Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Plural distributing means immediately upstream of runner
Reexamination Certificate
1999-11-29
2001-08-14
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Plural distributing means immediately upstream of runner
C415S206000, C415S208200
Reexamination Certificate
active
06273677
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a centrifugal pump with an axial inlet and an inflow guide device mounted upstream of the impeller, which guide device has several fixed guide vanes, which on the side facing the impeller each have an edge pointing towards or away from the direction of rotation of the impeller.
Centrifugal pumps with an axial inlet often have an inflow guide device mounted upstream of the first impeller. Their purpose is to remove a possible whirl from the transported fluid, such that an axial flow is present downstream of the inflow guide device.
The inflow guide device can be composed of several guide vanes, disposed uniformly around the perimeter of the inlet. The guide vanes can be attached to each other in the axis of the inlet and thus form a star or cross.
Inflow guide devices are known from DE 471 149 and DE 649 668 whose blades can be curved towards or away from the direction of rotation of the impeller in order to adapt to particular inflow conditions or to generate them. The curvature is bow shaped and extends in each case with the same axial length to the entire radial span of the blade. Here, when compared with the blade, the curvature has only a limited axial length.
In contrast to the previously described inflow guide device, which is equipped with seven blades and was relatively expensive, nowadays inflow crosses are preferred, that is, inflow guide devices comprising only four blades. These devices, inexpensive in themselves, are hardly able, however, to reduce an inherent disadvantage of the axial flow centrifugal pumps, the instability present in the pump's steady state characteristics. It is therefore the object of the invention to achieve such a reduction for a centrifugal pump of the type described above and on the whole to improve the flow conditions.
SUMMARY OF THE INVENTION
This object is achieved according to the invention in that the edge pointing in or opposite to the direction of rotation is formed by a swirl blade which is formed on the guide vane and located in the region of the inlet wall and which has a shorter radial length than the guide vane.
Experiments have shown that the efficiency of the flow machine is increased over a wide operating range by using the inventive design with a turbulence bade formed on the guide vane. This is especially true when the angle of incidence between the guide vane and the swirl blade is negative, that is, when the swirl blade points against the direction of rotation of the impeller.
In general, it can be said that the angle of incidence depends on the type of hydraulics. It can be determined based on measurements, that is, it can be determined with the purpose of achieving different effects on the pump's steady state characteristics at all operative conditions.
The effect of the swirl blade increases nearer to the wall. Therefore, it is advisable to increase the axial length of the swirl blade as it approaches the wall. Thus it is advantageous if, in designing the swirl blade, one starts with a right triangle whose hypotenuse is the edge facing the impeller.
The almost one-dimensional flow in the axial inlet is changed by means of the swirl blade into a three-dimensional whirling flow in the region of the wall of the inlet or of the inflow nozzle. This change leads to greater efficiency at all load conditions and reduces the instability of the pump. In particular, the kinetic energy of the gap flow and re-circulation flow is returned to the inflow so that energy is recovered. In cases of increased inlet flow, for example in the case of an overload, the pre-whirling increases.
In addition, because of the swirl blades, the beginning of the re-circulation upstream of the impeller shifts towards relatively low inlet flows. Thus, the hysteresis region on the pump's characteristic curve, dangerous to the operational performance of the pump, is displaced sharply to the left, something which substantially widens the range of the pump's use.
The change in the inflow which is achieved by the inflow guide device according to the invention leads to an adaptation of operative conditions which is more efficient and increases the breadth of applicability since the turbulence boundary is clearly displaced to the left. Due to the design in accordance with the invention, the flow onto the impeller is also improved, such that secondary currents and flow separations downstream from the impeller blades are minimized.
As a further development of the invention, it is suggested that one or more of the guide vanes each have on the edge opposite the impeller a pre-guide vane which is similar in shape and size to the swirl blade. It has been shown that this type of pre-guide vane further improves the flow guidance.
The invention can be realized by simple means if, as is known, the guide vanes are arranged in the form of a cross or a star.
The invention will be explained in further detail with reference to an illustrative working embodiment.
REFERENCES:
patent: 2083185 (1937-06-01), Anderson
patent: 2834536 (1958-05-01), McDonald
patent: 4854818 (1989-08-01), Meng
patent: 4884942 (1989-12-01), Pennink
patent: 5746575 (1998-05-01), Westphal et al.
Hellmann Dieter
Schill Juergen
Wang Baogang
Crowell & Moring , L.L.P.
KSB Aktiengesellschaft
Look Edward K.
Nguyen Ninh
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