Steady-state heat transfer to boiling liquid helium in simulated coil windings Page: 2 of 20
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from the conductor axis, form a pattern of parallel channels
approximately 12 cm long.
The conductor is pancake wound with the wide face down.
Turn-to-turn insulation is provided by a 42-mm-wide by 0.25-mm-
thick strip of Nomex* paper insulation. Pancake-to-pancake
insulation is provided by grooved, unperforated epoxy-fiberglass
sheets. The three winding pack constituents are shown in Fig. 1.
The test bundle (Fig. 2) is a stack 12 pieces high of 30.5-cm
lengths of GE/LCT-coil 3-T grade conductors separated by the Nomex
paper strips. Heaters were installed in three of the conductor
pieces by pulling the superconducting multifilamentary composite
wire from the surrounding copper carriers and soldering stainless-
steel-sheathed, NgO-insulated Nichrome wires into the resultant
grooves. The stack was divided into three groups of four conductor
pieces, the heated piece being the second one from the bottom in
each group of four pieces. The conductors in the lower two groups
were modified by drilling 1-mm-diam holes (with an average of two
per groove) between subelements and through the core, where grooves
on the top side coincided with grooves on the bottom side. Eight
Au-0.07 at. % Fe vs copper thermocouples with reference junctions
in the bath were installed in each of the three heated conductor
pieces (four in the subelements and four in the core between
subelements). The unheated pieces immediately above and below the
heated pieces were each instrumented with two thermocouples in the
core.
In assembling the stack Nomex strips, modified by punching
them with 4-mm-diam holes on 0.5-in. centers in a rectangular
pattern with six holes per inch length of conductor, were placed
between the conductor pieces in the lowermost group of four
pieces. Unperforated Nomex strips were placed between pieces of
the other two groups. The stack of 12 instrumented pieces was
placed between two grooved pieces of G-10 epoxy-fiberglass insu-
lating sheets with the same groove and land dimensions as the
GE/LCP interpancake spacers. The stack with surrounding insulation
was placed in a clamping mechanism (Fig. 2), and the aluminum
bolts tightened for an estimated pressure of about 14 MPa (2000 >si)
after cooldown, a typical value for the GE/LCT coil windings when
energized. The clamping mechanism and the stack were placed in a
pivot mechanism with an activating rod extending to room tempera-
ture which allowed continuous variation of angle from -3* to 90*
from horizontal when the sample was in a liquid helium bath.
*
Reference to a company or product name does not imply approval or
recommendation of the product by Union Carbide Corporation or the
U.S. Department of Energy to the exclusion of others that may be
suitable.
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Walstrom, P.L. Steady-state heat transfer to boiling liquid helium in simulated coil windings, article, January 1, 1981; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc1105410/m1/2/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.