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

CEC 2007 - Abstracts
C1-J Pumps and Compressors
C1-J-01 Pressure Oscillator Losses at High Frequency
and High Pressure
P.E. Bradley, M.A. Lewis, R. Radebaugh, National
Institute of Standards and Technology; A. Veprik,
Ricor Ltd, Cryogenic Vacuum Systems.
High frequencies show potential for reducing the size of both the
pressure oscillator and cold head for a given cooling power while
leading to a faster cool-down. Previously, we made comparisons of
pressure oscillator efficiency employing a total loss method of
subtracting internal thermodynamic losses from the PV power at the
piston face for frequencies up to 70 Hz with mean pressures up to 2.5
MPa for a load optimized for around 45 Hz. In this paper we present
similar comparisons for high frequency operation up to 120 Hz and
high mean pressure up to 3.5 MPa for an appropriately optimized
load. Both small and large pressure oscillators from 4 cm3 to 25 cm3
are evaluated for high frequency and high pressure operation. We
discuss pressure and flow losses for the high frequency (120 Hz) and
high pressure (3.5 MPa) operation compared with 30 to 60 Hz
frequency and 2.0 to 2.5 MPa pressure operation. Pressure ratios
ranged from 1.0 to 1.3. The overall compressor efficiency, the
delivered PV power to a load divided by the electrical input power to
the compressor is determined for the high frequency and high pressure
operation as well.
C1-J-02 Screw Compressor Characteristics for Helium
Refrigeration Systems
P.N. Knudsen, V. Ganni, Jefferson Lab.
The oil injected screw compressors have practically replaced all other
types of compressors in modern helium refrigeration systems due to
their large displacement capacity, minimal vibration, reliability and
capability of handling helium`s high heat of compression.
At the present state of compressor system designs, half the input
energy is lost in the compression system. Therefore it is important to
understand the isothermal and volumetric efficiencies of these
machines to help properly design these compression systems. This
presentation summarizes three separate tests that have been conducted
on Sullair compressors at the Superconducting Super-Collider
Laboratory (SSCL) in 1993, Howden compressors at Jefferson Lab
(JLab) in 2006 and Howden compressors at the Spallation Neutron
Source (SNS) in 2006. Although the compressor pressure ratio and
built-in volume ratio are the primary parameters affecting the
efficiencies of the screw compressor proper, it is evident from these
tests that the compressor skid design also strongly influences the
overall efficiencies and performance of the compression system. This
work is part of an ongoing task at JLab to understand the theoretical
basis for these efficiencies and their loss mechanisms, as well as to
implement practical solutions.
C1-J-03 Designing Liquid Cryogenic Systems for Use
with Centrifugal Pumps
J.E. Dillard, W.D. Batton P.E., J.A. Busby Ph.D., J.W.
Shull, M.R. Anderson, Barber-Nichols Inc.
A cryogenic system is a collection of interdependent components
working together; therefore, proper system performance is dependent
upon an understanding of each component’s relationship with other
components in the system. This paper examines the relationship
between centrifugal pumps and other components in liquid cryogenic
systems during cool down and steady state operation.
Two common problems which affect liquid cryogenic systems are
cavitation and cryogen vaporation; both can significantly decrease
mass flow and adversely effect overall system performance. However,
a system-based, rather than a component-based, design philosophy
can help avoid these problems. Additionally, cool down and steady
state operation are two equally important system modes. Excessively
tight design margins based exclusively on steady state operational
requirements can compromise a system’s ability to cool itself to its
operating temperature.
C1-J-04 Experience with dry running vacuum pumps in
helium service
R. Arztmann, Linde Kryotechnik AG.
A process vacuum system for helium using dry running vacuum
pumps only was shop tested and installed in a refrigeration plant to
serve cavities operating at 2K for a cryogenic storage ring.
The paper explains the joint development steps of Busch AG and
Linde Kryotechnik AG to use dry running vacuum pumps for helium
service at ambient temperature. A roots type booster pump followed
by a non lube rotary screw pump provides very good performance in a
helium vacuum pump system. Variable frequency drives on both
pumps allow to adjust the pump characteristics to a wide range of
operating parameters. Operation without friction of sealing elements
in the compression space also of the screw pump promises extended
maintenance intervals and virtually no wear on the rotors. The current
plant operation at Max Plank Institute in Heidelberg, Germany
Laboratory will provide additional experience for further applications.
C1-J-05 Thermal Design of a Superconducting Bearing
with a Magnetic Journal at Room Temperature.
X. Granados, Q Lloberas, ICMAB-CSIC; J López, R
Maynou, CEIB.
Interaction between permanent magnets and superconducting pellets
provides a stable and durable way for bearing in both thrust and axial
bearing. The axial symmetry of the magnetic field, and that of the
inertia axis, allow achieving non-friction rotating coupling thus
improving reliability and a simplification of the bearing design. The
cooling requirement of the superconductors is a main concern because
the life and the losses of the bearing are essentially the life and
efficiency of the cooling system. In this work we present the thermal
design of a passive thrust bearing with a room temperature magnetic
journal and a plane superconducting stator. In this paper, we discuss
the main points for optimization of the gap thermal isolation in order
to achieve the minimum losses-stiffness ratio.
Tuesday, 07/17/07 Poster
1:30pm - 3:00pm
C1-K Low Temperature Superconducting
Magnet Systems - I
C1-K-01 Leak-tight welding experience from the
Industrial assembly of the LHC cryostats at CERN.
V. Parma, N. Bourcey, P. Campos, A. Mongelluzzo, A.
Poncet, CERN; P. Limon, FNAL; G. Musso, SERCO.
The assembly of the approximately 1700 LHC ring cryostats at
CERN involved extensive welding of cryogenic lines and vacuum
vessels. More than 6 km of welding requiring leak tightness to a rate
better than 1.10-9 mbar.l.s-1 on stainless steel and aluminium piping
and envelopes was made, essentially by manual welding but also
making use of orbital welding machines. In order to ensure the
fulfillment of safety regulations of pressure vessels and to comply
with the leak-tightness requirements of the vacuum systems of the
machine, welds were executed according to high qualification
standards and following a severe quality assurance plan. Leak
detection by He mass spectrometry was extensively used. Neon leak
detection was used successfully to locate leaks in the presence of
helium backgrounds. The use of SF6 as a tracer gas with a sniffer was
also tried.
This paper presents the quality assurance strategy adopted for welds
and leak detection. It presents the statistics of non-conformities on
welds and leaks detected throughout the entire production and the
advances in the use of alternative leak detection methods in an
industrial environment.
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