类金刚石和厚有机膜促进水蒸气滴状冷凝传热的实验研究

Experimental investigation of dropwise condensation of steam on diamond-like carbonate and thick fluor-containing organic films

为了寻找适宜的表面处理技术制备能长期地维持滴状冷凝传热型态 ,实验研究了垂直黄铜管外类金刚石和含氟有机薄膜水蒸气常压下冷凝传热特性。两种表面均能促进水蒸气的滴状冷凝型态 ,但类金刚石表面上液滴形状较扁 ,脱落频率不高 ,而有机膜表面的液滴形状、大小以及脱落频率均优于类金刚石表面。在管内冷却水雷诺数为 1 .0× 1 0 4～ 2 .0× 1 0 5时 ,类金刚石和含氟有机薄膜表面的热流密度和冷凝传热系数分别为 4 85～ 80 7k W/ m2 和 1 8～ 2 3k W/ ( m2 · K)、1 71～ 330 k W/ m2 和 4 .8～ 7.2 k W/ ( m2 · K)。含氟有机薄膜表面表现了优良的涂层结合强度 ,寿命实验已经持续了近 1 0个月。

In order to find an appropriate surface processing technique for preparing a special organic film on metal tube and maintaining long-term dropwise condensation heat transfer pattern, experimental investigation was carried out on the dropwise condensation characteristics on a diamond-like carbonate (DLC) film and on a thick fluor-containing organic (TFCO) film, which were coated on the external surface of brass tubes. The test tube was vertically oriented and the experiments were conducted at the atmospheric pressure. The visual observation showed that these two films promote dropwise condensation pattern of steam very well. However, the droplets on DLC film seem to be flatter and depart with a lower frequency than those on the thick organic film. The heat flux and the heat transfer coefficient of steam were 485～807 kW/m 2 and 17.5～23.0 kW/(m 2·K) for DLC film, while 385～679 kW/m 2 and 11.8～14.6 kW/(m 2·K) for the TFCO film, at the cooling water Reynolds number ranging from 1.0×10 4 to 2.0×10 5. The TFCO film has maintained good dropwise condensation for about 10 months, however, the processing conditions for DLC film need further investigation to improve the adhesion of DLC film to metallic substrate and the film's physiochemical property as well.