Thermal Conductivity of Nanoparticle - Fluid Mixture

Effective thermal conductivity of mixtures of uids and nanometer-size particles is measured by a steady-state parallel-plate method. The tested uids contain two types of nanoparticles, Al2O3 and CuO, dispersed in water, vacuum pump uid, engine oil, and ethylene glycol. Experimental results show that the thermal conductivities of nanoparticle– uid mixtures are higher than those of the base uids. Using theoretical models of effective thermal conductivity of a mixture, we have demonstrated that the predicted thermal conductivities of nanoparticle– uid mixtures are much lower than our measured data, indicating the de ciency in the existing models when used for nanoparticle– uid mixtures. Possible mechanisms contributing to enhancement of the thermal conductivity of the mixtures are discussed. A more comprehensive theory is needed to fully explain the behavior of nanoparticle– uid mixtures. Nomenclature cp = speci c heat k = thermal conductivity L = thickness Pe = Peclet number Pq = input power to heater 1 r = radius of particle S = cross-sectionalarea T = temperature U = velocity of particles relative to that of base uids ® = ratio of thermal conductivityof particle to that of base liquid ¯ =. ® ¡ 1/=. ® ¡ 2/ ° = shear rate of ow = density Á = volume fraction of particles in uids Subscripts e = effective property f = base uid property g = glass spacer p = particles r = rotationalmovement of particles t = translationalmovement of particles I.

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