Thermocapillary bubble flow and coalescence in a rotating cylinder: A 3D study

• In stationary cylinder, the thermocapillary migration of two bubbles was found to be linear.
• Centrifugal and Coriolis forces can be used to control bubble agglomeration.
• When the ratio of thermocapillary to the centrifugal forces is 1, the effects of rotation are important.
• The current study is novel and has never been numerically investigated.
• Centrifugal and Coriolis forces can be used to control bubble agglomeration.

The process of thermocapillary bubbles rising in a rotating 3D cylinder in zero gravity was analysed and presented numerically with the aid of computational fluid dynamics (CFD) by means of the volume of fluid (VOF) method. Calculations were carried out to investigate in detail the effect of the rotational speed of the hosted liquid on the trajectory of both single and group bubbles driven by the Marangoni force in zero-gravity conditions. For rotational speeds from 0.25 to 2 rad/s, bubble displacement with angular motion was found to be directed between the hotter surface and the rotational axis. This is contrary to the conventional bubble flow from areas of high pressure to low pressure, radial direction, or from cold to hot regions, axial direction. The results demonstrate that for the ratio of rotational speeds to the thermocapillary bubble velocity larger than unity, the surface tension gradient is the dominant force and the bubble motion towards the hotter. On the other hand, for ratio less than 1, the bubble motion is dominated and is significantly affected by centrifugal force. As rotation speed increases, the amount of deflection increases and the Marangoni effect vanishes. The current study is novel in the sense that single- and multi-bubble motion incorporating thermocapillary forces in a rotating liquid in a zero-gravity environment has never been numerically investigated.