MINIATURE ENGINEERING SYSTEMS GROUP

(http://www.mmae.ucf.edu/~kmkv/mini)

Reverse Turbo Brayton Cycle Reverse Turbo Brayton Cycle CryoCooler Development for CryoCooler Development for

Liquid Hydrogen SystemsLiquid Hydrogen Systems

OBJECTIVEOBJECTIVE ANDAND RELEVANCERELEVANCE

• 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 APPROACHCURRENT APPROACH

Thermodynamic SchematicThermodynamic Schematic- showing the two working cycle steps- showing the two working cycle steps

Mechanical Mechanical SchematicSchematic

- current focus is - current focus is on the on the

development of development of lower step of the lower step of the thermodynamic thermodynamic

cycle cycle (highlighted in (highlighted in

yellow)yellow)

COMMENT FROM MARCH 04 NASA COMMENT FROM MARCH 04 NASA PANELPANEL

• Too many tasks with insufficient resources to meet them !

RESPONSERESPONSEThe project tasks have been narrowed to the The project tasks have been narrowed to the following significant goals –following significant goals –• Compressor development,Compressor development,• Motor development, andMotor development, and• Integration of Compressor and Motor.Integration of Compressor and Motor.The integrated compressor/motor is key to The integrated compressor/motor is key to RTBC, and is useful for many other NASA and RTBC, and is useful for many other NASA and non-NASA applications.non-NASA applications.

The development of foil bearings and heat The development of foil bearings and heat recuperator have been de-scoped from this recuperator have been de-scoped from this project. These areas are being targeted project. These areas are being targeted through other funding agencies/projects.through other funding agencies/projects.

DESIGN AND TEST HELIUM COMPRESSOR WITH DESIGN AND TEST HELIUM COMPRESSOR WITH SIMILARITY PRINCIPLESIMILARITY PRINCIPLE

m

P̂

VariablesSimilarity

tttt

ND

RT

ND

Dp

RTmf

DN

Ppr

,,,

ˆ,,

2

002

00

0053

00

Compressor similarity function:

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.

Single-stage compact helium

compressor Rotating speed Rotating speed (RPM)(RPM)

108108kk

Mass flow rate (g/s)Mass flow rate (g/s) 10.610.6Impeller diameter Impeller diameter (mm)(mm)

4848

Inlet pressure (bar)Inlet pressure (bar) 11Inlet temperature Inlet temperature (K)(K)

300300

Gas constant Gas constant (J/kg*K)(J/kg*K)

286286

Specific heat ratioSpecific heat ratio 1.41.4Pressure ratioPressure ratio 1.551.55Compression power Compression power (W)(W)

823823

Equivalent air test using similarity

principle

Open-loop air test

Performance Variables

Rotating speed Rotating speed (RPM) - (RPM) - NN

313313kk

Mass flow rate (g/s) - Mass flow rate (g/s) - 4.64.6Impeller diameter Impeller diameter (mm) - (mm) - DD

4848

Inlet pressure (bar) – Inlet pressure (bar) – PP0000

22

Inlet temperature (K) Inlet temperature (K) – – TT0000

300300

Gas constant (J/kg*K) Gas constant (J/kg*K) - - RR

20792079

Specific heat ratio - Specific heat ratio - γγ 1.671.67Pressure ratio - Pressure ratio - prprtttt 1.71.7

Compression power Compression power (W) - (W) -

33753375

SINGLE-STAGE COMPACT CENTRIFUGAL HELIUM SINGLE-STAGE COMPACT CENTRIFUGAL HELIUM COMPRESSORCOMPRESSOR

Impeller/

diffuser assemb

ly

Coupler

Motor

Cooling

water

Compressor Collector

-10k 0 10k 20k 30k 40k 50k 60k 70k 80k 90k 100k110k

1.0

1.1

1.2

1.3

1.4

1.5

1.6

Pr

Speed (RPM)

test data test data fitting line design performance design point CFD data

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

2.4 2.6 2.8 3 3.2 3.4

Old Diffuser

Surge Line (OD)

New Diffuser

Surge Line (ND)

ND

OD00

03

P

P

%8.44

KN 108Air,

D)Diffuser(OOldWith

6

00

00

.

10P

Tm

D)Diffuser(NNewWith

%8.69

COMPARISON OF THE COMPRESSOR COMPARISON OF THE COMPRESSOR PERFORMANCE – WITH OD AND NDPERFORMANCE – WITH OD AND ND

OD ND

0. 76 0. 78

0. 83 0. 86

0. 09 0. 75

0. 45 0. 70Diff

Overall

IGV

Imp

OLD DIFFUSER NEW DIFFUSER

PMSM DESIGN AND PMSM DESIGN AND FABRICATIONFABRICATION

• 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 Shaft and casingHollow shaft and permanent

magnet

OPEN-LOOP CONTROLLEROPEN-LOOP CONTROLLER

• Using low impedance MOSFET and Using low impedance MOSFET and high drive current chip to increase high drive current chip to increase efficiency. efficiency.

• Optimizing v/f drive scheme. Optimizing v/f drive scheme. • Adjusting modulation index and Adjusting modulation index and

switching frequency for best switching frequency for best performance.performance.

accelerationdeceleration Programm-

ableSVPWM

signalgenerator

InterfaceThreephase

VSI

Programmable deadtime generator

PMSM

Motor

f * f

f

V

DSP

7407

a11

a22

3a3

4a4

b1

b2

b3

b4

5

6

7

8

26312110

Vout1

5V DSP 5V

0.1u

0.1u

0.1u

330 ohm

0.1u

GND_5V

GND_5V

GND_28VGND_5V connects together with GND_28V

2.2K

2.2K

10 ohm

10 ohm

10 ohm

200 ohm

200 ohm

5V

Control block Control block diagramdiagram

Schematic diagramSchematic diagram

PMSM PMSM TESTINGTESTING

• Free spin/no-load test. Free spin/no-load test. Testing - AnimationTesting - Animation

• The data for speed above 130,000 rpm are the The data for speed above 130,000 rpm are the estimated results. estimated results.

• The projected efficiency at 200,000 rpm with The projected efficiency at 200,000 rpm with 2000 W output is around 90% (meets Year 2 goal).2000 W output is around 90% (meets Year 2 goal).

20 40 60 80 100 120 140 160 180 2000

20

40

60

80

100

120

140

160

180

200

Inp

ut

po

wer

to

th

e m

oto

r (W

)

Motor speed (krpm)

PUBLICATIONSPUBLICATIONS and and PATENTS (pending) PATENTS (pending) on Cryocoolers on Cryocoolers (since September 03)(since September 03)1)1) ““Two-Stage Cryocooler Development for Liquid Hydrogen Systems”, 2003 Space Two-Stage Cryocooler Development for Liquid Hydrogen Systems”, 2003 Space

Cryogenics Workshop.Cryogenics Workshop.2)2) ““Design of a Super-High Speed PMSM for Cryocooler Application”, 2003 Space Design of a Super-High Speed PMSM for Cryocooler Application”, 2003 Space

Cryogenics Workshop.Cryogenics Workshop.3)3) ““Mesoscopic Energy Systems”, accepted to be published in Annual Review of Heat Mesoscopic Energy Systems”, accepted to be published in Annual Review of Heat

Transfer, 2004.Transfer, 2004.4)4) ““Development of a Super-High Speed PMSM Controller and Analysis of the Development of a Super-High Speed PMSM Controller and Analysis of the

Experimental Results”, The Eighth World Multi-Conference on Systemics, Cybernetics Experimental Results”, The Eighth World Multi-Conference on Systemics, Cybernetics and Informatics, 2004.and Informatics, 2004.

5)5) ““Development of a new V/f Control for a Super-High Speed PMSM”, The Eighth World Development of a new V/f Control for a Super-High Speed PMSM”, The Eighth World Multi-Conference on Systemics, Cybernetics and Informatics, 2004.Multi-Conference on Systemics, Cybernetics and Informatics, 2004.

6)6) ““Design and Simulation of a Cryogenic Electrical Motor”, AP-S International Design and Simulation of a Cryogenic Electrical Motor”, AP-S International Symposium and USNC/URSI National Radio Science Meeting, 2004.Symposium and USNC/URSI National Radio Science Meeting, 2004.

7)7) ““Design of a Super-High Speed Cryogenic Permanent Magnet Synchronous Motor”, Design of a Super-High Speed Cryogenic Permanent Magnet Synchronous Motor”, EPE-PEMC 2004, (Invited paper: Special section about high and super-high speed EPE-PEMC 2004, (Invited paper: Special section about high and super-high speed motor).motor).

8)8) ““Design of a Super-High Speed Axial Flux PMSM”, submitted to 2004 IEE Proceedings Design of a Super-High Speed Axial Flux PMSM”, submitted to 2004 IEE Proceedings on Electric Power Applications.on Electric Power Applications.

9)9) ““Miniature Joule-Thomson (JT) Cryocoolers for Propellant Management”, The 2004 Miniature Joule-Thomson (JT) Cryocoolers for Propellant Management”, The 2004 ASME International Mechanical Engineering Congress and Exposition.ASME International Mechanical Engineering Congress and Exposition.

10)10) ““Numerical Simulation of a Single-Stage Centrifugal Compressor”, abstract submitted Numerical Simulation of a Single-Stage Centrifugal Compressor”, abstract submitted to IGTI 05.to IGTI 05.

11)11) ““Mechanical Analysis of a High-Speed PMSM”, abstract submitted to IGTI 05.Mechanical Analysis of a High-Speed PMSM”, abstract submitted to IGTI 05.12)12) ““A New Design Approach of a Super High-Speed Permanent Magnet Synchronous A New Design Approach of a Super High-Speed Permanent Magnet Synchronous

Motor”, submitted to Journal of Applied Physics.Motor”, submitted to Journal of Applied Physics.13)13) ““A DSP-Based Super High Speed PMSM Controller Development and Optimization”, A DSP-Based Super High Speed PMSM Controller Development and Optimization”,

accepted by IEEE DSP2004 (11th Digital Signal Processing Workshop & 3rd Signal accepted by IEEE DSP2004 (11th Digital Signal Processing Workshop & 3rd Signal Processing Education Workshop).Processing Education Workshop).

14)14) ““Design of An Optimal V/f Control for a Super High Speed Permanent Magnet 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 Synchronous Motor”, accepted by IEEE IECON 2004 (The 30th Annual Conference of the IEEE Industrial Electronics Society).the IEEE Industrial Electronics Society).

• Compact, High Speed Centrifugal Compressor with High Efficiency.Compact, High Speed Centrifugal Compressor with High Efficiency.• Compact, Recuperative Heat Exchanger with High Effectiveness.Compact, Recuperative Heat Exchanger with High Effectiveness.• Compact, High Speed Permanent Magnet Synchronous Motor with High Energy Compact, High Speed Permanent Magnet Synchronous Motor with High Energy

Density and High Efficiency.Density and High Efficiency.• Cryogenic High Speed MotorCryogenic High Speed Motor.

• Partnered with Rini Technologies, Inc. (Dr. Dan Rini)-Rini Technologies, Inc. (Dr. Dan Rini)-development of a miniature heat recuperator and a 77 K RTBC cryocooler.• Frequent communication with –

- AFRLAFRL (DoD cryocooler needs)- NIST NIST (Cryocooler needs and space mission requirements)- NASA KSCNASA KSC (miniature heat recuperator and JT cryocooler)- NASA GRC, ARC, JPLNASA GRC, ARC, JPL (NASA cryocooler needs and space

mission requirements)• Collaborated with Heli-Cal, Inc.Heli-Cal, Inc. (Mr. Gary Boehm)(Mr. Gary Boehm)-high speed flexible coupler development.• Communication with NASA GRC (Dr. Christopher Dellacorte)NASA GRC (Dr. Christopher Dellacorte)-foil bearing design.• Collaborated with Electrodynamics Associates, Inc. (Mr. Jay Vaidya)Electrodynamics Associates, Inc. (Mr. Jay Vaidya)--development of high speed mesoscale motors.• Collaborated with UF (Dr. Nagaraj Arakere)-UF (Dr. Nagaraj Arakere)-rotordynamic issues in the design of mesoscale high-speed rotors.

SIGNIFICANT SIGNIFICANT COLLABORATIONSCOLLABORATIONS

RELATED WORK AND OTHER SOURCES OF FINANCIAL SUPPORTRELATED WORK AND OTHER SOURCES OF FINANCIAL SUPPORT1. Miniature Joule Thomson Cryocooler, funded by NASA KSC and

ASRC, 2002-till date2. Development of a Compact Heat Recuperator, funded by MDA and

AFRL, 2002-till date3. Development of a 77K Reverse Turbo Brayton Cryocooler, funded by

MDA and AFRL, 2003-till date; NASA JSC, 2004-till date4. 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 PLANSFUTURE PLANS• To design and develop a one-step (thermodynamic) cycle To design and develop a one-step (thermodynamic) cycle cryocooler operating between room temperature and 18 Kcryocooler 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 compressorTo design and develop a two (compression) stage compressor for the above cryocooler.

• To design and develop a 5.4 kW motorTo 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 shaftTo 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 To characterize the tribological coatings for the one-step cryocoolercryocooler 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. TWO-STEP SINGLE-STEP RTBC VS. TWO-STEP RTBCRTBC

• Pros:Pros:– SimplicitySimplicity– Light weightLight weight– CompactCompact

• Cons:Cons:– Difficulty in helium Difficulty in helium

compressor development compressor development due to larger pressure ratio due to larger pressure ratio and higher rotational speedand higher rotational speed

• Pros:Pros:– System flexibility (neon in top, helium in System flexibility (neon in top, helium in

bottom)bottom)

– Ideal for liquid HIdeal for liquid H22/O/O22 transfer line cooling down transfer line cooling down

– The two steps of the cycle can be individually The two steps of the cycle can be individually designed for maximum efficiencydesigned for maximum efficiency

– Helium compressor working at cryogenic Helium compressor working at cryogenic temperature (helps to reduce the rotational temperature (helps to reduce the rotational speed)speed)

• Cons:Cons:– System complexity causes extra weight and System complexity causes extra weight and

sizesize– Coupling of the two steps needs complicated Coupling of the two steps needs complicated

controllercontroller– Different working fluids cause mixing problemsDifferent working fluids cause mixing problems

TWO-STAGE INTERCOOLED MOTOR-COMPRESSOR TWO-STAGE INTERCOOLED MOTOR-COMPRESSOR ASSEMBLYASSEMBLY

Ultra-Ultra-compactcompact

Light weight Light weight 10 kg10 kg

High speed 313K High speed 313K rpmrpm

Low Low maintenancemaintenance

Two stage Pr = Two stage Pr = 2.82.8

High efficiency High efficiency 58%58%

Flow rate = Flow rate = 4.6 g/s4.6 g/s

Features:Features:

GIFFORD McMAHON VS. RTBC CRYOCOOLER GIFFORD McMAHON VS. RTBC CRYOCOOLER COMPARISONCOMPARISON

Motor/Compressor unit

Heat regenerator,

Flexible lines,

Cold head

Cryomech G-M Cryocooler Cryomech G-M Cryocooler AL330AL330

(40W @ 20K)(40W @ 20K)

UCF Miniature RTBC UCF Miniature RTBC CryocoolerCryocooler

(20–30W @ 18K)(20–30W @ 18K)

The rest of the cryocooler

Motor/Compressor unit

Ceramic micro-channel heat recuperator,

Cold head,

Expander/Alternator

119-176 kg

24 kg

10 kg

12 kg

The rest of the cryocooler

143-200 kg

22 kgTotal weight Total weight

COP 0.005 COP 0.005

PROJECT TIMELINEPROJECT TIMELINE

Task 1. Design and Fabrication of Miniature Centrifugal CompressorTask 1. Design and Fabrication of Miniature Centrifugal CompressorTask 2. Design of a High-speed, High-efficiency PMSMTask 2. Design of a High-speed, High-efficiency PMSMTask 3. Miniature Centrifugal Compressor Design Verification by Task 3. Miniature Centrifugal Compressor Design Verification by Numerical Simulation and Testing (with appropriate scaling)Numerical Simulation and Testing (with appropriate scaling)Task 4. Fabrication and Testing of PMSMTask 4. Fabrication and Testing of PMSMTask 5. Two-stage Centrifugal Compressor – Design and FabricationTask 5. Two-stage Centrifugal Compressor – Design and FabricationTask 6. 5.4 kW PMSM – Design and FabricationTask 6. 5.4 kW PMSM – Design and FabricationTask 7. Integration and Preliminary Testing of the Motor/Compressor Task 7. Integration and Preliminary Testing of the Motor/Compressor AssemblyAssemblyTask 8. Overall System Optimization – Systematic Testing of the Task 8. Overall System Optimization – Systematic Testing of the Motor/ Compressor Assembly, Evaluation, Possible Design ChangesMotor/ Compressor Assembly, Evaluation, Possible Design Changes

Start Date: July 01, 2002; Estimated End Date: September 30, 2006; Estimated Start Date: July 01, 2002; Estimated End Date: September 30, 2006; Estimated Duration: 51 monthsDuration: 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 51

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