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) Determining the shape and size of exhaust hood for horizontal smoke emission source
The cross-section shape of the hood is similar to the horizontal projection of the smoke emission source as far as possible.
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).
The sectional dimensions of the hood are calculated according to the following formula:
The meaning of the symbols in the formula (a).
(2) Determination of flue gas emission source and hood size of vertical furnace door
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.