Thermal Conductivity of Nanoparticle - Fluid Mixture

TLDR

A more comprehensive theory is needed to fully explain the behavior of nanoparticle‑fluid mixtures. The study discusses possible mechanisms contributing to the enhanced thermal conductivity of nanoparticle‑fluid mixtures. The authors measured effective thermal conductivity of nanoparticle‑fluid mixtures using a steady‑state parallel‑plate method, testing water, vacuum pump fluid, engine oil, and ethylene glycol with Al₂O₃ and CuO nanoparticles. Experimental measurements reveal that nanoparticle‑fluid mixtures exhibit higher thermal conductivity than base fluids, while existing theoretical models significantly underestimate these values. Nomenclature defines symbols for specific heat, thermal conductivity, thickness, Peclet number, input power, particle radius, cross-sectional area, temperature, relative velocity, thermal conductivity ratio, shear rate, density, volume fraction, and subscripts.

Abstract

Effective thermal conductivity of mixtures of e uids and nanometer-size particles is measured by a steady-state parallel-plate method. The tested e uids contain two types of nanoparticles, Al 2O3 and CuO, dispersed in water, vacuum pump e uid, engine oil, and ethylene glycol. Experimental results show that the thermal conductivities of nanoparticle ‐e uid mixtures are higher than those of the base e uids. Using theoretical models of effective thermal conductivity of a mixture, we have demonstrated that the predicted thermal conductivities of nanoparticle ‐e uid mixtures are much lower than our measured data, indicating the dee ciency in the existing models when used for nanoparticle ‐e 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 ‐e uid mixtures. Nomenclature cp = specie c heat k = thermal conductivity L = thickness Pe = Peclet number P q = input power to heater 1 r = radius of particle S = cross-sectional area T = temperature U = velocity of particles relative to that of base e uids ® = ratio of thermal conductivity of particle to that of base liquid ¯ = .® i 1/=.® i 2/ ° = shear rate of e ow Ω = density A = volume fraction of particles in e uids Subscripts