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Thermal conductivity and mechanical effects of silicon carbide nanoparticles uniformly dispersed in water were investigated. Mean size of SiC particles was 170 nm with a polydispersity of ∼30% as determined from small-angle x-ray scattering and dynamic light scattering techniques. Room temperature viscosity of the nanofluids ranged from 2 to 3 cP for nominal nanoparticle loadings 4–7 vol %. On a normalized basis with water, viscosity of the nanofluids did not significantly change with the test temperature up to 85 °C. Optical microscopy of diluted nanofluid showed no agglomeration of the nanoparticles. Thermal conductivity of the fluid was measured as a function of the nominal nanoparticle loading ranging from 1 to 7 vol %. Enhancement in thermal conductivity was approximately 28% over that of water at 7 vol % particle loadings under ambient conditions. Enhancements in thermal conductivities for the nanofluids with varying nanoparticle loadings were maintained at test temperatures up to 70 °C. Results of thermal conductivity have been rationalized based on the existing theories of heat transfer in fluids. Implications of using this nanofluid for engineering cooling applications are discussed. [ABSTRACT FROM AUTHOR]

Subcooled flow boiling heat transfer experiments were performed with water and ethylene glycol/water mixtures at five flow velocities and four fluid inlet temperatures. Both turbulent flow and laminar flow were tested in a special test facility with its experimental test section heated from the bottom surface only. Boiling curves and subcooled flow boiling heat transfer coefficients of the tested fluids were determined from the experimental measurements. Predictive correlations of the subcooled flow boiling heat transfer coefficients were developed based on the experimental data. Comparisons are presented of wall temperatures between the experimental measurements and the correlation predictions. [ABSTRACT FROM AUTHOR]

Heat transfer enhancement criteria for nanofluids over their base fluids are presented based on three separate considerations: Reynolds number, flow velocity, and pumping power. Analyses presented show that, among the three comparisons, the constant pumping power comparison is the most unambiguous; the constant flow velocity comparison can be quite reasonable under certain conditions but the constant Reynolds number comparison (the most commonly used in the engineering literature for nanofluids) distorts the physical situation, and therefore, should not be used. [ABSTRACT FROM AUTHOR]