MINIATURE ENGINEERING SYSTEMS GROUP

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MINIATURE ENGINEERING SYSTEMS GROUP

• Two-Stage CryoCooler Development for Liquid
  Hydrogen Systems

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Miniature Engineering Systems GroupCore 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-fabricatio
n and tribology, actuators Dr. Linan An
Polymer-derived ceramic
micro-fabrication Dr. Chan Ham
Control, micro-satellites Dr. K.B. Sundaram
Micro-fabrication, thin film, sensors,
micro- and meso-scale motors and generators Dr.
Tom Wu RF MEMS, miniature
electromagnetic devices Dr. Neelkanth Dhere
Tribological coatings, multilayer thin films,
sensors Dr. Joe Cho
Bio-MEMS, Magnetic MEMS, MOEMS, micro/nano
fabrication, micro fluidics
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Outline of the presentation

• Introduction,
• Compressor design and CFD analysis,
• Development of Gas Foil Bearings,
• Motor design,
• Work in progress,
• Work to be completed by Sep 03,
• Plans for next year.

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Two Stage CryoCoolerNeon RTBC and Helium RTBC
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Thermodynamics schematic
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System Performance

• Top cycle is capable of removing heat at liquid
  Nitrogen temperature with cooling power 1000 W
• 2-stage RTBC cycle is capable of removing heat at
  liquid Hydrogen temperature with cooling power
  50W
• COP 0.007

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Design Features

• Top cycle can work separately as a liquid
  nitrogen cryocooler or it can work with bottom
  cycle as a liquid hydrogen cryocooler.
• State-of-the-art aerodynamics design of the
  2-stage intercooled neon centrifugal compressor
  and the 4-stage intercooled helium centrifugal
  compressor.
• Integrated motor and oil-free non-contact
  bearings for high speed and efficiency.
• Innovative micro-channel high effectiveness heat
  exchanger.

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Schematic of the bottom cycle showing the four
stage Helium compressor
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Single Stage Centrifugal Compressor Development
Motor
Coupler
Compressor
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Single Stage Compressor

• Three of the parts are still to be manufactured.
• Impeller
• Diffuser
• Inlet Guide Vane
• Plastic models have been created showing
  conceptual idea.
• Rest of the compressor and the experimental
  set-up has been constructed.
• Motor and brackets, as well as cooling jacket for
  motor
• Compressor housing and brackets

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Parts not fabricated yet
Impeller
Diffuser
Inlet Guide Vane
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Experimental Set-up
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Future of Compressor Development

• Machine the diffuser and inlet guide vane, and
  cast the impeller.
• Assemble compressor and begin tests at low speeds
  to allow for break-in of bearings.
• Test at maximum design speed of 150,000
  revolutions per minute and collect data.

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CFD SIMULATION OF IGV
Fully Structured 3D Grid (Created in GAMBIT, 330K)
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Reverse flow occurs at outlet of IGV. (Solved by
Fluent 6.0)
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CFD-IGV
CFD simulation results show that pressure loss
through IGV is about 5000 Pa. As expected, IGV
creates an acceptable flow angle at the eye of
impeller. However, certain amount of reverse flow
still exists in spite of careful design. This may
be eliminated by the interaction of IGV and
rotor, which would be simulated in the next
stage. If the flow reversal still persists, IGV
design will be modified by adjusting angle of IGV
vanes.
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DEVELOPMENT OF GAS-FOIL BEARINGS

• Phases
• Pro-art search (gave no favorable result),
• Conceptual Design (of first generation Leaf Foil
  Bearings),
• Modeling and Analysis,
• Detailed design for fabrication and testing.

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SCHEMATIC OF THE CONCEPTUAL DESIGN
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CONCEPTUAL DESIGN CONFIGURATION

• It contains an outer hollow cylinder to which the
  foils are attached.
• An inner hollow cylinder would have long cut
  grooves extending to about 90 of its length
  through which the foils would pass and hold the
  shaft in position during start-up and at stop.
• The outer hollow cylinder can be rotated about
  the shaft center axis of rotation and the
  rotation of which would cause the foils to lose
  contact with the shaft thus making the same
  bearing as Gas Bearing and also as a Gas Foil
  Bearing.

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CONCEPTUAL DESIGNS FOR VARIOUS COMPONENTS
FOLLOWED BY THE ASSEMBLY ?
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EXPLODED VIEW
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Specifications of the Motor
Output Shaft Power 2000W
Shaft Speed 200krpm
Shaft Diameter 14mm
Max. Length 100mm
Max. Outer Diameter 44mm

• The motor efficiency needs to be as high as
  possible.
• Size and weight are also important issues.

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Some Popular Motor Types

• Induction motor (IM) low cost, but low
  efficiency at high speed due to higher iron loss.
• Switched reluctance motor (SRM) high
  reliability, but iron loss is very critical at
  high speed.
• Permanent magnet synchronous motor (PMSM) very
  high efficiency due to no exciting copper loss in
  the rotor. High power density with high energy
  density permanent magnet Nd-Fe-B.
• Brushless DC motor (BLDC) high power density as
  PMSM, but the large harmonics will reduce
  efficiency significantly at high speed.

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Radial Flux PMSM Structure
Shaft
Stator Outer Diameter 30mm Stator Inner
Diameter 23mm Rotor Diameter 14mm PM Width
6mm PM Height 9mm Motor Active Length 70mm
PM
Laminated low loss core
Winding
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Winding Method

• 2-pole, 3-phase.
• 5 coils/phase/pole.
• Two layer lap winding.
• Pitch factor 12/15.
• First coil bottom1?top13.
• Round copper wire AWG14.
• Bare diameter 0.0641in (1.63mm).
• Diameter after insulation 0.0673in (1.71mm).

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Simulated Results
Flux Distribution
FFT
Back EMF
FFT
Simulated torque 0.11N.m and ripple 0.3, when
25A phase current.
Very low harmonics in the air gap flux
distribution and back EMF voltage.
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Efficiency
Copper Loss 48.7W
Iron Loss 8.4W
Estimated Stray Loss 15W
Windage Loss 15W
Motor Efficiency 95.6
Control Efficiency 95
Total Efficiency 90.8
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Work in progress

• Design of shaft/rotor for the system.
• Minor changes to motor design basing on the
  shaft design.

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Work to be completed by Sep03

• One Stage Compressor testing and simulation.
• Design of the four stage helium compressor.
• Motor not integrated with compressor this
  year.
• Gas Foil Bearings Mathematical modeling and
  Analysis with simultaneous focus on tribological
  coatings to be deposited on foils.

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Plans for next year

• Fabrication and testing of the four stage helium
  compressor for the bottom cycle. It would be an
  integrated compressor-motor system.
• Development of the micro-channel high
  effectiveness heat exchanger.