鉛直平板での凝縮熱流束に対する圧力の影響に関する数値解析
Numerical Simulation for Effects of Pressure on Condensation Heat Fluxes on a Vertical Flat Plate

村瀬　道雄 (Michio Murase)　　　高木　俊弥 (Toshiya Takaki)　　　三好　弘二 (Koji Miyoshi)

要約
本研究では，数値流体力学（CFD）コードFLUENTを使用し，鉛直流路内の蒸気と空気の混合気体から鉛直平板への壁面凝縮に関する数値解析を行い，蒸気質量分率Y_s,inと混合気体速度u_inが凝縮熱流束q_cに及ぼす影響を評価し，適切なq_cの従来相関式を選定している．これまでに，大気圧条件でY_sin = 0.113，0.226，0.453，0.68，0.84でu_in = 0.27～3.2 m/sについてq_cの流れ方向分布を評価した．本報告では，圧力がq_cに及ぼす影響を評価するために，P = 0.3 MPa，Y_sin = 0.113, 0.226, 0.340, 0.453，u_in = 0.27～3.2 m/sで数値解析を行った．0.3 MPaではCFD計算値q_c,CFDが大きくなり，大気圧ではq_c,CFDとよく一致するq_cの従来相関式での計算値より大きくなった．強制対流（FC）凝縮に対しては，q_c,CFDとよく一致するq_cの従来相関式は見当たらない．一方，u_inの減少に伴ってq_cが一定値に近づく自然対流（NC）凝縮に対しては，大気圧条件ではq_cを過大評価するSpaldingの相関式とサクション係数θ_Bの組合せがq_c,CFDとよく一致する計算値を与えた．

キーワード   格納容器，鉛直平板，壁面凝縮，数値解析，凝縮熱流束，圧力の影響

Abstract
In this study series, we have been carring out numerical simulation for wall condensation on a vertical flat plate from steam and air mixtures by using the CFD (computational fluid dynamics) code FLUENT to evaluate effects of the steam mass fraction Y_s,in and mixture velocity u_in on condensation heat fluxes q_c and to select suitable q_c correlations. We previously finished the numerical simulation for conditions of Y_s,in = 0.113, 0.226, 0.453, 0.68 and 0.84 and u_in = 0.27-3.2 m/s at the pressure of P = 0.1 MPa, and obtained the q_c distributions in the flow direction. Noe, in this study, we carried out the numerical simulation for conditions of Y_s,in = 0.113, 0.226, 0.340 and 0.453 and u_in = 0.27-3.2 m/s at P = 0.3 MPa to evaluate effects of the pressure on q_c. The q_c,CFD values obtained from CFD analysis at P = 0.3 MPa became larger than the q_c values with the correlation, which gave good agreement with the q_c,CFD values at P = 0.1 MPa. For forced convection (FC) condensation, a correlation, which gave good agreement with the q_c,CFD values, was not found. On the other hand, for natural convection (NC) condensation (where the q_c value approaches a constant value with decreasing u_in), the correlation by Spalding with the suction factor θ_B, which gave larger values than the q_c,CFD values at P = 0.1 MPa, gave good agreement with the q_c,CFD values at P = 0.3 MPa.

Keywords   containment vessel, vertical flat plate, wall condensation, numerical simulation, condensation heat flux, pressure effect

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