Penetration flow into a branch pipe causing thermal fatigue at a mixing tee

Abstract

Flow structure in a branch pipe of the mixing tee was investigated in order to improve the assessment method for thermal fatigue damage. The mixing tests were performed using a test section which was made of transparent acrylic resin and consisted of a horizontal main pipe and a vertical branch pipe. The penetration flow into the branch pipe was observed under the condition of branch flow with low flow velocity. The flow in the branch pipe was classified into three flow patterns: no penetration; entrained penetration; and impinged penetration. These flow patterns depended on the momentum ratio of the main and branch pipes. The entrained penetration was caused by the entrainment of the main flow into the separation region where the branch flow was bent by the main flow and separated from the branch pipe wall. The impinged penetration was the flow pattern in which the main flow impinged on the branch pipe wall and penetrated into the branch pipe. These penetration flows occurred intermittently and the penetration depth changed rapidly. The maximum penetration depth correlated with the momentum ratio.