Transient flow and heat transfer from a rotating sphere around its vertical axis floating in a stationary fluid

In this paper, for the first time, convective heat transfer from a sphere with time-dependent rotational velocity around a vertical axis floating in stationary fluid is numerically investigated and discussed. The simulation is based on the two-phase volume of fluid model, and the obtained results are shown by streamlines, isotherm and volume fraction contours, Nusselt number, and the film thickness of water. Computations are undertaken for sinusoidal pulsation and exponential form of time-dependent rotational velocity of sphere. The results show that the water is pulled up from the lower pole of the sphere by the centrifugal force caused by the sphere rotation, and its movement continues by the liquid film formation and is finally thrown out radially due to the dominance of inertial forces. The findings reveal that sinusoidal pulsation has higher heat transfer performance compared to steady-state rotation so that the effect of amplitude is more significant than the frequency of pulsation. In the case of the exponential function, the heat transfer rate decreases over time due to descending trend of this function for the rotational velocity of the sphere. Also, it is found that by increasing the immersion angle from 30 degrees to 60 degrees, the time-surface-averaged Nusselt number increases about 40% and 49% for the sinusoidal and exponential function, respectively.

Automated summary

In this paper, the convective heat transfer from a sphere with time-dependent rotational velocity around a vertical axis floating in stationary fluid is numerically investigated. The results show that sinusoidal pulsation has higher heat transfer performance compared to steady-state rotation, and the effect of amplitude is more significant than the frequency of pulsation. It is also found that the heat transfer rate decreases over time for the exponential function. Additionally, increasing the immersion angle leads to an increase in the averaged Nusselt number.