| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 94 === In the present study, surface-averaged heat transfer coefficient for natural convection in a square enclosure filled with nanofluids has been determined experimentally. The enclosure is heated differentially across the two vertical isothermal walls, while the other side-walls are assumed adiabatic. The nanofluids considered were prepared by dispersed various amount of alumina (Al2O3) nanoparticles in water or ethylene glycol as the base fluid. In preparing the nanofluids, it was observed that stable suspension of the nanoparticles in the base fluids can be achieved by adjusting properly the pH values of the nanofluids (pH = 3). In addition, thermophysical properties of the nanofluids prepared including the particle size, the density, viscosity, and thermal conductivity, were measured as a function of temperature as well as the mass fraction of the nanoparticles. The heat transfer experiments for natural convection in the enclosure have been undertaken for the relevant parameters in the following range：Rayleigh number, RaT,b = 10E6~10E8,the mass fraction of nanoparticles Cm =0.35%、1%、3.52%、6.86%、10.04%. The results obtained for the averaged heat transfer coefficient over the isothermally heated wall reveal that enhancement in the natural convection heat transfer across the enclosure does arise markedly by dispersing small mass fraction of alumina nanoparticles (Cm = 0.35%) in water or ethylene glycol.
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