Aperture array lna cooling
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(How best not to cool an LNA!). Aperture Array LNA Cooling. 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?. Presentation Overview: 1 – Aperture Array Review 2-PAD 2 – LNA Cooling Costing Model

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Aperture Array LNA Cooling

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Aperture array lna cooling

(How best not to cool an LNA!)

Aperture Array LNA Cooling

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?

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


Skads benchmark scenario

1000

SKA Reference Design

100

SKADS Benchmark

10

Field of View (deg2)

1

0.1

0.01

0.001

0.1

1

10

100

Frequency (GHz)

SKADS Benchmark Scenario

  • 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

  • Aperture arrays are the only technology that provide survey speeds great enough to allow deep HI surveys

    • FoV = 250deg2

  • Benchmark document available to download online at:

    • http://www.skads-eu.org/p/memos.php

1 – Aperture Array Review


Aperture array concept

Aperture Array Concept

1 – Aperture Array Review


Aperture array concept1

Aperture Array Concept

Look out for talk by:Georgina Harris

1 – Aperture Array Review


Aperture array electronics

Aperture Array Electronics

Front-end PCB

  • Look out for talks by:

    • Chris Shenton (digital), Tim Ikin (analogue)

1 – Aperture Array Review


Aperture array sensitivity

Aperture 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)

  • 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

1 – Aperture Array Review


Aperture array lna cooling1

front-end PCB

coax to antenna

twisted pair to receiver

cooling block

cooling lines

plastic casing

plastic casing

o-ring track

cooling block

hose fittings

milled fluid channel

Aperture Array LNA Cooling

  • Possible concept for cooling the front-end module using a metallic cooling block

front-end PCB

warmfluid out

coldfluid in

1 – Aperture Array Review


Cooling costing model

Cooling 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

  • The Matlab script is currently available to download online at:

    • http://www.physics.ox.ac.uk/users/schediwy/cooling/

2 – Cooling Costing Model


Cooling costing model1

Cooling 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”

  • The Matlab script is currently available to download online at:

    • http://www.physics.ox.ac.uk/users/schediwy/cooling/

2 – Cooling Costing Model


Cooling model a

  • Key:

  • chiller

  • pipe ‘D’

  • pipe ‘C’

  • pipe ‘B’

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


Cooling model b

  • Key:

  • chiller

  • pipe ‘D’

  • pipe ‘C’

  • pipe ‘B’

Cooling “Model B”

  • SKA aperture array station

  • Model B

  • chillers = 16

  • pipe ‘D’ = 0

  • pipe ‘C’ = 256

  • pipe ‘B’ = 4096

  • pipe ‘A’ = 65536

~60m

2 – Cooling Costing Model


Cooling model c

  • Key:

  • chiller

  • pipe ‘D’

  • pipe ‘C’

  • pipe ‘B’

Cooling “Model C”

  • SKA aperture array station

  • Model C

  • chillers = 256

  • pipe ‘D’ = 0

  • pipe ‘C’ = 0

  • pipe ‘B’ = 4096

  • pipe ‘A’ = 65536

~60m

2 – Cooling Costing Model


Features heat absorption

LNA cooling block

Individual Component Heat Power Absorption

Total System Heat Power Absorption

pipe A

pipe A

pipe C

pipe D

pipe B

total cooling capacity available from the chiller

pipe A

pipe B

pipe B

pipe C

pipe C

pipe D

pipe D

LNA cooling block

pipe A

pipe B

pipe C

pipe D

Features – 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


Features heat absorption1

pipe C

pipe D

pipe B

pipe A

Total System Heat Power Absorption

LNA cooling block

pipe A

pipe C

pipe D

pipe B

total cooling capacity available from the chiller

pipe A

pipe B

pipe C

pipe D

LNA cooling block

pipe A

pipe B

pipe C

pipe D

Features – 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


Features fluid pipes

pipe ‘C’ext = 100mmint = 20mm

pipe ‘D’external radius = 150mminternal radius = 50mm

pipe ‘B’ext = 58.5mmint = 6.5mm

pipe A0.82m3

pipe ‘A’ext = 34mmint = 2mm

pipe B2.17m3

pipe D5.02m3

pipe C2.57m3

Features – Fluid Pipes

  • Pipe and insulation dimension:

  • Fluid volumes:

2 – Cooling Costing Model


Features pressure flowrate

pipe A

pipe C

pipe D

pipe B

LNA cooling block

pipe A

pipe D

pipe D

pipe C

pipe B

pipe D

chiller

pipe C

pipe C

LNA cooling block

pipe B

pipe B

pipe A

pipe A

0 1 2 3 4 5 6 7 8 9Position in Loop

Features – 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

2 – Cooling Costing Model


Cooling model cost results

  • Model A60.0k€ (1.7%)

  • Model B 51.1k€ (1.5%)

  • Model C44.0k€ (1.3%)

6.6k€

17.5k€

6.6k€

6.6k€

9.9k€

17.0k€

16.1k€

9.9k€

9.9k€

7.4k€

2.7k€

14.1k€

1.6k€

7.4k€

4.0k€

7.4k€

7.4k€

2.7k€

Cooling Model Cost Results

  • 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


Electrical power consumption

Electrical Power Consumption

  • Model A= 42.5kW × 1= 42.5kW

  • 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

  • Model B= 2.57kW × 16= 41.1kW

  • Model C= 0.152kW × 256= 38.9W

2 – Cooling Costing Model


Cooling the lna pcb

Cooling the LNA PCB

  • Close-up photo of the Avago LNA showing the cold finger in contact with the PCB

thermocouple probe

GaA LNA

cold finger in contact with the PCB

3 – Experimental Cooling Work


Cooling the lna pcb1

Cooling the LNA PCB

  • The housing used to trap nitrogen to eliminate water condensation as the PCB warms-up to room temperature

LNA PCB

cold finger

LN2 reservoir

50Ω terminator

3 – Experimental Cooling Work


Lna noise temperature

LNA Noise Temperature

  • 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


Lna noise temperature1

LNA Noise Temperature

  • Plot of LNA noise temperature of the LNA PCB at 700MHz measured at 17 different LNA temperatures

3 – Experimental Cooling Work


Conclusions further work

Conclusions / 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

  • The Matlab script is currently available to download online at:

    • http://www.physics.ox.ac.uk/users/schediwy/cooling/

Conclusions


Questions

Questions?

  • The Matlab script is currently available to download online at:

    • http://www.physics.ox.ac.uk/users/schediwy/cooling/

Presentation End


Extra slides

Extra Slides

4 – Extra Slides


Lna cooling measurement

power supplies

spectrum analyser

50Ω cold load

copper coax

gain chain v02

liquid nitrogen bath

LNA Cooling Measurement

  • 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 model

Physics 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 model

Current 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 models

3 Different Cooling Models

  • Schematic representation of three models investigated using a Matlab cooling and costing simulation

pipe D

pipe B

pipe A

pipe C

x16

x16

x16

x16

antennapairs

Model A1 central chiller

chillers

subtiles

1

16

256

4096

65536

large pipe

small pipe

x16

x16

x16

antennapairs

Model B16 distributed chillers

subtiles

chillers

16

256

4096

65536

  • The physical layout of three concepts are shown on the next slide

large pipe

small pipe

x16

x16

antennapairs

subtiles

chillers

Model C256 distributedchillers

256

4096

65536

4 – Extra Slides


Cascade analysis

3

4

Cascade Element:

1

2

50Ω Terminator

Copper Coax

Gain Chain v02

Spectrum Analyser

Avago LNA

Cascade Analysis

  • Factors affecting Tsys:

    • sky temperature

    • front-end LNA

    • rest of system

4 – Extra Slides


Skads station data flow

SKADS Station Data Flow

4 – Extra Slides


Nitrogen atmosphere

Nitrogen Atmosphere

  • A photo of the demo-board after warming back up to room temperature

excess condensation collects on cold finger

no condensation visible on PCB

4 – Extra Slides


Lna temperature increase

LNA Temperature Increase

LN2 evaporated

Cold Finger Removed

4 – Extra Slides


Avago lna testboard 1

Avago LNA – Testboard 1

4 – Extra Slides


Aperture array mounting

Aperture Array Mounting

2.56m

4 – Extra Slides


Cat 7 and cooling

~13mm

~4mm

~13mm

~13mm

CAT 7 and Cooling

30 Leads

~35mm

Low DensityPoly Pipe 13mm X 100M: A$43.02 

CAT 7

37 Leads

37Leads

~13mm

4 – Extra Slides


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