Thermal conductivity and viscosity of water-in-oil nanoemulsions

The development of advanced heat transfer fluids with enhanced thermal conductivity is essential to improve the effective heat transfer behavior of conventional coolants. Thermal conductivity enhancement has been reported for colloidal suspension formulated with different nanoparticles and recently also for water-in-oil emulsion. In the present study, the concept of emulsifying water in oil by means of non-ionic surfactant is employed and physical properties such as thermal conductivity and viscosity are investigated experimentally. Dynamic light scattering shows that the droplet size is dependent on the water concentration: the higher the water concentration, the larger the water droplet size. Based on thermal conductivity and viscosity measurements of nanoemulsions, their performance as cooling media is compared with the performance of pure oil through consideration of the pumping power required to achieve certain heat removal goals. Under certain conditions nanoemulsions are showed to perform slightly better as coolant than their constituting oil although such performances do not seem to suggest any bright potential for general heat transfer applications. (C) 2008 Elsevier B.V. All rights reserved.