Fan shroud structure

A fan shroud structure for use with a rotary, axial flow fan having a plurality of circumferentially spaced, radially extending impeller blades, said blades having an effective axial width (AW) measured axially along the rotational axis of the fan between a first plane and a second plane, said planes being axially spaced and parallel with respect to each other and disposed substantially normal to the rotational axis of the fan, said first and second planes extending radially, respectively, through points on the leading edges of the blades of the radial tip portions thereof and through points on the trailing edges of the blades at the radial tip portions thereof, comprising,

• a generally cylindrical axially extending throat section encircling the fan;
• an annular, generally radially extending flat portion, said flat portion being radially spaced outwardly and axially from one axial end of said throat section;
• an annular, radially and axially curved, intermediate section extending between said one end of said throat section and said radial flat portion, said throat section, intermediate section, and said radial flat portion being effective to produce a low pressure region between the air stream flowing over the surface thereof and such surface when the fan is in operation, and the following relationships exist:
• RF = AW/3 plus or minus 12 percent of AW, CF = AW/3 plus or minus 12 percent of AW, and R = 2AW/3 plus or minus 12 percent of AW where RF is the radial length of the radial flat portion, CF is the axial length of the cylindrical throat section, and R is the radius of curvature of the intermediate section;
• and
• an annular supplementary low pressure vortex creating means formed in said throat and intermediate section, and radial flat portion of the fan shroud structure such that an additional low pressure region is generated between the air stream flowing over the surface of the fan shroud structure and such fan shroud structure surface when the fan is in operation.

A fan shroud structure for use with a rotary, axial flow fan having a plurality of circumferentially spaced, radially extending impeller blades, said blades having an effective axial width (AW) measured axially along the rotational axis of the fan between a first plane and a second plane, said planes being axially spaced and parallel with respect to each other and disposed substantially normal to the rotational axis of the fan, said first and second planes extending radially, respective, through points on the leading edges of the blades at the radial tip portions thereof and through points on the trailing edges of the blades at the radial tip portions thereof, comprising,

• a generally cylindrical, axially extending throat section encircling the fan, said first plane being substantially coincident with the radial plane containing one axial end of said throat section;
• an annular, generally radially extending flat portion, said flat portion being radially spaced outwardly and axially from the other axial end of said throat section;
• an annular intermediate section extending between said other axial end of said throat section and said radial flat portion, said throat section, intermediate section, and said radial flat portion being effective to produce a low pressure region between the air stream flowing over the surface thereof and such surface when the fan is in operation, said intermediate section being radially and axially curved, and the following relationships exist:
• RF = AW/3 plus or minus 12 percent of AW, CF = AW/3 plus or minus 12 percent of AW, and R = 2AW/3 plus or minus 12 percent of AW where RF is the radial length of the radial flat portion, CF is the axial length of the cylindrical throat section, and R is the radius of curvature of the intermediate section, and said first plane may be axially spaced from and on either axial side of radial plane containing said one axial end of said throat section a distance of 12 percent of AW and said second plane may be axially spaced from and on either axial side of a radial plane containing said end of said intermediate section opposite the end thereof operatively connected to said throat section a distance of 12 percent of AW;
• and
• an annular supplementary low pressure vortex creating means formed in said throat and intermediate sections, and radial flat portion of the fan shroud structure whereby an additional low pressure region is generated between the air stream flowing over the surface of the fan shroud structure and such fan shroud structure surface when the fan is in operation.