Sascha Schediwy [email protected]
Aperture Array LNA CoolingAperture Array LNA Cooling
Presentation Overview:
1 – Aperture Array Review 2-PAD
2 – LNA Cooling Costing Model physics and features results
3 – LNA Cooling Measurement description results
Presentation Overview
Is it economically viable (or even physically possible) to cool the tens of thousands of front-
end LNAs used in an SKA aperture array station?
(How best not to cool an LNA!)
Sascha Schediwy [email protected]
0.001
0.01
0.1
1
10
100
1000
0.1 1 10 100Frequency (GHz)
SKA Reference DesignSKADS Benchmark
Fiel
d of
Vie
w (d
eg2 )
SKADS Benchmark ScenarioSKADS Benchmark Scenario
1 – Aperture Array Review
Overall SKA concept Low Frequency
(0.1-0.3GHz)Sparse Apertura Array
Mid Frequency(0.3-1.0GHz)Dense Aperture Array
High Frequency(1.0-20GHz)Small Dishes
Benchmark document available to download online at: http://www.skads-eu.org/p/memos.php
Aperture arrays are the only technology that provide survey speeds great enough to allow deep HI surveys FoV = 250deg2
Sascha Schediwy [email protected]
Aperture Array ConceptAperture Array Concept
1 – Aperture Array Review
Sascha Schediwy [email protected]
Aperture Array ConceptAperture Array Concept
1 – Aperture Array Review
Look out for talk by:Georgina Harris
Sascha Schediwy [email protected]
Aperture Array ElectronicsAperture Array Electronics
1 – Aperture Array Review
Look out for talks by: Chris Shenton (digital), Tim Ikin (analogue)
Front-end PCB
Sascha Schediwy [email protected]
Aperture Array SensitivityAperture Array Sensitivity
SKADS benchmark scenario document: predicts the cost of an SKA aperture array station to be 3484k€ assumes a Tsys of 50K for mid-frequency aperture array a saving of 200k€ can be made if Tsys is reduced to 40K (§8.4)
1 – Aperture Array Review
0.1 1 101
10
100
Frequency (GHz)
Sky
Tem
pera
ture
(K)
Sky Temperature Plot Reducing Tsys “Vital to get below 50K” Peter Wilkinson Tsys might even be greater than 50K future developments will see noise LNA
decrease (14K from previous talk) however cooling may still be required
especially at high frequencies cooling will also deliver temperature
stabilisation
Sascha Schediwy [email protected]
Aperture Array LNA CoolingAperture Array LNA Cooling
Possible concept for cooling the front-end module using a metallic cooling block
o-ring track
milled fluid channel
hose fittings
plastic casing
cooling block
front-end PCB
plastic casing
coax to antenna
twisted pair to
receiver
cooling lines
cooling block
coldfluid in
warmfluid out
front-end PCB
1 – Aperture Array Review
Sascha Schediwy [email protected]
Cooling Costing ModelCooling Costing Model
The costing model / simulation code: includes physics dealing with thermodynamics and hydrodynamics costing includes: non-recurring expenses, replacement, electrical power does not include: labour costs, no uncertainty analysis written as a simple Matlab script (should be easy to convert, eg. Python) might be able to become a ‘design block’ in the general SKA costing model
Assumptions / principle limitations best estimates for input parameters used, some more inaccurate than others chiller cost is assumed to be linearly proportional with power consumption,
more costing ‘data points’ required to make a more accurate relationship chiller cooling capacity efficiencies assumed to be equal for small and large
chillers, more ‘real’ chiller specifications data are required
2 – Cooling Costing Model
The Matlab script is currently available to download online at:http://www.physics.ox.ac.uk/users/schediwy/cooling/
Sascha Schediwy [email protected]
Cooling Costing ModelCooling Costing Model
For the results in this presentation the code is configured to: compare cost of a cooling system with the total cost SKA aperture array as
specified in the SKADS Benchmark Scenario document (3500k€/station) compare the power consumption with total station use (1000kW/station)
Three scenarios are compared: 1 chiller located at the centre of the aperture array – “Model A” 16 chillers distributed throughout the aperture array – “Model B” 256 chiller distributed throughout the aperture array – “Model C”
2 – Cooling Costing Model
The Matlab script is currently available to download online at:http://www.physics.ox.ac.uk/users/schediwy/cooling/
Sascha Schediwy [email protected]
Cooling “Model A”Cooling “Model A” SKA aperture array station
Model A chillers = 1 pipe ‘D’ = 16 pipe ‘C’ = 256 pipe ‘B’ = 4096 pipe ‘A’ = 65536
~60m
2 – Cooling Costing Model
Key:
chiller pipe ‘D’ pipe ‘C’ pipe ‘B’
Sascha Schediwy [email protected]
Cooling “Model B”Cooling “Model B”
~60m
2 – Cooling Costing Model
SKA aperture array station
Model B chillers = 16 pipe ‘D’ = 0 pipe ‘C’ = 256 pipe ‘B’ = 4096 pipe ‘A’ = 65536
Key:
chiller pipe ‘D’ pipe ‘C’ pipe ‘B’
Sascha Schediwy [email protected]
Cooling “Model C”Cooling “Model C”
~60m
2 – Cooling Costing Model
SKA aperture array station
Model C chillers = 256 pipe ‘D’ = 0 pipe ‘C’ = 0 pipe ‘B’ = 4096 pipe ‘A’ = 65536
Key:
chiller pipe ‘D’ pipe ‘C’ pipe ‘B’
Sascha Schediwy [email protected]
Features – Heat AbsorptionFeatures – Heat Absorption Assumed ambient temperature 30°C, desirable LNA temperature −20°C Cooling much below this temperature is not possible with a glycol/water mixture The chiller cooling capacity was adjusted to compensate for the total heat
power absorbed by the cooling system Insulation thickness was increased until the LNA was the dominant factor
2 – Cooling Costing Model
1 2 3 4 5 6 7 8 90
5
10
15
20
25
30
35
40 Heat Power Dissipation
Position in Loop
Hea
t Pow
er (k
W)
LNA
coo
ling
bloc
k
pipe
A
pipe
A
pipe
B
pipe
B
pipe
C
pipe
C
pipe
D
pipe
D
Individual Component Heat Power Absorption
1 2 3 4 5 6 7 8 90
20
40
60
80
100
120
140 Heat Power Dissipation
Position in Loop
Hea
t Pow
er (k
W)
LNA
coo
ling
bloc
k
pipe
A
pipe
B
pipe
B
pipe
C
pipe
D
pipe
C
pipe
D
pipe
A
total cooling capacity available from the chiller
Total System Heat Power Absorption
Sascha Schediwy [email protected]
Features – Heat AbsorptionFeatures – Heat Absorption
1 2 3 4 5 6 7 8 90.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Coolant Temperature Increase
Position in Loop
Coo
lant
Tem
pera
ture
(deg
C)
LNA
coo
ling
bloc
k
pipe
A
pipe
B
pipe
C
pipe
D
pipe
A
pipe
B
pipe
C
pipe
D
2 – Cooling Costing Model
1 2 3 4 5 6 7 8 90
20
40
60
80
100
120
140 Heat Power Dissipation
Position in Loop
Hea
t Pow
er (k
W)
LNA
coo
ling
bloc
k
pipe
A
pipe
B
pipe
B
pipe
C
pipe
D
pipe
C
pipe
D
pipe
A
total cooling capacity available from the chiller
Total System Heat Power Absorption
Assumed ambient temperature 30°C, desirable LNA temperature −20°C Cooling much below this temperature is not possible with a glycol/water mixture The chiller cooling capacity was adjusted to compensate for the total heat
power absorbed by the cooling system Insulation thickness was increased until the LNA was the dominant factor
Sascha Schediwy [email protected]
Features – Fluid PipesFeatures – Fluid Pipes
8%
21%
24%
47%
Pipe Volume Plot
pipe D5.02m3
pipe C2.57m3
pipe B2.17m3
pipe A0.82m3
Pipe and insulation dimension:
2 – Cooling Costing Model
pipe ‘D’external radius = 150mminternal radius = 50mm
pipe ‘C’ext = 100mmint = 20mm
pipe ‘B’ext = 58.5mmint = 6.5mm
pipe ‘A’ext = 34mmint = 2mm
Fluid volumes:
Sascha Schediwy [email protected]
Features – Pressure/FlowrateFeatures – Pressure/Flowrate Chiller pressure must be great enough to drive fluid through cooling system If there is too much pressure resistance the chiller flow rate will decrease Flowrate was set so that Reynolds number is above 10,000 for all pipes Dominated by inertial forces, viscous forces are minimised, turbulent flow
1 2 3 4 5 6 7 8 90
5
10
15
20
25
30
35
40 Pressure Drop Plot
Position in Loop
Pre
ssur
e (k
Pa)
LNA
coo
ling
bloc
k
pipe
A
pipe
B
pipe
C
pipe
Dpipe
Apipe
B
pipe
C
pipe
D
2 – Cooling Costing Model
1 2 3 4 5 6 7 8 9 1010
-5
10-4
10-3
10-2
10-1
100
101 Volumetric Flow Rate Plot
Position in Loop
Vol
umet
ric F
low
Rat
e (m
3 /s)
0 1 2 3 4 5 6 7 8 9Position in Loop
LNA
coo
ling
bloc
k
pipe
A
pipe
B
pipe
C
pipe
D
pipe
A
pipe
B
pipe
C
pipe
D
chill
er
Sascha Schediwy [email protected]
Cooling Model Cost ResultsCooling Model Cost Results
Model A60.0k€ (1.7%)
Model C44.0k€ (1.3%)
Model B 51.1k€ (1.5%)
Individual Components Cost Plot
chiller
coolantpipe C
pipe B
pipe A
block6.6k€
9.9k€
7.4k€2.7k€
7.4k€
17.0k€ chiller
coolant pipe B
pipe A
block
Individual Components Cost Plot
16.1k€
4.0k€ 7.4k€
9.9k€
6.6k€
Individual Components Cost Plot
chiller
coolant pipe Dpipe C
pipe B
pipe A
block6.6k€
9.9k€
7.4k€
2.7k€
1.6k€14.1k€
17.5k€
All cooling models only cost a small fraction of the total aperture array Model C results in the lowest price, mainly due to the reduction in coolant used limitation: model currently does not take into account the difference in cooling
efficiency (coefficient of performance) of different classes of chillers
2 – Cooling Costing Model
Sascha Schediwy [email protected]
Electrical Power ConsumptionElectrical Power Consumption
Model A= 42.5kW × 1= 42.5kW
Model C= 0.152kW × 256= 38.9W
Model B= 2.57kW × 16= 41.1kW
All models require only a small fraction (~4%) of the electrical power of the total aperture array (~1000kW)
Because of chiller assumption electrical power consumption of all models is very similar
Balance could change when chiller efficiencies are considered in detail
2 – Cooling Costing Model
Sascha Schediwy [email protected]
Cooling the LNA PCBCooling the LNA PCB
cold finger in contact with the PCB
GaA LNA
thermocouple probe
Close-up photo of the Avago LNA showing the cold finger in contact with the PCB
3 – Experimental Cooling Work
Sascha Schediwy [email protected]
Cooling the LNA PCBCooling the LNA PCB
cold finger
50Ω terminator
LNA PCB
LN2 reservoir
The housing used to trap nitrogen to eliminate water condensation as the PCB warms-up to room temperature
3 – Experimental Cooling Work
Sascha Schediwy [email protected]
LNA Noise TemperatureLNA Noise Temperature
0
50
100
150
200
250
400 600 800 1000 1200 1400 1600Frequency (MHz)
Noi
se T
empe
ratu
re (K
)
T = +30deg
T = -10deg
T = -50deg
Plot of the broad-band noise temperature of the LNA PCB recorded at three different LNA temperatures (−50°C, −10°C and +30°C)
3 – Experimental Cooling Work
Sascha Schediwy [email protected]
LNA Noise TemperatureLNA Noise Temperature Plot of LNA noise temperature of the LNA PCB at 700MHz measured at 17
different LNA temperatures
3 – Experimental Cooling Work
45
50
55
60
65
70
75
80
85
-60 -50 -40 -30 -20 -10 0 10 20 30 40LNA Temperature (deg C)
Noi
se T
empe
ratu
re (d
eg K
)
Sascha Schediwy [email protected]
Conclusions / Further WorkConclusions / Further Work
Conclusions cooling 10,000’s of LNA is not physically ridiculous cooling could be economically beneficial cost a small fraction of the full aperture array (<2%) electrical power use is a small fraction of the full aperture array (~4%)
Further Work only three models were studied in detail; further optimisation of
parameter space may result in more work required on some cost inputs, particularly chiller
assumptions presently work on low-loss potting compounds to minimise
condensation problems
Conclusions
The Matlab script is currently available to download online at:http://www.physics.ox.ac.uk/users/schediwy/cooling/
Sascha Schediwy [email protected]
Questions?Questions?
Presentation End
The Matlab script is currently available to download online at:http://www.physics.ox.ac.uk/users/schediwy/cooling/
Sascha Schediwy [email protected]
LNA Cooling MeasurementLNA Cooling Measurement
gain chain v02
spectrum analyser
liquid nitrogen bath
power supplies
50Ω cold loadcopper coax
Photo of the experimental set-up used to measure the noise temperature of the LNA at various LNA temperatures
4 – Extra Slides
Sascha Schediwy [email protected]
Physics Used in ModelPhysics Used in Model
Prandtl number coolant specific heat coolant dynamic viscosity coolant thermal conductivity
Reynolds number coolant density coolant dynamic viscosity coolant flow velocity pipe hydrodynamic diameter
Hagen-Poiseuille Law coolant volumetric flow rate coolant dynamic viscosity pipe length pipe cross-sectional area
Heat transfer coefficient coolant thermal conductivity pipe Nusselt number pipe hydrodynamic diameter
Dittus-Boelter correlation Reynolds number Prandtl number
Heat power absorbed heat transfer coefficient ambient temperature coolant initial temperature insulation thickness insulation thermal conduction pipe surface area
4 – Extra Slides
Sascha Schediwy [email protected]
Current Limitations of ModelCurrent Limitations of Model Insulation Chiller flowrate large enough so that Reynolds number is above 10,000
for all pipes means: flow is dominated by inertial forces, viscous forces are
minimised, flow is turbulent Cooling agents other than a glycol-water mixture would be too
expensive, therefore minimum temperature limited to about −30°C Incompressible fluid – very small effect Laminar flow - Wall friction – Darcy-Weisbach equation – easy to include in the future Joint/Corner effects Chiller efficiencies
4 – Extra Slides
Sascha Schediwy [email protected]
3 Different Cooling Models3 Different Cooling Models
chillers x16 x16x16
1
x16
256 4096
subtilespipe B pipe A
6553616
antennapairs
pipe D pipe C
x16x16x16
256 4096
subtileslarge pipe small pipe
6553616
antennapairs
x16x16
256 4096
subtileslarge pipe small pipe
65536
antennapairs
Model B16 distributed
chillers
Model C256 distributed
chillers
chillers
chillers
Model A1 central chiller
Schematic representation of three models investigated using a Matlab cooling and costing simulation
The physical layout of three concepts are shown on the next slide
4 – Extra Slides
Sascha Schediwy [email protected]
Cascade AnalysisCascade Analysis
Gain Chain v02Avago LNA Spectrum Analyser50Ω Terminator
Copper Coax
1 2 3 4Cascade Element:
4 – Extra Slides
Factors affecting Tsys: sky temperature front-end LNA rest of system
Sascha Schediwy [email protected]
SKADS Station Data FlowSKADS Station Data Flow
Bunker
StationProcessor 1
0.3-1.0GHz Analog links
StationProcessor 2
StationProcessor X
…..
Dish P1Dish P2
Dish Px
Mid P1Mid P2
Mid Py
Low P1Low P2
Low Pz
.
InternalDigital links
n x Optical fibres per 2nd
stage processor
To Correlator
Mid Freq. AA
PhaseStandard &Distribution
.
.
.
.
..
20GHz Analog fibre links
300MHz Analog links
.
.
.
High Freq. dishes
Low Freq.AA
... Control processors
To CentralControl system
10Gb Digital fibre links
Phase transferover fibre (where used)
1st Stage ProcessorsBunker
StationProcessor 1
0.3-1.0GHz Analog links
StationProcessor 2
StationProcessor X
…..
Dish P1Dish P2
Dish Px
Mid P1Mid P2
Mid Py
Low P1Low P2
Low Pz
.
InternalDigital links
n x Optical fibres per 2nd
stage processor
To Correlator
Mid Freq. AA
PhaseStandard &Distribution
.
.
.
.
..
20GHz Analog fibre links
300MHz Analog links
.
.
.
High Freq. dishes
Low Freq.AA
... Control processors
To CentralControl system
10Gb Digital fibre links
Phase transferover fibre (where used)
1st Stage Processors
4 – Extra Slides
Sascha Schediwy [email protected]
Nitrogen AtmosphereNitrogen Atmosphere
no condensation visible on PCB
excess condensation collects on cold finger
A photo of the demo-board after warming back up to room temperature
4 – Extra Slides
Sascha Schediwy [email protected]
LNA Temperature IncreaseLNA Temperature IncreaseLNA Temperture Increase
-60
-50
-40
-30
-20
-10
0
10
20
30
40
00:00 00:10 00:20 00:30 00:40 00:50 01:00 01:10 01:20
Elapsed Time (hh:mm)
Tem
pera
ture
(deg
C)
Cold Load
Hot LoadLN2 evaporated
Cold Finger Removed
4 – Extra Slides
Sascha Schediwy [email protected]
Avago LNA – Testboard 1Avago LNA – Testboard 1Avago TB1 - S11 Reflection
-25
-20
-15
-10
-5
0
5
0.0 0.5 1.0 1.5 2.0Frequency (GHz)
Log
Mag
(dB
)
Avago TB1 - S21 Transmission
-25
-20
-15
-10
-5
0
5
10
15
20
0.0 0.5 1.0 1.5 2.0Frequency (GHz)
Log
Mag
(dB
)
4 – Extra Slides
Sascha Schediwy [email protected]
Aperture Array MountingAperture Array Mounting
2.56m
4 – Extra Slides
Sascha Schediwy [email protected]
CAT 7 and CoolingCAT 7 and Cooling
CAT 7
~13mm ~4mm
Low DensityPoly Pipe 13mm
X 100M: A$43.02
~35mm
~13mm ~13mm
37 Leads
30 Leads
~13mm
37Leads
4 – Extra Slides