Convection and Instability Phenomena in Nanofluid-Saturated Porous Media

In the last decade, a wide research effort from the heat transfer community has been oriented to nanofluid-saturated porous media. The interest in this subject is mainly motivated by the technological value of an improved design of heat exchangers with high thermal performances and a relatively small size. With this aim in mind, an optimal fluid-to-solid heat exchange is devised through a metal foam, and the usual fluid is replaced by a nanofluid. Hence, when nanofluid-saturated porous media are studied, the porous medium is preferably considered as one with a high thermal conductivity. The argument supporting the use of a nanofluid, instead of an ordinary fluid, is grounded on its enhanced features relative to the high thermal conductivity and the high heat transfer rates. These specific features, widely studied in the existing literature, are likely to go beyond what one could expect from reasonings based on a mere evaluation of the volumetric concentration of (metal or carbon) nanoparticles or nanotubes. It is what has been called the “magic” power of nanoparticles by Rao (2010). What Rao calls magic is the not yet convincingly explained anomalous thermal conductivity, heat transfer rates, and viscosity experimentally observed for nanofluids.