2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Comparison of Heat Transfer and Fluid Dynamic Performance of Nanofluids

D.P. Kulkarni, P.K. Namburu and D.K. Das
University of Alaska Fairbanks, US

Keywords:
nanofluid, rheology, heat transfer, pressure loss, arctic

Abstract:
Many recent studies have shown that nanofluids with metallic nanoparticles as suspension increase the thermal conductivity of base fluid by a substantial amount. Research on copper oxide (CuO) nanoparticles in water has revealed that a 60% increase in the thermal conductivity can be achieved with a 5% (volume) particle concentration. A 60% increase in the convective heat transfer coefficient can be achieved in CuO-water nanofluid with only a 2% (volume) particle concentration. The already high building heating costs in Alaska (and in similar circumpolar regions) are rising because of escalating fuel costs; it is our imperative duty to look for ways in reducing fuel consumption when heating buildings. The commonly used fluid to heat buildings in Alaska is an ethylene glycol and water mixture at a 60:40 proportion (by weight). We have performed a study of various nanofluids comprised of silicon dioxide (SiO2), aluminum oxide (Al2O3) and CuO nanoparticles suspended in a 60:40 ethylene glycol and water mixture for their heat transfer and fluid dynamic performance. First, the rheological properties of SiO2, Al2O3 and CuO nanofluids at different volume percentages were investigated at varying temperatures. The fluids were tested over temperatures ranging from -35?C to 50?C. The viscosity trends showed the great influence of temperature on various nanofluids. Also, we investigated the particle diameter effect (20 nm, 50 nm, 100 nm) on nanofluid viscosity. Subsequent experiments were performed to investigate the convective heat transfer enhancement of nanofluids in a turbulent regime. During analysis of the convection coefficient, the measured viscosity values of the nanofluids were used as well as the thermal conductivity and specific heats were used from the available correlations in the current literature. The experimental system (Figure 1) was first tested with deionized water to establish agreement with the Dittus-Boelter equation for Nusselt number and with Blasius equation for friction factor. Heat transfer coefficients of nanofluids increase with volume concentration, for example, a typical enhancement of a heat transfer coefficient of a 6% concentration of 45 nm CuO is about 54% at a Reynolds number of 8,000 (Figure 2). Similar results were investigated for aluminum and silicon oxide nanofluids in ethylene glycol/water base fluid. Pressure loss was observed to increase with nanoparticle volume concentration and also with increasing particle diameter. It was observed that an increase in particle diameter increased the heat transfer coefficient. Next, calculations were carried out for a building in Fairbanks, Alaska showing that nanofluid applications could result in fuel savings. Nanofluids also require smaller heating systems capable of delivering the same amount of thermal energy, thus reducing the initial equipment costs. Consequently, CO2 and NOx emissions reduced due to reduced fuel consumption, therefore, nanofluid application can mitigate global warming, which is more severe in the arctic regions.

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