Prediction method of metal surface temperature fluctuation for evaluation of high cycle thermal fatigue

Nuclear reactor plants often cause high-cycle thermal fatigue damages (thermal striping) due to turbulent temperature fluctuations resulting from the mixing of hot and cold fluid. The boundary layer attenuation effects for fluid temperature fluctuation have been greatly desired to be studied in order to improve the evaluation accuracy high-cycle thermal fatigue damages. This paper describes the strict derivation of the power spectrum method to evaluate effective heat transfer coefficients required to predict the surface temperature fluctuation from the measured fluid temperature. Two prediction methods of metal surface temperature fluctuation: 'Improved Time Range Method' and 'Frequency Range Method' were proposed using the effective heat transfer coefficient predicted by the power spectrum method and fluid temperature fluctuation data. The prediction errors of these methods were investigated using parallel impinging jet test data. It was found that the metal temperature fluctuations predicted by the two methods agreed with the corresponding experimental data and the validity of the methods were demonstrated. Metal surface temperature fluctuation was predicted by the two methods. The predicted results appeared to be in good agreement each other and no marked difference in prediction accuracy were found between the Time Range Method and the Frequency Range Method. (author)