U.S. patent number 3,902,819 [Application Number 05/367,052] was granted by the patent office on 1975-09-02 for method and apparatus for cooling a turbomachinery blade.
This patent grant is currently assigned to United Aircraft Corporation. Invention is credited to Jacob Holchendler, David Japikse, William F. Laverty, James J. Wesbecher.
United States Patent |
3,902,819 |
Holchendler , et
al. |
September 2, 1975 |
Method and apparatus for cooling a turbomachinery blade
Abstract
A turbomachinery blade operating at elevated temperature and in
a strong centrifugal field is cooled by a coolant loop located
within the blade constituting an open, mixed convection,
thermosyphon system utilizing water as the coolant and establishing
density differentials in the coolant within the loop by injecting
cooler water into one portion of the loop and extracting coolant
fluid from another portion of the loop to maintain system pressure
and coolant mass at desired levels to thereby establish continuous
coolant recirculation within the coolant loop.
Inventors: |
Holchendler; Jacob (East
Hartford, CT), Japikse; David (Manchester, CT), Laverty;
William F. (Glastonbury, CT), Wesbecher; James J.
(Glastonbury, CT) |
Assignee: |
United Aircraft Corporation
(East Hartford, CT)
|
Family
ID: |
23445744 |
Appl.
No.: |
05/367,052 |
Filed: |
June 4, 1973 |
Current U.S.
Class: |
416/1; 416/97R;
416/96R |
Current CPC
Class: |
F01D
5/18 (20130101); F01D 5/185 (20130101); Y02T
50/60 (20130101) |
Current International
Class: |
F01D
5/18 (20060101); F01D 005/18 () |
Field of
Search: |
;416/95-97,92,96A,97A,1
;415/114,115,1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
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|
|
|
|
|
879,485 |
|
Jun 1953 |
|
DT |
|
783,177 |
|
Sep 1957 |
|
GB |
|
237,475 |
|
Sep 1945 |
|
CH |
|
774,499 |
|
May 1957 |
|
GB |
|
Other References
The Oil Engine and Gas Turbine, Feb. 1958, pp. 396-398..
|
Primary Examiner: Powell, Jr.; Everette A.
Attorney, Agent or Firm: Hauschild; Vernon F.
Claims
We claim:
1. A turbomachinery blade adapted to be mounted for rotation on a
disc and to have hot gas pass thereover so as to thereby be
subjected to both centrifugal force and high temperature
including:
1. a coolant loop within the blade,
2. a cooling fluid filling said loop,
3. heat sink establishing means acting upon the cooling fluid in
one portion of said loop to establish a temperature and hence a
density differential between the cooling fluid in different parts
of said coolant loop to thereby establish a continuous circulatory
flow and recirculation of cooling fluid within the coolant loop
utilizing the thermal syphon principle, and
4. wherein said heat sink establishing means comprises a means for
injecting a coolant at lesser temperature than the cooling fluid
into said coolant loop at a selected location, and means to
discharge cooling fluid from the coolant loop at the same rate that
coolant is being injected into the coolant loop to thereby maintain
selected pressure level and coolant mass in the coolant loop.
2. A blade according to claim 1 wherein the cooling fluid is steam
above critical temperature and pressure and wherein the coolant is
water above critical pressure and at low temperature.
3. A blade according to claim 2 wherein the fluid extracted from
the coolant loop is discharged through the blade walls.
4. A blade according to claim 3, which blade has discharged slots
in the blade trailing edge and wherein the fluid is discharged
through said trailing edge slots.
5. A blade according to claim 1 wherein said blade comprises an
outer cover defining the blade tip and airfoil section walls and an
inner member inserted thereinto in blade-in-scabbard fashion and
sealably connected thereto, with both the blade outer cover portion
and the blade inner portion being selectively shaped to define said
coolant loop.
6. A blade according to claim 1 and including means to control
coolant circulation rate and temperature, rate of heat removal from
and the temperature of the blade.
7. A blade according to claim 1 and including means to control the
amount of coolant discharged from the coolant loop.
8. The method of cooling a turbomachinery blade utilizing the
thermosyphon principle including the steps of:
1. providing a plurality of substantially radially extending
passages in the blade interior joining a header extending along the
blade tip and a header extending along the blade root,
2. filling said passages with fluid which will be in the
supercritical state at blade operating conditions, and
3. establishing a density differential between the fluid in at
least one of said passages and the fluid in the remaining passages
to establish continuous circulation and recirculation of fluid
radially inwardly through the passages having the less dense fluid
and radially outwardly through the passage having the more dense
fluid to thereby cool the blade.
9. A turbomachinery blade adopted to be mounted for rotation on a
disc and to have hot gas passed thereover so as to thereby be
subjected both to centrifugal force and high temperature
including:
1. a blade root adopted to be connected to the blade disc,
2. a blade airfoil section shaped to define the blade tip, the
blade leading edge and trailing edge and attached to the blade root
to extend radially outwardly therefrom when the blade is mounted on
the disc and shaped to define therewithin a selectively shaped
passage system including a series of substantially radially
extending passage joining an outboard header and an inboard
header,
3. a blade tip located at the end of the blade airfoil section
opposite to the blade root,
4. a fluid which will operate at a supercritical state at blade
operating conditions, and
5. means to establish a density differential in the fluid in said
passages and thereby establish continuous circulatory flow of said
fluid radially outwardly through at least one of said radial
passages, through said outboard header, radially inwardly through
at least one of said radial passages and said inboard header in
multi-pass, recirculation fashion.
10. The method of cooling a turbomachinery blade utilizing the
thermosyphon principle including the steps of:
1. providing a plurality of substantially radially extending
passages in the blade interior joining a header extending along the
blade tip and a header extending along the blade root,
2. filling said passages with fluid,
3. establishing a density differential between the fluid in at
least one of said passages and the fluid in the remaining passages
to establish continuous circulation and recirculation of fluid
radially inwardly through the passages having the less dense fluid
and radially outwardly through the passage having the more dense
fluid to thereby cool the blade, and
wherein said last step includes cooling the temperature of the
fluid in at least one of the passages by direct heat sink injection
to increase its density so that, in accordance with the
thermosyphon principle, the more dense fluid will flow radially
outwardly to the tip header and the less dense fluid will flow
radially inwardly to the root header establish blade coolant
circulation.
11. The method of cooling a turbomachinery blade utilizing the
thermosyphon principle including the steps of:
1. providing a plurality of substantially radially extending
passages in the blade interior joining a header extending along the
blade tip and a header extending along the blade root,
2. filling said passages with fluid,
3. establishing a density differential between the fluid in at
least one of said passages and the fluid in the remaining passages
to establish continuous circulation and recirculation of fluid
radially inwardly through the passages having the less dense fluid
and radially outwardly through the passage having the more dense
fluid to thereby cool the blade, and
wherein the cooling fluid is supercritical and wherein water at a
temperature less than the supercritical is introduced to one of the
passages to establish a heat sink to produce the desired density
differential, and wherein supercritical steam is bled from the
system at the same rate that cooling water is added to the system
to maintain the coolant mass pressure, and the density differential
substantially constant in the system.
12. The method of cooling a turbomachinery blade utilizing the
thermosyphon principle including the steps of:
1. providing a plurality of substantially radially extending
passages in the blade interior joining a header extending along the
blade tip and a header extending along the blade root,
2. filling said passages with fluid,
3. establishing a density differential between the fluid in at
least one of said passages and the fluid in the remaining passages
to establish continuous circulation and recirculation of fluid
radially inwardly through the passages having the less dense fluid
and radially outwardly through the passage having the more dense
fluid to thereby cool the blade, and
including the additional step of controlling the density
differentials so established in the fluid so as to control the
recirculation rate of the cooling fluid in the passages, the
operating temperatures of the fluid being circulated, the rate of
heat removal from the blade into the cooling fluid, and blade metal
temperature.
13. The method of cooling a turbomachinery blade utilizing the
thermosyphon principle including the steps of:
1. providing a plurality of substantially radially extending
passages in the blade interior joining a header extending along the
blade tip and a header extending along the blade root,
2. filling said passages with fluid,
3. establishing a density differential between the fluid in at
least one of said passages and the fluid in the remaining passages
to establish continuous circulation and recirculation of fluid
radially inwardly through the passages having the less dense fluid
and radially outwardly through the passage having the more dense
fluid to thereby cool the blade, and
wherein the cooling fluid is supercritical and wherein water at a
temperature less than the supercritical is introduced to one of the
passages to establish a heat sink to produce the desired density
differential, and wherein supercritical steam is bled from the
system at the same rate that cooling water is added to the system
to maintain the coolant mass pressure, and the density differential
substantially constant in the system, and, further, wherein the
heat sink is positioned remote from the system bleed so as to
achieve maximum effective mixing with single phase fluids and
maintain constant steady state circulation rates.
14. A turbomachinery blade adapted to be mounted for rotation on a
disc and to have hot gas passed thereover so as to thereby be
subjected both to centrifugal force and high temperature
including:
1. a blade root adapted to be connected to the blade disc,
2. a blade airfoil section shaped to define the blade tip, the
blade leading edge and trailing edge and attached to the blade root
to extend radially outwardly therefrom when the blade is mounted on
the disc and shaped to define therewithin a passage system
including a series of substantially radially extending passages
joining an outboard header and an inboard header,
3. a blade tip located at the end of the blade airfoil section
opposite to the blade root,
4. a fluid filling said headers and said passages for circulation
therein, and
5. means to establish a density differential in the fluid in said
passages and thereby establish continuous circulatory flow of said
fluid radially outwardly through at least one of said radial
passages, through said outboard header, radially inwardly through
at least one of said radial passages and said inboard header in
multi-pass, recirculation fashion, and
wherein said density differential establishing means including:
1. means to inject a cooling fluid into one of said passages said
cooling fluid being at a lesser temperature than the temperature of
the circulating fluid in the other passages to thereby establish a
temperature differential and hence a density differential
therebetween and thereby produce thermosyphon circulation and
recirculation of fluid in the gravity field, and
2. means to extract fluid from said passage system at the same rate
that the cooling fluid is being introduced to said passage
system.
15. A turbomachinery blade adapted to be mounted for rotation on a
disc and to have hot gas passed thereover so as to thereby be
subjected both to centrifugal force and high temperature
including:
1. a blade root adapted to be connected to the blade disc,
2. a blade airfoil section shaped to define the blade tip, the
blade leading edge and trailing edge and attached to the blade root
to extend radially outwardly therefrom when the blade is mounted on
the disc and shaped to define therewithin a passage system
including a series of substantially radially extending passages
joining an outboard header and an inboard header,
3. a blade tip located at the end of the blade airfoil section
opposite to the blade root,
4. a fluid filling said headers and said passages for circulation
therein, and
5. means to establish a density differential in the fluid in said
passages and thereby establish continuous circulatory flow of said
fluid radially outwardly through at least one of said radial
passages, through said outboard header, radially inwardly through
at least one of said radial passages and said inboard header in
multi-pass, recirculation fashion, and
wherein said density differential establishing means including:
1. means to inject a cooling fluid into one of said passages said
cooling fluid being at a lesser temperature than the temperature of
the circulating fluid in the other passages to thereby establish a
temperature differential and hence a density differential
therebetween and thereby produce thermosyphon circulation and
recirculation of fluid in the gravity field, and
2. means to extract fluid from said passage system at the same rate
that the cooling fluid is being introduced to said passage system,
and, further,
wherein said blade has at least one aperture in the blade trailing
edge and wherein the extracted fluid is discharged through
apertures in the blade trailing edge to cool the blade trailing
edge.
16. A turbomachinery blade adapted to be mounted for rotation on a
disc and to have hot gas passed thereover so as to thereby be
subjected both to centrifugal force and high temperature
including:
1. a blade root adapted to be connected to the blade disc,
2. a blade airfoil section shaped to define the blade tip, the
blade leading edge and trailing edge and attached to the blade root
to extend radially outwardly therefrom when the blade is mounted on
the disc and shaped to define therewithin a passage system
including a series of substantially radially extending passages
joining an outboard header and an inboard header,
3. a blade tip located at the end of the blade airfoil section
opposite to the blade root,
4. a fluid filling said headers and said passages for circulation
therein, and
5. means to establish a density differential in the fluid in said
passages and thereby establish continuous circulatory flow of said
fluid radially outwardly through at least one of said radial
passages, through said outboard header, radially inwardly through
at least one of said radial passages and said inboard header in
multi-pass, recirculation fashion, and
wherein said density differential establishing means including:
1. means to inject a cooling fluid into one of said passages said
cooling fluid being at a lesser temperature than the temperature of
the circulating fluid in the other passages to thereby establish a
temperature differential and hence a density differential
therebetween and thereby produce thermosyphon circulation and
recirculation of fluid in the gravity field, and
2. means to extract fluid from said passage system at the same rate
that the cooling fluid is being introduced to said passage system,
and, further,
wherein said blade has at least one aperture in the blade trailing
edge and wherein the extracted fluid is discharged through
apertures in the blade trailing edge to cool the blade trailing
edge, and, still further, wherein said fluid extraction means
includes an orifice joining one of said headers to a blade trailing
edge header which is connected to the hot gas stream through said
blade trailing edge apertures.
17. A turbomachinery blade adapted to be mounted for rotation on a
disc and to have hot gas passed thereover so as to thereby be
subjected both to centrifugal force and high temperature
including:
1. a blade root adapted to be connected to the blade disc,
2. a blade airfoil section shaped to define the blade tip, the
blade leading edge and trailing edge and attached to the blade root
to extend radially outwardly therefrom when the blade is mounted on
the disc and shaped to define therewithin a passage system
including a series of substantially radially extending passages
joining an outboard header and and inboard header,
3. a blade tip located at the end of the blade airfoil section
opposite to the blade root,
4. a fluid filling said headers and said passages for circulation
therein, and
5. means to establish a density differential in the fluid in said
passages and thereby establish continuous circulatory flow of said
fluid radially outwardly through at least one of said radial
passages, through said outboard header, radially inwardly through
at least one of said radial passages and said inboard header in
mulit-pass, recirculation fashion, and
wherein said density differential establishing means including:
1. means to inject a cooling fluid into one of said passages said
cooling fluid being at a lesser temperature than the temperature of
the circulating fluid in the other passages to thereby establish a
temperature differential and hence a density differential
therebetween and thereby produce thermodyphon circulation and
recirculation of fluid in the gravity field, and
2. means to extract fluid from said passage system at the same rate
that the cooling fluid is being introduced to said passage system,
and, further,
wherein said blade has at least one aperture in the blade trailing
edge and wherein the extracted fluid is discharged through
apertures in the blade trailing edge to cool the blade trailing
edge, and, still further, wherein said fluid extraction means
includes an orifice joining one of said headers to a blade trailing
edge header which is connected to the hot gas stream through said
blade trailing edge apertures, and wherein said one header is the
inboard header.
18. A turbomachinery blade adpated to be mounted for rotation on a
disc and to have hot gas passed thereover so as to thereby be
subjected both to centrifugal force and high temperature
including:
1. a blade root adapted to be connected to the blade disc,
2. a blade airfoil section shaped to define the blade tip, the
blade leading edge and trailing edge and attached to the blade root
to extend radially outwardly therefrom when the blade is mounted on
the disc and shaped to define therewithin a passage system
including a series of substantially radially extending passages
joining an outboard header and an inboard header,
3. a blade tip located at the end of the blade airfoil section
opposite to the blade root,
4. a fluid filling said headers and said passages for circulation
therein, and
5. means to establish a density differential in the fluid in said
passages and thereby establish continuous circulatory flow of said
fluid radially outwardly through at least one of said radial
passages, through said outboard header, radially inwardly through
at least one of said radial passages and said inboard header in
multi-pass, recirculation fashion, and
wherein said density differential establishing means including:
1. means to inject a cooling fluid into one of said passages said
cooling fluid being at a lesser temperature than the temperature of
the circulating fluid in the other passages to thereby establish a
temperature differential and hence a density differential
therebetween and therebyproduce thermosyphon circulation and
recirculation of fluid in the gravity field, and
2. means to extract fluid from said passage system at the same rate
that the cooling fluid is being introduced to said passage system,
and, further, wherein said blade has at least one aperture in the
blade trailing edge and wherein the extracted fluid is discharged
through apertures in the blade trailing edge to cool the blade
trailing edge, and, still further, wherein said fluid extraction
means includes an orifice joining one of said headers to a blade
trailing edge header which is connected to the hot gas stream
through said blade trailing edge apertures, and wherein said
orifice is caused to operate in chocked condition.
19. A turbomachinery blade adapted to be mounted for rotation on a
disc and to have hot gas passed thereover so as to thereby be
subjected both to centrifugal force and high temperature
including:
1. a blade root adapted to be connected to the blade disc,
2. a blade airfoil section shaped to define the blade tip, the
blade leading edge and trailing edge and attached to the blade root
to extend radially outwardly therefrom when the blade is mounted on
the disc and shaped to define therewithin a passage system
including a series of substantially radially extending passages
joining an outboard header and an inboard header,
3. a blade tip located at the end of the blade airfoil section
opposite to the blade root,
4. a fluid filling said headers and said passages for circulation
therein, and
5. means to establish a density differential in the fluid in said
passages and thereby establish continuous circulatory flow of said
fluid radially outwardly through at least one of said radial
passages, through said outboard header, radially inwardly through
at least one of said radial passages and said inboard header in
multi-pass, recirculation fashion, and
wherein said density differential establishing means including:
1. means to inject a cooling fluid into one of said passages said
cooling fluid being at a lesser temperature than the temperature of
the circulating fluid in the other passages to thereby establish a
temperature differential and hence a density differential
therebetweeen and thereby produce thermosyphon circulation and
recirculation of fluid in the gravity field, and
2. means to extract fluid from said passage system at the same rate
that the cooling fluid is being introduced to said passage system,
and
wherein said system circulatory fluid is steam above critical
pressure and temperature and wherein said lower temperature cooling
fluid is water above critical pressure and at low temperature.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to turbomachinery blades, such as turbine
blades, and more particularly to method and apparatus for cooling
such blades.
2. Description of the Prior Art
In the turbomachinery blade cooling art, thermosyphon systems have
been used previously. In Ledinegg U.S. Pat. No. 2,667,326, a closed
loop thermosyphon cooling system is used, however, the coolant is
evaporated in a single pass through the turbine blade, and thence
is returned to a remote heat sink in the turbomachinery disc for
condensation prior to recirculation through the turbine blades.
Also, geometric separation of the coolant inlet and outlet from the
blades is made possible only by the presence of different phases at
the inlet and the outlet. Eckert U.S. Pat. No. 2,778,601 teaches a
thermosyphon blade cooling system which is open loop and utilizes
water as its cooling fluid, however, the system is single pass and
the cooling media is passed through the turbine blade but a single
time and is then discharged overboard. In addition, no special
effort is made to deliberately define and separate the inlet and
exit coolant flow location. Bruckmann U.S. Pat. No. 2,779,565 is
similar to Eckert, albeit air is used as the cooling media but in
single-pass fashion. Schneider U.S. Pat. No. 3,623,825 utilizes
liquid metal, without phase change, in a particular portion of a
heat exchanger within the blade in a sealed compartment and thereby
presents sealing, maintainability, and weight problems. These
single pass systems are inefficient and the systems utilizing heat
sinks remote from the blade are unnecessarily complicated and
heavy.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide an improved
method and hardware for cooling turbomachinery blading utilizing an
open, mixed convection thermosyphon system within the blade.
In accordance with the present invention, the turbomachinery blade
coolant is preferably steam at high pressure and at temperature
above critical, into which coolant at low temperature, and high
pressure is injected in order to create a concentrated heat sink
and thereby establish a density differential so as to produce
continuous thermosyphon multi-pass pumping of the coolant.
In accordance with a further aspect of the present invention, a
selected amount of cooling fluid is discharged from the system at
the same rate at which the low temperature coolant is added to the
system to maintain system pressure and coolant mass at a selected
level. During transient operating conditions, the inlet and exit
flow rates may differ.
It is still a further important teaching of this invention that the
coolant flow within the blade is at a rate many times as great
(frequently tenfold or more) as the rate of injection of low
temperature coolant thereby minimizing the variation of coolant
temperature in the different parts of the blade, giving a high heat
transfer coefficient as required to cool the blade while avoiding
the problems associated with change of phase (particularly
boiling), and making the cooling system thermodynamically
efficient.
It is a very important feature of this invention that the coolant
is recirculated within the blade without the need for having heat
transferred from the coolant prior to recirculation.
An advantage of this system is that water may be used as the
coolant, and therefore our system may use a coolant which has good
thermal properties, ready availability especially in stationary and
marine installations, which is economical, and which requires no
special handling, as is the case with many other coolants.
It is a further important feature of this blade cooling system that
the heat sink is positioned solely within the blade, and bears no
relationship to the supporting disc or other related
turbomachinery.
It is a further feature of this invention that the turbomachinery
blade be fabricated so as to include a coolant loop therewithin
comprising an outer header extending substantially along the blade
tip, an inner header extending substantially along the blade root,
and passages or conduits extending between the headers, and further
preferably including a blade trailing edge header and a discharge
passage or passages joined to the main coolant loop through an
orifice so as to permit the extraction of fluid from the cooling
loop in a selective fashion so as to maintain system pressure and
fluid mass at desired levels and to regulate the mixing process at
the inlet location.
According to another feature of our invention, the fluid extracted
from the system is used for cooling purposes, and preferably to
cool the blade trailing edge.
It is a further feature of this invention to teach a unique coolant
loop for a turbomachinery blade in which the coolant remains in a
supercritical state as it goes through multiple passes throughout
the loop.
Other objects and advantages of the present invention may be seen
by referring to the following description and claims, read in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a showing of turbomachinery utilizing this invention.
FIG. 2 is a cross-sectional drawing through a turbomachinery blade
utilizing the present invention but the number of coolant passages
have been reduced to better permit description.
FIG. 3 is a view taken along line 3--3 of FIG. 2 and shows a
representative number of coolant passages.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 we see turbomachinery unit 1, which may be a
gas or steam turbine or compressor, and which comprises at least
one rotor 2 mounted for rotation about axis 3 and including a disc
4 supporting a plurality of blades 10 about the periphery thereof.
Rotor 2 is mounted within housing 5, from which vaned stator 6
projects to control the angle of entry of the gas flowing through
turbomachinery 1 as it approaches blades 10.
Referring to FIGS. 2 and 3 we see turbomachinery blade 10, which
includes blade tip 12, blade root 14, leading edge 16, trailing
edge 18, and airfoil portion 20 extending between root 14 and tip
12. Blade 10 is adapted to be supported from a rotor disc 2 of a
turbomachinery compressor or turbine, for example, to be rotated
therewith during turbine engine operation and to have hot gases
passed thereover so that the blade 10 is operating both in a high
temperature environment and a strong centrifugal force environment.
For a more complete description of an illustration of a
turbomachinery blade and its associated turbine and/or compressor
parts, reference may be had to U.S. Pat. Nos. 2,711,631 and
2,747,367.
Blade 10 is fabricated so that coolant loop 22 is positioned
therewithin and includes outboard header 24 extending along the
blade tip 12, inboard header 26 extending along the blade root 14,
and outflow passage 28 and inflow heat exchanger passages 30
extending between these headers and with passages 30 located
adjacent to the blade convex and concave surfaces 29 and 31. The
cooling system also includes blade trailing edge header 32 which
communicates with inboard header 26 through choked orifice 34, and
which communicates with the gas flow passage 35 external of blade
10 through a plurality of apertures 36 extending along and through
the blade trailing edge 18. Coolant pressure and temperature levels
in loop 22 are controlled by the sizing of orifice 34. Orifice 34
is preferably adjacent to inner header 26 but could be adjacent to
outer header 28. Blade 10 may be fabricated in any convenient
fashion, for example, blade outer portion 38, which includes blade
tip 12 and airfoil section 20 may serve as a blade wall member into
which blade internal portion 40 may extend in projecting from root
14 in blade-scabbard fashion, thereby defining those passages
enumerated above the blade outer portion 38 and blade inner portion
would be sealably connected by welding or the like.
The preferred cooling fluid in coolant passage 22 is water in the
form of steam operating at supercritical temperature and pressure
to form an open, mixed convection-thermosyphon cooling system. This
supercritical steam passes outwardly from inboard header 26 through
passage 28 to outboard header 24 and therefrom inwardly through
passages 30 to inboard header 26 and recirculation again outwardly
through passage 28 in multi-pass fashion. Preferably, passage 28 is
located in a central portion of the blade while the heat exchanger
passages 30 are located near the blade outer surfaces 29 and 31.
The motive force to create this circulation is derived from the
heat sink positioned near the blade root 14 in passage 28,
specifically at the end of tube member 42 through which water, at
supercritical pressure but at a temperature lower than the
supercritical steam is injected into the inner end of passage 28.
The mixing of this low temperature coolant from conduit 42 serves
to lower the temperature of the coolant in conduit 28 below the
temperature of the coolant in conduits 30 to establish both a
temperature and density differential therebetween, thereby
establishing a continuing flow of the coolant in cooling fluid
system 22 outwardly through passage 28 into outer header 24, and
then inwardly through passages 30 to inner header 26, and continued
recirculation through this route as desired to effect blade
cooling. To maintain the system fluid at desired pressure and total
mass, a selected amount of coolant is discharged through orifice 34
into blade trailing edge header 32, from which it is discharged to
gas flow path 35 through blade trailing edge apertures 36 for the
purpose of cooling the blade trailing edge. Orifice 34 is sized so
that the rate of coolant so discharged is at the same flow rate at
which the low temperature coolant is entering the system through
conduit 42. Low temperature coolant for conduit 42 may be stored
and/or supplied in any convenient fashion, such as within or from
the rotor disc 2. In this fashion, an open, mixed convention
thermosyphon cooling system is established. This system therefore
effects coolant (supercritical steam) recirculation by low
temperature coolant (water) injection and this provides a
uniqueness to our system over other known thermosyphon systems in
that our system establishes a flow rate in coolant which is on the
order of 10 times as great as the flow rate of the injected low
temperature coolant and this has the advantages of minimizing the
variation of coolant temperature in the different parts of blade
10, giving the high heat transfer coefficients required to cool the
blade while avoiding the problems associated with change of phase
of the coolant, particularly boiling, and making the cooling system
thermodynamically efficient.
The present coolant system is said to be open because the coolant
fluid is being discharged from the system through trailing edge
ports 36, is said to be mixed convection since the system operates
by both free and forced convection, and is said to be a
thermosyphon because the continuous pumping and recirculation of
the coolant is brought about by the functioning of the heat sink to
establish density differentials within the cooling system 22.
In the present invention, the heat added to blade 10 during
operation for given external (gas-side) conditions, is proportional
to the temperature level and flow rate of the recirculating coolant
which is proportional in turn, to the flow rate of injected
coolant. It will therefore be seen that this system functions as a
convective (or thermal) amplifier.
The three main elements of this blade cooling system are: (1) a
coolant loop 22 within the blade 10, (2) a low temperature coolant
injection system (conduit 42) which is used to produce the pumping
force to circulate the coolant in the loop 22, and (3) a discharge
orifice system 32-36 to exhaust spent coolant to the turbomachinery
gas path and maintain the required coolant pressure and mass level
in the blade. The cooling of the blade is primarily accomplished by
the transfer of heat to the supercritical water flowing radially
inwardly through the heat exchanger passages 30.
By way of explanation of the operation of this system on the
thermosyphon principle, let us assume that supercritical steam in
inner header 26 is at 950.degree.F, and that water at 100.degree.F
is introduced thereinto through conduit 42 in the lower part of
outflow passage 28 so as to produce a mixed temperature therein of
900.degree.F. This 900.degree. water will flow into tip header 24
and then flow back to the inner header 26 through exchanger tubes
or passages 30 wherein heat transfer from the passage walls causes
the supercritical steam to be elevated to the 950.degree.
temperature by the time it reaches inner header 26. It will
therefore be seen that the mean or average temperature of the
supercritical steam in the heat exchanger passages 30 is
925.degree. and that the temperature of the supercritical steam in
passage 28 is 900.degree., giving a 25.degree.F temperature
differential. This temperature differential produces a density
differential so that the more dense supercritical steam at
900.degree. will be acted upon to a greater degree by the
centrifugal force generated by the rotating rotor 2 than the less
dense supercritical steam in heat exchanger conduits 30, thereby
establishing the pumping force action of the thermosyphon principle
which will cause the fluid to so continue to circulate through
coolant loop 22, so long as this temperature differential, and
hence the density differential, is maintained. To maintain this
temperature differential, the cool water at 100.degree.F is
continuously injected into the inner end of passage 28 and
supercritical steam is discharged from the system at an equal rate
to maintain the pressure and mass of the coolant in loop 22 at
desired levels. To obtain maximum benefit from the supercritical
steam being discharged from the system, we pass that steam through
the trailing edge header and out the trailing edge of the blade so
that it cools the trailing edge of the blade.
It is important to note that in our construction the cooling fluid
(steam) can be held totally in the supercritical range at all times
throughout its many passes through the cooling loop, thereby
avoiding boiling problems. A second advantage of operation in the
supercritical range is that the operating temperature is high
enough so that overcooling the blade does not occur which would
extract too much heat from the gas flowing over the blade and
diminish the cycle efficiency. However, we are maintaining the
blade cool enough to insure its structural integrity.
We wish it to be understood that we do not desire to be limited to
the exact details of construction shown and described, for obvious
modifications will occur to a person skilled in the art.
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