Experimental investigation of mixed convection heat transfer of nanofluids in a circular microchannel with different inclination angles

Abstract

In this study, the characteristics of mixed convection heat transfer of nanofluids in circular microchannels with 500 μm diameter were investigated experimentally. In the study, water and water-based SiO2 nanofluids were used as the working fluid, and volumetric particle ratios of the nanofluids were selected as 0.2 and 0.4%. The thermal conductivity and viscosity characterizations of all fluids were performed in the temperature range of 20–60 °C, and the characteristics related to the temperature obtained from the measurements were used in calculations. The effect of the microchannel inclination angle and particle volumetric ratio on the mixed convection heat transfer characteristics was investigated. Upon examining the results, it was revealed that the range of 13–35% of the total heat transfer was generated by the natural convection effects. Increasing the inclination angle of the test section provided an enhancement between 4 and 13% in the total heat transfer. Furthermore, the increase in the volumetric particle ratio increased both forced convection heat transfer and the natural convection heat transfer components. Adding nanosized SiO2 particles into the water caused the total heat transfer to increase from 12 to 14% for 0.2 vol% and from 29 to 32% for 0.4 vol%.