Field synergy analysis on the mechanism of heat transfer enhancement by using nanofluids

A numerical simulation investigation on the flow of nanofluids in a circular tube was carried out. The simulations have two parts. Firstly, pressure drop of pure water (single-phase base fluid) flowing in a circular tube was calculated in order to verify the correctness of the simulation model with experimental results. Secondly, numerical simulations for nanofluids were conducted with consideration of different mass fractions of nanoparticles. The influencing mechanisms of nanoparticles for base fluid were further discussed. On one hand, adding nanoparticles causes changes in the fluid velocity distribution in fluid region which further leads to changed fluid flow properties in the radial direction. On the other hand, nanoparticles increase the heat transfer performance of the whole fluid with changed temperature gradient. The combination of the changed velocity field and temperature gradient field leads to the enhancement of the heat transfer process in nanofluids. The results show that the enhancement of heat transfer by nanofluids is achieved by the augmented synergy of the temperature gradient field and the velocity field.