Discussion: “Effects of Various Parameters on Nanofluid Thermal Conductivity” (Jang, S. P., and Choi, S. D. S., 2007, ASME J. Heat Transfer, 129, pp. 617–623)

Abstract

In a series of articles, Jang and Choi (1-3) listed and explained their effective thermal conductivity (keff) model for nanofluids. For example, in the 2004 article (1), they constructed a keff correlation for dilute liquid suspensions interestingly, based on kinetic gas theory as well as nanosize boundary-layer theory, the Kapitza resistance, and nanoparticle-induced convection. Three mechanisms contributing to keff were summed up, i.e., base-fluid and nanoparticle conductions as well as convection due to random motion of the liquid molecules. Thus, after an order-of-magnitude analysis, their effective thermal conductivity model of nanofluids readsDisplay Formulakeff=kf(1−φ)+knanoφ+3C1dfdpkfRedp2Prφ (1) where kf is the thermal conductivity of the base fluid, φ is the particle volume fraction, knano=kpβ is the thermal conductivity of suspended nanoparticles involving the Kapitza resistance, C1=6×106 is a constant (never explained or justified), df and dp are the diameters of the base-fluid molecules and nanoparticles, respectively, Redp is a “random” Reynolds number, and Pr is the Prandtl number. Specifically,Display FormulaRedp=C¯RMdpν (2) where C¯RM is a random motion velocity and ν is the kinematic viscosity of the base fluid.