SILENCER FOR THE DISCHARGE FROM A CENTRIFUGAL BLOWER

Abstract: Silencer for connection to the outlet of a centrifugal blower, comprising slots for the thoroughgoing flow from the blower, surrounded by sound absorbing material, the silencer thereby being arranged in such a way that the flow from the blower enters the silencer slots being arranged at the smallest cross section opening of the centrifugal blower, e.g. at the cross section of the tongue (7) of the blower, and that a partition wall (4) being arranged in the silencer between two slots, the partition wall (4) having increasing thickness from the inlet to the outlet thereby ensuring that the total flow cross section is substantially constant from the inlet to the outlet of the silencer.

Description: Silencer for the Discharge from a Centrifugal Blower The present invention is related to a silencer for the s discharge of a centrifugal blower, according to the preamble of the claims. Centrifugal blowers of the known type comprise a discharge having a constriction in the shape of a tongue formed in such a way that the effective discharge opening only covers o 60-70 % of the total cross section. This constriction provides the medium from the blower with a velocity profile having an oblique distribution across the cross section of the discharge, as can be seen from figure 1 which schematically discloses the discharge velocity along the cross section in four different s distances from the discharge. As can be seen from figure 1 in the drawing, the highest velocity exists approximately near the circumference of the blower wheel. Known silencers for centrifugal blowers lead the air flow from the blower into a box which normally is constructed o with a forechamber, sound absorbing plates at a distance from each other in such a way that channels are established between them, as well as a second chamber before the discharge. The purpose of the forechamber is to distribute the air evenly to all slots between the plates, before the air enters the slots. Such 5 structures necessarily are voluminous and the costs increases correspondingly for production as well as installation. Furthermore, the flow medium will experience a pressure loss in the chamber due to loss of velocity pressure. The flow medium also will experience further losses due to friction and 0 impacts on the different parts of the structure. Based on the above, it is an object for the present invention to provide a silencer for a centrifugal blower having the same properties for the sound dampening as known embodiments, but with a substantially smaller need for space, a strongly cost 5 reduction in the construction and which also gives substantially smaller pressure loss for the medium, as friction loss as well as impact loss. The above is achieved with the silencer according to the present invention as defined with the features stated in the claims. The drawing discloses in figure 1 schematically the distribution of the velocity across the cross section of the centrifugal blower at four different distances from the discharge in a traditional blower, figure 2 discloses schematically the silencer according to the present invention secured to a centrifugal blower, seen in a vertical section, figure 3 discloses the blower in figure 2 in perspective, figure 4 discloses a front view of the blower in figure 3, figure 5 discloses a vertical section V in a slot in the silencer in figure 3 and figure 6 discloses a horizontal section VI through the silencer in figure 3. With the silencer according to the present invention is achieved that the medium gains the pressure drop which the medium has accumulated on its way through the silencer, as the velocity pressure is transformed to static pressure, corresponding to the friction pressure through the silencer. The conditions for the outlet of the silencer are optimized and additionally the velocity profile is completely equalized through the silencer. Also the silencing effect is improved. Figures 2-6 disclose one embodiment of the silencer according to the present invention, having vertically arranged sound dampening slots 5 for thoroughgoing flow of the medium. Depending of the local arrangement and other parameters, these slots may be arranged vertically or horizontally. The silencer preferably may have a shape as disclosed in figure 5 where the connecting funnel 6 ensures that the inlet of the silencer completely corresponds with the outlet 2 of the centrifugal blower. In this way negative effects from the tongue 7 of the centrifugal blower are avoided. The silencer has a shape according the diffusor principle where two slots 5 extend from the outlet 2 of the blower 1 to the outlet of the silencer. A thin partition wall 4 is arranged between the slots 5 and a surrounding isolating material 3 covers the vertical slots 5 above and below and at the sides. To achieve as little losses as possible for the connection between the blower and the silencer, the air velocity is set to approximately 20 m/s and to establish a transition between the outlet 2 of the centrifugal blower and the dampening portion of the silencer thereby establishing a diffusor effect. The transition is made in such a way that a constant total cross section is maintained from the inlet of the silencer, by a s tapered portion 8, whereby an increased sound dampening effect is achieved. Constant cross section in the transition area is achieved by increasing the width of the transition wall 4 and thereby make the width of the slots 5 smaller along the tapered o portion 8 and at the same time increase the height of the slots 5. The entire partition wall 4 may as such be tapered along its length from silencer inlet to its outlet, or the partition wall may be a parallel prolongation of the tapered s portion 8. 0 5 0 5

Claims: Patent claims 5 1. Silencer for connection to the outlet of a centri¬ fugal blower, comprising slots for the thoroughgoing flow from the blower, surrounded by sound absorbing material, CHARACTERIZED IN the silencer being arranged in such a way that the flow from the blower enters the silencer slots being arranged at the o smallest cross section opening of the centrifugal blower, e.g. at the cross section of the tongue (7) of the blower, and that a partition wall (4) being arranged in the silencer between two slots, the partition wall (4) having increasing thickness from the inlet to the outlet thereby ensuring that the total flow s cross section is substantially constant from the inlet to the outlet of the silencer. 2. Silencer according to preceding claims, CHARAC¬ TERIZED IN the transition comprising an tapered portion (8) at the outlet (2) increasing its thickness to the thickness of the o transition wall (4) between the two slots (5) in such a way that the width of the slot opening decreases due to the angle of the tapered portion substantially corresponding to the increase of the height of the slot opening, due to the vertical opening angle of the slots only along a first portion (8) of the wall length. 5 3. Silencer according to preceding claims, CHARAC¬ TERIZED IN the slots (5) being arranged vertically. 0 5

Inventors: SAETRE THOR, SAETRE, THOR
Applicants: AURANOR A S, SAETRE THOR, AURANOR A.S, SAETRE, THOR
Application year: 1996
Main classification: F04D29
IPC codes: F04D29, F24F13