Experiencing the effect of dimple diameter on heat transfer characteristics of a tube using (Al2O3 and CuO)/H2O nanofluids (NFs)

Abstract

Enhancing the heat transfer in heat exchangers is crucial for various industrial applications. One promising approach is the use of dimpled tubes containing nanofluids (NFs). This study investigates the effect of different dimple diameters on the heat transfer characteristics of dimpled tubes using NFs, aiming to improve the thermal performance of heat exchangers. Numerical simulations were conducted in ANSYS Fluent 17.2 to analyze the friction factor and Performance Evaluation Criteria (PEC), assessing the feasibility of employing dimpled tubes with NFs. Water was selected as the base fluid, with CuO and Al₂O₃ nanoparticles (NPs) of 30 nm diameter. The simulations were performed under low turbulent flow conditions, with Reynolds numbers ranging from 2500 to 6000. The study examined the impact of three dimple diameters (1 mm, 2 mm, and 4 mm) and varying NF concentrations (0.1%, 0.3%, and 0.5%) for both CuO/H₂O and Al₂O₃/H₂O NFs. Results indicated that increasing dimple diameter enhances both the Nusselt number and friction factor. Although PEC also increased, higher Reynolds numbers led to reduced heat exchanger efficiency. Among the NFs, Al₂O₃/H₂O demonstrated superior heat transfer properties and overall performance. Increasing NFs volume fraction up to 0.5% further improved the Nusselt number and PEC. The optimal configuration was achieved with a 4 mm dimple diameter and 0.5% Al₂O₃/H₂O at a Reynolds number of 2500, yielding the highest PEC value of 3.77.