Heat transfer properties of nanoparticle-in-fluid dispersions (nanofluids) in laminar flow

The convective heat transfer coefficients of several nanoparticle-in-liquid dispersions (nanofluids) have been measured under laminar flow in a horizontal tube heat exchanger. The nanoparticles used in this research were graphitic in nature, with aspect ratios significantly different from one (l/d ≈ 0.02). The graphite nanoparticles increased the static thermal conductivities of the fluid significantly at low weight fraction loadings. However, the experimental heat transfer coefficients showed lower increases than predicted by either the conventional heat transfer correlations for homogeneous fluids, or the correlations developed from the particle suspensions with aspect ratios close to one. New correlations on heat transfer need to be developed for nanofluid systems.