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The pressure loss and heat transfer characteristics of single-phase water flows and non-boiling air-water flows through a slender 180° return bend with a rectangular cross-section are investigated. Such slender ducts appear in various applications. In comparison to abrupt return bends the unsymmetrical flow field affects a bigger surface. Therefore, there is an interest to quantify the impact of such curvature effects. For the pressure loss consideration, the curvature ratios are 19.9, 40, and 58.1, whereas for heat transfer, the focus is on the latter, the hydraulic diameter and aspect ratio are 3.9 mm and 1.067, respectively. The numerical results are compared to published experimental ones. From the numerical modeling results, where three different approaches of turbulence modeling were tested, it is confirmed that above a curvature ratio of 90 it seems reasonable to neglect curvature effects on pressure drop. The validated conjugate heat transfer models are utilized to develop local and global relationships for the Nusselt number ratios between the convex and concave surface. The two-phase flow modeling is realized via a homogenous flow model approximation. The results show that the modeling provides reasonable results and that the impact of curvature on such flows can be relevant.

Numerical Investigation of Pressure Loss and Heat Transfer Characteristics in 180-Degree Bends