Study on the Heat Transfer Capability of Silicon Carbide - Ethylene Glycol Nanofluid S. Bobbo, L. Colla, M. Scattolini, L. Fedele Consiglio Nazionale delle Ricerche, Istituto per le Tecnologie della Costruzione Corso Stati Uniti, 4, 35127 Padova, Italy. email sergio.bobbo@itc.cnr.it ABSTRACT Ethylene glycol-based (EG) nanofluids containing silicon carbide (SiC) in the concentrations 0.1, 1 and 5 wt% were characterized, in order to understand their potentiality to improve the heat transfer efficiency of the base fluid. First of all, the stability was verified almost every day for 30 days using a Dynamic Light Scattering (DLS) technique. Then, nanofluids thermal conductivities and dynamic viscosities were measured, analysing their dependence on temperature and nanoparticle concentration. The fluids show an increment in thermal conductivity (λ) more than proportional to the increment of nanoparticle concentration at a given temperature. Moreover, λ increases with temperature. The dynamic viscosity (µ) increment is small at low nanoparticle concentrations and quite significant at 5%wt concentration. Increasing the temperature, the absolute value of viscosity decreases but the increment is increasing. Keywords: nanofluid, thermal conductivity, viscosity, silicon carbide, ethylene glycol 1 INTRODUCTION Nanofluids, i.e. suspensions of nanoparticles in liquids [1], seem to be very promising as thermal vectors in systems where secondary fluids are applied. It has been found [2-3] that it is possible to get an unproportional increase in thermal conductivity and heat transfer coefficient also at relatively low nanoparticle concentrations. Moreover, nanoparticle material, dimension and shape can affect the efficiency of nanofluids as thermal vectors [4]. Particular attention must be put on the suspension stability, considering its Zeta potential, pH, type and concentration of dispersants [5-6]. Obviously, the addition of nanoparticles can determine a change in viscosity. Then the study of the rheological properties of nanofluids is fundamental to determine the possible increase in energy required to pump the nanofluid. In the last years, several papers have been published in the literature on thermal properties and/or viscosity for nanofluids with various kinds of added nanoparticles, showing different behaviours [e.g., 7, 8, 9]. Here, an ethylene-glycol (EG) based nanofluid with silicon carbide (SiC) nanoparticles has been studied. EG can be used as a heat-transfer fluid in heating applications with maximum operating temperatures higher than water boiling temperature. SiC is characterized by high thermal conductivity, i.e. 490 W/mK [10] (e.g. common oxides) and it is supposed to enhance the thermal properties of EG more than other common materials such as metal oxides. Only few data are available for thermal conductivity of EG-SiC nanofluids, while no rheological properties were found in the literature. First of all, the stability of three considered suspensions, at 0.1, 1 and 5 wt%, was studied. Then, thermal conductivity and dynamic viscosity were measured in the temperature ranges between 10°C and 70°C and 10°C and 90°C, respectively. These measurements will be preliminary to future analysis of the heat exchange coefficient for this fluid. Both thermal conductivity and viscosity are necessary to properly evaluate fluid-dynamic regimes and heat transfer behaviour (e.g. to calculate non-dimensional numbers such as Re, Pr, Nu). 2 EXPERIMENTAL 2.1 Materials EG-based nanofluids containing SiC at concentrations 0.1, 1 and 5 wt% were supplied by Nanograde Llc. An anionic dispersant (not specified by the manufacturer) was added to the suspensions at concentrations 0.008, 0.08 and 0.4 wt%, respectively. 2.2 Nanofluids stability characterization The stability of the EG-SiC suspensions was studied by means of a Zetasizer Nano ZS (Malvern), based on Dynamic Light Scattering (DLS). It was used to check the actual average dimension of the nanoparticles in solution and verify the dependency of the diameter size from the concentration of the solution. The declared nanoparticle size by the supplier is 10-50 nm. The actual mean particle diameter was measured every day for a period of 30 days to evaluate its stability. Two NSTI-Nanotech 2012, www.nsti.org, ISBN 978-1-4665-6275-2 Vol. 2, 2012 345