Prediction Method of Condensation Heat Transfer from Steam-Air Mixture for CFD Application

Abstract

In our previous study, we measured the radial and axial temperature distributions of steam-air mixture in a vertical circular pipe (diameter, 49.5 mm; cooling height, 610 mm). The measured temperatures were used to evaluate the condensation heat flux qc and heat transfer coefficient hc, where the bulk quantities were defined at the center of the circular pipe. It is sometimes difficult to define the bulk quantities in a three-dimensional computation for a complex geometry or complex flow field. In this study, therefore, we evaluated a prediction method for hc without the definition of the bulk quantities by using the measured temperature distributions. We applied existing hc correlations to an arbitrary radial location y from the condensation surface, and obtained the distribution of local hc. As a result, we found that hc was radially almost constant in the turbulent boundary layer (dimensionless distance of y + > 20). This means that existing hc correlations are applicable to computational cells of y + > 40 in a three-dimensional computation.

Numerical simulation of experiments for wall condensation from mixtures of saturated steam and air in a vertical tube

“…We (Murase et al, 2021) confirmed that existing qc correlations by Araki et al (1995) and Liao and Vierow (2007) (which were derived from the analogy between heat and mass transfer and diffusion model, respectively) could be applied to predict qc in the wide range from the turbulent layer to the bulk by changing the characteristics length from d to 2y (when y equals the radius R, 2y equals d, and the correlation becomes the original one). The modified qc correlations are:…”

“…In our previous studies, we measured radial and axial temperature profiles of saturated steam and air mixtures in a vertical tube with the diameter of d = 49.5 mm (Murase et al, 2019). We confirmed that existing qc correlations (Araki et al, 1995;Liao and Vierow, 2007) defined between the bulk and condensation surface could be approximately applied to the region from the turbulent layer to the bulk (Murase et al, 2021), and we experimentally evaluated profiles of dimensionless temperature T + and steam mass fraction Ys + (Murase et al, 2022), which are used for wall functions in turbulent analyses with coarse computation cells. However, the qc correlations and wall functions are applied in CFD analyses by using computed results, and computed temperatures are often smaller than measured ones in the boundary layer (Legay-Desesquelles and Prunet-Foch, 1986;Kang and Kim, 1999).…”

飽和蒸気と空気の混合気体の流れにおける温度と蒸気質量分率の分布

“…モデルを検証する温度分布データは少なく、平板 でのデータ [11,12]に限られている。壁面に接する 計算セルが大きい CFD 解析では壁関数が広く使 用されている。Kelm ら [7][8][9]は Kader [13]による 単相流での壁関数を蒸気と空気の混合気体に適 用しているが、その妥当性は確認されていない。 本研究では、凝縮伝熱モデルの検証データの提 供を主目的として、直径 49.5 mm、冷却長さ 610 mm の鉛直管を用いて飽和蒸気と空気の混合気体 における半径方向と流れ方向の温度分布を測定 した [14]。 測定結果から凝縮熱伝達率 hc を評価し、 従来の hc の相関式 [15,16]と比較的よく一致する ことを確認した [17]。前報 [18]では、従来研究に よる hc の相関式 [15,16] Table 1 Experimental conditions [14].…”