Investigation of the heat transfer in a square microchannel with Al₂O₃-H₂O nanofluids

The progressing miniaturisation and increasing power demand of microelectronic devices require efficient cooling systems to avoid thermal damage. Future cooling systems have to be capable of dealing with heat loads of more than 200 W/cm², at small temperature differences. However, the convective heat transfer in microchannels is limited due to the laminar flow regime. Nanofluids, i. e. fluids with suspended particles of nanometer size, have been shown to enhance the heat transfer. Nevertheless, their potential was recently controversially discussed in the literature. Therefore, reliable experimental heat transfer investigations are necessary to understand the underlying physical phenomena and help to establish design rules for future microelectronic cooling systems. For this reason the aim of the current study was to design and test a platform for the characterization of the fluid flow and the heat transfer in a straight microchannel. The heat transfer using pure water and water with 30-60 nm Al₂O₃ nanoparticles were investigated at two different volume concentrations, 1% and 2.5% and Reynolds numbers ranging from 70 to 300. The results imply that the experimental platform allows for reliable and reproducible measurements of heat transfer and its sensitivity to the appropriated fluid and the flow properties. It could be shown that the heat transfer coefficient can be enhanced by up to 5.5% using 2.5% water-Al₂O₃ nanofluids compared to distilled water.