Patent ID: 7206724

Claim:
A method for determining the shape of a scroll cage for a forward-curved centrifugal blower wheel in a blower housing having a blower cut-off end comprising: determine the blower wheel dimensions (R wheel ×blower wheel depth); calculate ρ o , the radius of a blower circle, comprising the distance from the center of the blower wheel to the blower cut-off end, using the formula: ρ o =R wheel +δ, where δ, the radial wheel clearance, is selected from the range of: 10 mm ≦δ≦20 mm; determine ρ e , the distance from the center of the blower wheel to a discharge point of the scroll cage at the tangential point of the scroll cage and the blower housing, and calculate b, the difference between ρ e and ρ o using the formula: b=ρ e −ρ o ; select a diffusing angle α, the angle between the blower circle and the blower cut-off at the blower cut-off end, from the range of: 8°<α<13°; calculate a development angle φ o , the polar angle between the radial line from the center of the blower wheel to the blower cut-off end and the radial line from the center of the blower wheel to the discharge point, using the formula: φ o tan α=(180/π)(b/ρ o ); and plot the scroll cage profile on polar coordinates starting at the cut-off end using the formula: ρ=ρ o +φb/φ o (for 0≦φ≦φ o ) where ρ is the distance from the center of the blower wheel to the scroll cage and ending at the discharge point at (φ o , ρ e ).