US2635805A

US2635805A - Turbine with cooled rotor

Info

Publication number: US2635805A
Application number: US775532A
Authority: US
Inventors: Baumann Hans
Original assignee: BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Germany; BBC Brown Boveri France SA
Priority date: 1946-09-24
Filing date: 1947-09-22
Publication date: 1953-04-21
Anticipated expiration: 1970-04-21
Also published as: DE849327C

Description

April 21, 1953 H. BAUMANN 2,635,805

TURBINE WITH cooLED RoToR Filed Sept. 22, 1947 T k X Q 1f I l I Z ITA@ Z Huwnnmmnnn mf nu d/ //W., ZU uuuuuuuuu /Q UUUUH 3mm Z/ww Myjer/5.

Patented Apr. 21, 1953 TURBINE WITH COLED ROTOR Hans Baumann, Baden, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie., Baden, Switzerland, a joint stock company Application September 22, 1947, Serial No. 775,532

In Switzerland September 24, 1946 3 Claims. (Cl. 230-116) This invention relates to gas and steam turbines, and particularly to the cooling of the turbine rotors.

The cooling of the highly stressed rotors of gas and steam turbines is of increased importance when it is desired to employ motive uids of high temperatures, and the prior cooling methods have been open to various limitations and objections. It is known to blow a cooling agent upon the end surface of the rotor, and also to cool the inlet end of the cylindrical surface of the rotor by introducing a cooling layer of air or gas within the annular stream of motive gas. The cooling layer is thrown outwardly by centrifugal force and, except at the iirst row of blades, the cylindrical surface of the rotor is exposed to the full heat of the motive uid.

These types of cooling have the drawback that the heat transfer radially of the rotor takes place by conduction through the metal of the rotor, but design requirements are frequently best satisiied by constructions which leave 4cylindrical or annular spaces within the rotor, and these spaces act per se as heat insulation. It has been proposed to improve the cooling in hollow rotors of reversing turbines by means of a liquid within the rotor. It was thought that the liquid would increase the rate of heat transfer along the cylindrical rotor Wall, and that the inactive section of the turbine rotor would thereby cool the rotor section which was then in operation. It was found that the liquid Within the rotor gave rise to vibration and noise. Water could not be employed as the cooling medium in view of its relatively low boiling point and mercury, although theoretically satisfactory as a heat transfer liquid, increased the vibration. Even if it were possible to iind a liquid which would be reasonably satisfactory, this cooling system would still be open to the objection that centrifugal force holds the liquid against only those surfaces which are farthest from the axis of rotation. There is substantially no cooling of radial disks or partitions within a rotor, and these elements are the structural parts which are subjected to the highest mechanical stresses and which therefore require intensive cooling.

Objects of the present invention are to provide turbines in which the rotors are constructed with internal recesses, and which afford a more vigorous cooling of the cylindrical surfaces and of any radial disks than has been possible with prior turbines. Objects of the invention are to provide turbines and turbine-compressor assemblies having hollow rotors, and in which a high rate of cooling or heat transfer axially of the rotor is eifected without introducing a liquid heat-transfer medium into the hollow rotor. More specilically, an object is to provide turbines in which the rate of heat transfer between the parts of a rotor with internal recesses is increased by placing the air or gas within the recess or recesses under a heavy pressure. A further speciiic object is to increase the rate of heat transfer in turbine rotors by employing hydrogen under heavy pressure as the heat-transfer medium within the recess or recesses of the rotor.

These and other objects and the advantages of the invention will be apparent from the following speciiication when taken with the accompanying drawings in which:

Fig. l is a schematic view, in longitudinal section, of a hollow rotor for a high temperature turbine, the rows of blades being omitted.,

Fig. 2 s a curve sheet showing the temperature gradient along a hollow rotor, curve I being for a rotor of the known type with a gas filling at atmospheric pressure, while curve II shows the temperature gradient when the rotor is charged with a gas under high pressure.

Fig. 3 is a longitudinal central section through a turbine embodying the invention, and in which the rotor includes a radial disk or partition which divides the hollow interior of the rotor into two cylindrical recesses or chambers, and

Fig. 4 is a longitudinal central section through the rotor of a turbine-compressor, the rotor being constructed in accordance with this invention to effect a cooling of the turbine section of the rotor by heat transfer to the compressor section thereof.

In Fig. 1 of the drawing, a hollow rotor body is illustrated somewhat schematically as comprising end disks a and b connected by a cylindrical wall c, the disks being secured to shafts s which support the rotor body in suitable bearings not shown. It is assumed that the highly heated motive fluid flows from right to left along the cylindrical rotor surface c and the blades, not shown, and establishes a maximum temperature T at the right-hand end of the cylindrical wall c. The end disk a is cooled in any conventional or desired manner, for example as described hereinafter with reference to Fig. 3, and the minimum temperature T' of the cylindrical wall is therefore at the meeting edges of the wall c and the disk a.

In prior rotor constructions of this general type. the major heat transfer has been by conduction through the walls of the rotor body, and heat transfer by convection currents of the air within the hollow rotor has contributed only in a minor way to the cooling of the cylindrical surface ol the rotor. The temperature gradient along a rotor of this type for a temperature difference Ati between the ends of the rotor is shown by curve I of Fig. 2.

The convection currents are set up withinthe hollow rotor since the walls of the gas chamber are at diierent temperatures and the gas chamber is located in a eld of force, i. e., of centrifugal force. The radial acceleration in turbine rotors may be of the orderof l03to .'104 g, where g is the acceleration of gravity, and the present invention takes advantage of this 'high acceleration to increase the heat transfer of the conduction currents of the enclosed gas or mixtures of gases, for example air, to 4a high'value approximately that of conduction through metal.

According to the invention, the gas mixture, air or gas g within the rotor is placed under heavy pressure to increase the heat transfer of theconduotion currents. The rate of heattransfer increases with the mass,.or pressure at a given temperature, of the gas or gas mixture within the hollow rotor. The term heavy pressure signifies pressures above atmospheric and of the order of several atmospheres and upward, but the appropriate heavy pressure value depends upon the composition of the gas or gas mixture and the cooling requirements for Ythe particular turbine or turbine-compressor assembly. For example, when charged with air under a pressure of 100 atmospheres, and turbulent .convection streams, the rate of heat transfer is twenty-one times that obtained with air under atmospheric pressure. The air layer adjacent the cool end wall a is relatively dense and heavy, as compared to the air layer adjacent the hot end wall b of the rotor, and the air layer at the coolwall a is therefore thrown outwardly by centrifugal force, as is indicated by the arrows on the lines p which show the paths of the convection currents within the rotor. In this case a temperaturegradient along the rotor as shown by curve II in Fig. 2 is obtained, the temperature difference between the ends of the rotor being Atn.

The rate `of heat transfer, and therefore the cooling action, may be increased still further by a suitable selection of the high pressure gas within the rotor. For example, if hydrogen is substituted for air within the rotor, the. cooling action is increased two-fold.

In a turbine las illustrated in Fig. 3, a rotor I is provided with a plurality Yof rows .of blades 2 and is supported, by stud shafts 3 and bearings 4, for rotation within a stationary turbine casing 5 carrying rows 6 'of blades which are interleaved with the blade rows of the rotor. The rotor I includes end disks or' plates a', a and at least oneintermediate disk b which subdivides the space Within the hollow rotor I into a plurality 0f cylindrical chambers 1, 8 of circular crosssection. Streams 9 of a cooling medium are supplied through conduits I, II to flow over the disks a', a at the inlet and outlet ends, respectively, of the turbine'rotor. The chambers l, 8 are charged With air or gas under high pressure, and the relatively .dense heavy layers of air .or

lgas at the inner faces of the disks a', a' are thrown outwardly by centrifugal force to establish convection currents along paths p. A high order of heat transfer from the intermediate disk b to the end disks a', a is thus established.

The detailed construction of the rotor I is not 'an essential feature of the invention and .it is to be understood that the invention may be applied to rotors of various designs and constructions Which have one or more interior chambers.

The invention is of special advantage in the case of turbo-compressors of the type in which the turbine blades I2 and compressor blades I3 are carried by a single rotor body I4, las shown in Fig. 4. The rotor body is hollow at the compressor section and is filled with gas g under heavy pressure and it may be hollow or, as illustrated, may be solid at the turbine section. The gas .or air is relatively cool and dense adjacent the inlet end wall a" of the compressor section, and the gas or air is thrown outwardly along wall a to setvflow along convention current paths p. The compressor load is of course increased somewhat by the .transfer of heat from the turbine section to the compressor section, but the heat transfer is small with respect to the volume of air handled by the compressor and the increased power 'requirement imposed upon the turbine'to facilitate the cooling of the turbine rotor is neg-V rotor, thus affording the additional and specific` advantages:

(a) loW heat tensions in starting and stopping operation of the turbine,

(b) small axial moment of inertia and from this the possibility of great acceleration with Variable speed turbines,

(c) freedom in the design of rotors vfor turbines for use on ships and aircraft,

(d) a uniform distribution of the cooling effect along the cylindrical surface of the rotor.

It is to be understood that this invention is not limited to turbines with the rotor constructions herein described and illustrated, and that various changes which may occur to those familiar Awith the design and construction of high temperature turbines fall within the spirit and scopev "of the invention as stated in the following claims.

I claim:

1. In a turbine or compressor-turbine assemblyior operation by high temperature motive fluids, arotor having a cylindrical wall carrying blades Aand radial walls cooperating with said cylindrical wallto form a closed interior chamber of cylindrical form, means for cooling a radial Wall of said rotonand a gas non-liquefiable at atmospheric temperatures confined within said closed chamber under super-atmospheric pressure, said gas being hydrogen.

2. In a turbine or compressor-turbine assembly .for operation by high temperature motive uids,

a rotor having a cylindrical wall carrying blades and radial walls cooperating with said cylindrical wall to forma closed interior chamber of cylindrical form, means for cooling a radial wall .of sa1d rotor, anda gaseous coolant consisting of air confined Within said closed chamber under a pressure of the order of atmospheres.

3. A rotor for a turbine-compressor, said rotor comprising a rotor body, a series of rows of turbine blades carried by said rotor body, a series .of rows of compressor blades carried by said rotor body, the section of the rotor body carrying said compressor blades including a cylindrical Wall and radial walls cooperating therewith to form a closed interior chamber of cylindrical form, means for cooling a radial Wall of said chamber, and a gaseous coolant consisting of air confined Within said closed chamber under a pressure of the order of 100 atmospheres.

HANS BAUMANN.

Referens cited in the me of this patent UNITED STATES PATENTS Number Number Number Name Date Planiol et al Feb.. 20, 1945 Kimball Sept. 3, 1946 Ray May 25, 1948 FOREIGN PATENTS Country Date Great Britain Oct. 28, 1920 Great Britain Dec. 2, 1926 Germany Oct. 3, 1938