Patent GB-1024584-A (GB)
Title: Improvements in or relating to centrifugal blowers, compressors, pumps or the like
IPC: F04D29/58
Filed: 1963-01-30
Abstract: 1,024,584. Centrifugal pumps, blowers and compressors. K. D. McMAHAN. Jan. 30, 1963 [Feb. 27, 1962], No. 3909/63. Heading F1C. The multi-stage compressor (or blower or pump) shown in Fig. 1 comprises an annular diffuser 30 (which may be vaneless as shown), at the exit from each impeller 14, followed (except in the final stage) by several diffuser volutes 31, Figs. 1 and 2 (not shown), which pass through the corresponding interstage casing member 22, each volute opening on the opposite side of the member 22 into an elbow 33, Fig. 5, which directs the gas radially inwardly as a jet through a radial passage 34 leading to the eye 35 of the next impeller. To compensate for the tendency of the flow through each elbow 33 to be displaced towards the outer bend 37 by a centrifugal force, guide vanes may be provided within the elbow. Alternatively, as shown, the outer bend extends through a greater angle than the inner bend 36, i.e., through approximately 150 degrees instead of approximately 90 degrees. For the same purpose and also to prevent breakaway of flow from the inner bend 36, the area of flow is reduced by at least 15%, say approximately 26%, from the inlet end of the elbow 33 to its outlet end, the width parallel to the impeller axis at the inlet end being approximately 2¢ times that at the outlet end. In addition, a protuberance 38 is provided on the upstream part of the inner bend 36 to increase the effective radius of the inner bend. As a result of these measures, the path J 1  of the momentum of the gas jet becomes directed towards the axis A of the compressor (but is displaced by an angle a of approximately 2 degrees from the radial centre line B of the radial passage 34) whereby the jet enters the eye 35 without a rotational component. The radial passages 34 are free from walls on the circumferentially facing sides of the gas jets, i.e., the jets flow through an annular space between the elbows 33 and the eye 35. In addition, the axially-facing walls of the radial passages may be recessed so as to be spaced from the jets. Each jet diverges at each side by an angle b of about 3 degrees and generates eddies e x  and e y  which are suppressed and cancelled out by the interaction of the jet with the adjoining jets, this latter effect being assisted by slight further reductions in the flow area between the elbow 33 and the cylindrical outer boundary of the eye 35 and between the latter and the cross-section of the eye in a plane perpendicular to the impeller axis, totalling approximately 25%. Where less than four jets are provided, whereby the angle of intersection between adjacent jets exceeds 90 degrees, guide vanes 80, Fig. 11 (not shown), may be provided at each intersection. At the exit from the final stage, each volute 31b, Figs. 1 and 4 (not shown), is followed by an elbow 33b which turns the flow into a direction substantially parallel to the impeller axis. In other respects the elbows are similar to the elbows 33, each being provided with a protuberance 38b and having its outer bend 37b extending through a greater angle than the inner bend 36b. Each elbow 33b is followed by a passage 51 having a substantially rectangular cross-section similar to that of the passages 34 and having an initial portion 52 substantially parallel to the compressor axis and a portion 53 extending radially inwardly to an annular axial outlet 54. Two compressors (one or both of which may be of single-stage type) may be joined together to operate in series, with the outlet 54 of one abutting the inlet 26 of the other. The radial passages 34 may be of alternately large and small flow area and alternately large and small circumferential spacing. The compressor stages may be of successively decreasing size.