WUT Experience in Measurements of the Heat Transfer Thought SC Cable

Electrical Insulation

Jaroslaw Polinski*, Maciej Chorowski*, Michal Strychalski*, Rob van Weelderen**

Mini-Workshop on Thermal Modeling and Thermal Experiments for Accelerator Magnets – CERN 30th Sep – 1st Oct 2009

* Wroclaw University of Technology, Poland** CERN, Switzerland

Outline

• Motivation of the heat transfer program at WUT (new HT method)

• Experimental set-up at WUT• Sample holder design• Sample compression idea• Insulation schemes and sample preparation• Test results• Conclusions

Motivation of the heat transfer program at WUT

„Stack of the conductors” – the most common measurement method of the heat transfer through S.C. cable electrical insulation

CERN stack holder KAK and CEA Saclay stack holder

Motivation of the heat transfer program at WUT

Stack method New method

Heater

T sensor

Method comparison

Stack method• Advantages

– The most similar with real magnet coil configuration

• Disadvantages– the amount of the heat

transferred through insulation by particular HT path is difficult to determinate

New method• Advantages

– allows determination of the heat transfer resistance of the insulation and the Rutherford type cable

• Disadvantages– cable sample

configuration is „far” from magnet coil configuration

Superfluid helium cryostat designs

He I

He IIpressurized

Radiationshield

Vacuumcontainer

Vacuum pumpoutlet J-T valve

regulation

J-T valve

Heatexchanger

valve

plate

Measurmentvessel

1200

800

168.3 x 2

219.1 x 2

He IIsaturated

304 x 1

200

valveregulation

Insertradiation

shield

Instrumentationvacuum feed

through @ 4K

Insrtumentationport

Insrtumentationport

Inner vacuumjacket

Outer vacuumjacket

Scheme of pressurized superfluid helium cryostat

Solid

Critica l Point

He IIHe

1 10T [K ]

1

10

100

1000

10000

P. [

kPa

]

Pressu ried H e II

Saturated He II

G as

line

Superfluid helium cryostat designs

Radiation screen with MLI

Measurement vessel with instrumentation

External vacuum jacetduring leak test

HeII cryostat set-up in WUT

He I

SprężonyHe II

NasyconyHe II

He I

Butla z helem

gazowym

Pompa o wysokiej wydajności

Zawór regulacyjny

Zbiornik helowyDwuobjętościowy kriostat helowyHe II Cryostat He I dewar

HeI dewar pressurization system

He IIs vessel pressure control valve

High capacity vacuum pump

Holder designs

Cable sample

T sensor

Heater

Holder body

Capillary

Compressive lid

Compressive element

Sealing substanceSample seat

Bolts

Holder designs

Holder body

Holder designs

Cable sample seat

Holder designs

Cable sample seat with sample and compressing element on the top

Holder designs

Holder installed in the cryostat (left) and covered by measurement vessel (right)

Sample compression idea

• Except bolts, all holder elements are made of Invar• Bolts are made of stainless steal• Compression applied on the sample:

samp

ssInvssbb

A

EANp

Nb – number of bolts

Ab – bolt rod cross section area, m2

SS – thermal expension of stainless steal, m/m

Inv – thermal expension of invar, m/m

ESS – Young modulus of stainless steal, Pa

Asamp – cable sample surfacae, m2

Sample compression idea

For:• 6xM12 bolts with rod cross section area Ab=80mm2 • Thermal expansion of Invar (300–2K) - =0.00038• Thermal expansion of SS (300–2K) - =0.0031• Young moduls of SS: ESS=2.1.109 Pa• Sample surface: Asamp=98×16 mm × mm

The compression applied on the sample p=160MPa

But• Mechanical deformation of the cable sample is

assumed to be as for Invar material• Due to complex cable structure its precise

mechanical deformation is theoretically very difficult to determinate

Sample compression idea

Therefore:• Additional mechanical tests have to be

performed where sample compression values vs. room temperature pre-compression will be determined

• The mechanical tests preparation is already started

• The test will be performed in LN2 and results scaled to He temperature

Insulation schemes

Dipole type

Quadruple type

Enhance type A

Enhance type B

Cable sample preparation and installation

Cable sample preparation and installation

Cable sample preparation and installation

Cable sample preparation and installation

Tests description

Test No

Insulation type Side

A/B

Sample sealing

substance

Sample seat sealing

(Apiezon)

Compressing element

Capillary

1 D/A Piceine No No OPEN

2 D/D Piceine No No OPEN

3 A/AEpoxy

resine1Yes No OPEN

4 Q/QEpoxy

resine2Yes Yes OPEN

5 B/B3M Scotch

Weld DP 150Yes Yes CLOSE

Reference data

0.00001

0.0001

0.001

0.01

0.1

1

0.01 0.1 1

B. Baudouy a,*, M.X. Francßois b, F.-P. Juster a, C. Meuris: „He II heat transfer through SC cables electrical insulation” - Cryogenics 40 (2000) 127-136

First layer: Kapton 150 HN (37.5 mm), 50% overlap, 11-mm widthSecond layer: Adhesive Kapton 120 (30 mm), 4 mm spacing

Drum method

Test results

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 200 400 600 800 1000 1200 1400 1600 1800 2000q, W/m2

DT

, K

Scheme D - Side A

Scheme A - Side B

Reference

Test no.1

Sealing substance – Piceine

Tbath=1.8K

Test results

Test No 1 conclusions

• Observations:– Obtained results are of 2 orders of magnitude higher than

„Reference Results”– After samples dismounting a visual inspection shows that

piceine don’t fill the space between insulation and cable sample seat very well

• Correction to be done– Piceine sealing substance should be applied more precisely

Test results

Test no.2

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 500 1000 1500 2000 2500Q, W

DT

, K

Scheme D - Side A

Scheme D - Side B

Reference

Sealing substance – Piceine

Tbath=1.8K

Test results

Test No 2 conclusions

• Observations:– Obtained results are still 2 order of magnitude higher than

„Reference Results”– After samples dismounting a visual inspection shows that

piceine don’t fill the space between insulation and cable sample seat very well

• Correction to be done– Piceine sealing substance should be substitute with some epoxy

resin– Sealing between sample seat and the holder body should be

created. To allow disassemble of the sample seat from the holder body after test an Apiezon vacuum grease have been chosen

Test results

Test no.3

Sealing substance – Epoxy 1

Sample seat sealing - YES

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 50 100 150 200 250Q, W

DT

, K

Scheme A - Side A

Scheme A - Side B

Reference

Tbath=1.8K

Test results

Test No 3 conclusions

• Observations:

Story of Some Compressing Elements

• Michal: The cryostat is ready. We can start the test.• Jarek: Great!!! By the way: what is that?• Michal: This is one of the compressing element from the holder.• Jarek: .....? .....? ....? • Michal: What?• Jarek: Why the these elements aren’t installed in holder?• Michal: Because if you install them after the holder is not fit to the

measurement vessel. It is 1 or 2 mm too width• Jarek: .....? .....? ....?• Michal: These elements are important?• Jarek: Quite

Test results

Test No 3 conclusions

• Observations:– Lack of the compressing elements in the holder for test No:1, 2

and 3– Obtained results are „only” 1 order of magnitude higher than

„Reference Results”– After samples dismounting a visual inspection shows air bubbles in

sealing epoxy resin

– In test No 1, 2 and 3 the „Lambda transition” occur at T=1.85K what corresponding to pHeIIp=20mbar

Test results

Test No 3 conclusions

• Correction to be done– Reducing of the compression elements to high allows the holder

installation in the measurement vessel– Test the other type of the epoxy resin– Solve the problem of „low temperature lambda transition”

Test results

Solve the problem of „low temperature lambda transition”

He I

He IIpressurized

Radiationshield

Vacuumcontainer

Vacuum pumpoutlet J-T valve

regulation

J-T valve

Heatexchanger

valve

plate

Measurmentvessel

1200

800

168.3 x 2

219.1 x 2

He IIsaturated

304 x 1

200

valveregulation

Insertradiation

shield

Instrumentationvacuum feed

through @ 4K

Insrtumentationport

Insrtumentationport

Inner vacuumjacket

Outer vacuumjacket

He I

He IIpressurized

Radiationshield

Vacuumcontainer

Vacuum pumpoutlet J-T valve

regulation

J-T valve

Heatexchanger

valve

plate

Measurmentvessel

1200

800

168.3 x 2

219.1 x 2

He IIsaturated

304 x 1

200

valveregulation

Insertradiation

shield

Instrumentationvacuum feed

through @ 4K

Insrtumentationport

Insrtumentationport

Inner vacuumjacket

Outer vacuumjacket

Test results

HeI bath

HeIIp bathHeIIs bath

Solve the problem of „low temperature lambda transition”

Lambda valveJT valve

Test results

Test no.4

Sealing substance – Epoxy 2

Sample seat sealing - YES

Compressing element – YES

0

0.1

0.2

0.3

0.4

0.5

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00

q, W/m 2

DT

, K

próbka Q - strona A

próbka Q - strona B

Reference

Tbath=1.8K

Test results

Test No 4 conclusions

• Observations:– Obtained results are already in this same order of magnitude as

„Reference Results”, but „Reference Results” are for uncompressed insulation since our sample is compressed.

– „Lambda transition” occur at DT=0.45K i.e. T=2.25K– After samples dismounting a visual inspection shows no air

bubbles in new sealing epoxy resin

Test results

Test No 4 conclusions

• Correction to be done– heat transfer thought capillary should be experimentally

determined– T sensors should be re-calibrated in pressure controlled

superfluid saturated helium– sealing of the capillary should be considered

Capillary sealing

Capillary scheme

Capillary sealing

Test results

Test no.5

Sealing substance –3M Scotch Weld DP 150

Sample seat sealing - YES

Compressing element – YES

Capillary - CLOSE 0

0.1

0.2

0.3

0.4

0 10 20 30 40 50 60 70 80

q, W/m2

DT

, K

Scheme B - Side A

Scheme B - Side B

Reference

Tbath=1.8K

Test results

Test No 5 conclusions

• Observations:– Obtained results seems to be already correct. – „Lambda transition” occur at different temperature for each side

and for both case it not correspond to T-lambda temperature• possible reason: after reviewing of the temperature data recorded

during the test it was found that connection of the heater wires to power supply results in change in temperature reading values. Since temperature regulation in measurement bath is based on one of T-sensor reading value after power supply connection a real temperature in HeIIp bath was different.

• Correction to be done- Rewinding the instrumentation wires or grounded the cryostat

and/or acquisition system

Conclusion

• Numbers of problems concerned the heat transfer test have been solved

• To start the new tests series with electrical insulations mechanically wrapped on the cables a following actions have to be taken:– determination of the final („cold”) sample compression values in

function of the pre-compression in room temperature– instrumentation reading problem have to be solved