Abstract In the present study, the importance of the thermal dispersion and the turbulent heat flux in porous media and their effects on the macroscopic distribution of thermal energy are investigated. To this end, turbulent flow and heat transfer within five unit-cells mimicking porous media are solved using large eddy simulation. It is shown that the thermal dispersion and the turbulent heat flux are negligible as compared to the convection term in the macroscopic energy equation. When further scrutinizing this equation, it is revealed that except for the longitudinal components of the thermal dispersion, the other components of thermal dispersion and turbulent heat flux may be neglected away from the boundaries as compared to the interfacial heat transfer. Visualizations of vortices show that the size of the turbulence structures within the cells is of the same order as the size of the pores; therefore, the turbulent heat flux is limited to the intra-pore level. Finally, a discussion is provided on the accuracy of the gradient type diffusion model commonly used for turbulent heat flux in porous media in the absence of macroscopic turbulence. It is shown that the intra-pore turbulence does not affect the macroscopic transport of thermal energy within the porous media studied.

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多孔介质中热扩散和孔内湍流热通量的研究

摘要 在本研究中，研究了多孔介质中热扩散和湍流热通量的重要性及其对热能宏观分布的影响。为此，使用大涡模拟解决了五个模拟多孔介质的单元格内的湍流和传热问题。结果表明，与宏观能量方程中的对流项相比，热扩散和湍流热通量可以忽略不计。当进一步研究这个方程时，发现除了热扩散的纵向分量外，与界面传热相比，热扩散和湍流热通量的其他分量在远离边界的地方可以忽略不计。涡旋的可视化显示细胞内湍流结构的大小与孔的大小在同一数量级；因此，湍流热通量仅限于孔隙内水平。最后，讨论了在没有宏观湍流的情况下，通常用于多孔介质中湍流热通量的梯度型扩散模型的准确性。结果表明，孔内湍流不影响所研究的多孔介质内热能的宏观传输。