The effect of different carrier fluids on heat transfer performance in a microfluidic serpentine device

In this work, the efficiency of heat transfer and the related fluid-mechanic performance inside a microflu- idic device are investigated by varying the type of carrier fluid at different flow rates. The experimental analysis has been conducted on a serpentine channel configuration by considering five different fluid mix- tures. The results displayed and emphasized the relevant role of viscosity on thermal performance in the laminar regime. The corresponding Nusselt number values have been identified in terms of Reynolds and Prandtl numbers. Specifically, high-viscosity mixtures exhibited Nusselt number values strongly correlated with Prandtl number. So far, heat transfer for these mixtures is improved as a result of the greater extent of the thermal entrance region and of the higher thermal gradient. Nusselt-Reynolds trends for such mix- tures also presented a consistent rate of increase, this increment being however severely limited by the action of viscous dissipation as Reynolds number increases. On the other hand, mixtures with low viscos- ity showed high correlation between Nusselt and Reynolds numbers. The importance of local turbulence phenomena for such low-viscosity fluids becomes one of the main factors in heat transfer enhancement, also for small-scale thermal sinks in laminar regime. In fact, for such mixtures, thermal performances are incremented by the combining effects of local mixing phenomena at each bend of the serpentine and by the increasing extension of the thermo-hydraulic development region.