Experimental investigation of mixed convection heat transfer of nanofluids in minichannels for aiding and opposing flow conditions

In this study, the characteristics of heat transfer, and mixed convection for aiding and opposing flow states in nanofluids of minichannels are experimentally analyzed. The diameters of the minichannels used in the study are respectively; 1.20 mm, 1.5 mm and 1.9 mm. In the experiments, pure water as work fluid and at %0, 25 and %0, 75 volume ratios, pure water based SiO2 nanofluid are used. Besides, pure water and the properties of thermal (20-60oC) conductivity and viscosity of nanofluids are experimentally specified. In order to stay on the brinks of the mechanism of mixed convection, Reynold number is held between 20 and 60. According to the obtained data, it is clear that the increased diameter of minichannel and the ratio of nanoparticles significantly enhance Nusselt number. It is also inferred that the direction of secondary flows significantly effects experimentally average Nusselt number. If all the results are analyzed, the use of nanofluids and the augmentation, which is maximum %65 and minimum %25 in Nusselt number, are observed. And when compared to the state in countercurrent(opposing) flow, it is observed that an augmentation is maximum %18 and minimum %4 in Nusselt number.