The present invention refers to a mechanical seal assembly, comprising at least one mechanical seal and a Tesla pump.
Mechanical seal assemblies are known from the prior art in different configurations. During operation, relatively high temperatures may occur on the mechanical seal; on the one hand, these may be due to a high temperature of a medium to be sealed or due to the friction and swirl powers created during normal operation on the mechanical seal. To prevent damage to the mechanical seal, heat must therefore be discharged. To this end the medium to be sealed can be used on condition that it does not have excessively high temperatures, or alternatively a barrier medium. For circulating the medium used for heat discharge, external pumps are normally used. Furthermore, it is known to provide so-called pump rings for medium circulation, but their delivery rate is normally very limited.
It is therefore the object of the present invention to provide a mechanical seal assembly which while having a simple and inexpensive structure allows improved circulation of a medium in the area of the seal rings and is nevertheless of a very compact structure.
This object is achieved by a mechanical seal assembly comprising the features of claim 1. The sub-claims refer to preferred embodiments of the invention.
The mechanical seal assembly according to the invention with the features of claim 1 has the advantage that an enhanced delivery rate of a barrier and/or cooling medium is possible without the need for significantly increasing the constructional space. This is achieved according to the invention in that the mechanical seal assembly comprises a Tesla pump. The Tesla pump comprises a plurality of radially outwardly extending discs which are arranged on a cylindrical base portion. The discs are spaced apart from each other at a defined distance, so that the medium, which penetrates between the discs, is transported by rotation of the discs to the outer circumference of the discs and exits there out of the Tesla pump. The Tesla pump has a simple and robust structure and enables a high delivery rate together with a long service life. The Tesla pump has a stable characteristic and only poses a very small risk of cavitation.
Preferably, the mechanical seal assembly further comprises an additional delivery device which is arranged upstream of the Tesla pump. The additional delivery device preferably comprises a delivery thread which is co-rotating with the Tesla pump. This particularly improves an inflow of the medium to the Tesla pump, so that the pumping capacity of the Tesla pump is increased. Particularly preferably, the delivery thread comprises oblique delivery grooves which are inclined relative to an axial direction of the mechanical seal assembly. The oblique delivery grooves have in particular the advantage that the medium to be delivered is subjected to a flow component in circumferential direction, so that the medium is introduced in a rather flow-promoting manner between the discs of the Tesla pump. This can particularly improve the efficiency of the Tesla pump.
The Tesla pump preferably comprises a plurality of discs and a cylindrical base portion, the discs extending from the cylindrical base portion radially to the outside. Preferably, at least one of the discs comprises at least one axial opening preferably positioned next to the base portion. Preferably, all discs, except for an end disc which is arranged on an axial end of the Tesla pump, comprise at least one axial opening. Particularly preferably, plural axial openings are provided in the discs and, further preferably, uniformly distributed along the circumference. The axial openings in the discs have the effect that the medium can flow near the cylindrical base portion of the Tesla pump into the region between the discs of the Tesla pump and can then be delivered through the Tesla pump spirally to the outside. The axial openings thereby further improve the efficiency of the pump. Particularly preferably, axial openings are arranged on adjacent discs of the Tesla pump at the same circumferential positions. It is thereby ensured that the medium is guided up to the end disc, which is without an axial opening. This can further improve the degree of efficiency.
According to an alternative configuration of the present invention all of the discs of the Tesla pump preferably comprise at least one axial opening. An axial opening is here provided in an end disc, which is arranged at an axial end of the Tesla pump, with a smaller passage cross-section than the other axial openings in the other discs. This permits a flow through all of the discs of the Tesla pump, whereby it is ensured that on the one hand the medium can be transported to all interspaces between the discs and further also that the medium can be transported into a region in flow direction behind the Tesla pump so as to permit a cooling of the components, especially of the seal rings, at that place.
The geometrical shape of the axial openings can be chosen at will, but it is preferably cylindrical or provided as an elongated hole, particularly an arched or straight elongated hole. Further preferably, the axial openings are provided at the bottom of the discs of the Tesla pump and further preferably are each arranged in a row one after the other to ensure a good flow therethrough at minimum losses, if possible. Preferably, several axial openings are evenly distributed along the circumference of the discs.
Further preferably, the discs of the Tesla pump have delivery structures on at least one flat side. The delivery structures may e.g. be elements which are arranged in the form of an arc and protrude from the flat side of the disc or may be protruding elements extending in a straight line radially. The delivery structures on the disc promote the transportation of the medium, a height of the delivery structures, starting from the flat side, being chosen such that the delivery performance of the Tesla pump is promoted in addition. As an alternative, delivery structures are provided on both flat sides of the discs, so that delivery structures protrude from both sides into the gap between the discs.
To achieve a situation where the medium to be conveyed can pass in an improved manner between the discs of the Tesla pump, an outer circumference of the Tesla pump expands continuously, especially conically. A Tesla pump with a substantially conical shell shape is formed, ensuring improved delivery. Particularly preferably, the discs are spirally arranged on the cylindrical base portion. Alternatively, the discs are arranged in parallel with each other and have different outer diameters. The outer diameters of the discs are increasing in axial direction. The sizes of the discs are here increasing preferably uniformly in axial direction, so that a conical outer shell is obtained on the Tesla pump.
Further preferably, the cylindrical base portion is configured as a hollow cylinder, and at least one passage opening that permits communication with a space inside the hollow cylinder is provided in the hollow cylindrical base portion. The space within the hollow cylinder is preferably led up to the seal rings, thereby enabling a flow of the medium through the passage opening up to the seal rings so as to improve cooling in the region of the seal rings. The passage opening is preferably provided as one or plural radial bores arranged along the circumference of the hollow cylinder.
For a particularly compact structure the delivery thread of the additional second delivery device is preferably arranged on an outside of a bushing. Further preferably, the bushing is arranged in the area of the delivery thread on a rotary sleeve, and the Tesla pump is arranged on a hollow shaft portion of the bushing next to a fastening region.
Further preferably, an outflow bore for the medium to be conveyed is arranged radially outside of the Tesla pump.
Further preferably, the mechanical seal assembly comprises a second mechanical seal, the Tesla pump being arranged in axial direction between a sealing gap of the first mechanical seal and a sealing gap of the second mechanical seal. This ensures a particularly compact structure of a double-acting mechanical seal assembly.
Preferably, the Tesla pump is part of a cooling device for cooling the seal rings and/or other components of the mechanical seal assembly.
Particularly when a very viscous cooling medium is used, e.g. for cooling mechanical seal assemblies subjected to high temperatures, the assembly of the invention with the Tesla pump can significantly improve the delivery efficiency as compared with the formerly used delivery devices.
Embodiments of the invention will now be described in detail with reference to the accompanying drawing, in which:
A mechanical seal assembly 1 according to the first embodiment of the invention is shown in detail in
The mechanical seal assembly 1 comprises a first mechanical seal 2 and a second mechanical seal 3. The first mechanical seal 2 comprises a rotating seal ring 21 and a stationary seal ring 22, the two seal rings defining a sealing gap 23 between them. The second mechanical seal 3 comprises a rotating seal ring 31 and a stationary seal ring 32, the two seal rings also defining a sealing gap 33 between them. Hence, the mechanical seal assembly according to the first embodiment comprises a double-acting mechanical seal.
The rotating seal rings 21, 31 are each connected via a holding ring 11 to a rotating component 4, in this embodiment a rotating shaft. Furthermore, each of the two mechanical seals 2, 3 comprises a metal bellows 10 as a spring device. As can be seen from
The mechanical seal assembly 1 of the invention seals a product side 13 against an atmosphere side 14.
Furthermore, the mechanical seal assembly 1 according to the invention comprises a Tesla pump 6 and a delivery thread 7 as a second delivery device. The delivery thread 7 and the Tesla pump are arranged on a bushing 8 which is fixed to the rotary sleeve 9. The Tesla pump 6 comprises a plurality of parallel discs 61, each having an axial opening 63. The axial openings 63 are here arranged cylindrically and evenly distributed along the circumference of the discs 61 (cf.
The delivery thread 7 comprises a plurality of grooves 71 which are obliquely arranged relative to an axial direction X-X of the mechanical seal assembly. A stationary part 72 of the delivery thread 7 is provided by way of a smooth outer surface of a stationary component 50. Hence, the illustrated delivery thread 7 is a rotating delivery thread. Alternatively, a stationary delivery thread may also be provided where the delivery grooves are provided in the stationary component and the smooth outer surface on the rotating component. Further alternatively, an opposing delivery thread may also be provided, wherein grooves are provided in the rotating component and also in the stationary component in opposing arrangement.
A cooling medium is fed via an inflow bore 16 into an interspace 12 between the rotating component 4 and the housing 5. As outlined by the arrows, the cooling medium is here delivered from the interspace 12 through the delivery thread 7 towards the Tesla pump 6. On the Tesla pump 6, the cooling medium flows into the axial openings 63 of the Tesla pump and is transported by the rotating discs spirally in radial direction to the outside and to an outflow bore 15. As can particularly be seen in
Hence, in the first embodiment the delivery thread 7 is arranged in flow direction upstream of the Tesla pump 6 and assumes a guiding function for the cooling medium, in addition to the delivery performance of the delivery thread 7, so that said medium can flow more easily into the interspaces 64 of the Tesla pump without the developing boundary layers of the medium being too much interfered with. The Tesla pump 6 is arranged on a hollow shaft portion 82 of the bushing 8 so that the Tesla pump 6 has as little mass as possible. This has the further advantage that the cooling medium can also pass into the portion of the metal bellows 10 on the first mechanical seal 2. The delivery thread 7 is provided on a fastening portion 81 of the bushing 8 which is connected to the rotary sleeve 9.
Although the Tesla pump 6 has a certain dimension in radial direction, it is very compact as regards its dimension, so that it can be installed without any problems under very different installation situations of mechanical seal assemblies because a necessary installation space does normally exist in radial direction of the mechanical seal assemblies on account of the stationary component. An axial length L1 of the Tesla pump is here equal to an axial length L2 of the delivery thread 7 (cf.
Hence, owing to the inventive idea of integrating a Tesla pump 6 in a mechanical seal assembly, an improved delivery of a medium used for cooling or blocking the mechanical seals and components adjacent thereto can be ensured without the need for a large constructional space. The Tesla pump is here very robust and can be produced at very low costs, especially since it does not require any expensive components, such as blades or the like. Owing to the integration of the Tesla pump 6 it is furthermore possible to dispense with an external delivery device, such as e.g. a rotary pump or the like, for delivering the cooling fluid flow.
A second embodiment of the invention shall now be described with reference to
As can particularly be seen in
Each of
Number | Date | Country | Kind |
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102011118294.6 | Nov 2011 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2012/004207 | 10/8/2012 | WO | 00 | 5/9/2014 |