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

CEC 2007 - Abstracts
C1-H-02 Application of Novel Regenerator Material
Within a Coaxial Two-Stage Pulse Tube Refrigerator
T. Koettig, F. Richter, R. Nawrodt, M. Thuerk, P.
Seidel, Friedrich-Schiller-University Jena.
We have developed a lead-based regenerator material which is
suitable for working temperatures below 20 K. This material can be
used as a substitute for the state of the art materials used today within
very low-temperature regenerators. This high efficient regenerator
matrix combines technological advantages with the possibility to vary
the thermodynamic and flow characteristics over a wide range,
continuously. Hence, our self-made electroplated screen material is
compared with standard regenerator materials (commercially available
woven screens and packed spheres). The gap between matrix
porosities of standard screens around 0.65 and the porosity of packed
spheres with 0.38 is stepwise investigated regarding the pressure drop
and heat transfer characteristic. The design parameters and the
influencing variables to optimise the regenerator performance will be
discussed. The utility of the shop-made lead coated regenerator
material is demonstrated in a coaxial two-staged pulse tube
refrigerator with working temperatures below 7 K.
C1-H-03 The Impact of Uncertainties Associated with
Regenerator Closure Parameters on the Predicted
Performance of Pulse Tube and Stirling Cryocoolers
J.S. Cha, W.M. Clearman, S.M. Ghiaasiaan, P.V.
Desai, G.W. Woodruff School of Mechanical
Engineering Georgia Institute of Technology.
Recent investigations have shown that computational fluid dynamics
(CFD) techniques can be used for modeling the entire pulse tube
(PTR) and Stirling cryocooler systems. However, the results of CFD
simulations can be trusted only if they are based on correct closure
relations. The hydrodynamic and heat transfer parameters associated
with regenerators are among the most important and poorlyunderstood
closure relations for these cryocooler systems. In this
investigation the impact of uncertainties associated with flow
resistance parameters, as well as solid-fluid heat transfer coefficients,
on the performance of PTR and Stirling cryocoolers is examined using
CFD simulations. This objective is achieved by performing
simulations where reference PTR and Stirling cryocooler systems
operating in steady-periodic conditions are modeled in their entirety.
The effects of uncertainties in the regenerator closure parameters on
the cryocoolers performance parameters, as well as their key local
hydrodynamic and heat transport processes, are quantified by the
parametric variation of the aforementioned regenerator closure
parameters.
C1-H-04 New Thermoacoustic Model, New Measurement
Principle and Experimental Results of Flowing and Heat
Transfer Characteristics of Regenerator
Y.Y. Chen, Graduate University of Chinese Academy
of Sciences; E.C. Luo, Technical Institute of Physics
and Chemistry, CAS; W. Dai, Technical Institute of
Physics and Chemistry,CAS.
Regenerators play key role in oscillating-flow cryocoolers or
thermoacoustic heat engine systems. However, their flowing and heat
transfer mechanism is still not well understood. In this paper, the
authors present a new methodology for studying flowing and heat
transfer characteristics of the oscillating flow regenerator. First we
will present a new thermoacoustic model for oscillating-flow
regenerator. In the model, the local flow and heat transfer
performance of the regenerator can be characterized by its equivalent
thermoacoustic viscous and thermal functions, and a dimensionless
local averaged temperature gradient. Then, we present a simple
acoustical method and experimental system to get the functions. Here,
pressure measurements and velocity measurements by hot wire
anemometry were performed with different screen-packed
regenerators to obtain the two functions. With the two measured
functions, local flowing friction factor and heat transfer coefficient
within the regenerators where mean temperature gradient exists can be
predicted. Finally, local flowing and heat transfer coefficients are
summarized with several dimensionless groups for general and
convenient using.
This work was supported by the Natural Science Foundation of
China(Grant No.50625620)
C1-H-05 Longitudinal Hydraulic Resistance Parameters
of Cryocooler and Stirling Regenerators in Periodic Flow
J.S. Cha, S.M. Ghiaasiaan, P.V. Desai, G.W.
Woodruff School of Mechanical Engineering Georgia
Institute of Technology.
The results of an on going research program aimed at the
measurement and correlation of anisotropic hydrodynamic parameters
of widely-used cryocooler regenerator fillers are presented. The
hydrodynamic parameters associated with longitudinal steadyperiodic
flow are addressed in this paper. An experimental apparatus
consisting of a cylindrical test section packed with regenerator fillers
is used for the measurement of axial permeability and Forchheimer
coefficients, with pure helium as the working fluid.The regenerator
fillers that are tested include stainless steel 400-mesh screens with
69.2% and 62% porosity, stainless steel 325-mesh screens with 69.2%
and 62% porosity, stainless steel 400-mesh sintered filler with 62%
porosity, and stainless steel sintered foam metal with 56% porosity.
The test section is connected to a Stirling type compressor on one end
and to a constant volume chamber on the other end. The
instrumentation includes piezoelectric pressure transducers at both
ends of the regenerator. For each filler material, time histories of local
pressures at both ends of the regenerator are measured under steady
periodic conditions over a wide range of oscillation frequencies. A
CFD assisted methodology is then used for the analysis and
interpretation of the measured data. The permeability and
Forchheimer parameter values obtained in this way are correlated in
terms of the relevant dimensionless parameters.
C1-H-06 A new correlation of friction factor for
oscillating flow regenerator operating at high frequencies
Y.L. Ju, Q.Q. Sheng, Shanghai Jiaotong University.
Regenerator plays an important role on the performance of low-power
cryocoolers, in particular at high operating frequencies. The ability to
accurately predict the pressure drop and phase shift across the
regenerator is directly related to the cooling capacity and efficiency of
a cryocooler. Many works have revealed that the friction factors under
unidirectional steady flow conditions are unsuccessful in predicting
the flow characteristics of regenerators typically operating at
oscillating flow and pulsating pressure conditions. Recent researches
have been conducted, using both theoretical analyses and
experimental measurements, either to correlate the conventional
friction factor by introducing additional parameters or to develop new
flow models to overcome the shortcoming of the steady-flow friction
factor. However, validation and application of these results for
cryocooler regenerators are still questionable because of the complex
and randomly oriented matrix geometry of actual regenerators. In this
paper, we will first summary typical experimental results and
correlations on the friction factor of regenerators for different sizes of
packed woven screens, at different frequencies, at room and cryogenic
temperatures. The comparison of those friction factor data will then be
presented to clarify the reason for their difference. Finally, a new
correlation of friction factor for oscillating flow regenerator, in terms
of two non-dimensional parameters, will be presented.
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