On the reliable estimation of heat transfer coefficients for nanofluids in a microchannel

Nanofluids (base fluid and nanoparticles) can enhance the heat transfer coefficient h in comparison to the base fluid. This open the door for the design of efficient cooling system for microelectronics component for instance. Since theoretical Nusselt number correlations for microchannels are not available, the direct method using an energy balance has to be applied to determine h. However, for low nanoparticle concentrations the absolute numbers are small and hard to measure. Therefore, the study examines the laminar convective heat transfer of Al₂O₃-water nanofluids in a square microchannel with a cross section of 0.5 x 0.5 mm² and a length of 30 mm under constant wall temperature. The Al₂O₃ nanoparticles have a diameter size distribution of 30-60 nm. A sensitivity analysis with error propagation was done to reduce the error for a reliable heat transfer coefficient estimation. An enhancement of heat transfer coefficient with increasing nanoparticles volume concentration was confirmed. A maximum enhancement of 6.9% and 21% were realized for 0.6% Al₂O₃-water and 1% Al₂O₃-water nanofluids.