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
System design, spray cooling, thermal management, thermalfluids 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
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.
Approach and Innovation
 Two Stage Reverse Turbo Brayton Cycle (RTBC) CryoCooler
reliable, efficient, compact and light weight
RTBC 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, endwall 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.
Efforts in Alternative Funding Sources
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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 presolicitation 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.
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.
Performance Comparison –
Quantifiable Research Results
Component Performance Commercially Short term Long term
characteristic
available
goal
goal
Compressor
(mesoscale)
Efficiency
35%
(Creare)
45%
75%
Motor
Speed
150,000
200,000
200,000
(rpm)
(Koford Motors)
Efficiency
30%
60%
96%
Performance Comparison –
Quantifiable Research Results
Component
Performance
characteristic
Commercially
available
Short term goal
Long term
goal
Controller
Efficiency
80%
60%
95 %
Effectiveness
98%
95%
99%
Size
(Length)
67 cm
(Creare Inc,.)
8 cm
< 8 cm
Heat
Exchanger
Performance Comparison –
Quantifiable Research Results
Component
Performance
characteristics
Commercially
Available
Short Term goal
Hardness
DLC (40 GPa)
TiN (25 GPa)
Long Term
Goal
TiN (20-25 GPa)
Tribological
Coatings
Coefficient of
Friction (COF)
DLC
COF
At Room Temp
0.1-0.15
At 770K LN2
0.24-0.48
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
Nitrides
At Room Temp
TiN (< 0.1)
At 770K LN2
ZrN (0.4-0.8)
COF
< 0.15
at 770K LN2
and
finally
satisfactory
operation in
the
Cryocooler
Overall System
Thermodynamic Schematic
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.
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’.
Tribological Coatings
Future Research
 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.
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.