Flow structure in a downward branch pipe with a closed end. Characteristics of flow velocity in the branch pipe

Many pipes branch off from a main pipe in industrial plants. The penetration of hot water into the branch pipe causes thermal stratification. The thermal stratification layer fluctuates and causes thermal fatigue. The characteristics of velocity distributions in the branch pipe for inner diameters from D_b=21 mm to 43 mm were investigated by laser Doppler velocimetry in this paper. As for the flow in the branch pipe at L=4D_b, the mean velocity of the spiral flow was a simple forced vortex which indicated a straight velocity distribution. The maximum circumferential velocity U_{θ max} and minimum axial velocity U_{z min} at L=4D_b were expressed with D_b and main flow velocity. Empirical formulas were proposed for estimating the distributions of U_{θ max} and U_{z min} in the axial direction. (author)