Cryogenic Experts Meeting (19 ~ 20.09.2007)Cryogenic Experts Meeting (19 ~ 20.09.2007)

Heat transfer in SIS 300 dipole

MT/FAIR – Cryogenics

Y. Xiang, M. Kauschke

• Heat transfer through laser cutting holes (M. Wilson, TU Dresden and GSI );

• Temperature margin check-up for the SIS 300 dipole IHEP design by using 2D ANSYS simulation;

• Optimization of the interlayer cooling channel and its connection channels based on 3D ANSYS calculation

• Heat transfer analysis of 1-phase and 2-phase helium recooling process in one 300 Tm dipole;

• Conclusions

Outline

Cryogenic Experts Meeting (19 ~ 20.09.2007)Cryogenic Experts Meeting (19 ~ 20.09.2007)

Concerns on large thermal resistance due to big helium space underneath the Kapton insulation of coil cables

Pv

heatflow

helium

insulated

gi

Pa

t

Pv

Fig 1: Gas bubble formed where Kapton wrap bulges away from cable at the edges.

Martin Wilson Report GSI 5 (25 Jan 2001)

A calculation of 0.35 K temperature rise through a stagnant gas film, assuming the film to be 0.5mm thick.

Two types of Laser cutting holes on cable insulation

Fig 2: Edge view of the cable with holes cut by Jena University

Martin Wilson Report GSI 17 (5 Feb 2004)

2.061.59

1.26 0.4

2.061.59

1.26 0.4

2.061.59

1.26 0.4

2.061.59

1.26 0.4

Heat transfer through a hole in the electrical insulation by CFD analysisM. Hieke, H. Quack (08.12.2004 )

Helium layer thickness: 20 m

w (m/s) 0.1 0.5 1.0

ktot without hole (W/m2 K) 66.7 90.4 98.2

ktot with hole (W/m2 K) 69.5 283.6 529.2

Helium layer thickness: 500 m

w (m/s) 0.1 0.5 1.0

ktot without hole (W/m2 K) 25.3 28.1 28.8

ktot with hole (W/m2 K) 41.9 217.6 375.7

Fig. 2 – CFX model for helium flow above insulation with a hole and temperature contours (helium layer 500 m, average velocity 0.1 m/s)

heat transfer coefficient (total)

2D ANSYS analysis at GSI about the influence of cooling hole on helium flow and heat transfer (07.2004)

Type A _ cooling hole of nominal width 630 micrometers

Type B _ cooling hole of nominal width 400 micrometers

Thickness of the four layers Kapton : 88 micrometers

Thickness of the helium space underneath the four layers Kapton : 31 micrometers

Thickness of the four layers Kapton : 102 micrometers

Thickness of the helium space underneath the four layers Kapton : 19 micrometers

Depth of the helium groove in the superconductor : 100 micrometers

The measurement shows the depth of the helium space underneath the Kapton layers is about 20 ~ 30 micon. For the cured cable it may be even smaller.

Observation and measurements for the cooling holes on cable insulation with microscope at GSI (13.05.2004)

purposes:• to check the temperature margin of the magnet design at IHEP, Moscow• optimization the interlayer cooling channel dimensions to ensure enough temperature margin for the magnet operation

Note: The cross section of the 2D model has ellipse shape because the coil is cut at 45 degree direction with respect to the magnet axis.

2D ANSYS analysis at GSI on the temperature margin check-up for SIS 300 6 T IHEP design (03.2006)

In the modelno cooling holes on the insulation!no helium space underneath the insulation!

supercritical helium (light blue), NbTi coil turns (violet), SS304 wedges (dark blue) and 0.1 mm polyimide film of insulation (not shown).

Ramping conditions of 6 T superconducting SIS 300 dipole (IHEP design)

"Design of 6T superconducting dipoles for the SIS 300" IHEP report 06.05.2003. "Design of 6T superconducting dipoles for the SIS 300" IHEP report 06.05.2003.

Assumed power loss curve of turns over one cycle based on IHEP 2005 AC losses data

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

0 1.1 2.2 3.3 4.4 5.5 6.6 7.7 8.8 9.9 11 12.1 13.2 14.3 15.4 16.5 17.6 18.7 19.8

time [s]

Heat

gen

erat

ion

rate

[W/m

m^3

]

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

6.5

7

Current [kA]

Averaged turn power loss over all turns of inner layer [W/mm^3] Averaged loss of all turns of inner layer over one cycle [W/mm^3]

Averaged turn power loss over all turns of outer layer [W/mm^3] Averaged loss of all turns of outer layer over one cycle [W/mm^3]

Assumed power loss curve of turns over five cycles based on IHEP 2005 AC losses data

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

0 9.9 19.8 29.7 39.6 49.5 59.4 69.3 79.2 89.1 99

Time [s]

Heat

gen

erat

ion

rate

[W/m

m^3

]

averaged loss of inner layer over turns [W/mm^3] averaged loss of outer layer over turns [W/mm^3]

Power loss curve over one cyclePower loss curve over one cycle Power loss curve over five cyclesPower loss curve over five cycles

Temperature profile of the inner and outer coil layers and helium flow in the interlayer cooling channel at certain time during the ramping

Temperature profile at end of 5 ramping cycles

Interlayer cooling channel

connection channel outlet

annular channel

connection channel inlet

• Highest temperature occurs in the coil blocks of outer layer with many turns (poor cooling conditions)

• High temperature occurs also at the turns of outer layer close to the pole (high field region);

• SS304 wedges help cooling the neighboring turns

Temperature profile and its changes of inner-, outer-turn layers and helium flow during the ramping

Animation video of temperature profile during 5 ramping cycles

Time history of temperature changes at three positions in the turns and of the helium flow nearby during ramping

The calculated temperature margin of the first pole turn by ANSYS is about 0.9 K if the critical temperature for this turn is 5.69 K (IHEP 2005 report). This fits the results in the IHEP 2005 report.

Temperature profile in the pole turn region and helium flow velocity when the highest temperature is reached during ramping (80 s)

Temperature differences between the coil cable and the helium are :

~ 0.3 K at the outler layer in the pole region;

~ 0.1 K at the first turn of inner layer in the pole region;

They are dominated by the temperature drop on Kapton insulation

The average helium velocity in the interlayer is about 0.01 m/s which corresponds to the mass flow rate of 0.005 g/s

purpose:• to allow as much the helium mass flow into the interlayer cooling channels as possible so as to improve the cooling performance

Optimization of the interlayer cooling channel and its connection channels based on 3D ANSYS calculation

Optimization results discussion

helix channelconnection channel

annular channel

Dimension of fishbone channel [mm]

1 x 4 2 x 4

Dimension of connection channel [mm]

0.5 x 2 0.5 x 4 2 x 2 1 x 4 2 x 2 2 x 4

Velocity in fishbone channel [m/s]

~0.018 ~0.037 ~0.042 ~0.056 ~0.033 ~0.047

Mass flow rate fishbone channel [g/s]

0.009 0.019 0.021 0.028 0.032 0.048

Temperature margin [K] 0.88 0.96 0.98

* Mass flow rate is kept constant at 38 g/s in the annular channel which is of 5 mm gap.The best combination is that both the helix channel and connection channels have the same height and width.

Investigation of 1-phase and 2-phase helium recooling process in SIS 300 dipole

Cooling concept of SIS 300 dipole (origins from HERA [and UNK] dipole)

One example to show how important is the recooling process

Test results of temperature profile of one Tevatron dipole (cryogenics 37, 1997)

Heat transfer coefficients of supercritical helium, liquid helium (nucleate boiling and convection) and vapor in 2-phase recooling over 3 m dipole length

Engineering Data Book III, Chapter 10, Boiling heat transfer inside plain tubes,

Temperature profile of 1-phase and 2-phase helium over 3m recooling process in one 300 Tm dipole

Parameters of LHC dipole heat exchanger has been used for the simulation

0.11 K

0.06 K

Heat load for one dipole: 15 W

coil

iron

iron

coil

iron

ironcoil

iron

iron

SIS 300 dipole – guiding plate for better recooling performance

The influence of part load operation on heat transfer coefficients in 2-phase recooling process

100 % load 50 % load

• The analysis shows that the Laser cutting holes technology is an effective way to improve the cooling performance but further investigation is needed on the other aspects (strength under rapid ramping, electric insulation characteristics estimation, etc.);

• Observation and measurements for the cooling holes on cable insulation shows the contribution of thermal resistance by helium space underneath the cable insulation can be neglected;

• Temperature margin check-up for the SIS 300 dipole IHEP design and optimization of the interlayer cooling channel and its connection channels have been successfully done;

• Heat transfer of 1-phase and 2-phase helium recooling process in one 300 Tm dipole has been simulated and ways to improve recooling performance has been discussed.

Conclusions

Cryogenic Experts Meeting (19 ~ 20.09.2007)Cryogenic Experts Meeting (19 ~ 20.09.2007)