Heat transfer of a U-bend in a cross flow of air at different angles of incidence

An experimental investigation into the incidence angle dependence on mean external heat transfer coefficient for a circular U-bend (180°) in a cross flow of air was performed. All tests were performed on a U-bend with a curvature ratio (δ) of 0.296 covering a Reynolds number range of 1.2 × 104 to 2.7 × 104, while imposing a uniform wall temperature boundary condition. It was found that the U-bend had maximum external heat transfer rate when the external air flow velocity vector was nearly parallel to the bend plane (angle-of-incidence equals 0°). As the angle-of-incidence increased, the external heat transfer coefficient for the U-bend decreased. As the angle-of-incidence approached 90°, the external heat transfer coefficient for the U-bend asymtoped to the value for corresponding flow over a circular cylinder of the same outer diameter.