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A Study of Thermal Transport of Nanofluids and Their Suitability for Electronics Cooling
Keywords: nanofluids, convective thermal transport, liquid cooling
Liquid cooling has remained a viable solution to the thermal management of high-heat-flux electronics. Nanofluids were proposed as a candidate for advanced coolant with superior thermal transport characteristics that may well suit the requirements of compact liquid cooling systems. In spite of extensive studies, a consensus is lacking on if and how the dispersed nanoparticles alter the thermal transport of nanofluids in convective flows. In this work, we report an experimental study of single-phase forced convection of Al2O3-water and Al2O3-Polyalphaolefin (PAO) nanofluids through a minichannel to examine the effects of the flow condition, thermophysical property and particle geometry on the pressure drop and heat transfer performance. The experiments for Al2O3-water nanofluids containing only spherical particles were conducted over the laminar, transition and early fully developed turbulent regimes. It was found that, owing to the particle-fluid interaction, nanofluids exhibit pronounced entrance region behavior in the laminar regime with a delayed transition to turbulent flow. Both the friction factor and convective heat transfer coefficient drop below these of pure water at the same Reynolds number in the transition regime, which, however, recover once the flow becomes fully turbulent. The experiments for Al2O3-PAO nanofluids containing both spherical and rod-like particles were performed in the laminar regime. It was found that in addition to the particle volume concentration, other parameters including the aspect ratio, dispersion state and aggregation of the nanoparticles have a significant impact on both the effective thermophysical property and thermal transport characteristics of the nanofluids. The results from this work suggest that, when applied for convective liquid cooling, aqueous nanofluids should be used under either laminar flow condition or fully developed turbulent flow condition with sufficiently high Re, in order to yield enhanced heat transfer performance, whereas the operation in the transition regime must be avoided. Further, the effects of shear-induced alignment and orientational motion of particles must be considered in designing compact heat exchangers using non-aqueous nanofluids containing non-spherical nanoparticles, such as carbon nanotubes (CNTs).
Dong Liu, Assistant Professor
University of Houston
Houston, TX

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