Abstract:

The conduction form factor (m), which is used to calculate the equivalent thermal conductivity of foam metal, is introduced through theoretical analysis, and m is calculated and analyzed based on a large number of experimental data reported in the literature. It is shown that m fluctuates with materials, porosities as well as pore densities of metal foams randomly and erratically. In other words, the directional deformation effect of porous foam structure should be taken into account sufficiently to accurately predict the effective thermal conductivity. Accordingly, by direct numerical simulation, a dimensionless criterion correlation characterizing the variation of m with directional deformation parameters which are defined as the ratio of cell diameter between the macro heat transfer direction of metal foam and its orthogonal direction was obtained. A new method for predicting directional effective thermal conductivity was further proposed by employing the conduction form factor, which was verified through literature reported experimental data. It is found that the effective thermal conductivity can be accurately calculated by the prediction method proposed in present study, with a small prediction deviation of 0.77%. Compared with previous theoretical prediction models derived on a basis of isotropic porous structure assumption whose prediction deviations from experimental data are more than 14%, our method can significantly improve the prediction accuracy of effective thermal conductivity.

Key words: porous media, metal foam, heat conduction, effective thermal conductivity, prediction, conduction form factor

摘要：

通过理论分析引入用于定向计算泡沫金属等效热导率的导热形状因子（m），并基于文献报道的大量实验数据对m进行了计算和分析。研究发现，m随泡沫金属材质、孔隙率及孔密度变化呈显著随机波动现象，无固定趋势或规律可循；泡沫金属等效热导率的准确预测需纳入多孔泡沫结构定向形变效应影响。鉴于此，通过直接数值模拟获得了m随孔胞形变参数（即沿泡沫金属宏观传热方向与其垂直方向的胞径比）变化的无量纲准则关联式，进而提出了基于m定向预测泡沫金属等效热导率的新方法。对比文献报道实验数据及基于各向同性结构假设的理论模型预测结果发现，上述方法可提高等效热导率的预测精度（平均偏差为0.77%）。

关键词: 多孔介质, 泡沫金属, 热传导, 等效热导率, 预测, 导热形状因子