Heat shield device in gas turbines

Details Heat shield device in gas turbines Heat shield device in gas turbines

2000-03-29

2002-07-09

Verdier, Christopher (Department: 3745)

Rotary kinetic fluid motors or pumps

Including heat insulation or exchange means

Working fluid on at least one side of heat exchange wall

C415S115000, C415S116000, C416S095000, C416S191000, C416S19300A, C416S19800R, C416S20100A, C416S215000

Reexamination Certificate

active

06416276

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to heat shield devices which are used in turbomachines, especially in gas turbines.
2. Description of the Related Art
The high cycle efficiencies of turbo- or hydrodynamic machines, especially gas turbines, which are now customary can only be achieved using high compression ratios of the working fluid in a compressor of the turbomachine. Air is generally used as the. working fluid here. High compression ratios or pressure ratios in a compressor lead in turn to the temperature of the flowing fluid at the compressor outlet rising as well. However, the temperatures of the working fluid resulting from the now customary compression of the fluid to about 30 bar or above are often above the maximum permissible material temperatures of the components of the turbomachine. Particularly in the compressor, the materials used hitherto have generally been materials with only a limited heat resistance. On the one hand, these materials with limited heat resistance are significantly cheaper than materials of higher heat resistance and moreover frequently have further advantages, such as good machineability or higher tensile strength. It is therefore desirable to continue manufacturing the components from these materials of lower heat resistance, particularly in the compressor zone. While, in the area of a rotor, the basic rotor element is protected from the working fluid by blade end elements of platform-like design, the basic rotor element is exposed directly to the working fluid, especially in the area of a stator constructed without a shroud ring. In order to prevent overheating of the basic rotor element, in particular, during the operation of the turbomachine, heat-accumulation segments were arranged here in the areas in which the basic rotor element is not protected from the working fluid by the blade end elements of the rotor blades (e.g. in DE 196 15 549). This arrangement comprises plate-shaped elements which are matched to the contour of the basic rotor element and can be secured on the basic rotor element by means of special anchoring devices. While the basic rotor element is produced from a simple ferritic material, the heat shield element is manufactured from a material which is highly heat resistant. However, the arrangement described in DE 196 15 549,especially the securing of the heat-accumulation segments, involves a very high outlay in terms of design and consequently is very expensive to produce. Moreover, this arrangement leads to a larger number of components of the turbomachine, giving rise in turn to higher costs, especially for assembly and maintenance. Another disadvantage of this arrangement is the increased risk that the rotor blades will scrape against the heat-accumulation segments. One reason for this increased risk is the difference in material properties, in particular different coefficients of thermal expansion and thermal conductivity of the guide vanes, the basic rotor element and the heat-accumulation segments, leading to thermal expansions which progress at different rates during the starting of the turbomachine or in the case of load changes of the turbomachine. Moreover, the components are subject to dimensional tolerances inherent in their manufacture. Owing to the increased number of components, it is easy for a situation to arise in which the gap between the guide vanes and the heat-accumulation segments is less than a nominal gap. This reduced dimensional accuracy of the gap can in turn lead to rubbing of the components in the event of mechanical or thermal expansion. Such rubbing leads at the very least to abrasion of the guide-vane tip and of the heat-accumulation segment, leading to enlargement of the gaps and consequently to a reduction in the efficiency of the turbomachine. However, rubbing of the guide vanes can also lead to damage of the guide vanes and even to the guide vanes breaking off.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to provide a device with the aid of which a basic rotor element of a rotor can be protected from the high temperatures of the working fluid and the disadvantages of the prior art can be avoided in an advantageous manner. At the same time, it should, in particular, be possible to produce the devices according to the invention with a low outlay on manufacture and thus economically in comparison with the prior art.
In addition to the basic rotor element, also referred to as the rotor disk, a conventional rotor, in particular a rotor of a turbomachine, comprises a multiplicity of rotor blades which are arranged in at least one row on the circumference of the basic rotor element. There is furthermore generally a row of guide vanes in front of or behind the row of rotor blades. The paired arrangement of in each case one row of rotor blades and one row of guide vanes is referred to as a stage of a compressor or a turbine of a turbomachine. Compressors or turbines of turbomachines generally comprise a plurality of stages arranged one behind the other. In a first aspect of the invention, a heat shield element or a plurality of heat shield elements lined up on the circumference of the basic rotor element is arranged between the basic rotor element of a rotor and the rotor blades of at least one row of rotor blades. According to the invention, the heat shield element or the lined-up heat shield elements in each case extends or extend in the axial longitudinal direction; of the basic rotor element at least both over the area of the row of rotor blades and over the area of a row of guide vanes positioned in front of or behind the row of rotor blades. In this arrangement, the heat shield element or heat shield elements completely surrounds and covers or surround and cover the basic rotor element in the areas of the row of rotor blades and the row of guide vanes. Over the entire circumference of the basic rotor element, the working fluid thus does not come into direct contact with the basic rotor element. As a consequence also, heat is not transmitted directly from the working fluid to the basic rotor element. The working fluid is here not necessarily the main working fluid of the turbomachine but can also be some other hot fluid from which the basic rotor element is to be shielded. An intermediate gap, which is as continuous as possible and in which a fluid, generally air, is advantageously present, preferably remains between the basic rotor element and the respective heat shield element. In order to transmit heat from the working fluid to the basic rotor element, multiple heat transfer is consequently required at the respective boundary surfaces and also conduction of the heat in the heat shield element. In this arrangement, the multiple heat transfer at the boundary surfaces advantageously increases the insulating effect of each heat shield element in relation to the basic rotor element. It has been found that, with the arrangement according to the invention of one or more heat shield elements, a significantly lower temperature is established in the basis rotor element than without these heat shield elements. It is thus possible, in the case of an arrangement according to the invention of the heat shield elements, to produce the basic rotor element from a material of limited heat resistance, e.g. a ferritic material, while the heat shield elements are preferably produced from highly heat resistant material, which preferably furthermore has a low thermal conductivity. The heat shield elements according to the invention are preferably employed in a compressor of a turbomachine since here even a slight reduction in the temperature loading of the basic rotor element is often sufficient to allow the use of ferritic materials for the basic rotor element.
By virtue of the embodiment according to the invention of the rotor, the outlay on manufacture can be considerably reduced compared with the embodiments known from the prior art. The embodiment according to the invention can thus be produced at considerably lower cost than p

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