Study on Resistance Characteristics of Capillary Flow in Screen Wick Based on CFD Method
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摘要: 丝网芯热管是一种基于两相流动相变循环原理设计的非能动输热设备，循环中的毛细力与流动阻力均与丝网芯结构密切相关，研究丝网芯的阻力特性对丝网芯结构选型与优化、热管性能提升具有重要的意义。本文基于计算流体力学（CFD）方法，建立丝网毛细流动的阻力模型，研究流体在多层丝网芯内的毛细流动的阻力特性。使用本文模型模拟毛细提升实验，模型与实验结果的相对误差小于5%。基于模型进一步分析堆叠结构及目数（50目、200目、400目）对丝网芯的流动阻力特性的影响。结果表明，堆叠丝网的网孔越密集流动阻力越大，粘性阻力系数近似与丝网目数呈正比，而等效惯性阻力也随丝网目数增加而增大；在雷诺数小于1的低流速区域，粘性阻力占据主导作用，而在雷诺数大于1的流速区域惯性阻力作用不可忽略；丝网芯的几何结构除影响流动阻力还将对毛细力产生影响。计算表明，丝网毛细压强和流动阻力均随丝网目数的增加而增强，毛细性能因子随目数的增加而增速放缓。考虑到平织丝网的工艺限制，400目丝网较为理想。Abstract: Screen wick heat pipe is a kind of passive heat transfer equipment based on the principle of two-phase flow phase change cycle. The capillary force and flow resistance in the cycle are closely related to the structure of the screen wick. The study of the resistance characteristics of the screen wick is of great significance to the selection and optimization of the screen wick structure and the improvement of the heat pipe performance. Based on computational fluid dynamics (CFD), a resistance model of capillary flow in screen is established to study the resistance characteristics of capillary flow in multi-layer wire screen wick. The model is used to simulate the capillary lifting experiment, and the relative error between the model and the experimental results is less than 5%. Based on the model, the effects of stacking structure and mesh number (50 mesh, 200 mesh, 400 mesh) on the flow resistance characteristics of screen wick are further analyzed. The results show that the denser the mesh is, the greater the flow resistance is, the viscous resistance coefficient is approximately proportional to the mesh number, and the equivalent inertia resistance increases with the increase of the mesh number. In the low velocity region where Reynolds number is less than 1, viscous resistance plays a dominant role, while in the velocity region where Reynolds number is greater than 1, inertia resistance cannot be ignored; The geometric structure of the screen wick not only affects the flow resistance, but also affects the capillary force. The calculation shows that the capillary pressure and flow resistance of the screen increase with the increase of mesh number, and the capillary performance factor slows down with the increase of mesh number. Considering the process limitation of plain woven screen, 400 mesh screen is ideal.
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Key words:
- Screen wick /
- Flow resistance /
- Viscous resistance /
- Inertial resistance /
- Capillary performance factor
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图 2 多层丝网毛细提升实验装置示意图
Figure 2. Schematic Diagram of Multi-layer Screen Capillary Lifting Experimental Device
图 4 50目丝网芯内压力场和流速分布
Figure 4. Distribution of Pressure Field and Velocity Field in the Screen Wick (50 Mesh Number)
图 6 毛细提升高度实验与模型的比较
Figure 6. Comparison between Capillary Lifting Height Experiment and Model
图 7 不同目数堆叠丝网的等效粘性阻力系数和等效惯性阻力系数对比
Figure 7. Comparison of Equivalent Viscous Resistance Coefficient and Equivalent Inertial Resistance Coefficient of Stacked Screen with Different Mesh Numbers
图 8 不同目数丝网的毛细压强与毛细性能因子
Figure 8. Capillary Pressure and Capillary Performance Factor of Screen with Different Mesh Numbers
表 1 不同目数下的丝网结构参数
Table 1. Structural Parameters of Screen under Different Mesh Numbers
丝网类型 目数 w/mm d/mm 特征尺寸/mm 平织丝网 50 0.2 0.308 0.254 平织丝网 200 0.05 0.077 0.0635 平织丝网 400 0.018 0.0455 0.03175 特征尺寸—（w+d）/2 
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表 2 50目丝网芯内速度与压降关系
Table 2. Relationship between Velocity and Pressure Drop in the Screen Wick under 50 Mesh Number
速度/(m·s−1) 压降/Pa 等效惯性阻力系数 等效粘性阻力系数 5.67×10−5 0.57 6.45×103 8.86×108 1.89×10−4 1.89 5.67×10−4 5.68 1.89×10−3 18.94 5.67×10−3 57.07
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表 3 200目丝网芯内速度与压降关系
Table 3. Relationship between Velocity and Pressure Drop in the Screen Wick under 200 Mesh Number
速度/(m·s−1) 压降/Pa 等效惯性阻力系数 等效粘性阻力系数 9.10×10−5 1.51 2.32×104 1.47×1010 3.02×10−4 5.03 9.10×10−4 15.08 3.02×10−3 50.29 9.10×10−3 151.03
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表 4 400目丝网芯内速度与压降关系
Table 4. Relationship between Velocity and Pressure Drop in the Screen Wick under 400 Mesh Number
速度/(m·s−1) 压降/Pa 等效惯性阻力系数 等效粘性阻力系数 5.00×10−4 257.90 3.12×104 4.57×1010 5.00×10−4 25.79 1.66×10−3 85.96 1.66×10−2 860.10 5.00×10−2 2588.15
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