Numerical analysis of the effect of air bubbles and gaps on thermal conductivity of hexagonal boron nitride/epoxy composites
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摘要: 气泡和气隙严重影响环氧树脂基复合材料的导热性能，研究气泡和气隙对复合材料热导率的影响有助于提高导热模型的准确性，可为进一步优化环氧树脂基复合材料的导热性能提供指导方向。采用有限元方法建立一种含气泡、气隙的六方氮化硼(h-BN) /环氧树脂复合材料单胞模型，分析气泡、气隙的尺寸和数量对复合材料导热性能的影响。通过与其他模型、实验数据的对比对模型的有效性进行了验证。结果表明，随着气泡尺寸和数量的增加，h-BN/环氧树脂复合材料热导率逐渐下降，且热导率随气泡尺寸的变化曲线存在转折点，直径大于单胞厚度的气泡对复合材料热导率的影响较大。随着气隙直径和厚度的增加，h-BN/环氧树脂复合材料热导率先缓慢后快速减小、最后呈直线趋势下降；随着气隙数量的增加，h-BN/环氧树脂复合材料热导率逐渐下降，且相较于基材中的气隙，位于填料与基材界面处的气隙对热导率的减弱更显著。Abstract: Air bubbles and gaps in epoxy matrix composites seriously influence its thermal conductivity. Research on the effect of bubbles and gaps on the thermal conductivity of composites benefits to improve the accuracy of thermal conductive model and provides guidance for optimization of thermal conductivity. A numerical model of hexagonal boron nitride (h-BN)/epoxy composites with air bubbles and gaps was established by finite element method. The effects of bubble size and number, gap size and number on the thermal conductivity of h-BN/epoxy composites were systematically analyzed. This model was validated by other thermally conductive models and experimental data. The results show that with the increase of bubble size and number, the thermal conductivity of h-BN/epoxy composites decreases gradually, and a turning point occurs in the thermal conductivity curve changing with bubble size. Bubbles with diameter greater than the thickness of unit cell have a great impact on the thermal conductivity of h-BN/epoxy composites. With the increase of gap diameter and thickness, the thermal conductivity of h-BN/epoxy composites decreases slowly first, and then fast. Finally, the thermal conductivity of h-BN/epoxy composites decreases linearly. With the increase of the gap number, the thermal conductivity of h-BN/epoxy composites decreases gradually. The air gaps at the interface of h-BN and epoxy have a greater influence than those in the epoxy matrix.
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Key words:
- composite /
- epoxy resin /
- air bubble /
- air gap /
- thermal conductivity /
- finite element analysis
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图 1 六方氮化硼(h-BN)/环氧树脂复合材料单胞模型(基材中含一个气泡(直径Db=2 μm)，界面处存在一个气隙(Dg=19 μm、厚度δg=0.1 μm))
Figure 1. Representative unit cell model of hexagonal boron nitride (h-BN)/epoxy composites (Containg one air bubble in the matrix (diameter Db=1 μm) and one air gap at the interface (diameter Dg=19 μm, thickness δg=0.1 μm))
图 2 h-BN/环氧树脂复合材料有限元模型及数值求解后的温度分布图
Figure 2. Numerical model of h-BN/epoxy composites and temperature distribution after numerical solution
图 3 h-BN/环氧树脂复合材料热导率数值计算结果与其他模型、实验结果的对比
Figure 3. Comparison of thermal conductivity of h-BN/epoxy composites among numerical results, other models and experimental results
图 4 含一个气泡h-BN/环氧树脂复合材料温度和热流分布图(Db=2 μm)
Figure 4. Diagrams of temperature and directional heat flux distribution of h-BN/epoxy composites containing one air bubble(Db=2 μm)
图 5 模型计算h-BN/环氧树脂复合材料热导率随着气泡直径、气泡数量的变化(实线表示气泡直径的影响、短划线表示气泡数量的影响)
Figure 5. Calculated thermal conductivity of h-BN/epoxy composites changing with bubble diameter and bubble number (Solid lines are the influence of bubble diameter, while dashed lines are the influence of bubble number)
图 6 含一个气隙h-BN/环氧树脂复合材料温度和热流分布图(Dg=19 μm、 δg=0.1 μm)
Figure 6. Diagrams of temperature and directional heat flux distribution of h-BN/epoxy composites containing one air gap (Dg=19 μm, δg=0.1 μm)
图 7 模型计算h-BN/环氧树脂复合材料热导率随着气隙直径、厚度、数量的变化(实线表示气泡直径的影响、点虚线表示气泡厚度的影响、短划线表示气泡数量的影响)
Figure 7. Calculated thermal conductivity of h-BN/epoxy composites changing with gas diameter, thickness and number (Solid lines are the influence of gas diameter, dotted lines are that of gas thickness, while dashed lines are that of gas number)
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