dimpled Helically Coiled Tubes

One effective approach to improving heat transfer in smooth helically coiled tubes (SHCTs) is the introduction of spherical dimples on the inner surface. Therefore, this study presents a numerical analysis of the heat transfer performance and flow resistance of SHCTs and spherical dimpled helically coiled tubes (DHCTs). A variety of parameters are investigated, including coil diameter, coil pitch, dimple pitch, dimple star number, and dimple diameter, within the Reynolds number interval of 10,000–25,000, while keeping the Prandtl number constant at 7.0. The novelty of the current research is the evaluation of how these parameters affect the Nusselt number (Nu), friction factor (f), and performance evaluation criteria (PEC) for DHCTs, with the results compared to those obtained for SHCTs. The study reveals that coil pitch has little effect on the thermal and hydraulic performance of SHCTs and DHCTs, while an increase in coil diameter leads to a noticeable decline in their performance. Increasing the dimple pitch enhances the Nu by about 1.34–1.74 times and raises the f by 1.28–5.32 times compared to SHCTs. Increasing dimple diameter improves Nu by 1.19–1.67 times and increases f by 1.28– 5.32 times. Among all parameters, changing the number of dimple stars has the greatest impact, with Nu increasing 1.37–1.91 times and f rising sharply from 3.12 up to 9.52 times relative to SHCTs. Nevertheless, the dimple diameter has a significantly stronger influence on the PEC than the other parameters, with variations capable of altering the PEC by as much as 23.7%. Overall, DHCTs outperform SHCTs in heat transfer under the same conditions, with a PEC reaching up to 1.21.