Authors: LePing Zhou George P Peterson Minani Yoda BuXuan Wang
Publish Date: 2012/03/27
Volume: 14, Issue: 4, Pages: 822-
Abstract
The role of temperature gradient induced nanoparticle motion on conduction and convection was investigated Possible mechanisms for variations resulting from variations in the thermophysical properties are theoretically and experimentally discussed The effect of the nanoparticle motion on conduction is demonstrated through thermal conductivity measurement of deionized water with suspended CuO nanoparticles 50 nm in diameter and correlated with the contributions of Brownian diffusion thermophoresis etc The tendencies observed is that the magnitude of and the variation in the thermal conductivity increases with increasing volume fraction for a given temperature which is due primarily to the Brownian diffusion of the nanoparticles Using dimensional analysis the thermal conductivity is correlated and both the interfacial thermal resistance and nearfield radiation are found to be essentially negligible A modification term that incorporates the contributions of Brownian motion and thermophoresis is proposed The effect of nanoscale convection is illustrated through an experimental investigation that utilized fluorescent polystyrene nanoparticle tracers 200 nm in diameter and multilayer nanoparticle image velocimetry The results indicate that both the magnitude and the deviation of the fluid motion increased with increasing heat flux in the nearwall region Meanwhile the fluid motion tended to decrease with the offwall distance for a given heating power A corresponding numerical study of convection of pure deionized water shows that the velocity along the offwall direction is several orders of magnitude lower than that of deionized water which indicates that Brownian motion in the nearwall region is crucial for fluid with suspended nanoparticles in convectionProject 50906024 supported by National Natural Science Foundation of China and Project 3102026 supported by Beijing Natural Science Foundation The authors acknowledge support from the Office of Naval Research ONR The authors also acknowledge gratefully the helpful discussions with Mr Yaofa Li Mr Necmettin Cevheri Dr Myeongsub Kim and Dr Bo Feng at the Georgia Institute of Technology
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