Dynamic stability, sedimentation, and time-dependent heat transfer characteristics of TiO₂ and CNT nanofluids

Nowadays, the stability and heat transfer properties of nanofluids have been extensively studied. However, for the practical application, the dynamic stability, sedimentation, and fouling characteristics are also important issues. Whether nanofluids can maintain stable heat transfer characteristics during intermittent operation in the system is also a worthwhile issue. In this paper, the dynamic stability, sedimentation, and fouling characteristics as well as the time-dependent heat transfer characteristics of TiO₂ and CNT nanofluids are investigated sequentially. The results show that compared with static condition, the dispersion stability of nanofluids is much better, and the sedimentation and fouling on solid surface are much less in dynamic condition. For the nanofluids in this paper, the sedimentation and fouling on solid surface are loose and can easily washed out after slight flushing. Rough surfaces are easier to adsorb the nanoparticles sedimentation and form fouling, but it can be greatly removed using ultrasonication. Long-term shutdown reduces the convective heat transfer enhancement of nanofluids, but it can be well restored after the action of ultrasonication.