An experimental investigation into the global external heat transfer coefficients for circular U-bends(180 deg bends) in a cross-flow air stream was performed using six different curvature ratios (δ) covering a Reynolds number range of 3000-80 000 while imposing a uniform-wall-temperature (UWT) boundary condition. The measurements specifically focused on a zero-degree angle-of-incidence, in which the external flow direction is parallel to the bend plane. A straight forward method to measure the global external heat transfer that is not dependent on geometry but limits the testing to UWT was employed.
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