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Abstract:
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This investigation conducts pool boiling experiments under saturated conditions (Tsat=60°C ) using nanofluids as coolants . Four different nanofluids were tested including zinc oxide (ZnO ) -water , aluminum oxide (Al2O3 ) -water , aluminum oxide (Al2O3 ) -water+ethylene glycol (ethylene glycol solution ) and gold (Au ) -water . At saturation (Tsat=60 °C ) , the pool boiling performance of Al2O3 -water and ZnO -water nanofluids were similar . The maximum CHF enhancement as compared to predicted Zuber's [1] CHF evaluated at an equivalent saturation temperature is about 180 % for Al2O3 -water nanofluids and about 240 % for ZnO -water nanofluids . In both cases , no degradation in the boiling heat transfer rate was observed for lower nanoparticle concentrations . The dispersion of Al2O3 nanoparticles in various ethylene glycol solutions is also found to enhance CHF by as much as ~130 % . A significant difference in the diameter of individual grains /particles (27 ± 16 .3 nm ) and the volume weighted average diameter of particles in solution (155 ± 80 nm ) indicates that the Al2O3 -water nanofluids consist primarily of nanoparticle agglomerates . Gravimetric fractionation of the nanofluid produced nanofluids with particle /particle aggregate average diameters that ranged from 69 - 346 nm . Over the size range tested , there was no significant CHF dependence on the average particle diameter . Finally , pool boiling results with monodispersed Au -water nanofluids of 2 nm and 40 nm sizes revealed that the smaller particle size enhanced CHF while the larger particles decreased CHF . |