Monitoring of wall temperature fluctuations for thermal fatigue in a horizontal mixing T-junction pipe

Turbulent penetration and unsteady thermal stratification can occur when hot and cold fluids mix in T-junction pipes at nuclear plants. Temperature fluctuations with large amplitude and high frequency caused by the unstable thermal stratification can lead to time-varying thermal stress and even induce thermal fatigue of T-junction pipes. Monitoring of wall temperature fluctuations of T-junction pipes at nuclear plants has received considerable interest because the thermal fatigue failure of these pipes could present severe environmental implications and large economic losses. In this study, mock-up tests and analyses were conducted to develop a monitoring program for monitoring the wall temperature fluctuations of mixing T-junction pipes. Using a test loop, we simulated the mixing flow of hot and cold fluids in a horizontal T-junction pipe at a nuclear plant. To monitor the wall temperature fluctuations of the horizontal T-junction pipe, we developed a program in MATLAB. The monitoring program could filter out unwanted noise from raw measured temperature data by the singular spectrum analysis and guarantee a grid-independent and time-step-independent solution. With high accuracy and computational efficiency, the monitoring program was able to monitor the wall temperature fluctuations of a horizontal mixing T-junction pipe by measuring temperatures on the outer wall.