大量不凝性气体存在时不同润湿性传热管冷凝传热特性实验研究

Condensation Heat Transfer Performance of Heat Transfer Tubes with Different Wettabilities in Presence of a Large Amount of Noncondensable Gas

为了提高大量不凝性气体存在时水蒸气的冷凝传热性能,实现对电力、化工、制冷等工业领域中余热的高效回收利用,基于水平管外冷凝传热实验系统,实验研究了氮气-水蒸气混合气体在不同润湿性光滑管和翅片管表面的润湿特性和冷凝传热特性。通过化学刻蚀与自组装方法对紫铜光滑管与翅片管表面进行疏水与超疏水改性处理,并且根据仿生原理,制备了亲水+疏水组合翅片管表面与亲水+超疏水组合翅片管表面。研究发现,当大量不凝性气体存在时,亲水+超疏水组合翅片管的冷凝传热特性最优,水蒸气体积分数对不同润湿性传热管的冷凝传热特性影响显著,并且随着水蒸气体积分数增大,超疏水翅片管和亲水+超疏水组合翅片表面的冷凝形式由珠状冷凝逐渐向膜状冷凝过渡。

To improve the condensation heat transfer performance of water vapor in of a large amount of noncondensable gas and realize the high-efficiency recovery the presence of industrial residual heat in electricity, chemical engineering, refrigeration and other fields, the outside condensation heat transfer performances of horizontal plain and finned tubes with different surface wettabilities were experimentally studied. The self-assembled monolayer coatings of n-octadecyl mercaptan using oxidation and etching treatments were employed to create the hydrophobic or superhydrophobic surfaces with nanostructures. The hydrophilic-hydrophobic and hydrophilic- superhydrophobic hybrid surfaces based on finned tubes were prepared. The experimental results showed that the hydrophilic-superhydrophobic hybrid finned tube achieved the highest condensation heat transfer performance in the presence of a large amount of noncondensable gases. The volume fraction of water vapor in the nitrogen-vapor mixture has important influence on the heat transfer characteristics. And as the vapor volume fraction increased, the dropwise condensation was transformed gradually to the film condensation on both superhydrophobic and hydrophilic-superhydrophobic hybrid finned tubes.