Natural convective heat transfer investigation of nanofluids affected by electrical field with periodically changed direction

Nanofluids with excellent thermal properties have significant advantages in the heat transfer enhancement. While, nanoparticles are easily deposited on the heat transfer interface or electrode after long-term running, which causes serious heat transfer instability. Therefore, the resuspension and natural convective heat transfer of nanofluids affected by electrical field with periodically changed direction were studied in the present study. Specifically, the variation of deposited nanoparticle layer on heat transfer surface was observed. Meanwhile, the resuspended nanofluid heat transfer characteristics were analyzed. Furthermore, mechanism of nanoparticle resuspension and heat transfer performance of resuspended nanofluid were also discussed. It is found that nanoparticles could be resuspended stably by electrical field with periodically changed direction. Meanwhile, the heat transfer performance of resuspended nanofluid under electrical field is significantly enhanced when compared to the pure base fluid, which is increased with the improvement of voltage, concentration, and direction switching time. The mechanism analysis shows that the deposited nanoparticles are resuspended by the driven of upward electric forces and drag of basefluid, and limit in a certain range by the periodically changed electrical field. Besides, A dimensionless heat transfer prediction model of nanofluid affected by electrical field with periodically changed direction was proposed, which has an acceptable reliability.