Flow and temperature fluctuation mechanism in a downward branch pipe with a closed end (4th. report, Influence of inner diameter on penetration depth and fluctuation characteristics)

Abstract

Hot water in a main pipe flows into a branch pipe and forms a thermally stratified layer with cold water at a bent section. Fluctuation of the thermally stratified layer may initiates thermal fatigue crack in the branch pipe. Penetration depth of the main flow and the fluctuation characteristics into the branch pipe with a closed end were investigated experimentally for the branch pipe inner diameters ( = Db) from 7 mm to 43 mm under uniform temperature conditions. The penetration depth of the main flow was correlated by the Reynolds number defined by the main flow velocity ( = Um) and Db. The fluctuation width of the penetration depth ( = ΔL) was large for Db less than 30 mm and small for Db more than 34 mm. It increased with increasing Um for Db less than 30 mm and was almost constant for Db more than 34 mm. Periods for the fluctuation of the penetration depth increased with increasing Um and Db. The maximum penetration depth predicted by the obtained correlation is available to the design preventing thermal fatigue in the branch pipe with a closed end.

Keywords

• cavity flow
• vertical branch pipe
• penetration depth
• thermal stress
• swirling flow
• thermal hydraulics