Bubble dynamics in a horizontal rectangular pipe with rough wall

Many researches on the flow mode of two-phase flow in horizontal pipes made so far have been related mostly to the pipes with smooth surfaces. In the horizontal two-phase flow at low velocity, bubbles flow along the top walls, and the behavior of the bubbles at this time is considered to be largely affected by the roughness of the walls. Such horizontal two-phase flow at low velocity appears in relation to the separation of bubbles from the surfaces of boiling facing downward, besides the hot leg at the time of small LOCA in PWR plants. In this research, the horizontal two-phase flow of air-water system at atmospheric pressure and normal temperature in a rectangular pipe was used, and mainly the effect of wall roughness on the behavior of bubbles was experimented. The experimental setup is shown. The flow mode was observed, the shape projected on a horizontal plane and the velocity of bubbles were measured with a high speed camera, and the thickness of bubbles was measured when the flow rate of water, that of air and wall roughness were changed. It was found that as the top surface was rougher, bubbles became smaller. Bubbles took the shape so that the sum of potential energy and surface energy became the minimum. The effect of the water velocity and wall roughness on the bubble shape was small. The velocity of bubbles was determined by their size and the water velocity, but the effect of the wall roughness was small. (Kako, I.)