MINIATURE ENGINEERING
SYSTEMS GROUP
(http://www.mmae.ucf.edu/~kmkv/mini)
Reverse Turbo Brayton Cycle
CryoCooler Development for
Liquid Hydrogen Systems
OBJECTIVE AND RELEVANCE
All of the previous attempts of flight cryocoolers have
cooling capacities less than 2 W at liquid hydrogen
temperature. There are commercially available cryocoolers
that have higher cooling powers but their weight restricts
their possible usage for in-space applications.
•
• The objective of this project is to design and build a
reliable, efficient, compact and light-weight reverse
turbo Brayton cycle cryocooler, which is capable of
removing 20-30 watts of heat at liquid hydrogen
temperature and thus significantly contribute to NASA
efforts on densification and ZBO storage of cryogenic
propellants for missions to Mars.
CURRENT APPROACH
Thermodynamic Schematic
- showing the two working cycle steps
Mechanical Schematic
- current focus is on
the development of
lower step of the
thermodynamic cycle
(highlighted in yellow)
COMMENT FROM MARCH 04 NASA PANEL
• Too many tasks with insufficient resources to meet them !
RESPONSE
The project tasks have been narrowed to the following
significant goals –
• Compressor development,
• Motor development, and
• Integration of Compressor and Motor.
The integrated compressor/motor is key to RTBC, and is
useful for many other NASA and non-NASA applications.
The development of foil bearings and heat recuperator have
been de-scoped from this project. These areas are being
targeted through other funding agencies/projects.
DESIGN AND TEST HELIUM COMPRESSOR WITH
SIMILARITY PRINCIPLE
Compressor similarity function:



 RT00
Pˆ
ND
ND 2 
 m

prtt ,tt ,
 f
,
,
,


3
5
2
00 N D

p
D


RT
00
00
 





Performance Variables
SimilarityVariables


Similarity Principle: When we scale up/down an existing compressor or change
its rotating speed or inlet conditions, the performance variables of the compressor
remain the same if we keep the similarity variables unchanged.
Equivalent air test using
similarity principle
Single-stage compact
helium compressor
Rotating speed (RPM) - N
313k
Rotating speed (RPM)
108k
Mass flow rate (g/s) - m
4.6
Mass flow rate (g/s)
10.6
Impeller diameter (mm) - D
48
Impeller diameter (mm)
48
Inlet pressure (bar) – P00
2
Inlet pressure (bar)
1
Inlet temperature (K) – T00
300
Inlet temperature (K)
300
Gas constant (J/kg*K) - R
2079
Gas constant (J/kg*K)
286
Specific heat ratio - γ
1.67
Specific heat ratio
1.4
Pressure ratio - prtt
1.7
Compression power (W) - Pˆ
3375
Pressure ratio
1.55
Compression power (W)
823
Open-loop air test
SINGLE-STAGE COMPACT CENTRIFUGAL HELIUM COMPRESSOR
Coupler
Compressor
Collector
Motor
Cooling
water
1.6
1.5
Pr
1.4
test data
test data fitting line
design performance
design point
CFD data
1.3
1.2
1.1
1.0
-10k 0
10k 20k 30k 40k 50k 60k 70k 80k 90k 100k110k
Speed (RPM)
Impeller/
diffuser
assembly
COMPARISON OF THE COMPRESSOR PERFORMANCE – WITH
OD AND ND
1.8
Old Diffuser
Surge Line (OD)
1.7
P03
P00
OLD DIFFUSER
New Diffuser
Surge Line (ND)
1.6
ND
With New Diffuser(ND)
OD
1.5
NEW DIFFUSER
  69.8%
1.4
1.3
  44.8%
With Old Diffuser(OD)
1.2
1.1
Air, N  108K
1
2.4
2.6
2.8
.
3
3.2
m T00
 106
P00
 IGV
 Imp
 Diff
 Overall
OD
ND
0.76
0.78
0.83
0.86
0.09
0.75
0.45
0.70
3.4
PMSM DESIGN AND FABRICATION
• Criteria for selection of materials - high speed application and efficient
cryogenic temperature operation.
• Design of motor structure and optimization of dimensions were done
to minimize losses.
• Both dynamic and static analyses of mechanical stresses including
rotordynamics were done.
• Thermal analysis including thermal stress due to temperature
gradients/transients and shaft expansion/contraction was performed.
Stator with winding
Hollow shaft and
permanent magnet
Shaft and casing
OPEN-LOOP CONTROLLER
f*
acceleration
deceleration
f
V
f


Programmable
SVPWM
signal
generator
Interface
Three
phase
VSI
PMSM
Motor
200 ohm 1
2
7407
3
4
200 ohm
5V
5V
DSP 5V
a1
a2
a3
a4
b1
2631
b2
b3
b4
10 ohm
330 ohm
5
2.2K
0.1u
6
0.1u
Vout1
7
8
2110
0.1u
10 ohm
0.1u
10 ohm
GND_5V
DSP
Programmable dead
time generator
Control block diagram
GND_5V
2.2K
GND_5V connects together with GND_28V
Schematic diagram
• Using low impedance MOSFET and high drive
current chip to increase efficiency.
• Optimizing v/f drive scheme.
• Adjusting modulation index and switching
frequency for best performance.
GND_28V
PMSM TESTING
200
Input power to the motor (W)
180
160
140
120
100
80
60
40
20
0
20
40
60
80
100
120
140
160
180
200
Motor speed (krpm)
• Free spin/no-load test.
Testing - Animation
• The data for speed above 130,000 rpm are the
estimated results.
• The projected efficiency at 200,000 rpm with 2000 W
output is around 90% (meets Year 2 goal).
PUBLICATIONS and PATENTS (pending) on Cryocoolers (since September 03)
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
14)
•
•
•
•
“Two-Stage Cryocooler Development for Liquid Hydrogen Systems”, 2003 Space Cryogenics Workshop.
“Design of a Super-High Speed PMSM for Cryocooler Application”, 2003 Space Cryogenics Workshop.
“Mesoscopic Energy Systems”, accepted to be published in Annual Review of Heat Transfer, 2004.
“Development of a Super-High Speed PMSM Controller and Analysis of the Experimental Results”, The Eighth
World Multi-Conference on Systemics, Cybernetics and Informatics, 2004.
“Development of a new V/f Control for a Super-High Speed PMSM”, The Eighth World Multi-Conference on
Systemics, Cybernetics and Informatics, 2004.
“Design and Simulation of a Cryogenic Electrical Motor”, AP-S International Symposium and USNC/URSI
National Radio Science Meeting, 2004.
“Design of a Super-High Speed Cryogenic Permanent Magnet Synchronous Motor”, EPE-PEMC 2004, (Invited
paper: Special section about high and super-high speed motor).
“Design of a Super-High Speed Axial Flux PMSM”, submitted to 2004 IEE Proceedings on Electric Power
Applications.
“Miniature Joule-Thomson (JT) Cryocoolers for Propellant Management”, The 2004 ASME International
Mechanical Engineering Congress and Exposition.
“Numerical Simulation of a Single-Stage Centrifugal Compressor”, abstract submitted to IGTI 05.
“Mechanical Analysis of a High-Speed PMSM”, abstract submitted to IGTI 05.
“A New Design Approach of a Super High-Speed Permanent Magnet Synchronous Motor”, submitted to Journal
of Applied Physics.
“A DSP-Based Super High Speed PMSM Controller Development and Optimization”, accepted by IEEE
DSP2004 (11th Digital Signal Processing Workshop & 3rd Signal Processing Education Workshop).
“Design of An Optimal V/f Control for a Super High Speed Permanent Magnet Synchronous Motor”, accepted
by IEEE IECON 2004 (The 30th Annual Conference of the IEEE Industrial Electronics Society).
Compact, High Speed Centrifugal Compressor with High Efficiency.
Compact, Recuperative Heat Exchanger with High Effectiveness.
Compact, High Speed Permanent Magnet Synchronous Motor with High Energy Density and High Efficiency.
Cryogenic High Speed Motor.
SIGNIFICANT COLLABORATIONS
• Partnered with Rini Technologies, Inc. (Dr. Dan Rini)-development of a miniature heat
recuperator and a 77 K RTBC cryocooler.
• Frequent communication with –
- AFRL (DoD cryocooler needs)
- NIST (Cryocooler needs and space mission requirements)
- NASA KSC (miniature heat recuperator and JT cryocooler)
- NASA GRC, ARC, JPL (NASA cryocooler needs and space mission requirements)
• Collaborated with Heli-Cal, Inc. (Mr. Gary Boehm)-high speed flexible coupler development.
• Communication with NASA GRC (Dr. Christopher Dellacorte)-foil bearing design.
• Collaborated with Electrodynamics Associates, Inc. (Mr. Jay Vaidya)-development of high
speed mesoscale motors.
• Collaborated with UF (Dr. Nagaraj Arakere)-rotordynamic issues in the design of mesoscale
high-speed rotors.
RELATED WORK AND OTHER SOURCES OF FINANCIAL SUPPORT
1. Miniature Joule Thomson Cryocooler, funded by NASA KSC and ASRC, 2002-till date
2. Development of a Compact Heat Recuperator, funded by MDA and AFRL, 2002-till date
3. Development of a 77K Reverse Turbo Brayton Cryocooler, funded by MDA and AFRL,
2003-till date; NASA JSC, 2004-till date
4. Portable Vapor Compression Cooler, funded by Army (Natick, 2002-till date; Edgewood,
2001-till date); NASA JSC, 2004-till date
The above funds include direct contracts to UCF; and SBIR/STTR funds through RTI.
FUTURE PLANS
• To design and develop a one-step (thermodynamic) cycle cryocooler operating
between room temperature and 18 K, and which would be able to remove 20-50 W of
heat at liquid hydrogen temperature and thus meet the project objective.
• To design and develop a two (compression) stage compressor for the above
cryocooler.
• To design and develop a 5.4 kW motor that could spin the above compressor to
313,000 rpm and to consider a fast DSP chip, soft switching and close-loop control to
further improve its performance.
• To design an integrated motor-compressor shaft, and thus eliminate the need for a
difficult-to-do high-speed flexible coupler.
For Project Enhancement (by Dr. Dhere, FSEC):
• To characterize the tribological coatings for the one-step cryocooler and thus reduce
friction and the wear which may occur as we reduce the tip clearance in the compressor
to improve efficiency. In the longer term, if any compliant surface gas bearings are
used, these coatings will minimize the wear and friction and thus reduce bearing losses
significantly and improve reliability. At low temperature, tribological coating is also
needed for the turboexpander.
SINGLE-STEP RTBC
VS.
•
•
•
Pros:
– Simplicity
– Light weight
– Compact
Cons:
– Difficulty in helium compressor
development due to larger pressure
ratio and higher rotational speed
•
TWO-STEP RTBC
Pros:
– System flexibility (neon in top, helium in bottom)
– Ideal for liquid H2/O2 transfer line cooling down
– The two steps of the cycle can be individually
designed for maximum efficiency
– Helium compressor working at cryogenic
temperature (helps to reduce the rotational speed)
Cons:
– System complexity causes extra weight and size
– Coupling of the two steps needs complicated
controller
– Different working fluids cause mixing problems
TWO-STAGE INTERCOOLED MOTOR-COMPRESSOR ASSEMBLY
Features:
Ultra-compact
Low maintenance
Two stage Pr = 2.8
Light weight 10 kg
High efficiency 58%
High speed 313K rpm
Flow rate = 4.6 g/s
GIFFORD McMAHON VS. RTBC CRYOCOOLER COMPARISON
Cryomech G-M Cryocooler AL330
UCF Miniature RTBC Cryocooler
(40W @ 20K)
(20–30W @ 18K)
Motor/Compressor
unit
119-176 kg
The rest of the cryocooler
Cold head
10 kg
The rest of the cryocooler
Heat regenerator,
Flexible lines,
Motor/Compressor
unit
Ceramic micro-channel
heat recuperator,
24 kg
Cold head,
12 kg
Expander/Alternator
Total weight
COP
143-200 kg
Total weight
22 kg
0.005
COP
0.005
PROJECT TIMELINE
Task 1. Design and Fabrication of Miniature Centrifugal Compressor
Task 2. Design of a High-speed, High-efficiency PMSM
Task 3. Miniature Centrifugal Compressor Design Verification by Numerical
Simulation and Testing (with appropriate scaling)
Task 4. Fabrication and Testing of PMSM
Task 5. Two-stage Centrifugal Compressor – Design and Fabrication
Task 6. 5.4 kW PMSM – Design and Fabrication
Task 7. Integration and Preliminary Testing of the Motor/Compressor Assembly
Task 8. Overall System Optimization – Systematic Testing of the Motor/
Compressor Assembly, Evaluation, Possible Design Changes
Start Date: July 01, 2002; Estimated End Date: September 30, 2006; Estimated Duration: 51 months
Months -
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
Task 1
Task 2
Task 3
Task 4
Task 5
Task 6
Task 7
Task 8
YEAR I
YEAR II
YEAR III
YEAR IV
TRL 2
BETWEEN TRL 2 AND TRL 3
BETWEEN TRL 3 AND TRL 4
TRL 4
51