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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(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


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

1 – Aperture Array Review


Aperture Array Concept

Look out for talk by:Georgina Harris

1 – Aperture Array Review


Aperture Array Electronics

Front-end PCB

  • Look out for talks by:

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

1 – Aperture Array Review


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


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

  • 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 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


  • 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


  • 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


  • 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


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


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


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


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


  • 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

  • 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

  • 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 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

  • 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 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

    • 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?

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

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

Presentation End


Extra Slides

4 – Extra Slides


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

  • 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

  • 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

  • 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


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

4 – Extra Slides


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

LN2 evaporated

Cold Finger Removed

4 – Extra Slides


Avago LNA – Testboard 1

4 – Extra Slides


Aperture Array Mounting

2.56m

4 – Extra Slides


~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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