Pumps – Motor driven – Interrelated or common lubricating or cooling means for pump...
Reexamination Certificate
2000-01-21
2001-11-27
Freay, Charles G. (Department: 3746)
Pumps
Motor driven
Interrelated or common lubricating or cooling means for pump...
C165S104130
Reexamination Certificate
active
06322332
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention proceeds from a device for the external cooling of an electrical drive motor of a centrifugal pump unit.
With centrifugal pump units which for example are applied for the delivery of waste water in hollows, wells or likewise, the leading away of the dissipated heat of the electrically dry-running drive motor is effected via the motor outer surface into the surrounding medium. The centrifugal pump unit is as a rule with the motor above the pump, assembled in the hollow or well and at the beginning of the delivery as a rule is completely submerged into the waste water. After a certain delivery time the motor protrudes from the waste water, and specifically when the level of the water has sunk correspondingly lower. Since the unit is driven in the on-off switching operation, with short running times normally no problems occur.
The situation is different when the units are to be set up dry, i.e. are not to be operated submerged. Since with e.g. motors designed closed for explosion-protective reasons, the motor cooling surfaces increase with the second power of the dimensions, but however the power of the motor increases with the third power, the limit of the application of these units with the removal of the dissipated heat to the surrounding air alone is very quickly reached.
Furthermore it is known to provide the drive motor on the outside with a jacketing surrounding it at a distance and to let the intermediate space thus formed be flowed through by a part flow of the pump delivery flow, which is known as so-called hood cooling. This manner of cooling is suitable however only for delivery mediums which do not contain any dirt components or other fine admixtures or impurities, since otherwise the flow accesses and exits on the pump side get blocked and the hood cooling becomes ineffectual due to this.
BRIEF SUMMARY OF THE INVENTION
The object of the invention lies in the provision of a device for the external cooling of the drive motor of a centrifugal pump unit, wherein the device also guarantees a considerably improved outer cooling of the drive motor also when the motor protrudes out of the delivery medium over a longer time duration.
The solution of this object proceeds from a device previously mentioned and is characterized further in that the device comprises a hermetically closed hollow body of heat-conducting material which circumferentially at least partly surrounds the motor and which with its wall surface on the motor side and on the pump side is in heat-conducting surface contact with the motor and the centrifugal pump, and that the hollow body is essentially filled with a fluid which transfers the motor heat and which, with a heated motor, is subject to a natural circular convection flow.
By way of this solution a considerably improved external cooling of the drive motor of the centrifugal pump unit for delivery of in particular waste water may also be achieved when the drive motor, with the unit in operation, is located for a longer time or permanently out of the liquid delivery medium. The heat produced by the stationary stator of the drive motor is transferred further to the fluid in the hollow body which on one side bears on the surrounding motor wall, and produces therein a liquid circulation. Since the advantageous annular hollow body on the other side at its lower end is in heat-conducting connection with the pump wall and the pump is flowed through by the much colder delivery fluid the heat from the fluid in the hollow space for the larger part gets into the colder delivery fluid in the pump and with this is led away. The remaining part of the heat of the fluid in the hollow body, via the free outer surface of this hollow body, goes into the surrounding air of the drive motor. A further advantage of this device, according to the invention, lies in the fact that the particle like admixtures of the delivery medium do not disadvantageously affect the cooling effect of the hollow body since they may not get into the hollow body.
An advantageous fluid in the hollow body is a mixture of water and another fluid which has a lower boiling point than water. Such a fluid is for example an alcohol. By way of such a fluid mixture the convection flow in the hollow body may be increased. This is the case when the heat transferred from the motor to the cooling liquid in the hollow space effects the creation of small vapor bubbies in the cooling fluid, which rapidly rise upwards and thus increase the circulatory speed of the mixture in the hollow space. The risen vapor bubbles then again condensate in the upper region of the hollow body, which is not filled with fluid.
On the wall region of the hollow body distant to the stator there arises, when the motor in the installed condition is arranged above the centrifugal pump, a downstream flow in the hollow body, by which means the fluid mixture goes downwards to the pump. Here the heat passage to the delivery fluid is effected in the pump. in order to deliver the main part of the developed dissipated heat of the motor to the delivery fluid. Then the fluid mixture again flows upwardly to the wall of the hollow body, which is proximal to the stator, and the mentioned flow procedures and heat transfers are repeated.
In order to further improve the circulation of the convection flow of the fluid or a fluid mixture in the hollow body it may be proceeded that the fluid filling of the hollow body is not more than about 95% of its volumetric capacity and that the remaining space of the hollow body is evacuated of air. By way of this the boiling point of the fluid filling is considerably reduced, so that the vapor bubble formation which encourages the flow sets in considerably earlier.
In order to have a defined flow path for the circulating flow in the hollow body, within the hollow body there is provided a separating wall. By way of this a distinct separation of upstream flow and downstream flow of the heat transferring fluid filling is achieved and it is further achieved that all heated fluid is led to the pump.
A further advantageous formation of the device according to the invention lies in the fact that it is formed as a separate constructional unit, so that it may be assembled at a later time on the motor of the centrifugal pump unit. It is however alternatively also possible to provide the device according to the invention as an integral component of the complete housing of the centrifugal pump unit.
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Jensen Niels Due
Olrik Henrik Gerner
Freay Charles G.
Grundfos a/s
Jacox Meckstroth & Jenkins
Rodriguez William
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