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[en] The phenomenon of choking which is observed for compressible flows is mathematically interpreted as the characteristic determinant of the flow equations being zero. If it is computed by a finite difference method, it is shown that a flow rate blockage results from a property of the matrix of the linearized finite difference equations. This property is reducibility
[fr]On considere un ecoulement compressible dans un canal. On montre que selon le schema aux differences finies utilise pour calculer numeriquement l'ecoulement, le fait que la vitesse en un point du canal atteigne la vitesse du son peut correspondre ou non au decouplage des solutions numeriques en amont et en aval du col sonique, c'est-a-dire au phenomene de blocage sonique
[en] The SPACE code offers several options for critical flow model. One of the option is Henry/Fauske-Moody model. When using this model, Henry-Fauske critical flow model is used for single phase liquid and Moody model is used for 2-phase flow. For Henry-Fauske model, SPACE code assumes non-equilibrium (NE) factor of 0.14. In previous OPRlO00 SBLOCA analysis methodology based on RELAPS code, non-equilibrium factor of 1.0 was used to get more conservative break flow. To develop SBLOCA analysis methodology for OPRlO00 using SPACE code, it was necessary to use different non-equilibrium factor from SPACE default values for Henry-Fauske model. The SPACE code was improved by adding additional option for Henry/Moody-Moody model, which uses user input non-equilibrium factor. To accept user input equilibrium factor, the SPACE code is improved by expanding lookup table used in Henry/Fauske-Moody model. To verify the new model, we perform verification calculations on LOFT L9-3 which is a represenrative integral effect test (IET).
[en] The critical properties of the zero-temperature superfluid-insulator transition in the fully frustrated quantum rotor model at incommensurate filling in two dimensions are studied. We develop a spherical approximation scheme for the model with phase frustration f = 1/2 by choosing a primitive unit cell composed of two sites. The finite-size scaling behavior of various physical quantities in the spherical limit provides the correlation length critical exponent ν = 0.5 and the dynamical critical exponent z = 2, which are consistent with the scenario of the generic superfluid insulator transition even in the presence of phase frustration.
[en] Highlights: • An extended Henry–Fauske model was evaluated for developing critical flow maps. • Suggestion of critical flow maps for critical flow rate and pressure. • Critical flow maps useful for instructive guidelines in engineering and experiments. - Abstract: Critical flow maps were suggested for a critical mass flux and pressure of steam–water flow with respect to upstream stagnation conditions using an extended Henry–Fauske model. Most of selected test data were compared to the model and found that the model showed nearly conservative predictions with reasonable ranges. The suggested critical flow maps showed quite different trends in the vicinities of saturated liquid region compared to Moody’s homogeneous model. The critical flow maps can be used as instructive guides, especially for an understanding of the critical flow phenomena in steam–water flow and the application of engineering design and experiments
[en] During critical operation of the KEMA Suspension Test Reactor (KSTR) deposition of fuel particles occurred onto the wall of the stabilizer, situated in the reactor core. After stopping of the KSTR operation the weight of the recovered fuel from the stabilizer amounted to nearly two kilograms. The thickness of the deposition layer varied from 17 to 20 mm. Post-irradiation examination revealed that during critical operation there had been a radial temperature gradient similar to that in some LWR fuel. At the centre the operation temperature was about 30000C, leading to partial fuel melting. In addition migration of uranium, thorium, iron and chromium was found, which can be explained by an evaporation-condensation process. It was noticed further that drifting of the pores was dependent on their position in the fuel layer. (orig.)
[en] Numerical simulation was made referring to the Yamagata's experiment for heat transfer of supercritical water flowing in a vertical tube. Numerical simulation was performed for the conditions of tube diameter of 7.5mm, heated tube length of 2m, operation pressure at 245 bar, bulk temperatures from 300 to 420 .deg. C, heat fluxes from 465 to 930 kW/m2 and mass velocity 1,260 kg/m2sec, by FLUENT code and compared to the Yamagata's experiments. At the heat flux, 465 kw/m2, a satisfactory results was obtained within the error range lower than 20% comparing calculations with Yamagata's experiment, and the difference between turbulence models was not so big. But at the heat flux, 930 kw/m2, the difference between the calculations and Yamagata's experiment increased to about 25%, and the difference between turbulence models increased significantly. The case using RNG and enhanced wall treatment option of the turbulence models predicted the Yamagata's experiment most well
[en] The traffic bottleneck plays a key role in most of the natural and artificial network. Here we present a simply model for bottleneck dynamical characteristics consideration the reliability on the complex network by taking into account the network topology characteristics and system size. We find that there is a critical rate of flow generation below which the network traffic is free but above which traffic congestion occurs. Also, it is found that random networks have larger critical flow generating rate than scale free ones. Analytical results may be practically useful for designing networks, especially for the urban traffic network. (interdisciplinary physics and related areas of science and technology)
[en] The effects of the major parameters such as pipe length, pipe diameter, water subcooling, and system pressure on the critical flow rates of both the upper and the lower boundaries have been examined. The critical flow rates are sensitive to pipe diameter, pipe length and system pressure, but not to the subcooling of water over the practical operating ranges. The condensation-induced waterhammer region boundary maps have been presented to be used in the system design and operation to avoid the condensation-induced waterhammer incidents in the long horizontal pipe systems
[en] I study the dynamics of a superfluid vortex in a random potential, as in the inner crust of a neutron star. Below a critical flow velocity of the ambient superfluid, a vortex is effectively immobilized by lattice forces even in the limit of zero dissipation. Low-velocity, translatory motion is not dynamically possible, a result with important implications for understanding neutron star precession and the dynamical properties of superfluid nuclear matter