Thermal Analysis of Carbon Nanotubes Suspended in PAO Mixtures 2010-01-1732

Poly Alpha Olefins (PAO) are extensively used as cooling fluid for thermal management in avionics cooling applications owing to their superior physical and chemical properties, such as greater fluidity at low temperature, lower volatility, a higher viscosity index, lower pour point, better oxidative and thermal stability as well as low toxicity. Solvents doped with minute concentration of nanoparticles are termed as “Nanofluid”. Anomalous enhancements in thermo-physical property values as well as in heat transfer performance of nanofluids have been reported using nanofluids (compared to that for the neat solvent). The thermal interfacial resistance between the nanoparticle and the solvent molecules (Kapitza Resistance) is the dominant factor controlling the efficacy of the nanofluids for cooling applications. In this study Molecular Dynamics (MD) simulations were performed to estimate the interfacial thermal resistance between carbon nanotubes and surrounding fluid molecules for PAO solvent. Heat transfer from a heated (5,5) arm chair carbon nanotube to PAO molecules is explored in the simulations. The fluid molecules considered are mixtures of n-heptane, n-tridecane and n-nondecane and their isomers. The results of equilibrium molecular structure of the system shows a peak in the density of the fluid near the nanotubes surface followed by oscillations for a few atomic distances and subsequently the density fluctuations approach the value corresponding to the density of the bulk liquid. These results are consistent with the experimental studies showing the peaks in the fluid densities near the solid surface. The results of the interfacial thermal resistance show the dependence of the Kapitza Resistance on the ability of the molecules and their mixtures to wrap around the carbon nanotubes. The more effective a molecule can wrap around the nanotubes, the less will be the interfacial thermal resistance. So long straight chains offer more resistance than branched chains due to the stearic hindrance effect. The results from this study can be utilized to “design” more effective PAO nanofluids for enhancing their efficacy in cooling applications.