Astarita, G. Cardone

The aim of the present study is to obtain surface flow visualisation, as well as local and spanwise averaged heat transfer measurements near a 180° sharp turn in a rectangular channel. The channel aspect ratio (width to height ratio) varies from 1 to 5 and the ratio between the width of the channel and that of the partition wall is always equal to 5. Heat transfer measurements are performed by means of the heated-thin-foil technique, which practically corresponds to a constant heat flux boundary condition, and by using infrared (IR) thermography. Two different heating conditions, in particular heating from one side (asymmetrical), or from two sides (symmetrical), are implemented. The convective heat transfer coefficient is evaluated from the measured temperature maps and the local bulk temperature of the flow which is obtained by making a one-dimensional balance along the channel. Results are presented in terms of local, or averaged, Nusselt number which is normalised with the classical Dittus and Boelter correlation. The fluid used during the test is air and the Reynolds number, based on the flow average velocity and channel hydraulic diameter, is varied between 16,000 and 60,000.