Druck-Materie 20b.qxd - JUWEL - Forschungszentrum Jülich

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The results show the system of multiple parameter optimization can be beneficial. The advantage of the current system is that the whole flight-lines and moderator are required to move as the pre-moderator is changed and this saves significant human effort. It is the ability to move a large number of objects coherently that allows models with significant amount of engineering detail to be optimized. 5. CONCLUSIONS We have a first version of a geometry handling package for MCNPX simulations. It can be used to refine a geometry without direct configuration of the components. This shows promise to allow optimization of significantly more complex models than are currently parameterised. REFERENCES [1] M. de Berg, Computational Geometry: Algorithms and Applications , Belin, Springer, 2000 ACKNOWLEDGEMENTS The authors wish to acknowledge the invaluable help provided by D. Picton on problems with MCNPX. 76
ABSTRACT ACoM – 6 6 th Meeting of the Collaboration on Advanced Cold Moderators Jülich, 11 - 13 September 2002 Fluid Dynamics of Cryogenic Two-Phase Flows Karl Verfondern, Wilfried Jahn Forschungszentrum Jülich GmbH, European Spallation Source Project 52428 Jülich, Germany The objective of this study was to examine the flow behavior of a methane hydrate/methane-liquid hydrogen dispersed two-phase fluid through a given design of a moderator chamber for the ESS target system. The calculations under simplified conditions, e.g., taking no account of heat input from outside, have shown that the computer code used, CFX, was able to simulate the behavior of the two-phase flow through the moderator chamber, producing reasonable results up to a certain level of the solid phase fraction, that allowed a continuous flow process through the chamber. Inlet flows with larger solid phase fractions than 40 vol% were found to be a “problem” for the computer code. From the computer runs based on fractions between 20 and 40 vol%, it was observed that with increasing solid phase fraction at the inlet, the resulting flow pattern revealed a strong tendency for blockage within the chamber, supported by the “heavy weight” of the pellets compared to the carrying liquid. Locations which are prone to the development of such uneven flow behavior are the areas around the turning points in the semispheres and near the exit of the moderator. The considered moderator chamber with horizontal inlet and outlet flow for a solid-liquid two-phase fluid does not seem to be an appropriate design. 1. INTRODUCTION Both hydrogen and methane are currently being widely applied as cryogenic moderator material in target systems of neutron sources. Supercritical hydrogen is the material of choice for the reference design of the European Spallation Source (ESS) cryogenic moderator, as has also been selected for the US spallation source SNS as well as for the respective Japanese project SNS. Solid methane as moderator material, which is also in use in different facilities, is known to outperform liquid hydrogen in terms of neutronic characteristics. It is, however, not appropriate for higher power neutron sources such as the ESS because of its radiation-induced decomposition, where exothermal recombination processes of the radicals represent a significant risk. In order to combine the advantages of both materials and mitigate their drawbacks, a mixed moderator concept of solid methane pellets plus liquid hydrogen (LH2) has been proposed first by Lukas in 1988 [1], which is expected to provide a high cold neutron intensity and narrow pulses of thermal neutrons and to operate also at higher powers. The aim of the study here is the computer simulation of the flow behavior of the above mentioned solid-liquid two-phase system within the moderator chamber as presently designed for the ESS facility. The calculational tool is a Computer Fluid Dynamics (CFD) code, which is principally able to handle multi-phase flows in complex geometries. Multi-phase flow refers to a situation where more than one fluid, not necessarily different phases of the same species, may be present. Unlike multi-component systems, multi-phase flows consist of species which are mixed at much larger than molecular scale. All phases will potentially have differ- 77
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ACoM - 6 6th 6 International Worksh
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Forschungszentrum Jülich GmbH Inst
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Preface These are the Proceedings o
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List of participants, cont’d. Kü
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Pepe M. 43 Petriw S. 43 Picton D.J.
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Experimental background, results an
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• Light water ice as H(H2O) at T
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In Table 2 a survey is given about
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sigma-T in barns/molecule Figure 4.
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2.3 Liquid water Compared to the so
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presented. The corresponding experi
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3.2 Gaseous hydrogen and deuterium
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Rho(Omega) normalised 160 140 120 1
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elatively free and can also suffer
Page 30 and 31: Figure 16. Heat Capacity for Solid
Page 32 and 33: o-D2 and p-H2 at 5K for an ucn ener
Page 34 and 35: Figure 22. UCN Upscattering Rates i
Page 36 and 37: ho(omega) normalised 40 35 30 25 20
Page 38 and 39: derived from Walker [52]. The neutr
Page 40 and 41: Since there is only a small gain of
Page 42 and 43: 7. CALCULATION OF SCATTERING LAW DA
Page 44 and 45: For the validation of these data se
Page 46 and 47: [36] Nielsen, M.: Phonons in Solid
Page 48 and 49: 2. THE CASE OF MOLECULAR SOLIDS An
Page 50 and 51: γ r ( 0) ≅ 2 2 2 T erf e ( ) / 2
Page 52 and 53: 4. PRELIMINARY APPLICATION Solid Me
Page 54 and 55: [5] Meeting on Moderator Concepts a
Page 56 and 57: state. Conversely, the monatomic hy
Page 58 and 59: Note that the equilibrium trihydrog
Page 60 and 61: para hydrogen system under irradiat
Page 62 and 63: [12] T. E. Fessler and J. W. Blue,
Page 64 and 65: tion of neutron intensities, partic
Page 66 and 67: varied between calculations but the
Page 68 and 69: 5. THE OPTIMISATION OF MULTIPLY GRO
Page 70 and 71: Figure 7. A comparison of time dist
Page 72 and 73: 4.8 cm hydrogen slab in front of a
Page 75 and 76: ACoM - 6 6 th Meeting of the Collab
Page 77 and 78: the moderator is annealed every 12
Page 79: The method requires two additional
Page 83 and 84: Heat transfer processes across phas
Page 85 and 86: 3. TWO-PHASE FLOW PATTERN IN THE MO
Page 87 and 88: continuous phase dominating, and a
Page 89 and 90: Also the velocity pattern has chang
Page 91 and 92: Figure 8. Methane pellets concentra
Page 93 and 94: ACoM - 6 6 th Meeting of the Collab
Page 95 and 96: sample volume and the nominal densi
Page 97 and 98: The results presented in this paper
Page 99: Table 10. Summary of energy transfe
Page 102 and 103: 2. EXPERIMENTAL Methane hydrate was
Page 104 and 105: Figure 4. Energy levels of methane
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Page 108 and 109: phase transitions from phase II to
Page 110 and 111: After melting phase I in the cryost
Page 112 and 113: 4. SOLID PHASES OF MESITYLENE-D0 AN
Page 114 and 115: G(ν) [a.u.] 8 6 4 2 Phase II Phase
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Page 118 and 119: A not quite as perfect cold spectru
Page 120 and 121: 2.2 Inelastic neutron scattering Th
Page 122 and 123: Figure 4. Inelastic spectra at the
Page 124 and 125: 3.2 Moderator performance The resul
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Page 128 and 129: Figure 2. The methane pelletizer, m
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Figure 5. The cryogenic hopper fill
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128
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ture
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The charging device scheme could be
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Table 1. Data of irradiation of met
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5. METHODS OF PROCESSING OF RAW EXP
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of radicals, that is, before a burp
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6.2 Condition for thermally stimula
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Table 4. Estimated values of an ene
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• Nine spontaneous burps were obs
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APPENDIX Some useful relations and
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APPENDIX. Graphs of burps. 148
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150
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152
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2. EXPERIMENTAL SETUP Fig. 1 will g
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All these parameters are kept const
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4. CONCLUSIONS We demonstrated that
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JESSICA (Juelich Experimental Spall
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The moderator system consists of th
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to change the temperatures and to p
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168
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supplied from the high pressure bom
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10 9 10 8 10 7 10 6 Para35%[Experim
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174
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2. TIME OF FLIGHT SPECTRA AND ENERG
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When applying this transformation t
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data were analyzed in more detail.
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182
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First of all, we should conclude th
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The equation (a) may also describe
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Even at h=0.01 mm which is too smal
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model and some consequences of its
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methane and 0.7-1.5% for water ice
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case: the sample of infinite size.
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Phase Diagram of the CH4-H20 system
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Reaction Chamber for Hydrate Produc
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Analysis: X-ray diffraction pattern
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Comparison with non-hydrate forming
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Mechanical Tests: Apparatus 220
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Morphology of Indium Jacket 222
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Schriften des Forschungszentrums J
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Schriften des Forschungszentrums J
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