Patent Application
20150176428
This application claims priority to German Patent Application No. 10 2013 226 742.8, filed Dec. 19, 2013, the contents of which are hereby incorporated by reference in their entirety.
The present invention relates to a turbomachine which is designed as a turbine, according to the preamble of claim 1.
In a turbomachine, basically, an energy transfer between a flowing fluid, for example saturated vapor, and the turbomachine itself takes place. In a turbomachine designed as a turbine, the energy transfer is carried out, for example, by means of guide vanes which are profiled in such a manner that by the flow flowing around the guide vanes, a pressure difference between front and back sides occurs and thereby effects the rotation of the guide vanes. Turbines are normally composed of a rotating part, the so-called rotor, and a stationary part, the so-called stator. In the latter, the supply of the working medium to the rotor and a potentially required change of state of the working medium takes place before the medium is guided through the rotor. The working medium transfers a large portion of its energy to the rotor from where the energy is output via a shaft. The housing of the turbomachine normally assumes the function of leading the working medium to the stator as well as of discharging the working medium from the rotor out of the turbomachine.
In some operating states it is desired that the turbomachine, for example the turbine, is not to be acted on with working medium or with a lower mass flow than the available mass flow. In order to achieve this, so-called bypass channels are known from the prior art, which bypass the turbine of the turbomachine and branch off from a feed channel upstream of the turbine and end in said feed channel again downstream of the turbine. Such turbomachines are also used in connection with internal combustion engines in motor vehicles, for example for power generation, wherein in this case, they are integrated in a so-called Rankine cycle in which a working medium such as, e.g., water, ethanol or another organic medium or mixture of different media in liquid and vaporous aggregate states is used.
A method for utilizing waste heat from an internal combustion engine for generating electricity using such a Rankine cycle is known from DE 10 2007 016 557 A1, for example. Here, the working medium is first driven so as to form a circular flow, wherein, at the same time, heat is transferred from an exhaust gas flow of the internal combustion engine to the working medium. Thereby, the heat transfer effects evaporation of the working medium, wherein the saturated vapor, that is, the saturated vaporous working medium is subsequently fed to the expansion machine, thus to the turbine. In the expansion machine, the working medium is relaxed from its overheated state and thereby releases energy, and changes subsequently in a condenser into a liquid aggregate state. In liquid form, it is subsequently brought to a higher pressure level by a pump that is integrated in the Rankine cycle, and is evaporated in the exhaust gas heat exchanger integrated in the exhaust gas flow.
However, the disadvantage of the method known from the prior art is that in particular during a starting phase, it is not necessarily possible to prevent that the working fluid reaches the turbine in still liquid form and causes damage therein, for example by erosion due to droplet impingement.
The present invention is therefore concerned with the problem of providing an improved embodiment for a turbomachine of the generic kind, which overcomes in particular the disadvantage known from the prior art.
This problem is solved according to the invention by the subject matters of the independent claims. Advantageous embodiments are subject matter of the dependent claims.
The present invention is based on the general idea to provide also at least one bypass channel in a generic turbomachine known per se having a turbine arranged in a housing, which bypass extends completely within the housing and bypasses the turbine and which, in particular during a starting phase of the turbomachine, is acted on with working medium until said working medium has reached the desired overheated state required for damage-free operation of the turbine and can then be guided through the turbine. A heat level that is too low can result in insufficient heating of the working medium, specifically during startup of the turbomachine, so that the working medium, for example when entering the stator, is not present in the form of saturated vapor and therefore can cause erosion due to droplet impingement. This is reliably prevented by the bypass channel which, according to the invention, extends within the housing since the working medium can now be guided past the turbine until it has reached its saturated overheated state. Through this arrangement according to the invention of the at least one bypass channel completely within the housing, the latter is heated during the starting phase of the turbomachine by the vapor fed through the at least one bypass channel, as a result of which the turbomachine overall is ready earlier for operation. Due to the fast heating of the housing and therefore also of the stator of the turbomachine, the operating temperature, which lies above the condensation temperature, is reached more quickly than if the bypass channel is decoupled from the housing, as it is always provided in the previous prior art. As soon as the housing temperature is higher than the condensation temperature, the liquid working medium still remaining in the turbine evaporates, wherein due to this active evaporation in the turbine chamber, it can be prevented that liquid working medium is distributed during startup of the turbine in the region of the rotor and consequently can damage the turbine. The turbomachine according to the invention comprising the bypass channel arranged completely within the housing therefore kills two birds with one stone, namely, on the one hand, preventing damage in the turbine caused by droplet impingement and, on the other, quicker reaching of the operating temperature.
Advantageously, heat transfer elements, in particular ribs, for improved heat transfer to the housing are arranged in the bypass channel. Such heat transfer elements increase the surface area within the bypass channel and therefore provide for increased heat transfer from the working medium to the housing or the stator of the turbomachine so that the latter reaches its operating temperature more quickly. Of course, such heat transfer elements can be arranged within the at least one bypass channel in almost any form and shape.
In another advantageous embodiment of the solution according to the invention, a plurality of bypass channels extending substantially parallel are arranged within the housing. Through this, the housing can be heated up uniformly and, in particular, significantly quicker, as a result of which not only more homogenous heating, but also evaporation of the liquid working medium in the turbomachine at various locations and at the same time can be achieved. It is conceivable here that after branching off from a feed channel, the at least one bypass channel splits up in a fan-shaped manner, or that a plurality of bypass channels, each of which can also be connected individually, for example by means of a valve device, can be acted on with hot working medium for heating the housing of the turbomachine.
The present invention is further based on the general idea to use an aforementioned turbomachine in an internal combustion engine having a Rankine cycle and to integrate said turbomachine in said Rankine cycle. An exhaust gas heat exchanger (evaporator) integrated in an exhaust gas flow of the internal combustion engine, a condenser, a reservoir and a pump are also arranged in the Rankine cycle. By using the turbomachine according to the invention having the at least one bypass channel arranged within the housing of the turbine or the turbomachine, damage to the turbine caused by erosion can be prevented and the turbine's service life can thereby be increased. Moreover, reaching the operating temperature of the turbomachine more quickly due to the above described facts is possible. If switching between the bypass mode, in which the working medium is guided through the at least one bypass channel, and the operating mode, in which the working medium is guided through the turbine, takes place in the internal combustion engine according to the invention, this has only little retroactive effect on the cycle as long as bypass channel and turbine have the same properties. This makes it possible to reduce the alternating pressure load for all components, in particular for the exhaust heat exchanger. Since such alternating pressure loads are often the reason for mechanical failure of heat exchangers or exhaust gas heat exchangers, a significant advantage can also be achieved in this manner.
Further important features and advantages of the invention arise from the sub-claims, from the drawings, and from the associated description of the figures based on the drawings.
It is to be understood that the above-mentioned features and the features still to be explained hereinafter are usable not only in the respective mentioned combination, but also in other combinations or alone, without departing from the context of the present invention.
Preferred exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, wherein identical reference numbers refer to identical or similar or functionally identical components.
In the figures, schematically:
According to
For a better heat transfer from the bypass channel 4 to the housing 2, heat transfer elements 6, which can be formed like ribs, for example (cf. cross-sectional illustration on the bottom right in
Optionally, at least one separate and heat-insulated bypass channel 4′ can also be provided, which also bypasses the turbine 3, but is not or only marginally connected to the housing 2 in a heat-transferring manner. Also, it is not necessary that the bypass channel 4′ extends completely within the housing 2. For example, the turbomachine 1 can be designed as an axial impulse turbine. When viewing again the bypass channel 4 according to the
When viewing
With the turbomachine 1 according to the invention it is possible to not only increase the service life of a turbine 3 significantly since erosion due to insufficiently heated working medium is no longer a concern, but it is also possible to use the turbomachine 1 earlier because via the at least one bypass channel 4, which is arranged completely within the housing 2, rapid heating of the housing 2 and the turbine 3 is possible.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102013226742.8 | Dec 2013 | DE | national |
