Experimental investigation on a microfluidic U-turn channel for heat transfer applications

In the present work, an experimental set-up designed to allow investigations of the carrier fluid local behaviours in terms of velocity and temperature fields is presented. The study is carried out on a U-turn microfluidic channel, to bear a complete view of the thermo-fluidic system. The experiments have been performed by Infrared Thermal Imaging, which allows deriving the thermal field on the microchannel external walls, and inferring the internal thermal profiles through specific transfer functions in laminar and transitional regimes. Maps of thermal transients allow deriving cooling performances, which are used to identify the local thermal efficiency of the microchannel and relate it to the global efficiency. Velocimetry measurements have been conducted with a Micro Particle Image Velocimetry (μPIV) setup at different flow rates. This analysis has been coupled with thermal results to obtain a description of the effects of local fluid flow phenomena in transitional turbulent regime on the global heat transfer efficiency of a U shaped microchannel. The interactions among thermal and flow fields are specifically related to secondary recirculating flows, close to the turns, where high cooling rates and high magnitude of local velocity fluctuations are measured.