The process analysis and dynamic force calculation of an air bubble detaching from a flat coal surface

Abstract

ABSTRACT The process and dynamic force of an air bubble detaching from a flat coal surface were investigated and calculated, respectively. The detachment process was captured by a high-speed camera, the dynamic contact angle and the contact area which obtained from the images indicated that the detachment process can be divided into two phases: bubble stretching phase and bubble sliding phase. The main forces acting on the bubble were confirmed to be a capillary force, the increased pressure force, and external detaching force through dynamic force calculation of the detachment process. Combined with the dynamic force calculation, it was found that there was a maximum external detaching force at the boundary between bubble stretching phase and bubble sliding phase, and the maximum external detaching force is defined as critical detachment force, which determined whether the sliding phase could occur. Under the same conditions of the coal surface and the solution properties, the critical detachment force showed a proportional relationship to the bubble size, it could be used to predict the critical detachment forces of different bubble sizes.