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KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) www.kit.edu
Thermal insulation
Institute for Technical PhysicsHolger Neumann
Don‘t be afraid of low temperatures
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
2
Content
Relevance of thermal insulation in cryogenics
Overview of different insulation materials
Multi-layer insulation (MLI) – SuperinsulationDescriptionHeat transfer calculations
Special characteristics
Example: Thermal insulation development for a flexible cryogenic line
Conclusions
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
3
Relevance of thermal insulation in cryogenics
Example 1:The efficiency of a 4.4 K-refrigerator is about 10% of the Carnot-Coefficient of Performance (COP)⇒ ε = 0.0015
⇒ The heat load of 100 W at 4.4 K requires a power input of about 70 kW
Example 2:1000 litres-vessel LHe with an evaporation rate of 1%/day→ decrease of the insulation quality of 10% (~ 30 mW)
⇒ Increase of the operating costs of ~ 1000 €/yearor additional LHe-acquisition costs of ~ 2000 €/year
FluidtEnvironmen
FluidC TT
T−
=ε
Cryogenics → ∆T = TEnvironment – TFluid → great value
→ latent heat are very small
→ needed energy input for generating low temperatures is very high(Carnot)
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
4
Overview of different insulation materials
10-6.0 10-5.0 10-4.0 10-3.0 10-2.0 10-1.0
MLI
micro-sphere
powderwith smallpieces ofmetal foils
fibreglas
powder
atmospheric pressurevacuum
air (1 bar) ~ 2,6 10-2.
heat conductivity [W/(m K)] between ~ 300 K - 77 Kλ .
foams, powdersfibres
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
5
Multi-layer insulation (MLI) – Superinsulation – Descript ion
MLI consists of:
reflecting layers → reduction of heat transfer due to radiationspacer elements with low heat conductivity between the reflecting layers
high vacuum
prevention of convection
minimisation of heat conduction of residual gas
MLI is presently the most effective kind of thermal insulationdeveloped in the fifties by Peterson (Sweden)first established in the sixties by space industry
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
6
SI-materials:
reflecting layers: mostly aluminium metallized mylar films / pure aluminium foilsspacer elements: mostly net of glas fibre or foils / paper or polyester / tulle or silk
or
unit of reflector and spacer:metallized mylar films, crinkled or embossed to reduce the contact surface between the reflecting layers without spacer elements
attention: SI-anisotropy ⇒⇒⇒⇒ delicate regarding installation (many bugs are poss ible)
Multi-layer insulation (MLI) – Superinsulation – Descript ion
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
7
Multi-layer insulation (MLI) – Superinsulation– Heat transfer calculations
i1iiT
i1ii1ii
i
i4
1i4i
TT
1ii,overall
ACf)T(Ts
Af)(1)T(T)T(T8
R2p
211
Af)(1)T(T1
ε
1ε
1QQ
1ii,
1ii
⋅⋅⋅−⋅λ
+
⋅−⋅−⋅+⋅π⋅
⋅⋅⋅α−
α⋅−κ+κ+
⋅−⋅−⋅−+
σ==
+
++
++
+
+
&&
100
125
150
175
200
225
250
275
300
T[K
]
5 10 15 20 25
N
reine WärmestrahlungWärmestrahlung und -leitungreine Wärmeleitung
pure radiationradiation and conductionpure conduction
radiation
residual gas heat conduction
solid heat conduction
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
8
Multi-layer insulation (MLI) – Superinsulation– Heat transfer calculations
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
9
Multi-layer insulation (MLI) – Superinsulation– Heat transfer calculations
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
10
Multi-layer insulation (MLI) – Superinsulation– Special characteristics
influence of contact pressure
1-3: Al layers with fibre glass paper of different thickness4: Dracon Al-metallized with glass silk tissue5-6: theoretical values (without solid heat conduction)
optimum number of layers / density of layers
x
x
xx
0 10 20 30 40 50 1/cm 60
N/D
0.05
0.10
0.15
mW/(m K).
1
2 3
4
56
effe
ctiv
e h
eat c
ond
uctiv
ity λ
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
11
.0
5
10
15
20
25
30
35
40
45
0 200 400 600 800
diameter of tube [mm]
q[W
/m2 ]
0
0,5
1
1,5
2
2,5
3
q[W
/m]
empirical values for different transferlines and cryostatswith 20 - 50 layers MLI between RT and 80 K(winding technique on tubes and cylinders)
q [W/m] = q [W/m ] d2 π. . . .
q [W/m ] with 3 blankets (RT - 80 K)2.
Multi-layer insulation (MLI) – Superinsulation– Special characteristics
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
12
0
1
2
3
4
5
6
7
8
9
0 50 100 150 200 250 300 350 400
d [mm]
q[W
/m2 ]
T = 280 Kp < 2 10 mbar
warm-6.
only one aluminiumlayer (LN )2
1 blanket
2 blankets
3 blankets
IR 300.12 MLI blanket techniqueopen / closed symbols LHe / LN - experiments 2
MLI winding technique
Multi-layer insulation (MLI) – Superinsulation– Special characteristics
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
13
Multi-layer insulation (MLI) – Superinsulation– Special characteristics
0 10 20 30 40 50
N
0
2
4
6
8
10
12
14q
[W/m
2 ]
qrad=f(ewall=0.1; eshield=0.03; TW=300 K; TC=77 K)IHI: JacobIHI: FZKIHI: Ohmori [1992]Jehier: FZK, TESSI mit d=320 mmJehier: FZK, THISTA mit d=219 mm
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
14
Multi-layer insulation (MLI) – Superinsulation– interim conclusion
Important
quasi-isothermal parting points
Avoiding of gaps → causes disproportionately high heat transfer
Avoiding of mechanical stress
→ causes exponentially increase of degradation with p
Relation between heat conduction and radiation = f(T)MLI is especially effective at high temperatures
MLI is less effective or disadvantageous at T < 100 K
optimal layer density
vacuum conditionsperforated layers
MLI with integrated getter materials
Superinsulation only meets this expression and expenditure if several possibilities of errors could be avoided
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
15
Multi-layer insulation (MLI) – Superinsulation– Example: Thermal insulation development for a flexi ble
cryogenic line
Requirements on a economic applicable HTS-cable
compact design → ∆insulation = 20 mm
⇒⇒⇒⇒ The use of MLI is mandatory
2K80K3002 mW
2qmW
1 ⋅≤≤⋅ ⋅→⋅&
KmW
102Km
W101 4
Isolation4
⋅⋅⋅≤λ≤
⋅⋅⋅ −−
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
16
Multi-layer insulation (MLI) – Superinsulation– Example: Thermal insulation development for a flexi ble
cryogenic line
superconductingcabel
welded tube(60/66 mm)
welded tube (100/110 mm)
welded tube (130/143 mm)
welded tube (198/220 mm)
multilayerinsulation
multilayerinsulation
vacuum
vacuum
spacer
protective outer PE-jacket
LHe
returnedGHe
state of the technology
W/m4,55/mQ ⋅=&Measurement results: corresponding2W/m8,52q ⋅=&
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
17
Improvement actions
Separation of MLI and supporting structures
Solid heat conduction of the supporting structures
→ as low as possible ⇒ small contact areas and cross sections
low heat load at the disconnecting points
Multi-layer insulation (MLI) – Superinsulation– Example: Thermal insulation development for a flexi ble
cryogenic line
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
18
Multi-layer insulation (MLI) – Superinsulation– Example: Thermal insulation development for a flexi ble
cryogenic line
protective outer PE-jacket
welded tubesHTSC-cable(cooled with LN )2
multilayer insulation
bars
supporting rings
vacuum between thewelded tubes
New concept
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
19
Multi-layer insulation (MLI) – Superinsulation– Example: Thermal insulation development for a flexi ble
cryogenic line
New concept
bar
part of the welded tube
contact-points
outer welded tube
inner welded tubewith HTSC-cable
multilayer insulation
floating-supportsystems
supporting ring
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
20
Multi-layer insulation (MLI) – Superinsulation– Example: Thermal insulation development for a flexi ble
cryogenic line
New concept
outer weldedtube
inner weldedtube
supportingrings
longitudinalbars
vertical connectionof the longitudinal bars
multilayerinsulation
about 1.0 m about 0.1 m
longitudinal cross section of the insulation of th e HTSC-cable symmetry line
evacuatedspace}
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
21
Multi-layer insulation (MLI) – Superinsulation– Example: Thermal insulation development for a flexi ble
cryogenic line
Experiments
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
22
10-5 10-4 10-3 10-2 10-1 100
101
102
2
3
4
5
678
2
3
4
5678
2
Nexans: straight without weightNexans: bended without weightNexans: straight with weightGfK-support structure: straight with weightGfK- : support structure straight without weightGfK- : support structure without weightbended spiral : support structure straight with weightspiral support structure straight without weight:
p [mbar]
q k[W
/m2 ]
Nexans GfK-support structure spiral support structure
straight without weight
straight with weight(lead rod)
bended without weight
Multi-layer insulation (MLI) – Superinsulation– Example: Thermal insulation development for a flexi ble
cryogenic line
Experiments
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
23
Multi-layer insulation (MLI) – Superinsulation– Example: Thermal insulation development for a flexi ble
cryogenic line
Experiments boundary condition:
]m/W[q 2m& Nexans
3,70
3,17
2,49
100%
85,59%
67,30%
∆ = 14,41%
∆ = 32,70%
GfK-support structure
spiral support structure
straight without weight
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
24
]m/W[q 2m&
6,60
4,72
3,10
100%
139,83%
67,30%
∆ = 39,83%
∆ = 34,32%
~ 430 N/m
Multi-layer insulation (MLI) – Superinsulation– Example: Thermal insulation development for a flexi ble
cryogenic line
Experiments
spiral support structure
Nexans
GfK-support structure
boundary condition:straight with weight(lead rod)
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
25
Conclusions
For cryogenics application (T < 120 K), vacuum insulation technology is mandatory
For LHe (4 K) – and LH2 (20 K) – applications, the use of the best kind of insulation, so MLI, is warrantable or just enough respectively
MLI is the best kind of thermal insulation if it is used professional
improvement factorsfactor ≥ 10 compared to other vacuum insulation materialsfactors 30 – 100 compared to evacuated powder insulation
further improvement factors of ~ 30 are possible by the use of evaporation enthalpy – multishield-technique
MLI can be flexible adapted very compact if the accessibility is ensured
Thermal insulation | H. Neumann | March 2009
KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)
26
Thank youfor yourattention