US2341871A - Centrifugal blower with spiral casing - Google Patents

Description

Feb 15, 11944. J KARRER CENTRIFUGAL BLOWER WITH SPIRAL CASING Filed July 19, 1940 m Tr) we WW M v w J I pecially at the outer circumference.

Patented Feb. 15, 1944 CENTRIFUGAL BLOWER WITH SPIRAL CASING Josef Karrcr, Zurich, Switzerland, nsslgnor to Maschinenfabrik Oerlikon, Oerlikon, Switzerland, a corporation of Switzerland Application July 19, 1940, Serial No. 346,281 In Switzerland July 29, 1939 '1 Claim.

The centrifugal blowers (fans and compressors) with spiral casing hitherto designed operate in such a manner that the rotor wheel conveys the medium drawn in to the spiral. In these cases the spiral casing can be designed only as a collecting chamber, that is to say, the medium con-' tinues to flow on with approximately the same velocity at the outlet of the rotor wheel in the spiral, and the velocity is converted into pressure in a diffuser outside the spiral. The spiral casing may also be designed with an increased cross section for the purpose of converting the velocities into pressure already in the spiral,

Both constructions are connected with great disadvantages; in .both cases the media entering the casing at the beginning of the spiral are deflected 360 up to their discharge from the spiral. As the media entering the casing at the end of the spiral from the rotor wheel continue to flow on in a. straight line, the media sufl'era mean deflection of 180". If the great velocities are taken into consideration, especially in blowers and compressors, it will be readily seen that great losses must occur in the spirals as made today. If the spiral casing is also designed as a diffuser the mean velocities, it is true, become smaller and consequently also the losses of flow. However. designing the spiral casing as a diffuser produces other drawbacks. The great velocities obtaining at the inlet of the spiral are gradually converted into pressure at least partially. The velocity decreases toward the outlet, and the static pressure increases. This takes place es- At the inher circumference new media always enter the spiral from the rotor wheel, and as here the velocities have not yet been converted into pressure, the static pressure is smaller at thednner circumference causing transverse currents and vortices to appear.

In order to eliminate these disadvantages, the invention proposes subdividing, in a centrifugal blower with spiral casing, said spiral easing into at least two partial spirals, with diffusers Joining the spirals. In that way the mean deflection can drop at least to 90, in the case of three partial spirals to 60, with four to 45", etc. The losses of deflection can thereby be reduced to very small values; for example, for the various angles of deflection the following coeflicients of resistance are found By transferring the principal conversion-ofpressure to the outside of the spiral, different pressures are moreover avoided as much as possible, thus obtaining the smallest losses and the highest degree of efllciency.

Another drawback of known designs consists in the casings being designed considerably wider than the rotor wheel, with the result that the media, after discharge from the rotor, are deflected laterally, which again leads to losses. This disadvantage also is eliminated with the subdivided spiral casing. For, by subdividing the spiral and transferring the principal conversion of velocity into pressure to the outside of said spiral, the cross sections of th partial spirals may be reduced to such a degree that the width of the spiral may be diminished approximately to that of the rotor wheel, or that at least the widening toward the outside does not exceed an angle of 20 and the height of the spiral does not exceed double the width of the rotor wheel, whereby favorable flowing condition are obtained.

If, for instance, the spiral casing has three partial spirals I, II, III, the mean deflection is only 60, and the loss drops to about of that of a blower of the usual design. 1 With more partial spirals the lossv becomes still smaller; however, too great a subdivision, more than six, produces hardly any gain. I

To the partial spirals are joined the diffusers, in which the pressure conversion principally takes place. The diffusers may be in the plane of the spiral or be deflected according to the conditions of the design.

In the case of a single stage blower and if the partial diffusers can not lead directlyto the place of use, all the partial diffusers may be led to a single outlet, for example by lengthening two diffusers and leading them to the third. Such lengthening and deflection causes only small losses, as the cross section may be made small in this case, and the velocities thus kept low.

0f course, the invention may be applied to all centrifugal machines with or gaseous media.

The annexed drawing explains the subject mat- .ter of the invention. Figs. 1 and 2 show a view and section respectively of a blower oi the usual design, with a blower wheel i and a spiral casing 2. 3 is the diffuser built on to it. The filament of how entering at A the spiral casing 2 will move on at the outer circumference and up to the outlet undergoes a deflection of 360 at point B. The last filament of flow entersat B (A) the casing from the rotor wheel and does not spiral casings for air,

undergo any deflection. Therefore, the mean of the deflection of the medium is 180.

Figs. 3 and 4 show an example of an embodiment of a centrifugal blower. according to the invention. This spiral casing possesses two partial spirals I and II. The mean deflection amounts to.90. The partial spirals I and II convey into the diffusers I and II. It is a single stage blower. The diffusers are led directly to the place ofuse; however, as shown in Figs. 5 and 6, they may also be combined to form one outlet by one of the diffusers, I, being extended to the other diffuser, II, by means of a transfer conduit III, the two diffusers being constructed to form one outlet IV. Fig. 7 gives a front view of the combination of th conduit III with the diffuser II to form the common outlet IV.

Having thus described my invention I claim;

A centrifugal blower having the combination of a rotatable fluid impeller, the peripheral region surrounding said impeller having therein a plurality of exposed sectoral spiral casings constituting the housing of the blower, each of said casings receiving fluid from said impeller for therethrough evolving a high velocity of the fluid, said plurality of casings jointly producing a total increase of emciency with reduction of losses of the centrifugal blower, a diffuser for each of said casings, joined to the outlet thereof for converting the velocity of its fluid into pressure, an outlet receiving the fluid from one of said diffusers, and a branching conduit joined to another of said diffusers conveying its fluid to said outlet therein merging it with said received fluid.

J OSEF' KARRER

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