In the effects of rib shapes on the heat

this study, heat transfer and friction factor for various rib shapes were analyzed
for a rectangular cooling channel of a gas turbine blade. Ratios of rib-height,
rib-width and rib-pitch to hydraulic diameter of the channel were taken as 0.1,
0.1 and 1.2 respectively. Numerical simulations were performed on various rib
shapes for Reynolds number, based upon the hydraulic diameter, ranging from
5000 to 20,000 and uniform heat flux of 800 W/m2. K-w turbulence
model was used to analyze the turbulence. The computational results for smooth
section were validated with Dittus-Boelter relation for Nusselt number, and
Blasius equation for the friction factor. Furthermore, the computational
results for area-averaged Nusselt number were compared with the experimental
data under the same conditions. The main aim of this study is to analyze the
effects of rib shapes on the heat transfer and fluid flow characteristics. Simulations
were done using air as the cooling medium but the effect of using steam,
instead of air, was also investigated in this study.


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Cooling channels are
provided in machine parts where heat generation occurs and this generated heat
needs to be removed out of the machine. If let to accumulate, the heat produced
can cause damage and result in failure of machine. Internal cooling channels
are found inside the gas turbine blades, high temperature propulsion systems,
electric generator coils, cylindrical lining of IC engines and many other
applications. In the case of gas turbine blades, bypass air bled from the last
stages of compressor acts as the coolant. This air bypasses the combustion
process thus remains cooler and is fed to the internal cooling channels of the
turbines blades, where it removes heat from the ho­t surfaces, keeping
temperatures within the thermal limits of the alloys used. Turbulators, or
commonly known as ribs, are a popular heat transfer augmentation device used in
the internal cooling channels of a gas turbine blade. These ribs break the flow
near the wall surface and cause increase in turbulence. The amount of turbulent
kinetic energy produced depends upon various factors such as rib shape,
rib-height, rib-width and rib-pitch etc. out of which rib shape is one of the
most important factors.


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