Unsteady Flow and Heat Transfer from a Horizontal Cylinder Floating in a Stationary Fluid Rotating with a Time-Dependent Angular Velocity

This paper deals with the unsteady flow and heat transfer from a floating horizontal cylinder in a stationary fluid rotating with variable angular velocity. The basis of this study is the use of time-dependent velocity functions for the rotational motion of the cylinder and exploring its effects on the characteristics of flow and heat transfer. In this regard, in addition to the sinusoidal function, exponential and linear functions in both ascending and descending modes are employed for the angular velocity of the cylinder, and the results are compared with the steady-state rotation. Based on the results obtained at zero immersion angle, changing the amplitude and frequency of the sinusoidal angular velocity is effective on the fluid behavior and heat transfer, while the effect of the starting phase can be neglected. Furthermore, the sinusoidal velocity leads to a decrease in liquid film thickness and an increase in heat transfer rate compared to the steady-state rotation. The ascending mode of exponential and linear velocity functions provide a higher thickness of the liquid film than the descending ones. The maximum and minimum film thickness are related to the ascending and descending exponential functions, respectively. Nevertheless, the maximum and minimum heat transfer rate corresponds to the descending linear and ascending exponential functions, respectively. Scrutiny of the findings demonstrates that increasing the immersion angle always promotes heat transfer, which is more impressive in the time-dependent velocity functions than the constant ones.