Thermal measurements in Glasgow

Richard Bates, Isaac Bonad, Craig Buttar

Contents

• In plane thermal conductivity measurements– Apparatus– Method– Results

Early photograph of the apparatus, before the experiment was inside the vacuum tank, but while the area was tidy

Vacuum chamber with 16 octal feed through service for thermocouple readout.

Copper cooling block with cooling service connections.

Two 4 input NI thermocouple data acquisition modules.

Computer controlled chiller

High performance woven matrix heating element.

PC interface with labview, DAQmx and chiller control Software.

16 PT 100 precision thermocouples

Thermal studies

Plastic insulating supports

DUT

H2O

V,I measured

ElectricalHeaters

Water cooledCu block

Al thermalshield PT100s

RTD1 RTD2 RTD3

Details of the measurement

• Radiation reduction– Radiation shield around the sample– Polystyrene balls filler– Cool outside of tank to Copper block temperature

• Conduction reduction– RTD wire 44SWG Manganin tied to the cooling block– Thermally insulating mounts for apparatus

• Convection reduction– Vacuum tank

• Accuracy– 4 wire temperature sensors and heater– Careful calibration of RTDs against each other (temperature

differences important)

Measurement details

• Sample size– Defined by thermal shield size and vacuum tank– Presently : 10cm x 1 cm– Max length at present : 20cm (limited by vac tank)

• Heater power– Max at present 0.5W– Easy to manage temperatures in the shield and only small

changes in sample temperature– Requires accurate temperature measurements (TPG ΔT = 0.5C)

• Cooling– Use anti-freeze based chiller : -20C minimum temperature– Peltier elements to further reduce temperature

The experiment

• Sample and thermal shield clamped to cold block

• Copper tower to clamp PT100 wires to cold block

• Heaters on sample and shield removed

Pocofoam under test

Thermal shield

Cooling block

PT100 with Manganin wire

Experiment sits inside a vacuum tank to isolate it from the external environment

Vacuum Chamber

Support/Insulation (polystyrene)

SolidWorks drawing of the experiment

• Experiment draw in SolidWorks

• Exported to Ansys for thermal simulation

Simulation

• Ansys FEA simulation performed on the simulation– Radiation losses to the environment included– Conduction losses to the environment included– Convection losses ignored

• Detailed simulation performed for sample of known thermal conductivity– Understand all heat loss paths to reproduce

experimental results– Undesired heat paths removed as much as possible

Ansys thermal simulation of the experiment

• Simulation includes all know heat sources, except convection

• Thermal profile of simulation and experiment shown to agree better than 2%

0

0.5

1

1.5

2

2.5

3

3.5

5 10 15 20 25 30 35

Temperature

Len

gth

Reduction of parasiticsCold Block

Heater

Samplelength

P=0

P1

T0

ΔT1

ΔT2

Analysis method

• Impossible to remove all parasitic heat paths, p, to the sample

• For zero intentional power have ΔT1

• Apply power P– Keep central temperature

constant T0

• As long as ΔT2 is not much larger than ΔT1 then parasitic effects cancel

A

l

T

Pk

ATk

Tp

l

T 1

)(

)(

0

01

ATk

TpP

l

T 1

)(

)(

0

02

)()(

00

PP gradgradA

PTk

Results• Measured

– TPG as a function of temperature– Pocofoam– Carbon-carbon– C-SiC TPG

0

500

1000

1500

2000

2500

-15 -10 -5 0 5 10 15 20 25

Temperature (C)

Th

erm

al C

on

du

ctiv

ity

(W/m

K)

Copper

Through-plane thermal conductivity measurements

V,I measured

Water cooledCu block

HeatedCu block

PT100s

Plastic thermalinsulation

System in a vacuum and surrounded by polystyrene for thermal insulationDUT size: 1 cm x 1 cm x 100umMeasure thickness with a travelling microscope

DUT

Pressure gaugeLoad cell

Screw, to apply pressure

Vacuum vessel

Future work

• System undergoing an upgrade– Extension of the operating range away from

room temperature (-20C to -50C)– Additional radiation shield around the set-up– Improved vacuum tank (aim 1x10-6mbar)– Use of Peltier elements to lower temperature– Goal to test to -50C or lower