大量不凝性气体存在时不同润湿性管束 对流冷凝传热实验研究
Experimental Research on the Convective Condensation Heat Transfer of Tube Bundles in the Presence of Large Amount of Noncondensable Gas

为了实现工业中大量不凝性气体存在场合下蒸气的高效冷凝传热,建立了混合蒸气水平管束外对流冷凝传热实验系统,通过化学刻蚀与自组装方法对光管管束、2D肋管管束和3D肋管管束进行疏水与超疏水表面改性处理。当大量不凝性气体存在时,对不同润湿性管束表面的冷凝形式及管束间冷凝液流型进行可视化观测。实验研究了冷却水流速、混合蒸气流速、水蒸气体积分数等因素对不同润湿性的冷凝式换热器对流冷凝传热系数的影响,并分析不同水蒸气体积分数条件下管束效应的影响。通过实验研究发现,当大量不凝性气体存在时,冷凝液在管束间形成滴状流,水蒸气体积分数对不同润湿性的冷凝式换热器的对流冷凝传热特性影响显著,随着管排数增加,对流冷凝传热系数增大,管束效应对超疏水光管管束的强化作用最大,当水蒸气的体积分数约为11％时,9排超疏水光管管束的对流冷凝传热系数是单排的1.53倍,而当水蒸气体积分数约为23％时,9排超疏水光管管束的对流冷凝传热系数是单排的1.34倍。
To achieve the highly efficient condensation heat transfer in the industry with large amount of noncondensable gas, an experimental system of convective condensation heat transfer for horizontal tube bundles containing air？？vapor mixture was established. The methods using self？？assembled monolayer coatings of n？？octadecyl mercaptan and etching treatment were employed to create the hydrophobic and superhydrophobic surfaces. The convective condensation heat transfer performances of plain, 2D finned and 3D finned horizontal tubes with different wettabilities were studied. The condensation behaviors on the surfaces and the flow patterns of the condensate between bundles were also observed. In the experiment, the effects of typical factors including the flow rate of cooling water, the flow rate of air？？vapor mixture, and the volume fraction of water vapor on the convective condensation heat transfer characteristics were investigated. It is found that the droplet flow of condensate may be formed between the tube bundles in the presence of large amount of noncondensable gas. As the number of tube row increases, the convective condensation heat transfer coefficient increases correspondingly and the heat transfer enhancement effect of tube bundle is more significant. When the vapor volume fraction is about 11％, the convective condensation heat transfer coefficient of superhydrophobic plain tubes with 9 rows is 1.53 times of single row, and that of superhydrophobic plain tubes with 9 rows reduces to 1.34 times of single row when the vapor volume fraction reaches about 23％