The characteristics of wall temperature fluctuation at the mixing tee with an upstream elbow were investigated and compared to those of the case without the elbow. The elbow of 90 degrees was installed in the inlet of the horizontal main pipe. The inlet flow velocities in the main and branch pipes were set to about 1.0 m/s and 0.7 m/s, respectively, to produce a wall jet pattern where the jet from the branch pipe was bent by the main pipe flow and made to flow along the pipe wall. A total of 148 thermocouples were installed near the pipe inner surface to measure the temperature distribution in the mixing tee. The upstream elbow decreased the temperature fluctuation intensity and the temperature fluctuation range at the inner surface. On the other hand, the distribution profiles and the dominant frequencies of temperature fluctuations were similar. The temperature fluctuation was also caused by the movement of a hot spot in the circumferential direction for both cases with and without the upstream elbow. The reduction of the movement of the hot spot in the circumferential direction decreased the temperature fluctuation for the case with the upstream elbow.

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