Abstract We report numerical simulations of assisting and opposing mixed convection in a side-heated, side-cooled cavity packed with relatively large solid spheres. The mixed convection is generated by imposing a movement on the isothermal vertical walls, either in or opposite to the direction of natural convection flow. For a fluid Prandtl number of 5.4 and fluid Rayleigh numbers of 106 and 107, we varied the modified Richardson number from 0.025 to 500. As in fluids-only mixed convection, we find that the mutual interaction between forced and natural convection, leading to a relative heat transfer enhancement in assisting - and a relative heat transfer suppression in opposing - mixed convection, is most prominent at a Richardson number of approximately one, when the Richardson number is modified with the Darcy number Da and the Forchheimer coefficient Cf = 0.1 as Rim = Ri × Da0.5/Cf. We focus on local flow and heat transfer variations in order to explain differences in local and average heat transfer between a coarse grained and fine grained (Darcy-type) porous medium, at equal porosity and permeability. We found that the ratio between the thermal boundary layer thickness at the isothermal walls and the average pore size plays an important role in the effect that the grain and pore size have on the heat transfer. When this ratio is relatively large, the thermal boundary layer is locally disturbed by the solid objects and these objects cause local velocities and flow recirculation perpendicular to the walls, resulting in significant differences in the wall-averaged heat transfer. The local nature of the interactions between flow and solid objects cannot be captured by a volume averaged approach, such as a Darcy model.

中文翻译：

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在填充粗粒多孔介质的差热腔中通过共轭传热辅助和对抗混合对流

摘要 我们报告了在填充有相对较大的实心球体的侧面加热、侧面冷却腔中辅助和对抗混合对流的数值模拟。混合对流是通过在等温垂直壁上施加沿自然对流流动方向或与自然对流流动方向相反的运动产生的。对于 5.4 的流体普朗特数和 106 和 107 的流体瑞利数，我们将修改后的理查森数从 0.025 改为 500。与仅流体混合对流一样，我们发现强制对流和自然对流之间的相互作用导致辅助中的相对传热增强 - 以及反向混合对流中的相对传热抑制，在理查森数约为 1 时最为突出，当理查森数用达西数 Da 和 Forchheimer 系数 Cf = 0.1 修改为 Rim = Ri × Da0.5/Cf 时。我们关注局部流动和传热变化，以解释在孔隙率和渗透率相等的情况下，粗粒和细粒（达西型）多孔介质之间的局部和平均传热差异。我们发现等温壁处的热边界层厚度与平均孔径之间的比率在晶粒和孔径对传热的影响中起着重要作用。当这个比值比较大时，热边界层会受到固体物体的局部干扰，这些物体会引起局部速度和垂直于壁面的流动再循环，导致壁面平均传热的显着差异。