CEC Abstracts in PDF format (as of 7/3/07) - CEC-ICMC 2013

CEC 2007 - Abstracts
C3-F-02 Performance of Heat Exchanger Models in
Upside-Down Orientation for the Use in HTS Current
Leads for W7-X
R. Lietzow, R. Heller , H. Neumann ,
Forschungszentrum Karlsruhe.
The sc magnet system of the W7-X stellarator requires 7 pairs of
current leads designed for a maximum current of 18.2 kA. The
Forschungszentrum Karlsruhe is responsible for the construction,
manufacturing and performance test of the current leads. Special
design feature is the installation of the current leads in upside-down
orientation, i.e., the low temperature end of the current lead is at the
top and the room temperature end at the bottom side leading to the
problem of free convection inside the heat exchanger (HEX) due to
density gradients of the helium between 4.5 K and 300 K (factor 500,
p = 0.15 MPa). The occurrence of free convection leads to a reduced
performance of the HEX and results in a higher mass flow rate
required for the operation of the current leads. To overcome the
problem it was decided to use HTS material in the temperature range
between 4.5 K and 60 K. The current lead can then be cooled with 50
K helium. The main reasons for choosing 50 K are: 50 K helium is
available at a higher pressure level from the refrigerator and the
density gradient between 50 K and 300 K is drastically reduced
(factor 6, p = 0.6 MPa). This will reduce the problem of free
convection.
In the paper the performance of HEX mock-ups built of different
HEX types will be described. The tests were performed with helium
cooling of various temperatures in normal and upside-down
orientation. These results were used to select the HEX type for the
W7-X current leads.
C3-F-03 Using High Temperature Superconducting
Leads in a Magnetic Field
M. A, Green, Lawrence Berkeley National
Laboratory; H. Witte, Oxford University.
HTS leads are increasingly used on superconducting magnets. In most
cases either the magnet is iron shielded or the magnet is actively
shielded so that the stray field at HTS leads is low. There are magnets
where the HTS leads must be located in a magnetic field. The two
general types of HTS leads that are commercially available are either
leads fabricated from bulk HTS materials or leads fabricated from
oriented HTS materials that have one or two planes of favorable
current density. HTS leads have been fabricated from a variety of
HTS materials. This paper will discuss how two or three types of
leads are affected by magnetic field. The performance of a HTS leads
is determined by the high temperature end of the lead. The protection
of HTS leads from quenching becomes an important consideration.
Examples of HTS leads in a magnetic field are shown muon
ionization experiment (MICE) magnets.
This work was supported by the Office of Science, United States
Department of Energy, under DOE contract DE-AC02-
05CH11231
C3-F-04 Implementation of HTSC leads for research
cryostats
Y. Shiroyanagi, G. Gopalakrishnan, S. An, D. Ko, T.
J. Gramila, Ohio State University.
Although the advantage of HTSC wires have been proven both in high
current applications and in the presence of active cryocoolers, their
implementation in liquid Helium research cryostats has not been as
successful. A central difficulty involves the need to establish a
specific temperature at the warm end of the HTSC wire, which is
inside the neck of the dewar where temperatures are generally not
well known. A novel approach to heat sinking of magnet leads[1] has
enabled detailed numerical modeling of the magnet lead system,
including the cooling capability of the exiting Helium gas. This
approach has permitted the incorporation of HTSC leads into He
research cryostats, while ensuring they remain cold enough to
superconduct. The overall structure of magnet lead system including
the HTSC wires, its relevant design features, and our characterization
of the system will be presented.
[1] A Novel Approach for Magnet Leads: submitted to JLTP.
Thursday, 07/19/07 Oral
10:30am - 11:45am
C3-G Low Temperature Superconducting
Magnet Systems - IV
C3-G-01 CFD Modeling of ITER Cable-in-Conduit
Superconductors. PART V: Combined Momentum and
Heat Transfer in a Spiral Rib-Roughened Pipe
R. Zanino, Politecnico di Torino; S. Giors, Varian
s.p.a.
Dual-channel cable-in-conduit conductors (CICC) are used in the
present design of superconducting magnets for the International
Thermonuclear Experimental Reactor (ITER). Supercritical helium
coolant flows both in the annular cable region, and in the central
channel, delimited by a (perforated) spiral. As the CICC
axial/transverse size ratio is typically ~ 100, 1D (axial) models are
customarily used for the CICC, but they require constitutive relations
for the transverse fluxes. A novel approach, based on Computational
Fluid Dynamics (CFD), was recently proposed [1], [2] to understand
the complex transverse thermal-hydraulic processes in an ITER CICC.
A 3D CFD tool, the commercial FLUENT code, was used to compute
the friction factor F in spiral rib-roughened pipes, mimicking the
central channel of an ITER CICC. The results where validated against
compact heat exchanger and ITER-relevant experiments. That
analysis is extended here to the problem of combined heat/momentum
transfer. The model is first validated against 2D and 3D data from
compact heat exchangers and then applied to the analysis of central
channel-like geometries relevant for ITER CICC, contributing to a
better understanding of the role of geometric parameters to optimize
both F and the Nusselt number (Nu). The question of the applicability
of the Colburn analogy between F and Nu is also analyzed.
[1]R. Zanino, et al., Adv. Cryo. Eng. 51 (2006) 1009.
[2]R. Zanino, et al., Fus. Eng. Des. 81 (2006) 2605.
C3-G-02 Stability analysis of the ITER TF coil conductor
L. Savoldi Richard, R. Zanino, Dipartimento di
Energetica, Politecnico.
The stability analysis of the International Thermonuclear
Experimental Reactor (ITER). Toroidal Field (TF) coil Nb3Sn
conductor is performed using the Mithrandir code [1]. The most
critical conductor in the winding pack, as well as the most critical
location along it, is identified by the Vincenta code analysis, which
also provides the initial and boundary conditions for the stability
analysis. Two different disturbances are considered: one short in space
and time (1 cm, 1 ms), simulating a disturbance of mechanical nature,
the other longer (3 m, 100 ms) corresponding to AC losses (plasma
disruption). Both disturbances are applied to the superconducting (SC)
cable at end-of-burn (EOB) in the reference ITER inductive operation
scenario. Using this approach, the Mithrandir analysis can be
restricted to the most critical conductor, using a much finer grid than
Vincenta, in order to capture the details of normal zone initiation and
possible recovery to SC state. The computed results, in terms of
minimum quench energy, are compared to the design values. Since the
results are strongly influenced by the choice of the heat transfer
coefficient between strands and helium as expected, this effect has
been also parametrically investigated.
[1] R.Zanino, S.DePalo and L.Bottura,
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