Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Casing having tangential inlet or outlet
Patent
1995-03-29
1996-09-03
Larson, James
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Casing having tangential inlet or outlet
4152081, F04D 2944
Patent
active
055518389
DESCRIPTION:
BRIEF SUMMARY
The present invention refers to a novel inlet bell for centrifugal fans having an impeller with a cover plate with a circular inlet opening, the inlet bell opening into the cover plate with an intervening gap for recirculated air.
PRIOR ART
Many shapes have already been designed and used for inlet bells of centrifugal fans. Those shapes are designed either for good performances of the fan or for minimum cost.
For obtaining a good performance prior art inlet bells have been made very smooth by manufacturing the pieces using spinning technique. This makes the inlet bells very expensive. In FIG. 1 an inlet bell of this kind is shown, with an outlet end manufactured using spinning technique, opening into the impeller of a centrifugal fan.
Where these high costs are not accepted, simple constructions with an inlet bell in the form of a cylinder, as in FIG. 2, or as a cone, as in FIG. 3, have been used with a resulting poor performance. This is due to undesirable eddies formed in the recirculation area adjacent the inlet of the impeller coverplate.
BRIEF DESCRIPTION OF THE INVENTION
The object of the invention is to provide an inlet bell with a good performance and at the same time a low manufacturing cost.
This is accomplished with the inlet bell according to the invention, which is characterized in that the inlet bell is provided with a conical inlet part, tapering towards the impeller, and a mouthpiece connected to the inlet part, and in that a circular flow guide means is arranged at the intersection between the inlet part and the mouthpiece of the inlet bell.
With this arrangement according to the invention a fairly good performance is achieved at a very reasonable manufacturing cost for the inlet bell. The object of the flow guide means is to obtain a separation of the flow from the inlet part of the bell with as small a disturbance of the flow as possible.
The flow guide means could be realized in several different ways.
According to a first embodiment of the invention the flow guide means is a protruding lip formed inside the mouthpiece by the tapering end of the inlet cone, which is partly inserted into the mouthpiece.
The performance may be further enhanced by providing a chamfered or rounded edge of the protruding lip, and/or forming the lip with a small curvature at the edge. With this arrangement the point where the flow separates from the surface is fixed. The costs for the chamfering or rounding the edge and the forming of a small curvature on the edge of a cylinder or cone is very low and easily done.
According to a preferred embodiment of the invention the conical inlet part has a cone angle .alpha. of between 25.degree. and 50.degree. in order to give the desired airflow into the fan.
According to a further embodiment of the invention the mouthpiece has the form of a cylinder. Preferably the ratio between the diameter of the circular flow guide means and the mouthpiece diameter d/D (see FIG. 5) lies between 0,8 and 1, and the ratio between the length of the mouthpiece 1 and the mouth piece diameter D between 0,1 and 0,28.
According to another embodiment of the invention the mouthpiece has a conical outwardly tapering form, the flow guide means being a protruding lip formed inside the mouthpiece by the tapered end of the inlet part, which is partly inserted into the mouthpiece.
According to still another embodiment of the invention the mouthpiece has a conical outwardly tapering form, the flow guide means being the edge formed between the two conical parts secured to each other at their respective narrow ends, the angle (.beta.) being at least 230.degree..
One advantage of the conical mouthpiece is that it provides a low resistance to the recirculating flow entering through the gap between the inlet mouthpiece and the impeller coverplate. This recirculating flow maintains pressure stability of the fan and can increase the pressure.
As in the case of the protruding lip, the outlet edge of the mouthpiece can be chamfered or rounded and/or might have a small curvature in order to further enha
REFERENCES:
patent: 1612568 (1926-12-01), Buder
patent: 1787652 (1931-01-01), Anderson
patent: 2209607 (1940-07-01), Nutting
patent: 3101890 (1963-08-01), Carlson
patent: 3627440 (1971-12-01), Wood
ABB Flakt AB
Larson James
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