Experimental Study on Fluid Mixing Phenomena in T-pipe Junction with Upstream Elbow

Temperature fluctuation in fluid causes high cycle thermal fatigue in shroud structure according to its amplitude and frequency. There are still some incidents of thermal fatigue and leakage in light water reactors (Japanese PWR Tomari-2 in 2003, French PWR CIVAUX in 1998), and also in sodium cooled reactors (French FBR PHENIX in 1992). Mixing tee is a typical component where temperature fluctuation occurs. An elbow is often used near the mixing tee and it brings biased velocity distribution and also the secondary flow, which decays unsteadily. Here, influence of upstream elbow in the main pipe was studied in the Water Experiment on Fluid Mixing in T-pipe with Long Cycle Fluctuation (WATLON) facility. Temperature distribution in the mixing tee was measured by a movable thermocouple tree and velocity field was measured by high speed PIV. Measured temperature showed that fluctuation intensity near the wall was larger in a case with the elbow than in a straight case under a wall jet condition where the jet exiting from the branch pipe was bent down to the pipe wall by high flow velocity in the main pipe. Measured flow velocity showed that biased flow velocity distribution and fluctuation due to the elbow influenced bending of branch pipe jet and the temperature fluctuation intensity around the jet.