| 摘要 |
A first wall with a plurality of openings to pass liquid and particulate matter, includes four arrangements of ribs on the back. The ribs are spaced from the openings to reduce surface contact with the liquid and particulate matter. The ribs of the first and second arrangements are of uniform height and intersect to form open ended boxes. The ribs of the third and fourth arrangements extend from ribs of the first and second arrangements respectively, each extended rib curving down from each side of a high point, to the rib from which it extends.
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