GB690951A - Improvements in or relating to centrifugal compressors - Google Patents

Abstract

690,951. Centrifugal compressors. CARRIER ENGINEERING CO., Ltd. Oct. 3, 1950 [April 26, 1950], No. 24185/50. Class 110(i) A centrifugal compressor comprises a penultimate stage comprising an impeller and a bladeless diffuser surrounding the impeller, and a final stage comprising an impeller and a volute, the impellers being of approximately the same diameter and the penultimate -stage producing 54 to 60 per cent of the total work done by the two stages. Guide vanes 9 impart whirl to the gas entering the first impeller 5 of a two-stage compressor. A bladeless diffuser 6 and a return channel 7 containing whirl-imparting vanes 10 lead the gas to the second impeller 13, from which it is discharged to a single- or multioutlet volute 15. 54 to 57 per cent of the total work of compression is done by the impeller 5, in which the area of flow decreases as the radius increases, so as to reduce the gas velocity by about 10 to 15 per cent. The angle between the blades 23 and the tangential direction varies from 40 degreesŒ5 degrees at the impeller periphery to 26 degrees Œ 3 degrees and 30 degreesŒ3 degrees at the edge 51 and edge 52 respectively, Preferably, the variation of blade angle is such as to maintain a constant angle of attack along the inlet edge of the blade. Over at least the last half of the length of the passageways of the impeller 13, the flow area increases with the radius so as to reduce the gas velocity by about 15 to 20 per cent, the velocity head at outlet being less than 2/3 of the corresponding head in the first stage. The angle between the blades and the tangential direction decreases with increasing radius over about the last half of the passageway length, with a value at the impeller periphery of 18 degrees Œ 3 degrees. Impeller 13 is about equal to impeller 5 in diameter, but the axial distance between the back plate and cover plate at the eye and periphery is 80Œ5 per cent and 75 to 100 per cent respectively of the corresponding measurement of impeller 5. The volute throat 36 is made greater in width than the impeller tip so as to reduce the gas velocity by 5 to 15 per cent. The sides 53 have angles of less than 30 degrees, giving a further reduction of 15 to 20 per cent to the tongue of the volute. In the volute proper and in the discharge pipe further reductions of 27 and 38 per cent respectively may be obtained.