形状係数測定における壁面伝達境界条件が及ぼす影響に関する研究

抄録

It is necessary to evaluate the geometry factor for predicting the flow accelerated corrosion (FAC) in the plant piping. Geometry factor is defined as the ratio of the wall mass transfer coefficient in the piping systems (such as orifices, elbows) to that in a straight pipe. In this study, the mass transfer coefficient is measured experimentally with electrochemical method for fully developed flow, downstream of orifice and 90-degree elbow. The experimental measurement is conducted with the pipe of the test section made of nickel, in which the whole pipe surface acts as electrode (in this paper, referred as ‘overall electrode condition'). In order to clarify the effect of the area of the electrode, obtained results are compared with the other experiments with only point electrode working (referred as ‘point electrode condition'). In addition, geometry factor is calculated with large eddy simulation (LES) and turbulent scalar transport is numerically analyzed. The values of geometry factor for the downstream of the orifice measured with overall electrode condition and point electrode condition are quantitatively different with each other, while those for elbow flow shows qualitative difference between them. Calculated values with LES are good agreement with measured values in overall electrode condition. Analysis of turbulent scalar transport reveals that, at the downstream of the orifice, the sweep component affects more strongly than the ejection component. Near the wall region in the elbow, the ejection component, on the contrary, is found to have a greater contribution than the sweep component.