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摘 要 ：建立了增膜型蒸发式冷凝器管外水膜流动可视化测试装置；研究了水平管外壁面水膜流型随管径及喷淋量的变化；归纳出管外水膜层流临界雷诺数阈值为15，湍流临界雷诺数阈值为25。喷淋流量增加的过程中，粗管子比细管子更容易达到湍流。管外水膜流动雷诺数中的特征长度与水膜厚度一个量级。水膜越厚，特征长度越大；管径越大，特征长度越大。 关键词 ：蒸发式冷凝器 水平管 水膜 流型 雷诺数 特征长度 Investigation For Water Film Flow Pattern And Its Characteristic Length Outside The Tube Of The Evaporative Condenser Jiang Bo Chen Liangcai Jiang Maocan Feng Zhili Yang Bo Liu Zhichun School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China Abstract: The changes of water film flow pattern outside the horizontal tube with the diameter and flow rate were studied experimentally. Experiments were performed on a vertical row of horizontal tubes with stainless steel plate between them. Its developed that the critical Reynolds number threshold of water film outside the tube is 15 for laminar flow, and 25 for turbulent flow. With the increase of flow rate, the flow pattern of the film outside the larger diameter tube gets into the turbulent state earlier than the smaller diameter tube gets into the same state. The characteristic length of water film flow Reynolds number is the same order of magnitude as the water film thickness. The thicker the water film, the greater the characteristic length; the larger diameter the tube, the greater the characteristic length. Keywords: evaporative condenser; horizontal tube; water film; flow pattern; Reynolds number; characteristic length