Non-Axisymmetric Mass Transfer Phenomenon behind an Orifice in a Curved Swirling Flow

Abstract

The purpose of this paper is to understand the mechanism of non-axisymmetric wall-thinning that caused a pipe break in the pipeline of the Mihama nuclear power plant in 2004. The wall thinning was caused by the flow accelerated corrosion which affects low carbon steel pipelines. The mass transfer rate measurement of the wall thinning behind an office in a curved swirling flow is carried out in a closed-circuit water tunnel using a benzoic acid dissolution method. The experimental results indicate that the high mass transfer rate is observed on one side of the pipe behind the orifice, which is similar to the observation of the wall-thinning rate in the Mihama case. This result suggests that the influence of the secondary flow in the long elbow combined with the swirling flow can produce the non-axisymmetric mass transfer phenomenon behind the orifice.

Influence of swirling flow on mass and momentum transfer downstream of a pipe with elbow and orifice

“…Fig. 8(a) shows the non-dimensional mass transfer coefficient K/K 0 downstream of the pipe with elbow and orifice without swirl at each circumferential position, which is compared with the perimeter-averaged distribution on the straight pipe downstream of the orifice without elbow measured by the benzoic acid dissolution method [17]. The mass transfer coefficient in the pipe with elbow and orifice agrees with that of the orifice flow by benzoic acid dissolution method within an experimental uncertainty.…”

“…The mass transfer coefficient in the pipe with elbow and orifice agrees with that of the orifice flow by benzoic acid dissolution method within an experimental uncertainty. Note that the experimental uncertainty by the plaster dissolution method is 5.2% and that by the benzoic acid dissolution method is 6.8% [17]. This result suggests that the influence of the secondary flow downstream of the elbow recovers to that of the straight pipe flow within 10d downstream.…”

“…Note that the plaster layer is 194 mm long with 3 mm in thickness. The merit of this plaster dissolution method is non-detrimental nature of the material, while the benzoic acid used in our previous experiment [17] may suffer from the health harmful gas in the casting process of the liquid benzoic acid at high temperatures. In the preparation of the solid layer of plaster on the pipe wall, the liquid plaster is casted into each half-pipe of the test section using the aluminum cylindrical guide of 56 mm in diameter.…”

“…Recent studies on the measurement of mass transfer coefficient downstream of the orifice in swirling flow are conducted in a water tunnel and found that the pipeline elements upstream of the orifice modify the characteristics of mass and momentum transfer [17,[20][21][22]. Although these experiments provide important findings, such as the occurrence of non-axisymmetric mass transfer downstream of the orifice, the influence of the swirl on the mass and momentum transfer downstream of the orifice is still not clear.…”

“…The swirl intensity of the flow, defined by the ratio of the circumferential momentum to the axial one, is estimated as 0.26 at 3 diameters upstream of the orifice. Since then, several experimental studies on the mass and momentum transfer downstream of the orifice have been carried out to elucidate the mechanism of pipe-wall thinning in the pipeline [12][13][14][15][16][17][18][19][20][21][22].…”