含不凝气水平管内膜状冷凝的传热特性

Heat Transfer of Film Condensation Inside a Horizontal Tube in Presence of Non-condensable Gas

为深入研究含不凝气水平管内膜状冷凝的传热特性,建立了含不凝气的水平管内膜状冷凝传热的数学模型。模型考虑了汽液两相流间的剪切应力引起的轴向压力梯度及不凝气在相界面处的扩散传质热阻,推导出液膜换热系数、液膜厚度、轴向压力梯度、冷凝液层角度及厚度和冷凝界面温度的理论关系式。通过对纯蒸汽冷凝液膜特性数学模型计算结果间的比较,验证了数学模型的通用性和准确性。研究结果表明:汽液两相流间剪切应力和不凝气对沿管长方向蒸汽冷凝温度的降低有显著影响,要通过增加管长来抵消其对传热性能降低的影响;进口蒸汽中不凝气浓度的降低,有利于减少传热管管长。

In order to get a better understanding of heat transfer characteristics of film condensation inside a horizontal-tube in presence of non-condensable gas（NCG）,the mathematical model was developed,which took into account of the axial pressure gradient caused by the interfacial shear and the diffusion mass transfer resistance through the boundary layer of NCG.The theoretical equations of local film condensation coefficient,condensing film thickness,axial pressure gradient,angle and depth of accumulated condensate and condensing interface temperature were given.The calculated characteristics of film condensation were fairly close to the previous,which justifies the expectation that the model is reliable and versatile.The results indicated that the interfacial shear and NCG significantly influenced the longitudinal reduction of condensation temperature.The reduction in heat transfer performance was compensated by increasing the tube length.A reduction in the mass concentration of NCG contributed to decreasing the tube length.