Experimental investigations of particle sizes effects on exergy and entropy characteristics of AL2O3 - MWCNT hybrid nanofluid along the transitional flow regime

Experimental investigation on particle size effect on entropy and exergy characteristics of AL2O3 - MWCNT hybrid nanofluid in transitional flow Regime was carried out with four different particle sizes (i.e., for Aluminum oxide (AL2O3), 20 nm, and 5 nm used while Multiwalled Carbon Nanotubes (MWCNT) <7 nm and 30–50 nm particles). 0.3 vol concentrations of three hybrid nanofluids with different particle size combinations (i.e., Al2O3(20 nm) – MWCNT(20–30 nm), Al2O3(20 nm) – MWCNT(<7 nm), and then Al2O3(5 nm) – MWCNT(<7 nm)) are prepared using a two-step method, at a percentage weight composition (PWC) of 60:40. Results shows that Nanofluid with Al2O3 (20 nm) and MWCNT (<7 nm) have shown the best performance. It has an exergy efficiency of 54.12% at turbulent Reynold number of 4500, while in the transitional flow regime, it records an exergy efficiency of 47.85%. Frictional entropy and thermal entropy in the transitional regime were reduced with hybrid nanofluid of Al2O3 (20 nm) and MWCNT (<7 nm) by 6.78% and 13.53%, respectively, as compared to Al2O3 (5)- MWCNT (<7) nanofluid. Both thermal and frictional entropy effects were better minimized in the turbulent regime than in the lamina and transitional regime, as they were reduced by 16.66 and 24.7%, respectively. The study also recommends that for further investigations, more samples need to be taken to reach clearer conclusion of the effect of particle size, and since this is a hybrid nanofluid the samples should be of different sizes from both nanoparticles.