Experimental investigation of CuO-water nanofluid flow and heat transfer inside a microchannel heat sink

This paper presents an experimental investigation of the hydraulic and thermal fields of a 29 nm CuO nanoparticle water nanofluid with various volume fractions, 0.24%, 1.03% and 4.5% flowing inside a rectangular microchannel heat sink under both laminar and turbulent conditions. The isothermal and heated tests are conducted for Reynolds number up to approximate to 5000 and to approximate to 2500, respectively. For a given fluid flow rate experimental results show an increase of the pressure drop and the friction factor with respect to water. This increase can be as high as 70%, 25%, and 0-30%, respectively, for the 4.5%, 1.03%, and 0.24% particle volume fractions. Although the laminar-to-turbulent transition was observed at nearly the same critical Reynolds number Re-c approximate to 1000 for water and the tested nanofluids, this value of Re-c is clearly lower than that corresponding to a smooth surface microchannel. Results show a slight heat transfer enhancement with respect to water for nanofluids with low particle volume fractions, 0.24% and 1.03%, while for the 4.5% fraction a clear decrease of heat transfer was found. In general, the nanofluid overall energetic performance, defined by the heat transferred/pumping power ratio, remains lower than that of water for a given Reynolds number. This ratio decreases with an augmentation of the particle volume fraction. (C) 2014 Elsevier Masson SAS. All rights reserved.