Thermophysical properties of MWCNT-Alumina/water nanofluid and their influence on the performance of free convection heat transfer

In the recent past, several studies have been done on the synthesis, characterization, and thermal management applications of nanofluids due to their phenomenal improvement in their thermal properties. This experimental study focuses on the impact of multi-walled carbon nanotubes (MWCNT)-Aluminum oxide (Al2O3)/water nanofluids on the effectiveness of free convection heat transfer. The nanofluids were manufactured using a 2-step approach by dispersing MWCNT and Al2O3 nanoparticles in water. Different percentage volume concentrations in the range of 0% to 0.6% were examined, along with different proportion ratios of MWCNT- Al2O3, specifically 75:25, 50:50, and 25:75. The primary motive of the current research was to synthesize and determine the thermophysical characteristics of the nanofluids, including thermal conductivity and viscosities. Subsequently, to determine the average heat transfer coefficient (HTC) under different heat flux conditions (3030, 4040, 4545, and 5050 W/m2), experiments were performed for various volume fractions and proportion ratios of nanofluids. The findings of the study indicate that, the average HTC initially improves with increasing particle volume fraction, reaching its peak at a concentration of 0.1%. However, beyond this point, the HTC diminishes as the particle percentage volume concentration keeps to rise. Furthermore, the variations in the average HTC with heat flux were found to be similar for all proportion ratios of MWCNT-Al2O3 nanoparticles at the 0.1% volume fraction. This experimental investigation provides valuable insights into the convection characteristics of MWCNT-Al2O3/water hybrid nanofluids. The observed trends contribute to a better understanding of the optimal particle volume fraction and proportion ratios for achieving enhanced heat transfer in natural convection systems. These findings can guide the design and optimization of nanofluid-based thermal management systems in various engineering applications.