Aperture Array LNA Cooling

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!)


0.001

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0.1

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10

100

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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


Aperture Array ConceptAperture Array Concept



Aperture Array ConceptAperture Array Concept


Look out for talk by:Georgina Harris


Aperture Array ElectronicsAperture Array Electronics


Look out for talks by: Chris Shenton (digital), Tim Ikin (analogue)

Front-end PCB


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)


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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


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



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/


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”




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


Key:

chiller pipe ‘D’ pipe ‘C’ pipe ‘B’


Cooling “Model B”Cooling “Model B”

~60m


SKA aperture array station

Model B chillers = 16 pipe ‘D’ = 0 pipe ‘C’ = 256 pipe ‘B’ = 4096 pipe ‘A’ = 65536

Key:



Cooling “Model C”Cooling “Model C”

~60m


SKA aperture array station

Model C chillers = 256 pipe ‘D’ = 0 pipe ‘C’ = 0 pipe ‘B’ = 4096 pipe ‘A’ = 65536

Key:



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


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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

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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


Features – Heat AbsorptionFeatures – Heat Absorption

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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


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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


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:


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:


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

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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


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10-4

10-3

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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


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


16.1k€

4.0k€ 7.4k€

9.9k€

6.6k€


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



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



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


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



LNA Noise TemperatureLNA Noise Temperature

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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)



LNA Noise TemperatureLNA Noise Temperature Plot of LNA noise temperature of the LNA PCB at 700MHz measured at 17

different LNA temperatures


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-60 -50 -40 -30 -20 -10 0 10 20 30 40LNA Temperature (deg C)

Noi

se T

empe

ratu

re (d

eg K

)


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



Questions?Questions?

Presentation End



Extra SlidesExtra Slides

4 – Extra Slides


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


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


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


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


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


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


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


LNA Temperature IncreaseLNA Temperature IncreaseLNA Temperture Increase

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Elapsed Time (hh:mm)

Tem

pera

ture

(deg

C)

Cold Load

Hot LoadLN2 evaporated

Cold Finger Removed

4 – Extra Slides


Avago LNA – Testboard 1Avago LNA – Testboard 1Avago TB1 - S11 Reflection

-25

-20

-15

-10

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0

5

0.0 0.5 1.0 1.5 2.0Frequency (GHz)

Log

Mag

(dB

)

Avago TB1 - S21 Transmission

-25

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0

5

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15

20

0.0 0.5 1.0 1.5 2.0Frequency (GHz)

Log

Mag

(dB

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4 – Extra Slides


Aperture Array MountingAperture Array Mounting

2.56m

4 – Extra Slides


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

Aperture Array LNA Cooling

Documents

Transcript of Aperture Array LNA Cooling