Thermal performance and friction factor of a cylindrical microchannel heat sink cooled by Cu-water nanofluid

• Study of heat transfer coefficient and friction factor of copper nanofluids.
• Study of thermal resistance vs concentration of the copper nanofluids.
• Study of local wall temperature vs concentration of the copper nanofluids.
• Development of correlations for Nusselt number and friction factor of Cu nanofluid.

The utilization of nanofluids of various types as cooling or heating working fluids has given incentive to enhanced heat transfer resulting in even smaller heat exchangers for a given heat duty. In this study, convective heat transfer coefficients and friction factor of copper nanofluids in a cylindrical microchannel heat sink were investigated. Copper nanoparticles with various mass fractions were used for two heat fluxes of 35 and 50 kW/m2. The effect of nanoparticle mass fraction and Re on local convective heat transfer coefficients, and the local Nusselt number was also studied. The experimental results showed that increased mass fraction of nanoparticles from 0.05 to 0.3 wt% resulted in lower thermal resistances of up to 21%. Moreover, the local heat transfer coefficients helped to experimentally determine the thermal entrance length for the microchannel heat sink. The presence of nanoparticles enhanced the entrance Nu up to 43% while the friction factor also increased up to 45.5% compared with that of pure water. Two correlations were finally proposed for the prediction of the Nusselt number and friction factor for the attempted nanofluid in the microchannel which agreed well with the experimental data.

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