Effects of Various Parameters on Nanofluid Thermal Conductivity

TLDR

Nanofluids exhibit enhanced thermal conductivity that classical Maxwell-type theories cannot explain, prompting the proposal of Brownian‑motion‑induced nanoconvection as a key nanoscale mechanism. This study aims to clarify the new concepts and simplifying assumptions underlying nanofluid conductivity models and to quantify how parameters such as nanoparticle‑to‑fluid conductivity ratio, volume fraction, size, and temperature affect effective thermal conductivity. The authors develop a model incorporating Brownian‑motion‑induced nanoconvection and analyze the influence of these parameters on the predicted effective thermal conductivity. Model predictions agree well with experimental data for nanofluids containing oxide, metallic, and carbon nanotube nanoparticles.

Abstract

The addition of a small amount of nanoparticles in heat transfer fluids results in the new thermal phenomena of nanofluids (nanoparticle-fluid suspensions) reported in many investigations. However, traditional conductivity theories such as the Maxwell or other macroscale approaches cannot explain the thermal behavior of nanofluids. Recently, Jang and Choi proposed and modeled for the first time the Brownian-motion-induced nanoconvection as a key nanoscale mechanism governing the thermal behavior of nanofluids, but did not clearly explain this and other new concepts used in the model. This paper explains in detail the new concepts and simplifying assumptions and reports the effects of various parameters such as the ratio of the thermal conductivity of nanoparticles to that of a base fluid, volume fraction, nanoparticle size, and temperature on the effective thermal conductivity of nanofluids. Comparison of model predictions with published experimental data shows good agreement for nanofluids containing oxide, metallic, and carbon nanotubes.