Experimental investigation of heat transfer and pressure drop in a minichannel heat sink using Al₂O₃ and TiO₂–water nanofluids

Nanofluids are known as a new generation of coolants. These fluids have attracted more attention in cooling applications, like electrical, optical, and solar systems recently, because of their unique rheological and thermal properties. In the present study, to evaluate the thermal behavior of the nanofluids, Al₂O₃ and TiO₂ nanoparticles with the size of 20 nm were completely dispersed in distilled water and circulated in a minichannel heat sink. The heat sink consists of 10 minichannels that have designed to cool thermoelectric generators. The results showed that by only dispersion of 0.5 vol% Al₂O₃ nanoparticles a 9.30% heat transfer enhancement observed. It was also obtained that the TiO₂-water sample showed a 4.56% heat transfer enhancement. The highest efficiency was obtained by utilizing the Al₂O₃-water nanofluid. This was attributed to the higher thermal conductivity of Al₂O₃ compared to TiO₂. Using both nanofluids resulted in higher pressure drop compared to the based fluid. At the Reynolds number of 1000, the pressure drop for Al₂O₃ and TiO₂ nanofluids increased as 3.33% and 3.88%, respectively. The increased pressure drop was attributed to higher density and viscosity of nanofluids. The classical theories are not available to justify the remarkable heat transfer enhancement obtained by adding a negligible amount of mentioned nanoparticles. It seems that new mechanisms such as the random motion of nanoparticles and generated microconvections by nanoparticle motion in the base fluid are responsible for considerable heat transfer enhancement.