Turbomachine with optimized cooling of the mechanical seal

Abstract

The invention relates to a turbomachine with a housing and a shaft rotating therein, wherein the shaft is sealed against the housing by means of at least one mechanical seal and a swirling flow of a working fluid located in the region of the mechanical seal is generated by the rotation of the shaft, characterized in that in the immediate vicinity of the mechanical seal at least one drive component driven by the shaft is provided for generating a secondary flow superimposed on the fluid flow in the region of the mechanical seal for convection cooling of the mechanical seal.

Description

The present invention relates to a turbomachine having a housing and a shaft rotating therein, wherein the shaft is sealed with respect to the housing by means of at least one mechanical seal and a swirling flow of a working fluid located in the region of the mechanical seal is generated by the rotation of the shaft.The turbomachines include all machines through which a working fluid or a fluid loaded with solids flows and which are provided with a bladed impeller for the conversion between mechanical energy (e.g. rotational energy of a shaft) and flow energy (e.g. total pressure of the fluid). Depending on the direction of the energy transmission, whether from the turbomachine shaft to the flow medium or from the medium to the shaft, a distinction is made between the "working machine" (e.g. centrifugal pump, turbocompressor, fan) and the "engine" (e.g. steam, gas, wind, liquid and in particular water turbine).The exit of the rotating shaft from the housing of the turbomachine is generally reliably and reliably sealed off by means of a mechanical seal. The heat generated by friction in the sealing contacts of the mechanical seal leads to a local temperature increase, which is to be minimized for prolonging the service life and increasing the reliability of the seal.The cooling of the mechanical seal by means of the working fluid flowing around the seal is due to the design and often inadequate depending on the application. In particular, unfavorable flow conditions can occur in the region of the mechanical seal due to the design, as a result of which the heat dissipation by means of the working fluid is insufficient. For example, the generation of local vortices and / or recirculation regions in the region of the mechanical seal has the result that the thermal energy of the mechanical seal absorbed by the working fluid is only conveyed locally in the circle, but cannot be transported away from the mechanical seal and can be emitted to the housing. In practice, attention has hitherto been paid to external cooling circuits for dedicated cooling of the seal. However, external circuits require additional design steps, which increases the complexity of the machine and increases manufacturing and maintenance costs.The problem addressed of unfavourable flow conditions in the region of the mechanical seal is to be demonstrated below with reference to the schematic illustration of FIG. 1, which shows only the relevant section of the housing 1 of a turbomachine with the mechanical seal mounted there. A subsection of the rotating working shaft 5 of the turbomachine, in particular of a centrifugal pump, can be seen. The shaft 5 exits the housing at one end to the outside, the shaft outlet is sealed by the mechanical seal consisting of the stationary counterring 3 and the sliding ring 4. The stationary counterring 3 is fixed to the housing 1 via the counterholder 2, the connection being sealed by the static seal 9. The rotating slide ring 4 is seated on the shaft 5 in a rotationally fixed manner. the reference numeral 6 denotes a static seal, the reference numeral 7 denotes a prestressing element, as a result of which the slide ring 4 is prestressed in the axial direction in the direction of the mating ring 3. The housing 1 also provides a sealing gap 8 in the direction of the bearing support of the pump, via which the working fluid can pass from the pump chamber into the region of the mechanical seal. The rotating shaft generates a swirling flow of the working fluid in the region of the mechanical seal.In particular, the surface contour 4 aof the rotating slide ring 4 decreasing in the direction of the stationary counter ring 3 has the result that a local vortex 11 arises in the housing space in the immediate vicinity of the slide ring seal, which is separated from the remaining flow 13 of the working fluid by a jet flow 12 extending radially / axially outwards from the slide ring seal in the direction of the housing. Due to the locally limited swirling / recirculation 11, the thermal energy absorbed by the working fluid there, generated by the frictional work in the sealing contact, cannot be effectively dissipated, because a heat exchange is possible only at the interface between the swirl 11 and the jet 12. The same applies to particles abraded from the sliding surfaces. In addition to the vertebra 11, several smaller unfavorable vertebrae 14 are produced by detaching them at inner and outer contours of the housing 1 and of the counterholder 2, in particular in the corner regions or in the region of radial shoulders, in particular in the axial transition between the rings 3, 4.The object of the present invention is to achieve an improved flow of the working fluid in the region of the mechanical seal by means of design measures, in order to be able to achieve a better heat dissipation and a better cooling of the mechanical seal in this way. In addition, the convective removal of particles from the region of the mechanical seal contact is to be optimized.This object is achieved by a turbomachine having the features of claim 1. Starting from the turbomachine of the generic type, it is proposed to provide at least one drive component driven by the shaft in the immediate vicinity of the mechanical seal, which drive component is suitable for generating a secondary flow superimposed on the swirl flow in the region of the mechanical seal. By arranging the additional drive component rotating with the shaft in the immediate vicinity of the mechanical seal and by its suitable configuration, a specifically defined secondary flow can be actively generated in the region of the mechanical seal, which ensures improved heat removal and / or particle removal, since local unfavorable vortex formations are prevented and efficient convective removal of the thermal energy by the working fluid is possible. In parallel, the convective removal of abraded particles in the region of the sealing contact is also promoted, i.e. improved flushing of the mechanical seal is achieved. The secondary flow is in particular a large-capacity flow circulating in an available installation space of the housing. The swirling flow of the working fluid located in the region of the mechanical seal can be generated by the rotating shaft.The turbomachine can be a pump, in particular a centrifugal pump.The at least one drive component can either be seated directly on the shaft or instead be arranged on a component rotating with the shaft, for example a prestressing element for axially prestressing the rotating slide ring. The drive component can be designed in the form of a rotating disk or a rotating bladed impeller. Preferably, the rotating drive component or components are configured such that pressure conditions are generated in the vicinity of the mechanical seal, which form one or more secondary flows with axial and radial components in addition to the swirl flow of the working fluid. The secondary flow(s) are directed specifically to the most important surfaces of the mechanical seal components to be cooled. Both the axial and the radial flow component are to be understood as a flow direction with respect to the shaft axis. In particular, at least one secondary flow is guided in a targeted manner along the surface of the mechanical seal, in particular of the rings of the mechanical seal. A targeted guidance along the relevant surface of a counterholder is also conceivable.It is particularly advantageous if one or more flow-conducting components are arranged in the space between the mechanical seal and the housing, in particular in the radial and / or axial space. For example, such a flow-guiding component can be arranged centrally in the space between the outer housing wall and the mechanical seal. The flow-guiding component extends both in the axial and in the radial direction, preferably the component extends annularly around the mechanical seal in the housing space. Such a flow-guiding component enables in particular a circulating secondary flow in the flow paths which are formed by the flow-guiding component itself and optionally one or more further components, such as the housing, the sliding rings, the prestressing element, the counterholder. It is conceivable, for example, for this flow-guiding component to define an axial flow channel between the housing wall and the flow-guiding component and a channel running parallel thereto between the mechanical seal and the flow-guiding component. Radial sections of the flow channel are preferably formed by the end-face housing surfaces or by a counterholder and the flow-guiding component.The material used as a flow-guiding component can be a solid material or alternatively hollow. Any cavity may preferably be filled by the working fluid or another fluid or material. The mounting of the flow-guiding component in the turbomachine can preferably be realized via one or more fixing points, via which the component is fixed to the housing inner wall or to the counterholder of the mechanical seal. It is particularly advantageous if the component provides an inner structure with optimized thermal conductivity and / or the one or more fixing points provide a high thermal conductivity, so that a good heat dissipation from the components to the housing or the counter holder is ensured.It is particularly advantageous if, on account of the embodiment according to the invention, an external circuit for cooling and / or flushing the mechanical seal can be dispensed with completely and cooling and / or flushing of the mechanical seal is provided exclusively via the working fluid.Furthermore, it can be provided that one or more guide elements are provided in the region of the housing wall, which lies in the immediate region of the secondary flow or the mechanical seal, and / or in the region of a counterholder of the stationary counterring and / or in the region of the drive component and / or in the region of the prestressing device and / or in the region of the rings of the mechanical seal, in order to avoid undesired vortex formations in corner regions or at radial shoulders. For example, the corners and edges of the housing parts or transitions between different components, in particular the transition between the sliding rings, are conceivable to the effect that radial shoulders are minimized and local, unfavorable vortex formation, for example as a result of flow separation, is avoided.It is also conceivable that surfaces wetted with working fluid are optimized with regard to their heat exchange by means of suitable texturing or other microscopic or macroscopic properties. Also, by suitable surface configuration, the achievable drag effect of the drive component can be improved.Further advantages and properties of the invention will be explained in more detail below with reference to an exemplary embodiment shown in the figures. The following are shown: FIG. 1 : shows a schematic structure of a turbomachine according to the prior art, FIG. 2 : shows an exemplary embodiment of the turbomachine according to the invention.FIG. 1 has already been described in detail in the introductory part, so that a repetitive description is omitted here. Components of the turbomachine according to the invention which are identical to the embodiment of FIG. 1 are identified by identical reference numerals. The modifications made to optimize the flow profile of the working fluid in the region of the mechanical seal will be discussed substantially below.The illustration of FIG. 2 shows the subsection of a centrifugal pump relevant here. The essential modification compared to the embodiment of FIG. 1 consists in providing a rotating drive component 20 which is actively driven via the shaft 5 and which can be designed, for example, as a disk with a viscous drag effect or as a bladed impeller. The rotating component 20 is used to generate pressure conditions in the vicinity of the mechanical seal, which lead to the formation of one or more secondary flows (axial and radial flow components in addition to the swirl flow), whereby working fluid is directed in a targeted manner to the most important surfaces of the mechanical seal components to be cooled. The drive component 20 is seated here on the circumference of the preload element 7 and rotates with the shaft 5 during regular operation of the turbomachine, but could alternatively also be mounted directly on the shaft. It is also conceivable that the biasing element 7 itself or a specific section of the shaft 5 can also be used as the drive component, in each case of course with a certain modification of its outer contour.The rotating drive component 20 generates the flow path with axial and radial components, which is drawn with arrows in FIG. 2 and circulates around a flow guide part 50 lying centrally in the radial space between the housing 1 and the mechanical seal 30, 40. This flow guiding member 50 may be made of a solid material or may be hollow, in the latter case the member 50 may be filled with working fluid or another fluid or material. The flow guide part 50 is mounted on the housing 1 via a plurality of fixing points, not shown here, and extends annularly around the shaft or mechanical seal. The inner structure and the fixing points of the flow guide part 50 are optimized for the heat dissipation; in particular, they consist of a material with high thermal conductivity, for example aluminum or copper. The outer contour of the flow guide component 50 is preferably designed for one or more operating points and / or operating point ranges of the turbomachine.As can be seen from the illustration, the secondary flow is generated by the drive component 20 in the region of the housing end facing the bearing support of the pump and flows first between the flow-guiding component 50 and the circumferential wall of the housing 1 in the axial direction toward the counterholder 2. guide elements 21 in the region of housing corners and housing edges or in the transition region to the counterholder 2 minimize the undesired formation of vortices in the region of shoulders and edges and thus ensure a detachment-free flow deflection at a high flow speed. In the region of the counterholder 2, the working fluid is directed radially downward in the direction of the mechanical seal and flows there in the axial direction between the flow-guiding component 50 and the sliding rings 30, 40 with the prestressing element 7 back to the drive component 20.In addition, the circumferential surfaces 30 a, 40 aof the sliding rings 30, 40 are fluidically optimized in order to avoid radial shoulders in the transition region and thereby further minimize the risk of local vortex formation. The embodiment of the surface contour of the circumferential surface 30 aof the stationary counter ring 30 enables a separation-free flow deflection in the direction of the rotating slide ring 40, as a result of which the working fluid flows along the contours 30 a, 40 awith the highest possible flow speed (Reynolds number). The surface contour 40 aof the rotating sliding ring 40 prevents the generation of an undesired axial / radial jet flow. In particular, the contour of the sliding ring circumferential surfaces is adapted to the contour of the opposite surface of the flow-guiding component 50.As a result of the secondary flow circulating over a large space, absorbed heat energy in the region of the sliding rings 30, 40 can be effectively transported away from the sliding ring seal and, for example, can be emitted to the outside via the flow-guiding component 50 with its heat-conducting fixing points.The individual essential features of the modifications of the turbomachine carried out in the region of the mechanical seal can be summarized once again below:The object of the invention is to set a flow state in a targeted manner by means of design measures, which flow state optimizes the convective cooling of mechanical seal rings and thus reduces the temperature within and in the vicinity of the seal contact. In this case, the intention is to generate as fast as possible a flow (high Reynolds number), in the form of a secondary flow with axial and radial velocity components superimposed on the swirl flow, along the surfaces to be cooled. The flow state thus represents a kind of internal circuit, which however is generated without additional active devices.The drive of the secondary flow takes place from the rotational movement itself. Here, the adhering condition of the fluid to rotating walls can be utilized together with the inertial effect of the rotation (centrifugal force). In particular at edges with an enlarged surface compared to a uniform contour, e.g. at edges of jumps in cross section or lamellar shapes, the drag action can be used to generate radial velocity components due to the adhesion condition of the fluid. For this purpose, the contour of the rotating mechanical seal rings 40 a, surfaces of prestressing devices 7 or of parts 20 on the shaft 5 or of the prestressing devices 7 which are installed separately for this purpose can be used. The flow guidance can be effected by one or more components 21, 50 which are installed in the radial space between shaft 5 / mechanical seal 30, 40 and housing 1 and are connected at one or more points to housing 1 and / or stationary counterholder 2. By means of the targeted flow guidance along the mechanical seal rings 30, 40, it is likewise possible to enable optimized and controlled removal of particles (which arise, for example, in contact or are of other origin and which have deposited thereon), and possibly their targeted transport into a filtering device. In the invention, no external connections, additional fluid circuits or further heat exchange devices are required, but the cooling effect is achieved internally by means of a specific flow guidance, driven by the rotational movement (as an energetic drive source).The fittings 20, 21, 50 can be integrated both in the first design of a mechanical seal and can be retrofitted subsequently into an existing product. The installations can be optimized for specific operating points (rotational speed, pressure, temperature, density and viscosity of the fluid) and / or operating point ranges, for example operating points or ranges which are predominantly approached.The wetted surfaces of the baffles may be optimized for heat exchange with the fluid, e.g., by texturing or other micro- and macroscopic surface properties. In addition, the surface properties can be deliberately adjusted to produce a better drag effect of the fluid. The heat transferred from the fluid into the installations 50 can be dissipated from the mechanical seal region by heat transport in the installations 50 and their connection to the housing 1, counterholder 2 or possibly shaft 5. The internals can consist of one or more materials and can be produced in different methods, for example die casting (aluminum), injection molding (plastic), 3D printing, machining (turned and milled).

Claims

Turbomachine having a housing (1) and a shaft (5) rotating therein, wherein the shaft (5) is sealed with respect to the housing (1) by means of at least one mechanical seal (30, 40), and a swirling flow of a working fluid located in the region of the mechanical seal is generated by the rotation of the shaft, characterized in that at least one drive component (20) driven by the shaft (5) is provided in the immediate vicinity of the mechanical seal (30, 40) for generating at least one secondary flow of the working fluid superimposed on the swirling flow in the region of the mechanical seal (30, 40) for convective cooling of the mechanical seal (30, 40).Turbomachine according to Claim 1, characterized in that the drive component (20) is arranged on a prestressing element (7) for axially prestressing the rotating slide ring (40) of the slide ring seal.Turbomachine according to one of the preceding claims, characterized in that the secondary flow generated has an axial and radial flow component.Turbomachine according to one of the preceding claims, characterized in that the secondary flow is guided in a targeted manner along the surfaces (30a, 40a) of the rings (30, 40) of the mechanical seal.Turbomachine according to one of the preceding claims, characterized in that one or more flow-guiding components (50) are arranged in the space between the mechanical seal (30, 40) and the housing (1) in order to guide the flow of the secondary flow.Turbomachine according to Claim 5, characterized in that the secondary flow circulates around at least one of the flow-guiding components (50).Turbomachine according to either of Claims 5 and 6, characterized in that the at least one flow-guiding component (50) is hollow or fully filled, in particular is filled by means of the working fluid or with another fluid or material.Turbomachine according to one of Claims 5 to 7, characterized in that the at least one flow-guiding component (50) is fixed on the housing (1) and / or on the counterholder (2) of the stationary counterring (30) of the mechanical seal via one or more fixing points.Turbomachine according to Claim 8, characterized in that an internal structure and / or the one or more fixing points of the at least one flow-guiding component (50) are optimized with respect to the heat dissipation, i.e. have a good thermal conductivity, in order to be able to dissipate the heat dissipated by the secondary flow via the fixing points to the housing (1) and / or to the counterholder (2).Turbomachine according to one of the preceding claims, characterized in that the turbomachine does not have an external circuit for cooling and / or flushing the mechanical seal.Turbomachine according to one of the preceding claims, characterized in that the drive component (20) is a rotating disk with a viscous drag effect or a rotating bladed impeller or a rotating structure differing therefrom for generating the necessary pressure gradient for driving a secondary flow.Turbomachine according to one of the preceding claims, characterized in that the radial shoulders in the transition region between different contours in the region of the secondary flows are reduced, in particular a radial shoulder in the transition region between the rings (30, 40) of the mechanical seal is minimal.Turbomachine according to one of the preceding claims, characterized in that surfaces which are wetted by the working fluid are optimized with respect to the heat exchange by means of texturing or other microscopic or macroscopic properties.Turbomachine according to one of the preceding claims, characterized in that one or more guide elements (21) for detachment-free flow guidance are provided in corner or transition regions of the housing (1) and / or of a counterholder (2) of the stationary counterring (30) and / or in the region of the drive component (20) and / or of the prestressing device (7) and / or of the rings (30, 40).

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