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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

An Investigation of Wall Temperature Characteristics to Improve the Evaluation Method for Thermal Fatigue at A T-Junction Pipe

Get access (open in a dialog) DOI: 10.1615/IHTC15.min.008678
pages 4751-4764

Аннотация

Thermal fatigue cracking may initiate at a T-junction pipe where high and low temperature fluids flow in from different directions and mix. Damage due to this phenomenon occurred in some pipes in nuclear power plants. Thermal stress is caused by a temperature gradient in a structure and by its variation due to fluid temperature fluctuations. It is important to investigate temperature distributions at the pipe inner surface, because the stress distributions depend on the heated region due to the hot jet flow from a branch pipe. In this study, wall temperature characteristics at a T-junction pipe were investigated to improve evaluation method for thermal fatigue. The test section is made of stainless steel and consists of a horizontal main pipe with diameter 150 mm(=Dm) and a T-junction connected to a vertical branch pipe with diameter of 50 mm(=Db). Flow patterns in a T-junction depend on the inflow velocity ratio of the main and branch pipes. The inlet flow velocities in the main and branch pipes were set to 0.99 m/s and 0.66 m/s respectively to produce a wall jet pattern where the jet from the branch pipe was bent by the main pipe flow and flowed along the pipe wall. It is known that this flow pattern shows high fluctuation intensity of the fluid temperature near the pipe wall. The temperature difference between the two pipe flows was 34.1 K. 148 thermocouples were installed to measure the wall temperature at the pipe inner surface near of the branch pipe and in the downstream region. The maximum values of both temperature fluctuation intensity and the temperature fluctuation range in the pipe wall were measured as 5% and 29% of the fluid temperature difference in the inlet. The distributions of these values are similar in the range from of the branch pipe to the downstream of 1Dm. The dominant frequency of the large temperature fluctuations in the region downstream from z = 0.5Dm was equal to 0.2 of the Strouhal number, which was equal to the frequency caused by the vortex streets generated around the jet flow.