| 摘要 |
A square spiral duct is provided to maximize the size of a sectional area, the efficiency of a fan and space utilization by smoothly moving air without resistance. A plurality of uneven parts(H) are inwardly formed at four corners of a square spiral duct(A), forming a curved line by forming arcs(C). A plurality of spiral seaming parts(S) are formed at an outer periphery of the square spiral duct. Reinforcing ribs(R) are formed between the spiral joining parts in a helical shape.
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