Experimental investigation of mixed convection heat transfer of nanofluids in minichannels

Industrial developments have made it possible to produce mechanical or electronic devices in mini and micro dimensions. The reduction in size causes the increase in the heat energy that is released during the use of the devices, which leads to increased cooling loads. This makes it necessary to remove heat energy more effectively from the system. Minichannels are important for systems that heat transfer is critical because they can remove heat energy highly and they have high surface area/volume ratio. Another option is to improve the thermal performance of the work fluid as well as reduce the size in order to be able to be removed a high amount of heat. In this study, heat transfer characteristics of nanofluids in minichannels by mixed convection are investigated experimentally. Circular cross section minichannels with diameters of 1,21 mm, 1,5 mm and 1,9 mm, respectively, were used in the study. Experiments were carried out with purified water based SiO2 nanofluid, which is pure water and nanoparticle volume ratios of 0,25%, 0,75% and 1,25%, respectively, as the working fluid. The thermal conductivity and viscosity measurements of nanofluids were made at 20-60°C temperature range. The Reynolds number range was held at 15-65 during the experiments in order to work under mixed convection conditions.