| 摘要 |
PROBLEM TO BE SOLVED: To miniaturize the scroll type casing of a centrifugal fan without imparting silencing performance by providing an enlarged shape represented by a specific formula. SOLUTION: A plurality of radial vanes is integrally connected together between a circular plate and an annular plate having intervals in a circumferential direction, and the impeller of a multiblade radial fan is stored in a scroll type casing. This scroll type casing has an enlarged shape represented by r= r0 .exp[αtanθc ] in a range ofα<=θ<=α+β, and represented by r=r0 .exp[(θ-β) tanθc ] in a range ofα+β<=θ<=2π. Hereat, r is the radius of a casing side wall measured from the center of the impeller, r0 is the outside radius of the impeller,θis an angle from a datum line,αis an angle from the datum line to a tongue,βis a predetermined angle andθc is an enlarged angle. Hereby, the scroll type casing can be miniaturized in comparison with the case that the enlarged shape of the scroll type casing including the circumference of the tongue is formed into a logarithmic spiral shape.
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