Thermal performance of radially rotating two-pass S-shaped zig-zag channel

The detailed Nusselt number distributions, Fanning friction coefficients and thermal performance factors of a radially rotating two-pass square S-shaped zig-zag channel are measured. The fanning friction coefficients are measured from the inner and outer sidewalls, as well as from the leading and trailing endwalls of the rotating channel. At the criterion of constant pumping power consumptions, the thermal performance factors (TPF) are evaluated. The test conditions specified by Reynolds number (Re), rotation number (Ro), density ratio (Δρ/ρ) and buoyancy number (Bu) are 5000 ≤ Re ≤ 15,000, 0 ≤ Ro ≤ 0.5, 0.03 ≤ Δρ/ρ ≤ 0.12 and 0.0049 ≤ Bu ≤ 0.15. The individual and combined impacts of Reynolds number, rotation number and buoyancy number on the endwall heat transfer properties for present rotating channel are illustrated using a selective set of heat transfer data. Acting by the Coriolis and rotating buoyancy forces to modify the flow structures, the area averaged Nusselt number ratios between the rotating and static channels for the leading and trailing endwalls fall in the respective ranges of 0.93-2.34 and 0.91-2.25. The heat transfer correlations which permit the evaluations of individual and interdependent effects of rotation number and buoyancy number on the regionally averaged Nusselt numbers over the rotating inlet leg, outlet leg and bend region are devised. Correlations evaluating the Fanning friction coefficients of the inner, outer, leading and trailing channel walls are also developed for present rotating channel. Due to the combined Re, Ro and Bu effects on the heat transfer properties and pressure drop performances of present S-shaped two-pass channel, the area averaged Nusselt numbers on leading and trailing endwalls are respectively raised to 3.17-6.83 and 3.22-6.92 times of the Dittus-Boelter Nusselt number (Nu∞) references. With the accompanying thermal performance factors in the range of 1.25-2.04 at all the static and rotating test conditions, present S-shaped two-pass channel appears as an efficient heat transfer enhancement method with cooling applications to gas turbine blades.