報告書番号

T99059

タイトル（和文）

大口径管内気液二相流におけるボイド率予測手法の高度化

タイトル（英文）

Improvement of Void Fraction Prediction Method for Two-Phase Flow in a Large-Diameter Pipe

概要 （図表や脚注は「報告書全文」に掲載しております）

原子力安全解析の気液二相流解析に使用されている構成方程式の、大口径管内流動への適用性を検証する為に、水・蒸気系及び水・空気系の大口径管内気液二相流のボイド率、平均気泡径、気相流速といった多次元流動特性を計測した。この結果より、気泡群中の先行気泡の後方に形成される気泡渦による後続気泡上昇速度の増大が水・空気系においても水・蒸気系と同様に見られた。また局所ボイド率に対する気泡渦無次元速度の大きさが水・空気系において水・蒸気系と定量的に殆ど同じ傾向であり、これまでに著者らが提案した相関式で気泡渦の影響を評価できることがわかった。そしてこの気泡渦の影響を考慮した相関式を二流体モデルに組込むことにより、大口径管内気液二相流同解析において、管断面内平均ボイド率を高精度に予測できることを示した。

概要 （英文）

In nuclear reactor safety analysis, two-fluid model is mainly used for two-phase flow analysis and many constitutive equations are introduced to the model. Most of these equations are derived from empirical data on two-phase flow in small-diameter pipes. However, the applicability of these equations to large-diameter pipes has not been validated sufficiently. To analyze the flow with high accuracy, the applicability of these equations to the flow analysis in large-diameter pipes must be clarified. It is empirically known that gas-liquid relative velocity is higher in large-diameter pipes than in small ones. This may lead to an overestimation of the void fraction in large-diameter pipes when analyzed using existing methods. To improve on this situation, the constitutive equation of interfacial drag force must be reevaluated. In this study, two-phase flow characteristics in large-diameter pipes were observed in both steam-water and air-water two-phase flow experiment. Local properties such as void fraction, bubble chord length and gas velocity were measured using optical void probes. In bubble clusters, trailing bubbles were accelerated by the wake of the leading bubbles and, consequently, the rising velocity of trailing bubbles became larger than that of leading bubbles. The correlation between local void fraction and wake velocity for the steam-water system and air-water system showed the same tendency. Taking into the account of the effect of the bubble wake, the void fraction in large-diameter pipes was predicted numerically, and several sets of empirical void fraction data for both steam-water and air-water systems were predicted with high accuracy.

報告者

キーワード