济南排烟罩采用自然排烟的排烟罩要求能产生一定的抽力，以便能排出应排走的全部烟气和周围吸入的空气。如果烟气流是不稳定的，或者烟气与周围空气间的重度相差不大，采用自然排烟罩是才合理的。
The natural exhaust hood used in Jinan smoke hood requires that a certain amount of smoking force be generated so as to discharge all the flue gas that should be discharged and the air inhaled around it. If the smoke flow is unstable, or the smoke and the surrounding air are not significantly different in severity, the use of natural exhaust hood is reasonable.
（1）水平烟气散发源排烟罩形状和尺寸的确定
(1) Determining the shape and size of exhaust hood for horizontal smoke emission source
排烟罩罩口的截面形状尽可能与烟气散发源的水平投影相似。
The cross-section shape of the hood is similar to the horizontal projection of the smoke emission source as far as possible.
排烟罩的收缩角度口宜等于或小于60°，大不应大于90°。为了降低排烟罩的高度，对于边长较长的矩形排烟罩可将长边分段设置。
The shrinkage angle of the exhaust hood should be equal to or less than 60 degrees, and the maximum should not be greater than 90 degrees. In order to reduce the height of exhaust hood, the long side of rectangular exhaust hood can be segmented.
排烟罩罩口边宜留有一定高度的垂直边（裙边），垂直边的高度 （ 为罩口面积）。
It is advisable to leave a certain height of vertical edge (skirt edge) and height of vertical edge (cover area).
罩口截面尺寸按下式计算：
The sectional dimensions of the hood are calculated according to the following formula:
式中各符号的意义（a）。
The meaning of the symbols in the formula (a).
（2）垂直炉门烟气散发源和烟罩尺寸的确定
(2) Determination of flue gas emission source and hood size of vertical furnace door
垂直炉门上方装设排烟罩的常见形式如右图（b）所示。排烟罩罩口尺寸A可按公式 确定，但确定罩口尺寸B必须确定烟气散发源的尺寸b。除按生产实践中的经验数据确定外，也可以用理论方法计算确定。
Common forms of smoke hood installed above vertical furnace doors are shown in the right figure (b). The size A of the hood can be determined according to the formula, but the size B of the hood must first determine the size B of the smoke emission source. In addition to the empirical data in production practice, it can also be determined by theoretical calculation.
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