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MINIATURE ENGINEERING SYSTEMS GROUP (http://www.mmae.ucf.edu/~kmkv/mini). Two-Stage CryoCooler Development for Liquid Hydrogen Systems. Miniature Engineering Systems Group Core Group of Faculty. Dr. Louis Chow Director - PowerPoint PPT Presentation
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MINIATURE ENGINEERING SYSTEMS GROUP
(http://www.mmae.ucf.edu/~kmkv/mini)
Two-Stage CryoCooler Development for Liquid Hydrogen
Systems
2
Miniature Engineering Systems GroupCore Group of Faculty
Dr. Louis Chow Director System design, spray cooling, thermal management, thermal fluids design/ experiment, thermodynamics
Dr. Jay Kapat Co-Director System design, design of turbo machinery, heat transfer and fluidic components, component and system testing
Dr. Quinn Chen Associate Director for Educational Programs Micro-fabrication and tribology, actuators
Dr. Linan An Polymer-derived ceramic micro-fabrication
Dr. Joe Cho Bio-MEMS, Magnetic MEMS, MOEMS, micro/nano fabrication, micro fluidics
Dr. Neelkanth Dhere Tribological coatings, multilayer thin films, sensors
Dr. Chan Ham Control, micro-satellites
Dr. K.B. Sundaram Micro-fabrication, thin film, sensors, micro- and meso-scale motors and generators
Dr. Abraham Wang Vibration and control, health monitoring, piezoelectric materials, shape memory alloy
Dr. Tom Wu RF MEMS, miniature electromagnetic devices
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Motivation and Objective Storage of cryogenic propellants (LH2 and LOX) for extended
periods have become increasingly important within NASA. There would be loss of propellants in storage tanks as well as in transfer lines both in space and ground applications due to heat leak.
The objective of this project is to design and build a cryocooler, which is capable of removing 50W of heat at liquid hydrogen temperature and thus contribute to NASA efforts on ZBO storage of cryogenic propellants and to attain extremely high hardness, extremely low coefficient of friction, and high durability at temperatures lower than 60 K for the tribological coatings to be used for this cryocooler.
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Approach and Innovation
Two Stage Reverse Turbo Brayton Cycle (RTBC) CryoCoolerreliable, efficient, compact and light weightRTBC bottom stage with He as the working fluid (immediate goal)RTBC top stage with Ne as the working fluid
Key Enabling / Innovative Features for the bottom stage:Compressor – Four stage centrifugal compressor with very high efficiency in its class. Design incorporates intercooling, inlet guide vanes, deswirler vanes, end wall contouring, axial diffuser at the exit integrated with after- or inter-cooler. Motor – The motor would be a high speed three phase PMSM with a magnet integrated rotor and high frequency soft switching control system.Recuperative heat exchanger for regeneration –Non-conventional design for reduction of axial or parasitic heat conduction, massively parallel design with micro-channels and special manifolds for ultra-high effectiveness, low pressure drop and uniform flow distribution.Gas foil bearings – Completely hydrodynamic gas foil bearings for both radial and axial support - key in minimizing losses associated with the compressor and the motor.Tribological coatings – Extremely hard coatings of titanium nitride (TiN), bilayer coatings of TiN and molybdenum disulphide (MoS2), diamond-like-carbon (DLC) coatings, bilayer coatings of DLC/MoS2 for low values of coefficient of friction at cryogenic temperatures.
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Overall Project Outline At A Glance
FY01-03 (15 months): Design: system/cycle, motor, 4-stage compressor, gas foil bearings (GFB) Fab/testing: 1-stage compressor, coatingFY03-04 (12 months): Design: 4-stage compressor1, Rotor system, GFB2
Fab/testing: Motor, Recuperative heat exchanger3, coatingFY04-05 (12 months): Fab/testing: 4-stage comp., other HXs, turbo-expander4, GFB w/coatingsFY05-06 (12 months): Integration and system testing
Notes:
1. This will be based on continued testing and optimization of the 1-stage compressor, which will be funded through an MDA/AFRL SBIR project awarded to Rini Technologies (RTI, our partner). This effort will be further helped if RTI wins another SBIR contract from NASA MFC in the Sep03 cycle.
2. We expect our partner Electrodynamics Associates to win an NASA GRC SBIR funds on LH2-cooled hyper-conducting motor with gas foil bearings. These funds will help in our efforts on GFB.
3. This effort is helped by (a) existing NASA KSC funds for a compact JT-system for in-line ZBO/pre-chilling/densification, (b) MDA/AFRL SBIR funds received by RTI on MEMS recuperative heat exchanger. This effort would be further helped if (c) RTI wins another SBIR from NASA GSFC on this topic in the Sep03 cycle.
4. This effort would be possible (a) through collaboration with Elliott Energy Systems (Stuart, FL) through scaling of their micro-turbines, and (b) potentially also through an SBIR from NASA KSC that RTI is competing on in the Sep03 cycle.
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Efforts in Alternative Funding Sources NASA KSC – Miniature Joule Thomson (JT) CryoCoolers for Propellant Management
(funded). KSC Partners: Bill Notardonato and George Haddad. Defense Advance Research Projects Agency (DARPA) – We have been invited to the pre-
solicitation workshop on micro cryocoolers. Communicating with potential team members and planning a proposal. Also, inviting Dr. Ray Radebaugh and Dr. Marty Nisenoff (leading, world-renowned experts in cryocoolers) to UCF campus for this DARPA proposal and ongoing projects.
Harris Corporation – We have reciprocal visits for possible joint proposals to DoD. Technology Associates, Inc. (based in Boulder, CO) – They have recently opened a branch
in UCF research park in order to collaborate with us, and have provided UCF subcontracts on multiple of their DoD/NASA contracts on MEMS cryocoolers.
Rini Technologies, Inc. – partner on this project and several DoD SBIR projects on miniature cryocoolers.
Lockheed Martin Missiles and Fire Control (LMMFC) – They have provided initial funding for miniature coolers. We are currently exploring opportunities of mutual interests. Their engineers are on this project time as part-time graduate students.
Proposal for collaboration in materials research in the areas of ultra-low friction (COF<0.01) of MoS2 and carbon-based coatings with European Research Institutes from National Science Foundation is being solicited. Preparing to submit.
Proposal on Threat Control submitted to DTRA in January 2003, which included miniature cryocoolers for sensors for nuclear treaty verification. Communicating with DTRA.
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Important Parameters to Measure Performance
Performance of the two stage cryocooler (with emphasis on performance of the bottom stage) – COP, weight and size. Compressor performance – weight, size, efficiency.Heat exchanger performance – effectiveness, size,
pressure drop, and weight. Motor performance – speed, weight, size, efficiency. Motor control system performance – switching frequency, efficiency. Gas foil bearings – load bearing capacity, wear during
start and stop, dynamic stability. Performance of tribological coatings – coefficient of
friction, hardness, wear resistance and durability at cryogenic temperatures.
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Performance Comparison – Quantifiable Research
Results
Component Performance characteristic
Commercially available
Short term goal
Long term goal
Motor Speed(rpm)
Efficiency
150,000(Koford Motors)
30%
200,000
60%
200,000
96%
Compressor
(mesoscale)
Efficiency 35%
(Creare)
45% 75%
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Performance Comparison – Quantifiable Research Results
Component Performance characteristic
Commercially available
Short term goal Long term goal
Heat
Exchanger
Effectiveness
Size
(Length)
98%
67 cm
(Creare Inc,.)
95%
8 cm
99%
< 8 cm
Controller Efficiency 80% 60% 95 %
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Component Performance characteristics
Commercially Available
Achieved to date all at RT
Long Term Goal
Tribological Coatings
Hardness DLC (40 GPa) TiN (25 GPa)
COF < 0.15
at 770K LN2 and
finally satisfactory operation in
the Cryocooler
TiN (20-25 GPa)
Coefficient of Friction (COF) DLC
0.1-0.15 COF
At Room Temp TiN=0.143
TiN/MoS2 on Glass = 0.05-0.1
TiN/ MoS2 on Al
= 0.12-0.18
TiN/ MoS2 on Si wafer = 0.045
At 770K LN2 0.24-0.48
Nitrides
At Room Temp TiN (< 0.1)
At 770K LN2 ZrN (0.4-0.8)
Performance Comparison – Quantifiable Research
Results
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Overall System
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Thermodynamic Schematic
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Single Stage Centrifugal Compressor
Purpose:
As the four stage compressor is very difficult to be designed, fabricated and tested, and
since a number of innovations are planned for size where no data is available in literature,
we design, fabricate and test a single stage compressor representing one of the four stages of the proposed four stage compressor
in order to obtain initial results and to generate a database for future design optimization of the four stage compressor.
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Design of a Single Stage Compressor
inlet guide vanes
impeller blades
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flow inlet
Inlet guide vanes Contoured
endwall
Full blades and splitter blades
Vaned, axial diffuser with multiple vane segments
flow exit
List of Innovations
16
Compressor Assembly Animation
This animation represents the assembly of the compressor housing containing the internal parts, coupled with the motor.
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Fabrication
Rapid PrototypingStereo lithography models used for visualization and fit.
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Fabrication
Manufacturing Impeller cast from A356
Aluminum.4-axis CNC machining of
diffuser and inlet guide vane.
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Rotor Balancing
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Testing
Measurement InstrumentationThermocouples for
temperature measurements.
Pressure transducers for pressure measurements.
Mass flow meter for flow rate measurements.
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Testing Performance Instrumentation
Digital Multimeter for power measurements.Oscilloscope for motor speed measurements.
22
Sliding Mesh - Grid
1. Most accurate method – unsteady fluid field gives interaction between igv-rotor-stator.
2. More computationally demanding.
23
Mixing Plane-Grid
1. Steady state solution – losing interaction between stator and rotor.
2. Cost effective.
24
Solution for IGV
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Preliminary Results from Impeller Flow Simulation
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Preliminary Mechanical Design of 4-stage Helium
Compressor
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Four Stage Compressor – Assembly Structure
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Four Stage Compressor – Rotating Part
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Compressor Future Work
To continue with the single stage compressor simulation and testing and to verify its design.
To integrate the single stage compressor into a four stage centrifugal helium compressor for the bottom cycle.
To design and check the fabrication feasibility of the four stage compressor.
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Permanent Magnet Synchronous Motor
Specifications
Output Shaft Power 2000 W
Shaft Speed 200,000 rpm
Shaft Diameter 16 mm
Max. Length 100 mm
Max. Outer Diameter 44 mm
Supply DC Voltage 28 V
Efficiency > 90 %
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Challenge
In the motor design, high speed will Increase core loss in the rotor and stator. Increase copper loss in the winding due to increased eddy
current loss. Increase bearing loss. Increase mechanical stress in the shaft.
In the motor control, high speed will Increase switching loss due to increased sampling frequency.Need sensorless control due to the unavailability of the
commercial position sensor at such a high speed.
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PMSM Configuration
3-phase, 2-pole
Slotless design
Rectangular Litz-wire
Laminated low loss stator core
Active length: 25.4 mm
Stator outer diameter: 38 mm
Winding pitch: 10/15
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Shaft Profile
Shaft will not fail under:
Bending stress
Shear stress
Shaft whirl
Operational speed is above the 1st critical speed.
Dynamic deflection at first critical speed :
0.361mm < 0.5mm (gap)
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Shaft Centrifugal Stress
Maximum Stress developed:
1210 MPa < 1700 MPa (Yield Strength of the Titanium based alloy)
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Air Gap Flux Density and Torque
Low harmonics of the normal flux density.
Tangent flux density is due to large airgap.
Torque is simulated with 60.8 A phase current (back EMF: 12 V).
0.0000 0.0001 0.0002 0.0003 0.0004-0.12
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
Torq
ue (N
.m)
Time (s)
1.5% ripple
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Major Task & Achievements in Control Design
Task: Design of reliable and efficient 3 phase, 2 pole 200krpm motor
controller with 10% speed margin. 95% efficiency of the control electronics (without LPF).
Achievements: Currently achieved 164 krpm.
82 krpm for a 100 krpm sample motor, which is equivalent to 164 krpm for the 200 krpm motor.
This speed limitation is mainly resulted from the insufficient capability of the sample motor.
80% efficiency of the control electronics including a LPF (89% without the LPF).
Tests on the efficiency, power factor, harmonics and the LPF.
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Controller Hardware and Software
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PMSM Loss
Copper loss 16.9 W
Shaft eddy loss 20 W
Iron loss 10.4 W
Bearing loss 10 W
Filters loss 11 W
Windage loss 12.8 W
Total loss 81.1W
%96)1.812000(2000 m
%95c%91 mc
Motor Efficiency:
Control Efficiency:
Total Efficiency:
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Permanent Magnet Synchronous Motor
Ongoing Research & Future Work
Performing dynamic simulation of the shaft. Fabricating and testing of a test-motor with
ball bearings. Designing of a controller for the new motor. Enhancing the efficiency by improving the
PWM and the LPF designs. Realizing the ‘close loop control’.
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Gas Foil BearingsConfiguration
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Gas Foil BearingsDimensions and Present
Analysis
Journal bearing outer diameter = 43 mm
Journal bearing inner diameter = 33 mm
Inner hollow cylinder thickness = 1 mm
Inner hollow cylinder axial length = 7 mm
Foil axial length = 6 mm
Gap between inner hollow cylinder and shaft = 5 mm
Present Analysis:
To determine the minimum shaft rotational speed at which
the foils lift-off and the shaft is completely air borne.
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Gas Foil BearingsSection under consideration for present analysis
43
Section meshed in Gambit
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To develop tribological coatings: Attain extremely high hardness, extremely low coefficient of
friction, and high durability at temperatures lower than 60 K.
Hard coatings at cryogenic temperature: Coatings such as diamond-like-carbon (DLC) and nitrides of
high-melting metals (e.g. TiN, ZrN) have coefficient of friction < 0.1 at room temperature but much higher values at cryogenic temperatures
A special cryogenic tribometer is required for study of friction and wear at cryogenic temperatures.
Tribological CoatingsObjective
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SampleID
N2 : ArRatio
Atomic PercentN : Ti
AverageHardness
AverageElastic
Modulus(GPa)
GPa HV(Kgf/mm2)
1 0.5: 6 N :Ti = 50.3:49.7 9.32 878.47 144.20
2 0.5 : 4 N :Ti = 53.05:46.95 ----- ----- -----
3 1: 4 N :Ti = 52:48 16.62 1567.02 200.21
Good adhesion, thickness uniformity and stoichiometry of TiN and MoS2 coatings on glass and aluminum substrates verified by peel test, Dektak Profilometry and energy dispersive spectroscopy (EDS).
TiN micro hardness measurements results:
HV –Vicker’s Hardness
TiN and MoS2 bilayers on Si wafer, glass and aluminum are prepared.
Expected excellent coefficient of friction (COF) and wear resistance.
TiN by DC and MoS2 by RF Magnetron Sputtering
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TiN Coating – Aluminum and Steel Substrates
Trial Run
Coefficient of Friction
Load (g) Average
Friction
1 0.15 27.4
0.1432 0.14 27.4
3 0.14 27.4
Fully reacted characteristic golden color.All trials run at 42 rpm at RT.Average COF for TiN/Al coating substrate =
0.143 TiN/MoS2 for friction measurement at USF.TiN for friction measurement at USF.
47
TiN and MoS2 broad peaks indicate nanocrystalline nature of sample.
XRD Plot - MoS2 Coating on Glass
0
20
40
60
80
100
120
0 10 20 30 40 50 60 70
2 Theta (Degrees)
Inte
ns
ity
(C
ou
nts
) (006)
X-ray Diffraction – MoS2 and TiN
XRD Plot - TiN Coating on Glass
0
20
40
60
80
100
120
140
30 35 40 45 50 55 60 65 70 75 80
2 Theta (Degrees)
Inte
ns
ity
(C
ou
nts
)
(111)
(200)
(311)
48
Scanning Electron Microscopy
- TiN and MoS2
Nanocrystalline Grains (average grain size less than 100 nm) of TiN is observed. EDS analysis have shown good stoichiometric ratio of Ti and N (Atomic Percent N : Ti = 52.91 : 47.09).
TiN MoS2
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TiN / MoS2 - Si Wafer
Coefficient of friction tests at UCF with the assistance of Dr. Chen and his colleagues requires deposition of TiN/MoS2 coating on bumps prepared by photolithography technique and also on plain Si wafer (1 cm2) to minimize the contact area between two rubbing samples and thereby providing more accurate coefficient of friction measurements.
TiN/MoS2 Sample
Si Sample with TiN /MoS2 film on bump
Bumps
SlidingForce
SlidingForce
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Friction Test [1N Normal Load ]
0
0.05
0.1
0.15
0.2
1 21 41 61 81 101 121 141 161 181
Time (Sec)
Co
effi
cien
t o
f F
rict
ion
Friction Test – Si Wafer
Average coefficient of friction for the TiN/MoS2 Bilayer
coating on Si wafer with 1 N normal load was = 0.045.
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Microwave assisted chemical vapor deposition (MWCVD) system has been installed.
Initial deposition and characterization of diamond-like-carbon (DLC) coatings being carried out.
Microwave CVD System
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Tribological Coatings Research Progress
Literature values for coefficient of friction (COF)
Hard Coating COF COF - 770K LN2 Hardness Wear Resistance
DLC 0.1-0.15 0.24-0.48 40 GPa Good
Nitrides Less than 0.1 (TiN) 0.4-0.8 (ZrN) 20-25 GPa Good
Current results obtained for this project better than state of art
Substrate roughness is an important criteria for COF
Tribological Coating Coating Pair Substrate COF Hardness
TiN Steel Aluminum 0.143 25 GPa
TiN / MoS2 TiN / MoS2 Si Wafer 0.045 -
TiN / MoS2 TiN Glass 0.05-0.1 -
TiN / MoS2 TiN Aluminum 0.12-0.18 -
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Deposition parameters for TiN, MoS2 and TiN+MoS2 Bilayer coatings on glass, Si wafer and aluminum substrates have been optimized.
Micro hardness and coefficient of friction for TiN on aluminum substrate comparable or better than state-of-art have been obtained.
Bilayer coatings expected to provide values comparable to RT at cryogenic temperatures.
Microwave assisted chemical vapor deposition (MWCVD) system has been installed.
Initial deposition and characterization of diamond-like-carbon (DLC) coatings is being carried out.
Tribological Coatings
Conclusion
54
Cryogenic temperatures degrade tribological properties.
However, hydrogen improves lubrication.
TiN and DLC provides good hardness and low friction.
Improved tribological properties expected for TiN/MoS2 and DLC/MoS2 bilayers at cryogenic temperatures.
Basic understanding of the role of hydrogen and effect of cryogenic temperatures on tribological properties.
Ultra-low COF (< 0.01 at RT) MoS2 coating study in collaboration with Dr. Martin, France.
Tribological CoatingsFuture Research
55
Next Year Work for the Project
To continue with the single stage compressor simulation and testing and to verify its design.
To design and check the fabrication feasibility of the four stage compressor.
To fabricate and test the permanent magnet synchronous motor.
To design and check the fabrication feasibility of high effectiveness micro channel heat exchanger.
To design and develop gas foil bearings for the overall system.
To achieve values of COF for the tribological coatings comparable to RT at cryogenic temperatures and finally satisfactory operation in the cryocooler.