مهدی بحیرائی

The two-phase Euler–Lagrange method is used here to study heat transfer characteristics of the CuO–water nanofluid in a straight tube under laminar flow regime. The comparison between two-phase and single-phase approaches shows that the Euler–Lagrange method presents more accurate results. The convective heat transfer coefficient increases with increment of particle concentration. Moreover, the amount of heat transfer enhancement increases along the tube length. The thermophoretic and Brownian forces affect the convective heat transfer and their effects become more prominent at greater distances from the tube inlet. In addition, the effects of these two forces on the convective heat transfer intensify at higher concentrations. The results obtained from the two-phase simulation reveal a higher particle concentration at the central regions as compared to regions near the wall. This can be one of the reasons for higher convective heat transfer coefficient obtained from the two-phase method in comparison with the single-phase approach. At low volume fraction, the nanofluid bulk temperature along the tube length obtained from single-phase and two-phase approaches does not differ considerably. However, at high volume fraction, the single-phase method is unable to predict the bulk temperature accurately. This can be attributed to the more intense interaction between the fluid and nanoparticles at higher concentrations.