蒸気と空気の混合気体から鉛直平板への凝縮熱流束の数値解析
Numerical Simulation for Condensation Heat Fluxes on a Vertical Flat Plate from Steam and Air Mixtures
高木 俊弥 (Toshiya Takaki) 村瀬 道雄 (Michio Murase) 三好 弘二 (Koji Miyoshi)
要約
本研究の目的は，原子炉の事故時における格納容器（CV）内での熱流体挙動を数値流体力学（CFD）コードで計算する際に境界条件として使用される凝縮伝熱の相関式を整備することである．CV壁を模擬する鉛直平板での壁面凝縮を実験的に評価するには大規模な装置が必要になるため，本研究では鉛直矩形流路に対するCFD解析により蒸気質量分率Ys,inおよび蒸気と空気の混合気体の速度uinを変数として流れ方向の凝縮熱流束qcの分布を評価している．本報告では，これまでのYs,in = 0.226，0.453，0.68に0.113と0.84（uin = 0.27～3.2 m/s）を追加してCFD解析を行い，qcの既存相関式と比較評価した．強制対流（FC）凝縮では，CFD計算値qc,CFDと既存相関式による計算値qc,FCは比較的よく一致した．一方，uinを減少するとqcが一定値に漸近する自然対流（NC）凝縮では，低Ys,in条件で既存相関式による計算値qc,NCはqc,CFDより大幅に大きくなり，qc,NC相関式を改善することが望ましい．
キーワード 格納容器，鉛直平板，壁面凝縮，数値解析，強制対流，自然対流, 凝縮熱流束
Abstract
The final objective of our study series is to present correlations for condensation heat transfer; which are used for boundary conditions in CFD (computational fluid dynamics) analysis for thermal-hydraulic behavior in the containment vessel (CV) of nuclear reactors during accident conditions. The distributions of condensation heat fluxes qc in the flow direction (x direction) are numerically evaluated with CFD computations by changing steam mass fraction Ys,in and velocities uin of steam and air mixtures, because a large-scale facility is needed to do experiments for wall condensation on a vertical flat plate in a vertical flow channel simulating a CV wall. In this report, CFD computations were carried out with Ys,in = 0.113 and 0.84 (uin = 0.27-3.2 m/s) in addition to the previous CFD computations with Ys,in = 0.226, 0.453 and 0.68. For forced convection (FC) condensation, the CFD values qc,CFD agreed relatively well with the qc,FC computed with existing correlations. On the other hand, for natural convection (NC) condensation (where the qc value approaches a constant value with decreasing uin), the qc,NC values computed with existing correlations were much larger under the condition of small Ys,in than the qc,CFD values, and improvement of the qc,NC correlation is expected.
Keywords thermal stress, fatigue, simplified elastic-plastic correction, component design
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