Abstract

Condensation heat transfer on stainless steel tube utilizing superhydrophobic coatings was investigated. The electrophoretic deposition and spraying methods were employed to coat the tubes’ outer surface. The mixture that was synthesized for spray coating was a hybrid paint. It incorporated polyurethane matrix and a colloidal suspension containing organic nanoparticles. The hybrid paint had a proper adhesion to the substrate which caused more durability compared to the electrophoretic coating. The agglomeration of nanoparticles in the hybrid paint caused the formation of particles with larger size compared to the particles in the electrophoretic coating. Consequently, contact angle hysteresis over electrophoretic coating was much lesser than spraying method. Dropwise condensation regime was observed over both the coatings as a result of hydrophobicity. Nonetheless, the condensation heat flux declined over the hybrid paint at high subcooling temperatures due to transition to the flooding condensation regime. This was due to the accumulation of ultra-small droplets as a result of high nucleation sites. The continuation of droplets sweeping was hindered by sticking to the substrate. The dropwise condensation was maintained over the electrophoretic coating and the transition to the film-wise condensation happened at larger wall subcooling temperature. The ability of the electrophoretic coating in shedding droplets efficiently was caused by higher hydrophobicity, high roughness density, and minimum droplet pinning.

摘要

研究了使用超疏水涂层的不锈钢管上的冷凝传热。采用电泳沉积和喷涂方法涂覆管的外表面。为喷涂而合成的混合物是一种混合涂料。它结合了聚氨酯基质和含有有机纳米颗粒的胶体悬浮液。与电泳涂料相比，混合涂料对基材具有适当的附着力，从而具有更高的耐久性。与电泳涂层中的颗粒相比，混合涂料中纳米颗粒的团聚导致形成更大尺寸的颗粒。因此，电泳涂层上的接触角滞后比喷涂方法小得多。由于疏水性，在两种涂层上都观察到滴状缩合状态。尽管如此，由于过渡到溢流冷凝状态，混合涂料在高过冷温度下的冷凝热通量下降。这是由于高成核位点导致超小液滴的积累。粘附在基材上阻碍了液滴清扫的继续。在电泳涂层上保持逐滴冷凝，并且在较大壁过冷温度下发生向膜状冷凝的转变。电泳涂层有效脱落液滴的能力是由更高的疏水性、高粗糙度密度和最小的液滴钉扎引起的。由于过渡到溢流冷凝状态，在高过冷温度下，混合涂料的冷凝热通量下降。这是由于高成核位点导致超小液滴的积累。粘附在基材上阻碍了液滴清扫的继续。在电泳涂层上保持逐滴冷凝，并且在较大壁过冷温度下发生向膜状冷凝的转变。电泳涂层有效脱落液滴的能力是由更高的疏水性、高粗糙度密度和最小的液滴钉扎引起的。由于过渡到溢流冷凝状态，在高过冷温度下，混合涂料的冷凝热通量下降。这是由于高成核位点导致超小液滴的积累。粘附在基材上阻碍了液滴清扫的继续。在电泳涂层上保持逐滴冷凝，并且在较大壁过冷温度下发生向膜状冷凝的转变。电泳涂层有效脱落液滴的能力是由更高的疏水性、高粗糙度密度和最小的液滴钉扎引起的。粘附在基材上阻碍了液滴清扫的继续。在电泳涂层上保持逐滴冷凝，并且在较大壁过冷温度下发生向膜状冷凝的转变。电泳涂层有效脱落液滴的能力是由更高的疏水性、高粗糙度密度和最小的液滴钉扎引起的。粘附在基材上阻碍了液滴清扫的继续。在电泳涂层上保持逐滴冷凝，并且在较大壁过冷温度下发生向膜状冷凝的转变。电泳涂层有效脱落液滴的能力是由更高的疏水性、高粗糙度密度和最小的液滴钉扎引起的。