Abstract

Nanofluids are defined as dilute suspensions with solid particles smaller than 100 nm. Nanofluids present some important advantages over the conventional colloidal suspensions such as high stability, reduced particle clogging and high heat transfer capabilities. Most of published works have been focused on the increment of thermal conductivity in water-based nanofluids with high nanoparticle loads. Solar nanofluids are a type of nanofluids with low nanoparticle loads and suitable for direct solar radiation harvesting. In this case, nanoparticles in the heat transfer fluid directly absorbs the solar radiation, transferring the heat to the heat transfer fluid. In this way, high efficiency from solar radiation to thermal energy can be obtained since the heat exchange area (nanoparticle surface area) is extremely high and the peak temperature is inside the heat transfer fluid. In most published works, thermal and optical characterizations of solar nanofluids are performed at room temperature conditions, far away from experimental conditions found in real applications. In this work, a complete thermal and optical characterization of a tetraethylene glycol – based nanofluid using tin nanoparticles have been performed. Nanoparticle morphology and nanoparticle cluster size have been characterized at room conditions and thermal conductivity, specific heat capacity and transmission spectrum have been measured at different temperatures between 50ºC and 150ºC. Nanoparticle morphology has been characterized by Transmission Electron Microscope and cluster size by Dynamic Light Scattering technique, thermal conductivity have been measured by the hot wire technique, the specific heat capacity by a Differential Scanning Calorimeter and the transmission spectrum by a fiber optic based spectrometer and a special designed nanofluid cuvette with controlled temperature conditions.