2011 Professional Knowledge Below 55

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Which of the following measures help reduce the noise generated by airflow flowing in pipes? A. Reduce the flow velocity of the fluid in the pipeline. B. Use elbows with a small radius of curvature in those sections of the pipeline where the flow velocity is high. C. Choose tees with a large angle between the flow directions, and provide sufficient straight sections of pipe to help stabilize the flow. D. Wrap sound-insulating material around the pipeline. The exact wording can be found in association documents and textbooks from Tianjin University; in points B and C, the descriptions are reversed – it should be elbows with a large radius of curvature and tees with a small angle between the flow directions. But I don’t understand this: a large radius of curvature corresponds to a small radius, so noise levels should be higher, right?