基于图像处理技术界定微纳复合织构防覆冰性能

Anti-icing Performance of Micro-nano Composite Texture Based on Image Processing Technology

目的制备具有防覆冰性能的微织构表面,准确评价微织构表面的结冰性能。方法采用激光二次扫描方法,以铝合金为基底,构筑沟槽-凹坑型复合微织构表面,以水滴在其表面结冰过程的图像为对象,采用阈值法分割图像和背景,对提取出的图像进行形态学运算,通过分析水滴结冰过程中的轮廓变化规律,研究水滴结冰过程的状态变化,进一步界定水滴的结冰时间。结果纳秒激光一次扫描形成的沟槽结构,增加了试件表面的粗糙度,使铝合金表面接触角由54.4°提高到116.5°,实现了铝合金表面的疏水性能。而二次扫描构建的沟槽-凹坑复合微织构,形成了C^w-C^n接触模型,进一步提高了试件表面的疏水性,试件表面接触角增大至154.4°。超疏水表面成核能垒高,且沟槽-凹坑复合微织构捕获的空气降低了固液界面的热交换速度,是铝合金表面结冰时间由11s延长到551s的原因。图像处理方法准确界定了水滴在结冰过程中的三个阶段。采用Harris角点检测法,可以实现精确判断结冰完成时间,减小了肉眼判断结冰状态所带来的主观误差。结论纳秒激光二次扫描构筑的沟槽-凹坑复合微织构可以有效提高Al7075表面的疏水性,并延缓水滴在其表面的结冰时间。图像法处理提取的表面轮廓,为研究分析水滴在结冰过程中的状态变化提供了一种新思路。

The work aims to prepare the micro-textured surface with anti-icing performance and evaluate the icing performance of the micro-textured surface accurately. The groove-pit type composite micro-textured surface was constructed with aluminum alloy as the base by laser secondary scanning method. By taking the image of water droplets on the surface of the ice as the object, the image and background were segmented by threshold method, and the extracted image was subject to morphological operation. By analyzing the contour change law during the process of water droplet icing, the change in the water droplet icing process was studied to further define the icing time of the water droplets. The groove structure formed by the nanosecond laser scanning increased the roughness of the surface of the test piece, and increased the contact angle of the aluminum alloy surface from 54.4° to 116.5°, thus achieving the hydrophobic performance of the aluminum alloy surface. The groove-pit composite micro-texture constructed by the secondary scanning formed a C^w-C^n contact model, which further improved the hydrophobicity of the surface of the test piece, and the contact angle of the test piece increased to 154.4°. The nucleation energy barrier on superhydrophobic surface was high, and the air captured by the groove-pit composite micro-texture reduced the heat exchange rate of the solid-liquid interface, which was the reason that the surface icing time of the aluminum alloy surface extended from 11 s to 551 s. The image processing method accurately defined the three stages of water droplets during the icing process. Harris corner detection method could accurately determine the icing completion time and reduce the subjective error caused by the naked eye to judge the icing state. The groove-pit composite micro-texture constructed by nanosecond laser secondary scanning can effectively improve the hydrophobicity of the surface of Al7075 and delay the icing time of water droplets on the surface. Processing the extracted surface contours by image method provides a new idea for studying the state change of water droplets during icing.