Extended Maxwell model for the thermal conductivity of nanofluids that accounts for nonlocal heat transfer

• A model for the effective thermal conductivity of nanofluids based on the nonlocal heat conduction theory is proposed.
• The model captures the trend of particle size dependency of the thermal conductivity of water-based alumina nanofluids.
• The model is shown to be consistent in the limits of pure fluid and for large particle sizes.

The thermal conductivity of nanofluids depends on factors such as particle size, volume fraction of particles in the suspension and intrinsic thermal conductivities of the base fluid and particles. To account for these factors, the traditional Maxwell model for the effective thermal conductivity of a mixture is modified to account for nonlocal heat transport that can arise due to the small characteristic length in a nanofluid – the particle size thus naturally appears in the modified model. The resulting model is calibrated and validated with experimental measurements of alumina nanofluids: overall, good agreement is found. Furthermore, the modified model is shown to be consistent in the limits of only the base liquid as well as for large particle sizes.