Microchannels with manufacturing roughness levels

There are heat transfer advantages to reducing the size of channels used for internal cooling gas turbine components. As channel sizes decrease, however, there are concerns as to how manufacturing surface roughness may affect the channels' expected pressure drop and heat transfer. For microchannel size scales, in particular, there is relatively little data indicating the effect of manufacturing roughness levels. The focus of this paper is to describe the development and validation of a testing method for microchannels as well as to determine the effect of manufacturing roughness levels on these small channels. Convective heat transfer coefficients and friction factors were deduced based on measured flow conditions and known boundary conditions. It was shown that at an average roughness height of 6.1 μm, which corresponded to 2.2% of the channel height, heat transfer was augmented by 1.1-1.2, while the friction factor was augmented significantly more by 2.1-2.6 over a smooth channel.