Heat Transfer and Fluid Flow Characteristics in a Two Pass Duct with Variable Rib Shapes: A CFD Analysis

Gas turbines are usually operated at higher temperatures to enhance their thermal efficiency. At higher operating temperatures, however, the gas turbine blades may fail due to thermal corrosion and cracking. Thus cooling in gas turbines becomes inevitable. The present investigation deals with study of heat transfer and pressure loss characteristics in a two pass channel with variable rib shapes. Four different rib shaped were studied namely square, arched, wavy, and zig-zag ribs. Reynolds Number was varied from 10,000–40,000 and a rib pitch to rib height ratio of 10 was fixed for the present study. Reynolds Averaged Navier Stokes (RANS) Equations were solved numerically in COMSOL Multi-physics 5.4 using the Conjugate Heat Transfer (CHT) module with κ-ω Turbulence model. Thermal performance index (η) for different rib shapes has been numerically evaluated by calculating the normalized Nusselt number ratios and friction factor ratios. It was found that the heat transfer augmenting capability of the ribs relies hugely on the rib shape and the Reynolds Number of the working fluid. At a Reynolds Number of 10,000, wavy ribs outperformed conventional square ribs by 24.96% in terms of normalized Nusselt number ratios and the thermal performance index (ɳ) of the wavy ribs increased by 26.74% when compared to conventional square ribs. Moreover, the frictional losses were minimum is case of wavy ribs.