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The turbulent convective heat transfer behavior of alumina (Al2O3) and zirconia (ZrO2) nanoparticle dispersions in water is investigated experimentally in a flow loop with a horizontal tube test section at various flow rates (9000<Re<63,000), temperatures (21–76°C), heat fluxes (up to ∼190kW∕m2), and particle concentrations (0.9–3.6vol% and 0.2–0.9vol% for Al2O3 and ZrO2, respectively). The experimental data are compared to predictions made using the traditional single-phase convective heat transfer and viscous pressure loss correlations for fully developed turbulent flow, Dittus–Boelter, and Blasius/MacAdams, respectively. It is shown that if the measured temperature- and loading-dependent thermal conductivities and viscosities of the nanofluids are used in calculating the Reynolds, Prandtl, and Nusselt numbers, the existing correlations accurately reproduce the convective heat transfer and viscous pressure loss behavior in tubes. Therefore, no abnormal heat transfer enhancement was observed in this study.

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In recent quenching heat transfer studies of nanofluids, it was found that deposition of nanoparticles on a surface raises its Leidenfrost point ͑LFP͒ considerably ͓Kim et al., Int. J. Multiphase Flow 35, 427 ͑2009͒ and Kim et al., Int. J. Heat Mass Transfer 53, 1542 ͑2010͔͒. To probe the physical mechanism underlying this observation, the effects of surface properties on LFP of water droplets were studied, using custom-fabricated surfaces for which roughness height, wettability, and porosity were controlled at the nanoscale. This approach reveals that nanoporosity is the crucial feature in efficiently increasing the LFP by initiating heterogeneous nucleation of bubbles during short-lived solid-liquid contacts, which results in disruption of the vapor film.

High-speed video and infrared thermometry were used to obtain time-and space-resolved information on bubble nucleation and heat transfer in pool boiling of water. The bubble departure diameter and frequency, growth and wait times, and nucleation site density were directly measured for a thin, electrically-heated, indium-tin-oxide surface, laid on a sapphire substrate. These data are very valuable for validation of two-phase flow and heat transfer models, including computational fluid dynamics with interface tracking methods. Here, detailed experimental bubble-growth data from individual nucleation sites were used to evaluate simple, commonly-used, but poorly-validated, bubble-growth and nucleate-boiling heat-transfer models. The agreement between the data and the models was found to be reasonably good. Also, the heat flux partitioning model, to which our data on nucleation site density, bubble departure diameter and frequency were directly fed, suggests that transient conduction following bubble departure is the dominant contribution to nucleate boiling heat transfer.

Separate effects of surface roughness, wettability, and porosity on the boiling critical heat flux The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters.

Transient hot-wire data on thermal conductivity of suspensions of silica and perfluorinated particles show agreement with the mean-field theory of Maxwell but not with the recently postulated microconvection mechanism. The influence of interfacial thermal resistance, convective effects at microscales, and the possibility of thermal conductivity enhancements beyond the Maxwell limit are discussed.

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