Heat transfer and pressure drop correlations for rectangular channels with ribs

To study the steam cooling technology for gas turbine blades, an experiment system was established including a steam generation and conditioning subsystem, a pre-plenum, a test section with instrumentation, a heating device for the test channel, an after-plenum and a data acquisition and control system. The heat transfer and friction loss characteristics of fully developed turbulent steam flow in 10 different ribbed rectangular channels were experimentally examined. The combined effect of the aspect ratio (W/H=0.25, 0.5, 1, 2 and 4), the rib angle-of-attack (α=30°, 45°, 60° and 90°) and Reynolds number (10, 000 to 80, 000) was analyzed. Semi-empirical correlations of heat transfer and friction were developed considering the influences of the channel aspect ratio, rib angle, and Reynolds number. The results show that an increase in the ribbed surface width increased both the heat transfer and friction loss of steam flow. The increase in Reynolds number enhanced the heat transfer significantly but had slight effect on the friction loss. The maximum heat transfer coefficient and friction factor were obtained at the channel with 60° ribs. These conclusions may provide reference to the advanced steam-cooled blade design for gas turbines.