Dr. Jacob Eapen's Talk

Jan 12, 2012 - 15:30

Jan 12, 2012 - 16:30

Room 118 (Creativity Hall Ground Floor) Chemical Engineering

Seminars

Dr. Jacob Eapen Assistant Professor Department of Nuclear Engineering North Carolina State University USA

Abstract: The early nanofluid experiments showed a fascinating increase in the thermal conductivity with very low nanoparticle volume fraction. While several experiments with well-dispersed nanoparticles have shown modest conductivity enhancements consistent with the Maxwell mean–field theory more instances of substantially larger enhancements are also reported in recent years. While these observations lend a reasonable confidence to the experimental methods the variability in the test results also highlights the difficulty of preparation and reproduction of consistent or standardized nanofluid samples. Several new mechanisms have been hypothesized in the recent years to characterize the thermal conduction behavior in nanofluids. In this talk it is shown that a large set of nanofluid thermal conductivity data is enveloped by the well-known Hashin and Shtrikman (H-S) mean-field bounds for homogeneous systems. The thermal conductivity in nanofluids therefore is largely dependent on whether the nanoparticles stay dispersed in the base fluid form low dimensional fractal-like configuration or assume an intermediate configuration. The experimental data which is strikingly analogous to those in solid composites and liquid mixtures provide a strong evidence for the classical nature of thermal conduction in nanofluids. Molecular dynamics (MD) simulations further demonstrate that H-S limits are universally respected even for sub–nanometer sized clusters.