Heat transfer process for penetration flow into a branch pipe causing thermal fatigue at a T-junction

The heat transfer process between a fluid and a wall at a T-junction was investigated for impinged penetration flow in which the hot mainstream flow impinged on the branch pipe wall and penetrated into the branch pipe on the downstream side. The temperature distributions of the fluid near the branch pipe wall and the pipe inner surface were simultaneously measured using thermocouples. The fluid temperature close to the branch pipe wall fluctuated as a result of the hot mainstream flow penetrating into the branch pipe, and these fluctuations caused temperature fluctuations on the pipe inner surface. However, the temperature fluctuation range on the inner surface did not exceed 40% of the range of the fluid temperature fluctuation, because fluctuations were attenuated due to the heat transfer process from fluid to structure. The power spectrum method was used to the heat transfer coefficient on the pipe inner surface. The evaluated heat transfer coefficient was 1.62 times larger than that calculated using the Dittus-Boelter equation. The temperature fluctuation range on the inner surface was successfully estimated by leveraging the derived heat transfer coefficient and the measured fluid temperature.