Experimental study on high cycle thermal fatigue in T-junction. Effect of local flow velocity on transfer of temperature fluctuation from fluid to structure

A quantitative evaluation on high cycle thermal fatigue due to temperature fluctuation in fluid is of importance for structural integrity in the reactor. It is necessary for the quantitative evaluation to investigate occurrence and propagation processes of temperature fluctuation, e.g., decay of fluctuation intensity near structures and transfer of temperature fluctuation from fluid to structures. The JSME published a guideline for evaluation of high-cycle thermal fatigue of a pipe as the JSME guideline in 2003. This JSME standard covers T-pipe junction used in LWRs operated in Japan. In the guideline, the effective heat transfer coefficients were obtained from temperature fluctuations in fluid and structure in experiments. In the previous studies, the effective heat transfer coefficients were 2 - 10 times larger than the heat transfer coefficients under steady state conditions in a straight tube. In this study, a water experiment of T-junction was performed to evaluate the transfer characteristics of temperature fluctuation from fluid to structure. In the experiment, temperatures in fluid and structure were measured simultaneously at 20 positions to obtain spatial distributions of the effective heat transfer coefficient. In addition, temperatures in structure and local velocities in fluid were measured simultaneously to evaluate the correlation between the temperature and velocity under the non-stationary fields. The large heat transfer coefficients were registered at the region where the local velocity was high. Furthermore it was found that the heat transfer coefficients were correlated with the time-averaged turbulent heat flux near the pipe wall. (author)