Impact of Lobe Topology on Thermal–Hydraulic Performance in Rhodonea‐Derived Tube Bundles

ABSTRACT Compact heat exchangers require design strategies that enhance convective heat transfer while avoiding an excessive hydraulic penalty. Previous studies have extensively examined internal dimples, corrugated passages, twisted tapes, vortex generators, side‐fin cold plates, and fixed noncircular tubes. However, these approaches either modify the internal passage, add auxiliary flow disturbing elements, or compare a limited set of fixed tube shapes. The thermal–hydraulic role of an external tube topology that can be varied mathematically while the cross‐sectional area is preserved, therefore remains insufficiently resolved. This study examines rhodonea‐derived external tube profiles to clarify how lobe number and geometric aspect ratio jointly affect boundary‐layer development, wake structure, pressure loss, and overall thermal–hydraulic merit. Three‐lobed families with c = 2, 3, and 4 were evaluated over eight a/b ratios by three‐dimensional steady finite‐volume simulations using the Simcenter FloEFD (Siemens) automatic laminar and turbulent flow treatment and wall‐modeling framework, spatial discretization of second order, grid‐independence verification, and validation against benchmark experimental data. The numerical framework reproduced the reference data set, with maximum deviations of 0.99% in Reynolds number, 4.22% in Nusselt number, and 6.33% in the Colburn factor. The results show that the four‐lobed family provides the most favorable j/f ‐based compromise within the investigated design space. The optimum configuration increased j/f from 0.405 for the circular reference to 0.450, which corresponds to an 11.1% improvement. In the same four‐lobed family, the maximum near‐surface fluid temperature decreased from 205.1°C for the circular reference to approximately 101.69°C–106.72°C across the tested a/b cases under identical operating conditions. This improvement is attributed to topology‐induced perimeter modification, curvature‐driven flow redistribution, wake fragmentation, repeated boundary‐layer renewal, and a more favorable qualitative interaction between the velocity field and the temperature gradient distribution. Therefore, the main contribution is not a general claim of universal tube optimization, but a validated and physically interpretable framework in which the influence of lobe topology is separated from arbitrary cross‐sectional area variation.