①通风管单位长度摩擦阻力(简称比摩阻)的计算表(或线算图)只适用于计算圆形风管的比摩阻,为利用该计算表(或线算图)求矩形风管的比摩阻,通常需要先把矩形风管的断面尺寸折算成相当的圆形风管的直径,即折算为当量直径[1],再由当量直径从圆形风管比摩阻计算表(或线算图)上查得矩 (1) The calculation table (or line calculation diagram) of the unit length of the ventilation pipe friction resistance (referred to as the specific resistance) is only applicable to calculate the specific resistance of the circular duct, in order to use this calculation table Than the friction resistance, usually need to first rectangular duct section size converted into equivalent diameter of circular duct, which is equivalent to the equivalent diameter [1], and then by the equivalent diameter from the circular duct than the friction calculation table ( Or line count chart) on the search moment