Rotary expansible chamber devices – Combined
Patent
1991-07-09
1992-08-11
Bertsch, Richard A.
Rotary expansible chamber devices
Combined
4182011, 417312, 60271, 181226, 181229, 181403, F04C 2906
Patent
active
051374390
DESCRIPTION:
BRIEF SUMMARY
SUMMARY OF THE INVENTION
The present invention relates to a screw rotor machine which has a sound silencing device mounted on the inlet and/or the outlet side thereof.
The problem of damping sound in screw rotor machines is difficult to master, at least when the space available therefor is restricted, as is normally the case.
This is mainly because both the inlet line and the outlet line, and particularly the latter, conduct low-frequency noise of large amplitudes in the machine, which must be dampened.
A suitable silencer for this purpose is the so-called De Laval nozzle. One distinguishing feature of this known nozzle is that a switch to critical flow-sound velocity occurs in the smallest throughflow area when a given pressure ratio is exceeded. The De Laval nozzle is therefore a non-linear resistance through which wide fluctuations in pressure on the inside of the silencer are unable to penetrate. This effect is particuarly valuable in the case of low-frequency pressure fluctuations, which normally require silencers of large volume. In order to utilize the De Laval nozzle effectively, throttling is adapted so that the mean flow rate will lie immediately beneath the sound velocity.
DETAILED DESCRIPTION
Adaptation of the throttling effect, however, is quite critical. When varying the size of the static gas flow, it is necessary to adapt the smallest area to the maximum gas flow, since otherwise the losses will be too high. This also means that a poor silencing effect, or no silencing effect at all, will be attained at part loads.
The object of the present invention is to provide a screw rotor machine provided with at least one silencer which is effective over substantially the whole capacity range of the machine.
This object is achieved in accordance with the invention with a machine having the characteristic features set forth in the following claim 1. The movable valve body, which is biased by a substantially constant spring force, functions to maintain a substantially constant pressure drop across the Laval-nozzle, thereby enabling the gas velocity to lie immediately beneath the speed of sound, this feature being a characteristic of the Laval-nozzle, irrespective of machine capacity. Movement of the valve body must also be dampened, so that solely slow changes in gas flow will be influential, such as when changing the capacity of the machine.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now be described in more detail with reference to the accompanying drawing, the single FIGURE of which is a schematic side view, in longitudinal section of an exemplifying embodiment of an inventive screw rotor machine provided with a sound damping device.
DETAILED DESCRIPTION
The machine illustrated in the drawing is a screw-rotor compressor 1, which forms part of a refrigerating system, and a drive motor 2, both of which machine members are mounted on top of an evaporator 3. An inlet line 4 passes from the evaporator to the low pressure side of the compressor 1, and an outlet line 5 passes from the compressor to a refrigerating circuit (not shown).
The outlet line 5 is connected to a pipe-bend which extends from the outlet port 6 of the compressor and in which a De Laval nozzle 8 is arranged. A spherical valve-body 9 is journalled downstream of the De Laval nozzle 8 for axial movement in relation to said nozzle, said movement being effected with the aid of a piston rod 10 which is slideably mounted in a sealing lead-through 11 mounted in the wall of the pipe-bend 7.
Attached to the piston rod 10 is a piston 12 which is slideably mounted in a cylindrical housing 13. The housing 13 has mounted therein a spring 14 which endeavours to hold the valve body 9 in sealing abutment with the through-flow opening 8A of the nozzle 8. The interior of the housing 13 contains a liquid, suitably oil, and communicates with a throttle valve 15 through the intermediary of two pipes 16 which discharge in the close proximity of the end walls of the housing 13. The valve 15 is provided with means 17 for adjusting the area o
REFERENCES:
patent: 2931169 (1960-04-01), Glenn
patent: 3534831 (1970-10-01), Nagamatsu
patent: 3720482 (1973-03-01), Tell
patent: 3884664 (1975-05-01), Edwards
patent: 3999898 (1976-12-01), Chomczyk et al.
patent: 4727651 (1988-03-01), Nakajima
Bertsch Richard A.
Cavanaugh David L.
Svenska Rotor Maskiner AB
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