Doctoral Degree Defense Defender: Lei Zhou Advisor: Dr. Louis C. Chow Dr. Jay Kapat Committee members: Dr. Louis C. Chow; Dr. Jay Kapat; Dr. Q. Chen; Dr. R. Chen; Dr. Larry Andrew Department of MMAE University of Central Florida NOV 10 th ,2003 A MINIATURE REVERSE-BRAYTON CYCLE CRYOCOOLER AND ITS KEY COMPONENTS: HIGH EFFECTIVENESS HEAT RECUPERATOR AND MINIATURE CENTRIFUGAL COMPRESSOR
Doctoral Degree Defense. A MINIATURE REVERSE-BRAYTON CYCLE CRYOCOOLER AND ITS KEY COMPONENTS: HIGH EFFECTIVENESS HEAT RECUPERATOR AND MINIATURE CENTRIFUGAL COMPRESSOR. Defender: Lei Zhou Advisor: Dr. Louis C. Chow Dr. Jay Kapat - PowerPoint PPT Presentation
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Doctoral Degree Defense
Defender: Lei ZhouAdvisor: Dr. Louis C. Chow
Dr. Jay KapatCommittee members: Dr. Louis C. Chow; Dr. Jay Kapat; Dr. Q.
Chen; Dr. R. Chen; Dr. Larry AndrewDepartment of MMAE
University of Central FloridaNOV 10th,2003
A MINIATURE REVERSE-BRAYTON CYCLE CRYOCOOLER AND ITS KEY COMPONENTS: HIGH EFFECTIVENESS HEAT RECUPERATOR
AND MINIATURE CENTRIFUGAL COMPRESSOR
Research Background
• Applications– Oxygen/Nitrogen liquefaction– Infrared image sensor array– Electronic device cooling– Out space exploration– HTS (High temperature superconductor) cooling
General refrigeration cycle
H eat re jection Q hto am bient at T h
H eat absorption
Q c watts at T c
Fluid expansionto reduce
tem perature
W ork done onprocess flu id
Power in v iacom pressoror drive unit
Q H X
H TS load at ~T c
ch
cCarnot TT
T
Carnotideal
1COP
)3.01.0(
COPCOP ideal
real
General COPOPERATING
TEMPERATURE CARNOT
COP (Watt Input per Watt
Lifted)
"TYPICAL" COP FOR >100 WATT HEAT LOADS
(Watt Input at 300 K per
Watt Lifted at Top) 273 K 0.11 ~ 0.4
200 K 0.52 ~ 2 150 K 1.01 ~ 4 100 K 2.03 ~ 8-10 77 K 2.94 ~ 12-20 50 K 5.06 ~ 25-35 40 K 6.58 ~ 35-50 30 K 9.10 ~ 50-75
Thermal efficiency analysis of miniature reverse-Brayton cycle(2)
1.5 2.0 2.5 3.0 3.5 4.00.235
0.240
0.245
0.250
0.255
0.260
0.265
0.270
0.275
0.280
COP
CO
P
Delta T (K)
Thermal efficiency analysis of miniature reverse-Brayton cycle(3)
0.60 0.65 0.70 0.75 0.80 0.85 0.90
0.10
0.15
0.20
0.25
0.30
COP
CO
P
Ec,Et
Result of thermal efficiency analysis:system parameters
2
turbine
6
generator compressor
motor
Heat exhausted=261W
Cooling Load=20W
1
34
5Heat regenerator
COP=0.083
Eff=0.993
T1=64K
T5=300.2K
T6=76.0K
T2=74.4K
T3=299.5K
T4=440K
Pmotor=262W
Pressure ratio=1.75
Mass flow rate=2.81g/s
Micro-channel heat recuperator
s
d
dw
L
Insulated surface
Thot,in
Tcold,in
Hot end Cold end
Stacked multi-layer construction
Physical model
Cold Neon
Hot Neon
d
d
wY
X
Z
0)]()([4
0)]}()([)]()([{
0)]()([4
2
2
xTxTdx
Tcm
xTxTxTxTdx
TkA
xTxTdx
Tcm
whhh
p
hhccw
sw
wccc
p
30PrRe
nk
dUCpPe
Numerical Model (1-D)
Hot gas node
Cold gas node
Wall
Interface
HjHj+1
Cj Cj+1
Wj Wj+1WtMetal
Material
Insulation material
Hot fluid
Cold fluid
Numerical simulation for single material
Fig.5 axial heat conduction in wall
0.000 0.005 0.010 0.015 0.02080
100
120
140
160
180
200
220
240
260
hot duct wall cold duct
Tem
pera
ture
(K)
Length (m)
20 40 60 80 100 1202
3
4
5
6
7
8
9
10
dT
cold
end t
em
pera
ture
diffe
rence
dT
(K)
Length L (mm)
dt VS. Length (total temperature different =220K)
L
dU
L
m
kNuL
TCpmdT
n
2
4
1-D Numerical for two material
Comparison of heat conductivity
Comparison of single material and two materials
Configuration 1+1 (1mm) 10+10 (10mm) 40+40 (40mm)
T(K)3 30 120
SiO20.377 0.848 0.853
Metal0.4005 0.5333 0.6198
Alternative Insulator/Metal
0.4003 0.937 0.991
Conclusion of micro-channel heat recuperator design
• 1-D numerical simulation is suitable for the performance estimation of the micro-channel heat recuperator
• With proper parameter selection, the micro-channel heat recuperator can achieve 0.99 effectiveness at an acceptable pressure loss
• For the reason of manufacturing, this heat recuperator may be constructed as many thin layers stacked together. It provides the possibility of two materials (one have high heat conductivity and another have very low heat conductivity) stacked alternatively to provide 0.99 effectiveness.
• This simulation provides the guidance to select the material to manufacture the heat recuperator. LTCC may be a good candidate due to its low heat conductivity and high solidity after cured.
Centrifugal compressor design• Advantages of single stage centrifugal compressor
– Simplicity: only 1 moving part– Reliability (better than reciprocating compressor)– Possible high efficiency– No vibration: high revolution speed (>>100 kRPM)– Compact
• Disadvantages:– Difficult design: complicated flow field– Relatively expensive: manufacturing rows of blades in
#: 3-D simulation results is provided by Xiaoyi Li
3-D results
3-D results
CFD results
Flow Separation inertia force and centrifugal force
Suggestion reduce the length of IGV add deswirl vane
Conclusion of compressor design
• 2-zone model is the most powerful 1-D design tool in centrifugal compressor design. With proper mathematics and interactive program codes, 3-D geometry can be designed and then implemented with pro/engineering software
• 3-D CFD simulation show the improvements should be done in next design. Mixed flow impeller with axial diffuser may have severe flow separation problem at the bending section. A deswirl vane is needed before this section
• Impeller may need to be refined with inducer to reduce entrance separation.
Testing conclusion• Straight Blade Impeller more effective than Curved Blade Impeller
• In order to run at full speed, an integrated Motor/compressor design is needed
• Compressor was on way to design conditions
– Pressure ratio of 1.7 at Operating speed of 150,000 rpm
– Mass flow rate of 4-8 grams per second
• Reduce losses
– Improve alignment
• Implement laser aligning procedures
• Introduce rigid coupler
• Incorporate one shaft throughout the assembly
– Incorporate air foil bearing / air journal bearing
• Only if power consumption remains high
CONCLUSIONS
• Miniature RTBC which can provide middle cooling power (1-20 Watt at 77K) may have high efficiency and small footprint.Its unique features including reliability, vibration free and low maintenance may have promising applications
• Its key components, including 0.99 effectiveness micro heat recuperator and meso-scale centrifugal compressor and related bearing technologies are key enabling technologies which can make it have good COP comparing to other competing cryogenic systems.
• The design of micro-scale heat recuperator and compressor is on the way to successful which provide solid evidence to the success of miniature RTBC technology