ABSTRACT
The impressive heat transfer enhancement revealed experimentally in nano“uid suspensions by Eastman et al. (2001), Lee et al. (1999), and Choi et al. (2001) con“icts apparently with Maxwell’s (1891) classical theory of estimating the effective thermal conductivity of suspensions, including higher-order corrections and other spherical particle geometries developed by Hamilton and Crosser (1962), Jeffrey (1973), Davis (1986), Lu and Lin (1996), and Bonnecaze and Brady (1990, 1991). Further attempts for independent conœrmation of the experimental results showed con“icting outcomes with some experiments such as Das et al. (2003) and Li and Peterson (2006) conœrming at least partially the results presented by Eastman et al. (2001), Lee et al. (1999), and Choi et al. (2001), while others such as Buongiorno and Venerus (2010) and Buongiorno et al. (2009) show in contrast results that are in agreement with Maxwell’s (1891) effective medium theory. All these experiments were performed by using the transient hot wire (THW) experimental method. On the other hand, most experimental results that used optical methods, such as the optical beam de©ection (Putnam et al., 2006), all-optical thermal-lensing method (Rusconi et al., 2006), and forced Rayleigh scattering (Venerus et al., 2006), did not reveal any thermal conductivity enhancement beyond what is predicted by the effective medium theory. A variety of possible reasons for the excessive values of the effective thermal conductivity obtained in some experiments have been investigated, but only few succeeded to show a viable explanation. Jang and Choi (2004) and Prasher et al. (2005) show that convection due to Brownian motion may explain the enhancement of the effective thermal conductivity. However, if indeed this is the case, it is difœcult to explain why this enhancement of the effective thermal conductivity is selective and is not obtained in all nano“uid experiments. Alternatively, Vadasz et al. (2005) showed that hyperbolic heat conduction also provides a viable explanation for the latter, although their further research and comparison to later published experimental data presented by Vadasz and Govender (2010) lead them to discard this possibility.
