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首页> 外文期刊>International Journal of Heat and Mass Transfer >Influence of boundary conditions on computation of the effective thermal conductivity of foams
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Influence of boundary conditions on computation of the effective thermal conductivity of foams

机译：边界条件对泡沫有效导热系数计算的影响

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摘要

Accurate numerical simulation of the effective thermal conductivity (ETC) of 3D pore-scale foam models requires a judicious choice of boundary conditions, as the computational domains are often smaller than the representative volume element, giving rise to considerable edge effects. Within the finite element ho-mogenization framework, a set of mixed boundary conditions are considered alongside the usual uniform and periodic boundary conditions. Validity criteria and order relations, demonstrated from entropy-based principles, are numerically verified on unit cell-based geometries, random virtual periodic foams, and non-periodic tomography-reconstructed foams of equivalent microstructure. A statistical treatment based on the integral range provides confidence intervals for the estimated ETC. For foam samples with random homogeneous porosity, the mixed boundary conditions are shown to fulfill the macrohomogeneity condition and thus provide thermodynamically valid ETC estimates. For periodic foams with irregular microstructure, the ETC is very slightly underestimated under the mixed boundary conditions. For non-periodic geometries, it is shown that periodic boundary conditions-commonly viewed as the reference-underestimate the ETC due to boundary geometry mismatch, while the mixed boundary conditions give a more accurate and precise estimate.
机译：3D孔径泡沫模型的有效导热率（ETC）的准确数值模拟需要明智地选择边界条件，因为计算域通常小于代表体积元件，从而产生相当大的边缘效应。在有限元Ho-Mogeneration框架内，一组混合边界条件被认为与通常的均匀和周期性边界条件一起。从基于熵的原理证明的有效性标准和订单关系在基于单元电池的几何形状，随机虚拟周期性泡沫和非周期性断层摄影 - 重建的等效微结构的非周期性断层摄影泡沫的数量验证。基于整体范围的统计处理为估计等提供了置信区间。对于具有随机均匀孔隙率的泡沫样品，显示混合边界条件以满足大型均匀性条件，从而提供热力学上有效的等估计。对于具有不规则微观结构的周期性泡沫，在混合边界条件下，ETC非常低估。对于非周期性几何形状，示出了由于边界几何错配而通常被视为作为基准低估等，而混合边界条件给出更准确和精确的估计。

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