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Abstract

Heat-transfer enhancement techniques such as fins, dimples, and grooves are widely employed to improve the thermal performance of heat exchangers; however, their application is often accompanied by increased pressure losses. Most existing studies investigate a single enhancement technique over a limited Reynolds number range, with few comparative analyses conducted at high Reynolds numbers using identical geometries. Therefore, this study numerically investigates the thermal–hydraulic performance of five pipe configurations using Computational Fluid Dynamics (CFD). All geometries share the same diameter (48.34 mm) and length (7.45 m) and are examined over a Reynolds number range of 4,000–57,000. The configurations include: (1) smooth pipe, (2) pipe with spherical convex dimples, (3) pipe with spherical concave dimples, (4) pipe with circumferential grooves of depth (e) to diameter (d) ratio of 0.20, and (5) pipe with circumferential grooves of e/d\ = \ 0.50. A mesh-independence study was performed for both smooth and dimpled pipes, followed by CFD validation against available experimental data and empirical correlations from three different sources in the literature. After validation, local temperature, pressure, and velocity fields were analyzed at the highest flow Reynolds number (Re = 57,000). In addition, the effects of Reynolds number on Nusselt number, friction factor, and thermal performance factor (TPF) were evaluated for each pipe case. Results indicate that dimples and grooves promote recirculation and near-wall mixing, enhancing heat transfer relative to the smooth pipe. The groove configuration with e/d\ = \ 0.50 achieved the highest TPF (≈ 1.45 at Re = 57,000), but with a 456% increase in friction factor. Whereas the e/d\ = \ 0.20 case provided a more balanced thermal–hydraulic performance.

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