報告書番号

T98050

タイトル（和文）

熱交換器縮流部のスケール付着に及ぼす流動および水化学因子の影響

タイトル（英文）

The effect of flow-hole structure and water chemistry on scale adhesion at the leading edge of a flow hole in a heat exchanger

概要 （図表や脚注は「報告書全文」に掲載しております）

熱交換器縮流部入り口近傍におけるスケール付着現象を解明するため、流路部の断面積と流速が同一で、水力直径の異なる四つ穴型および丸穴型試験片を用いてスケール付着試験を行い、以下の知見を得た。１.スケール付着に起因する差圧の上昇、および入水口部におけるスケール付着量は、四つ穴型試 験片の方が、丸穴型試験片より顕著であり、流速が速くなるほど増加する傾向が認められた。２.縮流部の流動解析より同一流速条件下では、四つ穴型構造の方が、丸穴型構造より縮流部入口 部の局所的な圧力降下と乱流エネルギーは大きいことを明らかにした。３.コロイド状の鉄酸化物粒子の方が、クラッド状の粒子よりも付着し易いことが分かった。

概要 （英文）

In the heat exchangers of power plants, scale deposition may occur, especially at the leading edge of contraction. The growth of scale can lead to an increase in pressure and cause oscillation of the water level.In our previous study, the dependence of flow on contraction geometry was analyzed numerically and empirically. It was shown that the contraction ratio of hydraulic diameter of the flow path contributed greatly to the difference in pressure drop and turbulent kinetic energy at the leading edge of the flow path. In this study, the effect of contraction geometry and flow rate on scale adhesion was studied in AVT chemistry at 270℃ using a high-velocity scale-adhesion test loop. The differential pressure and the amount of scale deposited due to scale adhesion at the leading edge of the flow path increased more in a quatrefoil-type flow path than in a drill-type flow path. The differential pressure and the amount of scale deposited also increased with increasing flow rate. Based on the results of the previous study, the flow behavior around the two different contractions under the above test conditions was also analyzed numerically. The test and analysis results indicated that the increase in scale adhesion at the leading edge of a quatrefoil-type flow path may be correlated with the localized increase in turbulent kinetic energy and pressure drop at the contraction inlet.

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