報告書番号

T98013

タイトル（和文）

大口径管内気液二相流評価手法の高度化（その３） -気泡渦の影響を考慮した界面せん断力評価手法の予測精度の検証-

タイトル（英文）

Improvement of Estimation Method of Two-Phase Flow in a Large Diameter Pipe (III); Validation of New Interfacial Drag Force Model Including Effect of Bubble Wake

概要 （図表や脚注は「報告書全文」に掲載しております）

二流体モデルにより気液二相流の挙動を精度よく予測するためには、解析条件に適用可能な構成式が必要不可欠である。しかしながら、既存の構成式の多くは主に小口径管内二相流を対象に開発されているため、大口径管内二相流に対する適用性は明らかでない。このため前報では、既存の構成式の大口径管内二相流への適用性を検討するため、大口径管を用いた水・蒸気二相流実験を実施した。この結果、本実験条件では気泡の多くは気泡渦に巻き込まれて終端速度よりも速い速度で上昇することを示すとともに、我々の得た実験データを基に気泡渦の影響を考慮した新たな界面せん断力評価モデルを開発した。本研究では、前報で開発したモデルを一部改良するとともに、一次元および軸対称二次元二流体モデルを用いて本評価モデルの妥当性を検討した。この結果本モデルは、大口径管内水・蒸気二相流の予測精度の向上に有効であることが明らかとなった。

概要 （英文）

A two-fluid model is still one of the most important two-phase flow models particularly for practical application such as nuclear reactor safety analysis, although several more detailed models have been recently proposed. In the two-fluid model, which requires a lot of constitutive equations to mathematically close the basic equations, the accuracy of numerical solutions greatly depends upon the constitutive equations used. The reasonable constitutive equations are hence indispensable for the numerical calculation based on the two-fluid model. One of the most important constitutive equations is that for interfacial drag force since it primarily affects mean void fraction, so that a number of correlations have been developed for the interfacial drag force. However, since the experimental data of two-phase flow in small-diameter pipes have been mainly used for validating the existing correlations, their applicability to the two-phase flow in large-diameter pipes has not sufficiently been tested. For this reason, we performed detailed measurements of steam-water bubbly flow in a large-diameter pipe in previous studies. It was inferred from our experimental data that a lot of bubbles were captured into the wake formed by other bubbles in front, to rise faster than their terminal velocities. This result suggested that the effect of bubble wake should be included in the constitutive equations of interfacial drag force. Consequently, a new correlation of interfacial drag force which includes a preliminary bubble wake model was developed. In the present study, increasing the measuring point with double sensor optical void probes and improving signal processing procedure, another series of experiments was carried out. Using the new experimental data, several modifications were made to the correlations representing the bubble size and the bubble wake, which are used in our interfacial drag force model. For testing the validity of the new model, calculated void fractions were compared with several experimental data sets of steam-water two-phase flow in large-diameter pipes. One-dimensional and axi-symmetric two-dimensional two-fluid models were used for this purpose. Since the present interfacial drag force model would be applicable only to bubbly two-phase flow, the experimental data in which the mean void fraction is less than 0.3 were used for this purpose. As a result, it was demonstrated that the new model is effective for accurate prediction in these experimental conditions.

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