Heat pipes can be used to effectively cool wing leading edges of hypersonic vehicles. . Heat-pipe leading edge development. Design validation heat pipe testing confirmed design. Three heat pipes embedded and tested in C/C. Single J-tube heat pipe fabricated and testing initiated. HPCLE work is currently underway at several locations

Glass, David E.

NASA Technical Reports Server

1Heat-Pipe-Cooled Leading
Edges for Hypersonic
Vehicles
Workshop on Materials and Structures for
Hypersonic Flight
University of California Santa Barbara
July 12-13, 2006
David E. Glass
NASA Falcon Lead
NASA Langley Research Center
david.e.glass@nasa.gov
https://ntrs.nasa.gov/search.jsp?R=20080014285 2019-08-30T04:20:07+00:00Z
2Agenda
♦ Introduction
♦Modeling
♦Fabrication and Testing
♦Future Direction and Challenges
♦Concluding Remarks
3♦ Heat pipes transfer heat isothermally by the
evaporation and condensation of a working fluid.
Heat-Pipe Operation
4Leading-Edge Heat-Pipe Operation
0
25
50
75
100
Heat flux,
Btu/ft2-sec
-40 -30 -20 -10 0 10 20 30 40
Position, in.
Upper
surface
Lower
surface
NASP ascent
(qmax = 495 Btu/ft2-sec)
Shuttle
Orbiter
Sharp LE,
hypersonic vehicl
5Heat Pipe Cooled Leading Edge History
1970 1990
1991
D. Glass et. al.
1999
•(Mo/Re)/Li Heat Pipe 
   Embedded in C-C
•Fab & Test
C. Silverstein
2001
•Hypersonic 
•Engine Cowl
•Mach 6 test
Cal Silverstein-1971
R=0.5”
Mach 8 Cruise Aircraft
C. Camarda
1978
½ scale Space
Shuttle
Design,
Fab/Test
Hastelloy x/Na
NASP
Merrigan/Seng
1989
Bench -scale
Nose cap
Boman & Elias
1990
Hastelloy-X/Na Heat pipe
1980
2005/6
C. Wojcik
1991
Nb-Zr/Li
1998
LMSSC_ AFRL/VA
2005
Superalloy/Li;
Superalloy/Na; Mo-Re/Li
6Agenda
♦ Introduction
♦ Modeling
♦ Fabrication and Testing
♦ Future Direction and Challenges
♦ Concluding Remarks
7Heat-Pipe Modeling
♦ Conduction, convection, or radiation coupling to environment
♦ Container - conduction only
♦ Wick/working fluid - conduction and heat of fusion
♦ Vapor
• Phase I - free molecular
• Phase II - continuum front moves toward
      cooler end.  Flow may be choked 
      at end of evaporator
• Phase III - continuum over 
      entire length in vapor region
      Sonic limit not encountered
8Heat-Pipe-Cooled Leading Edge Finite Element Analysis
Tmax
3-D finite element model
(non linear properties)
Tmax =
  2765°F
Thp = 2197°F
2765
2726
2687
2648
2609
2570
2531
2492
2453
2415
2376
2337
2298
2259
2220
2181
°F
9Agenda
♦ Introduction
♦ Modeling
♦ Fabrication and Testing
• NASA
• Air Force
♦ Future Direction and Challenges
♦ Concluding Remarks
10
NASA Langley Heat-Pipe Leading-Edge Experience
•   Shuttle
    -   Hastelloy-X
    -   Na working fluid
    -   Circular heat pipes
•   Advanced STS
    -   Hastelloy-X
    -   Na working fluid
    -   Rectangular heat pipes
•   NASP
    -   Mo-Re embedded in C/C
    -   Li working fluid
    -   D-shaped heat pipes
•   Experience in design, analysis, integration, and testing
11
NASP Carbon/Carbon Heat-Pipe-Cooled
Wing Leading Edge
Refractory composite 
structure
Mo-Re heat pipe
Lithium working fluid
Heat pipes passively reduce
leading-edge temperatures 
to reuse limits of composite
12
Description of Heat-Pipe-Cooled Wing Leading Edge
♦ Refractory composite structure
• C/C or C/SiC (3-D woven fabric)
• High use  temperature
• Lightweight
• 0.010 in. SiC oxidation protection coating
• CVD coating for minimization of coating temperature
♦ Heat-pipe working fluid
• Lithium
• 17 psia vapor pressure
at 2500°F (1370°C)
• Compatible with
refractory metals
♦ Heat-pipe container
• 0.010 in. arc cast Mo-41Re
• High strength 
• High use temperature
• Lighter than W-Re or pure Re
• Ductile at room temperature
• Weldable
13
Heat-Pipe-Cooled Leading Edge Development
•   Numerous small specimens to study various issues
•   Design validation heat pipe
    -   36-in-long straight heat pipe
    -   Operated up to 2460°F (1350°C)
    -   Throughput of 3.1 Btu/sec (3.3 kW)
    -   Radial heat flux of 141 Btu/ft2-sec (160 W/cm2)
    -   Developed leak due to difficulties with welded thermocouple
•   Three straight heat pipes
    -   28-in-long
    -   Operated up to 2300°F (1260°C) and 
        155 Btu/ft2-sec
    -   Embedded in carbon/carbon
    -   Testing to be performed at NASA LaRC
•   J-tube heat pipe
    -   30-in-long 
    -   Nose and wick fabrication issues resolved
    -   Transient performance tests at LANL
14
Heat-Pipe Fabrication and Testing
Design Validation Heat Pipe
•  Container:  0.01-in. arc cast
       Mo-41Re, 0.3-in. radius
•  Wick: 4 layers of 400 x 400
       Mo-5Re screen
•   Artery to reduce liquid pressure drop
    -  0.1-in. diameter, 400 x 400
       mesh screen
    -  Located on non-heated surface
    -  Spring in artery for support
    -  One end closed, pool at other end
•   Heat pipe with thermocouples
    and induction heat coils
15
Steady State Heat-Pipe Operation
 Design Validation Heat Pipe
Note:  Thermocouples ~ 4 in. apart.
0
400
800
1200
1600
2000
2400
2800
Temp, °F
0 4 8 12 16 20 24 28 32 36
Position, in.
Q = 3.1 Btu/s
Q = 0.38 Btu/s
Q = 0.38 Btu/s
q
16
Heat-Pipe Start-Up From the Frozen State
Design Validation Heat Pipe
(~ 4-in. spacing)
0
500
1000
1500
2000
Temp., °F
0 500 1000 1500 2000
Time, sec.
TC 1 TC 2
TC 5
TC 6
TC 3
TC 10
TC 7
TC 8
TC 9
TC #1 TC #2 TC #5TC #3
• • • •• Heat pipe
Induction heating
17
Heat-Pipe-Cooled Leading Edge Development
•   Numerous small specimens to study various issues
•   Design validation heat pipe
    -   36-in-long straight heat pipe
    -   Operated up to 2460°F (1350°C)
    -   Throughput of 3.1 Btu/sec (3.3 kW)
    -   Radial heat flux of 141 Btu/ft2-sec (160 W/cm2)
    -   Developed leak due to difficulties with welded thermocouple
•   Three straight heat pipes
    -   28-in-long
    -   Operated up to 2300°F (1260°C) and 
        155 Btu/ft2-sec
    -   Embedded in carbon/carbon
    -   Testing to be performed at NASA LaRC
•   J-tube heat pipe
    -   30-in-long 
    -   Nose and wick fabrication issues resolved
    -   Transient performance tests at LANL
18
Comparison of the Three Heat Pipes
Three Straight Heat Pipes
Heat pipe #1 0.0099 42 hrs @ 1650-1740°F
Heat pipe #2 0.0088 70 hrs @ 1650°F
Heat pipe #3 0.018 47 hrs @ 1650°F
Lithium, lb Wet in
•   Heat pipe #1
    -   2300°F, 155 Btu/ft2-s over 1.5 in.
    -  Nearly fully isothermal
•   Heat pipe #2
    -   2420°F
    -   @ 2075°F, non-condensible gas
        over last 6 in. of heat pipe
•   Heat pipe #3
    -   Never operated properly
28-in long
19
Heat Pipes Embedded In Carbon/Carbon
Three Heat Pipes in C/C
•   Three Mo-Re heat pipes 
•   3-D woven preform with T-300
    fibers in a carbon matrix
    -   increase through-the-thickness
        thermal conductivity
    -   eliminate delaminations with
        2-D C/C due to CTE mismatch
•   No oxidation protection coating on C/C, therefore must test
    in an inert environment
Hot spot
Heat pipeHeat pipe
20
C/C Heat Pipe Transient Testing
 Three Heat Pipes in C/C
1400
1500
1600
1700
1800
1900
2000
Temp., °F
5000 5500 6000 6500
Time, sec
x = 30.0 in.
x = 27.4 in.
130 V
180 V
0
500
1000
1500
2000
2500
Temp, °F
0 600 1200 1800 2400 3000 3600
Time, sec.
Vertical
Horizontal
x = 2.9 in.,
under
heaters
x = 30.0 in.
21
•   Numerous small specimens to study various issues
•   Design validation heat pipe
    -   36-in-long straight heat pipe
    -   Operated up to 2460°F (1350°C)
    -   Throughput of 3.1 Btu/sec (3.3 kW)
    -   Radial heat flux of 141 Btu/ft2-sec (160 W/cm2)
    -   Developed leak due to difficulties with welded thermocouple
•   Three straight heat pipes
    -   28-in-long
    -   Operated up to 2300°F (1260°C) and 
        155 Btu/ft2-sec
    -   Embedded in carbon/carbon
    -   Testing to be performed at NASA LaRC
•   J-tube heat pipe
    -   30-in-long 
    -   Nose and wick fabrication issues resolved
    -   Transient performance tests at LANL
Heat-Pipe-Cooled Leading Edge Development
22
Machine and Weld Nose Region
J-Tube Heat Pipe
Photograph of nose parts
23
Curved Wick Fabrication
 J-Tube Heat Pipe
Wick formed
on mandrel
Nose portion of wick
Wick being formed
around machined part
24
RF-Induction Heating of J-Tube Heat Pipe
 J-Tube Heat Pipe
•   RF-induction coil/concentrator heating of nose region on outer surface 
•   Test specific issue:  Hot spot in nose region
    -   Test
        -   Curved surface not insulated, thus higher throughtput required
    -   Flight vehicle
        -   Curved surface is “insulated”
25
J-Tube Heat-Pipe Checkout Tests
0
500
1000
1500
2000
Temp., °F
0 60 120 180 240 300 360 420 480
Time, min.
tc 1 - tc 8
Location of thermocouples
Start up of J-tube heat pipe Maximum temperature distribution
(not steady state)
0
500
1000
1500
2000
Temp, °F
-5 0 5 10 15 20 25 30
Position, in.
Stagnation line
Test 1 Test 2
Test 4
Test 3
Test 1
26
Test Induced Failure of Heat Pipe
•   Nominal operation during 4 tests
•   Test induced failure (concentrator arcing) during test 4
    -   Insulation outgassed during test (~0.1 Torr)
    -   Ionization between heating coil and heat pipe
Burn through due to
concentrator arcing
J-tube
heat pipe
27
Agenda
♦ Introduction
♦ Modeling
♦ Fabrication and Testing
• NASA
• Air Force
♦ Future Direction and Challenges
♦ Concluding Remarks
28
Overview: Heat Pipe Cooling for SOV Leading
Edges AFRL/Lockheed Martin
♦  Identify Specific Operational Requirements, and SOV Configuration
• Generated Performance Maps (Assuming Typical Requirements, and
Configuration)
♦ Using LM-TSTO Orbiter Requirements, Developed Heat Pipe Cooled
Leading Edge Designs for Moderate to High Heat Flux Cases
• Heat Pipe Design Option
− Modular Mo-Re Alloy Heat Pipe
− Developed Processing approaches for Mo-Re/Li Heat Pipe Design
• Heat Pipe Design Option
− Modular Superalloy/ Li Heat Pipe
− Successfully Designed, Fabricated, and Tested
♦ Developed Heat Pipe Design Solutions for Hypersonic Vehicles
• Sharp Hybrid Leading Edge
Designs
• Cowl Inlet Cooling (Fabricate
and Test Superalloy/Na Heat Pipe)
* First Superalloy/Li Heat Pipe
29
Performance Map for Heat Pipe Leading Edge
Cooling
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
1500 1900 2000 2100 2200 2300 2400 2500 2600 2700 2800
Radiation Temperature, F
0
1600 1700 1800
R
ad
ia
tio
n 
Eq
ui
l. 
Te
m
p.
 o
n 
R
ad
ia
tin
g 
Su
rf
ac
e,
 F
 
1.73
2.89
4.56
6.86
9.94
14.0
19.1
25.5
33.4
43.0
H
ea
t F
lu
x 
on
 R
ad
ia
tin
g 
Su
rf
ac
e,
 B
tu
/ft
2 -
se
c
0.5-in. radius
0.8 emissivity
65 Deb. Sweep angle
Stagnation Heat Flux
50 Btu/ft2-sec
100 Btu/ft2-sec
200 Btu/ft2-sec
400 Btu/ft2-sec
800 Btu/ft2-sec
Infinite Radiation length
40-in. Radiation Length
30-in. Radiation Length
20-in. Radiation Length
Hea
t So
urce
 Zon
e fo
r 
Rad
iatin
g Su
rfac
e
•  Generated Relationship Between the Cooling System Temperature and Radiation 
   Length and Aerothermal Environment for Different Leading Edge Radii
30
Technical Assessment of Key
HPCLE Design Options
♦ Key Design Options Very High Temp.
• Modular Mo Alloy/Li Heat Pipe
• Modular (or D) Mo-Re/Li Heat Pipes Embedded in C-C or  C/SiC
• Modular (or D) Mo-Re/Li Heat Pipe Design
♦ Key Design Options High Temp
• Superalloy/ Li Heat Pipe
♦  Trade Study Criteria
• Materials Cost
• Machining
• Joining
• Heat Pipe Durability
• Thermal Performance
• Structural Performance
• System Weight
• Life Cycle Cost
• Manufacturing Yield
• Start-up Risk
• Atmospheric Protection Risk
• Repair/Rework
♦ Other System Level Concerns
• Impact From Atmospheric Debris
• Oxidation Resistance
• Thermal Contact Resistance
• Robustness in Flight of Ground
• Toxicity of Li, in Case of Leak
• Manufacturing and Ease of Integration
• Comparison with Passive and Actively
Cooled Designs
Modular Mo-Re/Li
Heat Pipe
Embedded C-C (Mo-Re D
shaped)/Li Heat Pipe
31
Air Force Program Summary
♦Developed Performance Maps Providing HPCLE Design Solutions
♦Based on Analysis for TSTO-Based SOV Configuration
• # 1 Modular Mo-47%/Li Heat Pipe
• # 2 Modular Superalloy/Li Heat Pipe
♦Performed Superalloy/Li Heat pipe Life Compatibility Tests
• Successfully Demonstrated ~401 Hours Life
♦Design, Fabrication and Testing of  Prototype Articles
• 4” x 36” Superalloy/Li Heat Pipes
• Passed Functional Tests, Operational Performance Test (in Progress)
♦HPCLE Design Development for Hypersonic Cruise Vehicles (Ongoing) 
 
 
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
1500 1900 2000 2100 2200 2300 2400 2500 2600 2700 2800
Radiation Temperature, F
1600 1700 1800
R
a
d
ia
ti
o
n
 E
q
u
il
. 
T
e
m
p
. 
o
n
 R
a
d
ia
ti
n
g
 S
u
rf
a
c
e
, 
F
 
1.73
2.89
4.56
6.86
9.94
14.0
19.1
25.5
33.4
43.0
H
e
a
t 
F
lu
x
 o
n
 R
a
d
ia
ti
n
g
 S
u
rf
a
c
e
, 
B
tu
/f
t2
-s
e
c
He
at 
So
urc
e Z
on
e f
or 
Ra
dia
tin
g S
urf
ac
e
R
a
d
ia
ti
o
n
 E
q
u
il
. 
T
e
m
p
. 
o
n
 R
a
d
ia
ti
n
g
 S
u
rf
a
c
e
, 
F
 
H
e
a
t 
F
lu
x
 o
n
 R
a
d
ia
ti
n
g
 S
u
rf
a
c
e
, 
B
tu
/f
t2
-s
e
c
32
Additional Air Force-Funded Activities
♦Refrac Systems - Norm Hubele (480) 940-0068
• Wick/artery fabrication utilizing Mo-5Re alloy
• Wick/artery insertion technique
• Heat pipe container welding technique
• Diffusion bonding methods
• Modular heat pipe fabrication
• Novel lithium fill method development
• Alternate screen material evaluation
♦MR&D – Brian Sullivan (610) 964-6131
• Design and analysis of heat pipe cooled refractory composite leading
edges
♦Ultramet – Art Fortini (810) 899-0236 x118
• Low cost CVD heat pipe fabrication
♦ Lockheed – Suraj Rawal (303) 971-9378
• Small radius heat pipe cooled leading edge designs for hypersonic
cruise vehicles
33
Agenda
♦ Introduction
♦Modeling
♦Fabrication and Testing
♦Future Direction and Challenges
♦Concluding Remarks
34
Path Forward
♦For heat pipes to be utilized on the leading edges of flight
vehicles
•Designers must be willing to insert the technology
•The payoff must be significant and the technical evolution not
♦High temperature heat pipe options
•Superalloy or refractory metal
•Embedded or not embedded
♦Superalloy heat pipes offer increased heat flux capability to the
designer using “conventional” materials
♦Refractory metal heat pipes embedded in a refractory
composite offer a significant increase in heat flux capability
35
Different Materials At Elevated Temperatures Are
Problematic
•   Material compatibility, f(t,T)
    -   Problem: Brittle carbides,
            Carbon in heat pipe
    -   Solution: Coating on Mo-Re
•   Coefficient of thermal expansion mismatch
    (loose for stress, tight for thermal)
    
    -   Problem: Buckling of flat surface,
             Increased contact resistance
    -   Solution: Convex surface,
             Compliant or removable layer
36
Agenda
♦ Introduction
♦Modeling
♦Fabrication and Testing
♦Future Direction and Challenges
♦Concluding Remarks
37
Concluding Remarks
♦ Heat pipes can be used to effectively cool wing leading
edges of hypersonic vehicles
♦ Heat-pipe leading edge development
• Design validation heat pipe testing confirmed design
• Three heat pipes embedded and tested in C/C
• Single J-tube heat pipe fabricated and testing initiated
♦ HPCLE work is currently underway at several locations


Heat-Pipe-Cooled Leading Edges for Hypersonic Vehicles

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