N the area between two concentric circles 环面
The test section was composed of transparent vertical annuluses. The shape and size of electric heating rods were similar to nuclear fuel rods.
试验本体采用了透明的垂直环形通道，电加热元件的尺寸及形状与核燃料元件相同。
Performance of fluid can be improved remarkably by adding diversion annuluses within the tube segments where the cross section suddenly changes.
通过在各截面突变处设置管口导流环会有很好的降阻效果。
The disk, which is composed of continuous annuluses, can expand equivalent trangle by asymptotice line. We can obtain the circular area which is visually expressed by circumference and radius.
摘要把紧密相连的圆环构成的圆盘以渐开线展开成等面积的直角三角形，得出了较为直观的由周长和半径表示的圆面积公式。
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