Abstract
Pipelines with thermal stratification are common in nuclear power plants, and the thermal stratification may induce thermal fatigue and lead to leakage, so thermal stratification analysis of the pipeline is particularly significant. Due to the requirement of structural integrity, for the piping system of nuclear power plants, it is not allowed to trepan for installing sensors to measure the internal parameters. The inverse heat conduction problem (IHCP) based on the easily available temperature information of the outer wall can precisely estimate the boundary conditions of the inner wall. However, the precision of inverse estimation is influenced by the measuring precision, the number and the arrangement of measuring points. This work aims at the sensitive analysis about the measuring errors and the number and locations of measuring points. The research is based on an elbow pipe with thermal stratification—a pipe type commonly used in industry. Because it is easy to disturb the flow field to install sensors inside the pipeline, and it is difficult to calculate the convective heat transfer coefficient, the numerical experiments are taken in this study. The results showed that the IHCP with multi-parameters had certain anti-noise property and the number and locations of the measuring points had a certain influence on the calculation accuracy.
Highlights
Metal pipes are widely used in industry
The experimental temperature data for the fluid near the inner wall and the assumed convective heat transfer coefficient are employed in the direct heat conductin problem (DHCP) to calculate the temperature data for entire temperature field of the pipe, including the temperature data of the outer wall and the inner wall
A transient three-dimensional inverse heat conduction problem (IHCP) with multi-variables has been developed using the conjugate gradient method (CGM) in order to estimate the convective heat transfer coefficient and the temperature fluctuations in a fluid near the inner wall based on the temperature data of the outer wall
Summary
Material fatigue failure caused by thermal stress is common [1]–[3]. Pipelines are the most vulnerable to failure. As early as 1988, the NRC issued statements, that all nuclear power plants, regardless in service or proposed, were required to complete thermal stratification analysis and risk assessment of surge lines to ensure structural integrity [4], [5]. It can be seen the importance of thermal fatigue analysis for the pipe with thermal stratification
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