Effects of pore scale and conjugate heat transfer on thermal convection in porous media
Effects of pore scale and conjugate heat transfer on thermal convection in porous media
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DOI：
10.1017/jfm.2022.491
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发表时间：
2022-06
影响因子：
3.7
通讯作者：
David Korba;Like Li
中科院分区：
文献类型：
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作者：
David Korba;Like Li
摘要多孔介质中的热对流研究具有重要的理论意义和实用价值。通常，数值研究依赖于体积平均Darcy-Oberbeck-Boussinesq（DOB）方程，其中对流动力学假设仅由瑞利数（Ra）控制。这些模型的努塞尔数（Nu）预测Nu-Ra标度指数为0.9-0.95。然而，实验和直接数值模拟（DNS）表明标度指数低至0.319。DNS和DOB模型之间的溶质对流最近的研究结果表明，“孔尺度参数”没有捕获的DOB方程极大地影响对流。热对流还具有在不同相中的不同热传输特性（例如固体与流体的热导率比ks/kf和热容比σ）的额外复杂性。因此，在这项工作中，我们比较的DNS和DOB方程的热对流的结果。对于孔径的影响，DNS结果表明，随着孔径的减小，Nu增加。巨羽也被发现是更频繁和更小的孔隙尺寸减小。在共轭传热的影响方面，研究了两组情况（第1组在σ = 1时具有不同的ks/kf，第2组在ks/kf = 1时具有不同的σ），以比较不同孔隙率（ε）、ks/kf和σ值下的Nu-Ra关系。此外，我们报告说，边界层厚度是由DNS结果中的孔径，而由瑞利数和有效热容比，$\bar{\phi } = \phi +（1 - \phi）\sigma$，在DOB模型。
Abstract The study of thermal convection in porous media is of both fundamental and practical interest. Typically, numerical studies have relied on the volume-averaged Darcy–Oberbeck–Boussinesq (DOB) equations, where convection dynamics are assumed to be controlled solely by the Rayleigh number (Ra). Nusselt numbers (Nu) from these models predict Nu–Ra scaling exponents of 0.9–0.95. However, experiments and direct numerical simulations (DNS) have suggested scaling exponents as low as 0.319. Recent findings for solutal convection between DNS and DOB models have demonstrated that the ‘pore-scale parameters’ not captured by the DOB equations greatly influence convection. Thermal convection also has the additional complication of different thermal transport properties (e.g. solid-to-fluid thermal conductivity ratio ks/kf and heat capacity ratio σ) in different phases. Thus, in this work we compare results for thermal convection from the DNS and DOB equations. On the effects of pore size, DNS results show that Nu increases as pore size decreases. Mega-plumes are also found to be more frequent and smaller for reduced pore sizes. On the effects of conjugate heat transfer, two groups of cases (Group 1 with varying ks/kf at σ = 1 and Group 2 with varying σ at ks/kf = 1) are examined to compare the Nu–Ra relations at different porosity (ϕ) and ks/kf and σ values. Furthermore, we report that the boundary layer thickness is determined by the pore size in DNS results, while by both the Rayleigh number and the effective heat capacity ratio, $\bar{\phi } = \phi + (1 - \phi )\sigma$, in the DOB model.