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

CEC 2007 - Abstracts
C3-H-05 Performance of Helium Circulation System 1
(HCS1)
T. Takeda, M. Okamoto, K. Atsuda, A. Kobayashi, K.
Katagiri, Univ. of Tokyo.
We have developed a system to collect evaporated helium gas, to cool it
down to liquid and to return it into a FRP dewar for MEG
(Magnetoencephalography) using two GM cryocoolers without
delivering any disturbing noises to the MEG. The key idea is to utilize
relatively high temperature helium gas (about 40K) cooled by the first
stage of the GM cryocoolers to get rid of invading heat to the dewar,
but not to use liquid helium directly to keep the dewar cooled down.
The gas is fed at the neck tube of the dewar. The evaporated helium gas
in the dewar is collected swiftly while it is in the low temperature
(about 8K) and is returned to liquid without using much energy.
A transfer tube that passes the liquid helium, the low temperature
helium gas (about 8K) and the relatively high temperature helium gas
has been developed to accomplish the above idea. A refiner to collect
the contaminating gases such as oxygen and nitrogen effectively by
freezing the gases is developed. It has an electric heater to remove the
frozen contamination in the form of gases into the air. A gas flow
controller is also developed, which automatically control the heater to
cleanup the contamination. The magnetic, vibrational and acoustic
noises are attenuated to be low enough for MEG measurements. The
system can circulate at least 35.5 litters of evaporated liquid helium per
day and usable at least for one year without any maintenance.
C3-H-06 Design Parameters for Cryogenic
Thermosyphons
H. Timinger, B. David, R. Eckart, J. Overweg, Philips
Research Europe-Hamburg.
Cryogenic thermosyphons are the thermal conductors of choice for a
variety of applications like e.g. conduction-cooled superconducting
devices. They exhibit a small effective thermal resistance at small
cross-sections. A careful design, however, is crucial to ensure
sufficient heat transport for all possible heat loads. The aim of this
work is to obtain experimental results on the effective thermal
resistance dependent on the length, the cross-sectional area, and the
working fluid fill level of a thermosyphon for different heat loads.
For the experiments, a modular thermosyphon was designed with 4
different adiabatic tubes of length [cm]/cross-sectional area [sqcm]
10/0.8, 10/3.14, 30/0.8, and 30/3.14, which can be mounted between
condenser and evaporator. The thermosyphon was operated with
different fill-levels of either nitrogen or neon and different heat loads.
The thermal resistance between condenser and evaporator was
determined, dependent on the design parameters mentioned above.
Additionally, the useful temperature range of operation was
determined for nitrogen and neon. The results of the experiments are
summarized in diagrams and provide useful reference data for the
design of cryogenic thermosyphons.
C3-I Fluid Mechanics - II
C3-I-01 Surface oscillation of liquid nitrogen induced by
step reduction of gravity acceleration
M. Stief, M.E. Dreyer, ZARM – Univ. of Bremen -
Germany.
For space application, which involve the handling of cryogenic liquids
e.g. liquid hydrogen or oxygen, the concern of free surface behavior
upon change of acceleration level arises. With reduction of gravity
acceleration hydrostatic loose there dominance and the free surface
and therefore the motion of liquids is dominated by capillary forces.
So far the characteristics of the fluid motion subjected to a sudden
reduction of gravity acceleration has been mostly investigated with
conventional storable liquids. Because cryogenic liquids have
different characteristics, these results provide only limited estimations
for considered space applications. To overcome this knowledge gap
experiments with liquid nitrogen inside partly filled right circular
cylinder have been performed at the droptower in Bremen, which
provides 4.7s of very low gravity acceleration level and a steep
transition from 1g to 0g. The oscillation of the free surface where
optically observed by video system during microgravity and processed
for detection of the motion of the center location of the free surface
and contact line of the liquid at the cylinder wall.
The funding of the research project by the German Aerospace Center
(DLR) under grant numbers 50JR0011 and 50WM0241 is gratefully
acknowledged.
C3-I-02 Pressure drop of cable-in-conduit conductors
with different void fraction
C. Marinucci, P. Bruzzone, F. Staehli, EPFL, CRPP
Fusion Technology; L. Bottura, CERN, AT Dept..
Pressure drop cable-in-conduit conductors (CICC) was measured at
CRPP. The conductors are single channel CICC’s with different void
fraction in the range 38 to 28 %. Several conductor samples are
investigated and tested in SULTAN by supercritical helium and in a
room temperature facility by pressurized water. In particular,
experiments are performed on samples at different degree of
compaction, measuring the void fraction after each compression step.
In this way it is possible to assess the friction factor of the cable
bundle as a function of the void fraction. The reduction of the
experimental data to obtain the friction factor as a function of
Reynolds number is performed by (a) established methods using the
correlation proposed by Katheder and (b) a new porous media analogy
model. We discuss the results and in particular the comparison of
these two methods of correlation.
C3-I-03 Flow of Saturated Liquid Nitrogen through
Micro-Scale Orifices
T.A. Jankowski, E.N. Schmierer, F.C. Prenger, S.P.
Ashworth, Los Alamos National Laboratory.
The flow of saturated liquid nitrogen through micro-scale orifices has
been characterized experimentally. Measurements of pressure drop
and flow rate were made with liquid nitrogen flowing through orifices
ranging in diameter from 35 micron to 250 micron, with orifice length
to diameter ratios ranging from 2 to 15. The design of the
experimental apparatus, the instrumentation used, and the
experimental uncertainties are presented. Difficulties with clogging
of the micro-scale orifices and with obtaining repeatable and reliable
results at cryogenic temperatures are discussed. Finally, experimental
results are shown to agree with previous investigations of flow
through micro-scale orifices using room temperature refrigerants.
C3-I-04 A Rotating Heat Pipe for Cooling of
Superconducting Machines
T.A. Jankowski, F.C. Prenger, E.N. Schmierer, Los
Alamos National Laboratory; A. Razani, The
University of New Mexico.
A curved rotating heat pipe for use in superconducting motor and
generator applications is introduced here. A numerical model of the
curved rotating heat pipe [1], which has been validated with room
temperature experiments, is used to predict the performance of
rotating heat pipes using cryogenic working fluids. Heat pipe model
results are compared to results for a single-phase gas-cooled
refrigeration system in typical superconducting generators and motors.
The nearly isothermal operation of the heat pipe is shown to reduce
the temperature gradients seen by the superconducting coil compared
to the forced flow gas system. Furthermore, because of the passive
nature of the heat pipe operation, the heat pipe concept may be
advantageous when considering the overall refrigeration system.
Finally, because of their modular nature, the use of multiple heat pipes
provides redundancy in the cooling system.
[1] T. A. Jankowski, “Numerical and Experimental Investigations of a
Rotating Heat Pipe,” Ph.D. Dissertation, The University of New
Mexico, 2007.
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