Scale-inspired enhanced microscale heat transfer in macro geometry

This paper demonstrates the feasibility of achieving enhanced microscale heat transfer effects in macro geometry systems using conventional fabrication methods. An annular microchannel, of mean channel gap 300 μm and length 30 mm, is formed by securing a cylindrical insert of mean diameter 19.4 mm within a cylindrical pipe of internal diameter 20 mm. The Fish Scale (FS) profile is introduced on the insert surface to improve the convective heat transfer coefficient, for a constant heat transfer area. The effect of the FS enhancement profile on the heat transfer and flow characteristics are experimentally studied using water, with Reynolds number ranging from 350 to 4600. Results show that the FS profile enhances heat transfer by promoting early laminar-to-turbulent flow transition. The highest convective heat transfer coefficient achieved is 47.9 kW/m2·K, using the FS profile with a scale height of 0.21 mm and scale pitch of 2.1 mm, at Reynolds number of about 4400. New working correlations for the average Nusselt number and friction factor are proposed for the enhanced FS microchannels. These correlations may be used in the future to design macroscale heat exchangers employing economical conventional fabrication techniques and yet exhibiting superior microchannel heat transfer capabilities.