Effect of twist ratio on the thermal-hydraulic behavior of an aluminum oxide/cupric oxide nanofluid heat exchanger

Hybrid nanofluids contain two or more nanoparticles mixed with a conventional coolant to enhance the thermophysical properties at the molecular level. The current research investigates the performance of heat exchangers under the influence of hybrid nanofluids. Simulation is performed using Ansys 2020 R2 and RNG k-epsilon model is used to solve the problem because it is the most accurate model suggested for turbulent flow. A single-pass heat exchanger of length 650 mm and diameter 20 mm was investigated and inserted with twisted tapes of twist ratios(y/W) 4 and 3 for volume concentrations ranging from 0.5 to 3%. A hybrid metal matrix nanofluid, a mixture of Al2O3 and CuO in a ratio of 70:30, was used as a working fluid to conduct the study. It is astonishing to find that with the increase in volume concentrations of hybrid nanofluid, there is a significant increase in Nusselt number, which is 370% for twisted tape of twist ratio 3. The study also revealed that there is minimal effect of volume concentration on the friction factor, although inserting twisted tape increases the friction factor 294% more than the plain tube. The thermal performance factor of the heat exchanger with twisted tape of Twist ratio = 3 is 3.52 times more than that of a plain tube. An empirical correlation between the Nusselt number and the friction factor is established for various volume concentrations and twist ratios. We conclude that the use of a hybrid nanofluid with higher thermophysical characteristics is beneficial for obtaining a high thermal performance system.