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）水平煙氣散發(fā)源排煙罩形狀和尺寸的確定

　　(1) Determining the shape and size of exhaust hood for horizontal smoke emission source

　　排煙罩罩口的截面形狀盡可能與煙氣散發(fā)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.

　　排煙罩的收縮角度口宜等于或小于60°，大不應大于90°。為了降低排煙罩的高度，對于邊長較長的矩形排煙罩可將長邊分段設置。

　　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.

　　排煙罩罩口邊宜留有一定高度的垂直邊（裙邊），垂直邊的高度  （  為罩口面積）。

　　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計算：

　　The sectional dimensions of the hood are calculated according to the following formula:

　　式中各符號的意義（a）。

　　The meaning of the symbols in the formula (a).

　?。?）垂直爐門煙氣散發(fā)源和煙罩尺寸的確定

　　(2) Determination of flue gas emission source and hood size of vertical furnace door

　　垂直爐門上方裝設排煙罩的常見形式如右圖（b）所示。排煙罩罩口尺寸A可按公式  確定，但確定罩口尺寸B必須確定煙氣散發(fā)源的尺寸b。除按生產實踐中的經驗數(shù)據(jù)確定外，也可以用理論方法計算確定。

　　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.