Wall Region Porosity Distributions for Packed Beds of Uniform Spheres with Modified and Unmodified Walls
Wall Region Porosity Distributions for Packed Beds of Uniform Spheres with Modified and Unmodified Walls
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具有改性和未改性壁的均匀球体填充床的壁区域孔隙率分布
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
Dale E. Kleins
中科院分区：
文献类型：
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作者：
J. Mcwhirter;M. Crawford;Dale E. Kleins
本文用数学方法推导了均匀球填充床壁面附近的孔隙率（局部空隙率）分布。这项调查支持研究的方法，减少或消除所谓的壁效应，或旁路流，这伴随着增加孔隙度时，球体接触到一个固体边界。限制旁路流量在某些应用中是重要的，例如在填充床核反应堆中，其中旁路流量允许一些冷却剂避开高功率密度堆芯区域。确定了四种基本孔隙度分布。第一个调查的情况下，球对一个平的墙壁被包装在最紧密的可能的包装密度。然后通过改变球体间距来降低该密度，直到最小孔隙率与实验获得的孔隙率相匹配。在其他情况下，各种方式的嵌入球的壁区域孔隙率的壁的效果进行检查。通过将球体部分地嵌入壁中，减小了壁处的孔隙率，从而消除了旁通流的最直接原因。孔隙率是通过计算平行于壁面的平面中固体面积与总面积的比率而得到的。局部孔隙率是作为一个函数，从壁在一个半球直径内的区域中的壁的距离。还计算了壁区域的平均孔隙率。这项研究已应用于流动的情况下，如填充床化学反应堆，球床核反应堆和填充床中的流动。
A mathematical derivation of the porosity (local void fraction) distribution near the walls of packed beds of uniform spheres is presented. This investigation supports the study of methods of reducing or eliminating the so-called wall effect, or bypass flow, which accompanies the increase in porosity when spheres come in contact with a solid boundary. Limiting the amount of bypass flow is important in certain applications such as in packed bed nuclear reactors where bypass flow allows some coolant to avoid the high power density core region. Four basic porosity distributions are determined. The first investigates the case where spheres against a flat wall are packed in the tightest possible packing density. This density is then reduced by changing the sphere spacing until the minimum porosity matches that obtained experimentally. In the other cases, the effect of various ways of embedding spheres in the wall on the wall region porosity is examined. By partially embedding spheres in the wall, the porosity at the wall is reduced and the most direct cause of the bypass flow is thereby eliminated. The porosity is found by evaluating the ratio of the solid area to total area in a plane which is parallel to the wall. The local porosity is derived as a function of distance from the wall in the region within one-half a sphere diameter from the wall. The average porosity of the wall region is also calculated. This research has application to flow situations such as packed bed chemical reactors, pebble bed nuclear reactors and flow in packed beds.