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MINIATURE ENGINEERING SYSTEMS GROUP. 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

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Miniature engineering systems group


Two-Stage CryoCooler Development for Liquid Hydrogen Systems

Miniature engineering systems group core group of faculty
Miniature Engineering Systems GroupCore Group of Faculty

Dr. Louis ChowDirector

System design, spray cooling, thermal management, thermalfluids design/experiment,thermodynamics

Dr. Jay KapatCo-Director

System design, design of turbo machinery, heat transfer and fluidic components, component and system testing

Dr. Quinn ChenAssociate Director for Educational Programs

Micro-fabrication 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

Outline of the presentation
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.

Two stage cryocooler neon rtbc and helium rtbc
Two Stage CryoCoolerNeon RTBC and Helium RTBC

System performance
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

Design features
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.

Schematic of the bottom cycle showing the four stage helium compressor
Schematic of the bottom cycle showing the four stage Helium compressor

Single stage compressor
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

Miniature engineering systems group

Parts not fabricated yet…



Inlet Guide Vane

Future of compressor development
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.

Miniature engineering systems group


Fully Structured 3D Grid

(Created in GAMBIT, 330K)

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.

Miniature engineering systems group




  • Pro-art search (gave no favorable result),

  • Conceptual Design (of first generation Leaf Foil Bearings),

  • Modeling and Analysis,

  • Detailed design for fabrication and testing.

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’.

Miniature engineering systems group


Specifications of the motor
Specifications of the Motor ASSEMBLY

  • The motor efficiency needs to be as high as possible.

  • Size and weight are also important issues.

Some popular motor types
Some Popular Motor Types ASSEMBLY

  • 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.

Radial flux pmsm structure
Radial Flux PMSM Structure ASSEMBLY


Stator Outer Diameter = 30mm

Stator Inner Diameter = 23mm

Rotor Diameter = 14mm

PM Width = 6mm

PM Height = 9mm

Motor Active Length = 70mm



Laminated low loss core

Winding method
Winding Method ASSEMBLY

  • 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).

Simulated results
Simulated Results ASSEMBLY

Flux Distribution


Back EMF


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.

Efficiency ASSEMBLY

Work in progress
Work in progress ASSEMBLY

  • Design of shaft/rotor for the system.

  • Minor changes to motor design basing on the shaft design.

Work to be completed by sep 03
Work ASSEMBLY to be completed by Sep’03

  • 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.

Plans for next year
Plans for next year ASSEMBLY

  • 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.