Heat transfer and friction in circular ducts with shaped ribs

An experimental investigation on large scaled models of gas turbine ribbed circular cooling channels was performed in order to measure heat transfer coefficients and friction factors. Heat transfer coefficients maps were evaluated using narrow band thermo-chromic liquid crystals within a transient technique. Friction factors were evaluated measuring the pressure drop along the ducts with piezoresistive pressure sensors in cold tests. The streamwise averaged Nusselt numbers were fitted in order to highlight the Reynolds number dependence and a comparison with smooth ducts was performed in terms of heat transfer and friction enhancement. Finally a comparison with some published correlations for square and rectangular ducts was done and correction factors were evaluated in order to obtain heat transfer coefficients and friction factors for the present circular ribbed ducts.