ICONE15-10308 PREDICTION OF THERMAL STRATIFICATION PHENOMENA IN A BRANCH PIPE USING NUMERICAL SIMULATION

Abstract

Recently the JSME has published the guideline for the high-cycle thermal fatigue in pipelines in nuclear power plants, which is caused by the temperature fluctuation in mixing tees with high difference of temperature between two fluids. Many experimental studies have been conducted to establish the evaluation method for the thermal fatigue of pipe. The cavity flow is one of typical flow patterns which cause the high-cycle thermal fatigue. It is driven by the main flow as a stagnant branch flow, where the other end of the branch pipe connected to the main pipe is closed by a valve and so on. When the flow in the main pipe is hotter than the branch flow, heat of the main flow is transported to the branch flow. According to experiments, the thermal stratification is formed in the branch pipe and the stratification surface fluctuates. These phenomena will threaten the structural integrity of the piping system. In order to estimate the high-cycle thermal fatigue of the pipe wall, it is necessary to predict the location of thermal stratification, the amplitude of temperature fluctuation and its frequency. The purpose of this study is to clarify the mechanism of this phenomena using numerical fluid dynamics simulation and to predict the location of thermal stratification. We evaluated the effect of various numerical turbulent models on the branch flow and found that proper numerical modeling of shear force by the main flow and the velocity distribution on the wall boundary in the branch pipe are important for high-accuracy prediction of the location of the thermal stratification. The paper will discuss the numerical modeling and the results compared with experimental results for the cavity flow.