Predicting the void fraction of a two-phase flow outside of tubes is essential to evaluate the thermohydraulic behaviour in steam generators. Indeed, it determines two-phase mixture properties and affects two-phase mixture velocity, which enable evaluating the pressure drop of the system. The two-fluid model for the numerical simulation of two-phase flows requires interaction laws between phases which are not known and/or reliable for a flow within a tube bundle. Therefore, the mixture model, for which it is easier to implement suitable correlations for tube bundles, is used. Indeed, by expressing the relative velocity as a function of slip, the void fraction model of Feenstra et al. and Hibiki et al. developed for upward cross-flow through horizontal tube bundles is introduced and compared. With the method suggested in this paper, the physical phenomena that occur in tube bundles are taken into consideration. Moreover, the tube bundle is modelled using a porous media approach where the Darcy–Forchheimer term is usually defined by correlations found in the literature. However, for some tube bundle geometries, these correlations are not available. The second goal of the paper is to quickly compute, in quasi-real-time, this term by a non-intrusive parametric reduced model based on Proper Orthogonal Decomposition. This method, named Bi-CITSGM (Bi-Calibrated Interpolation on the Tangent Subspace of the Grassmann Manifold), consists in interpolating the spatial and temporal bases by ITSGM (Interpolation on the Tangent Subspace of the Grassmann Manifold) in order to define the solution for a new parameter. The two developed methods are validated based on the experimental results obtained by Dowlati et al. for a two-phase cross-flow through a horizontal tube bundle. 相似文献
In this paper, the microvoid multistage nucleation model [14,15] suggested by the authors of this paper has been studied on the micro ductile damage and fracture of metallic material under large elastic-plastic deformation.Using this model, the analyses of micro damage and fracture for various axisymmetric tensile specimens and for TPB and CCP cracked specimens have been carried out. And the results from these analyses on damage development and fracture are in good agreement with the experimental ones for axisymmetric specimens and reasonable for cracked specimens from the microscopic point of view.The project surported by National Science Foundations of China. 相似文献
The reduction of void formation in local Al contact structures is of high interest in studies dealing with passivated emitter and rear contact (PERC) solar cells. So far, several processing parameters and their impact on local contact formation were investigated in detail. However, up to now density variation of Al in dependence on temperature and Si content in the melt were not taken into account as a principal reason for void formation. In this context the current assumption of a constant volume of the Al paste particles is discussed in more detail. Based on the results of energy dispersive X‐ray spectroscopy, void formation implies either an expansion of paste particles or their burst during contact formation.
In a recent paper, Tacher and coworkers proposed an interesting numerical technique to generate granular porous media. In this contribution, we present a similar procedure based on a sedimentation algorithm, that is able to overcome some of the difficulties present in the former technique. These are: (a) the impossibility to choose a priori a grading curve for the generated medium while retaining a realistic stacking where each grain is connected to at least three of its neighbours, and, (b) he random pattern of the grains in the porous medium, arising from their location inside the remaining void space of a box according to an arbitrary space filling criterion. We propose to generate threedimensional granular media by simulating the deposition of spherical grains in a viscous fluid. We argue that the resulting chaotic grain pattern, by reflecting the actual generation process of sedimentary aggregates more closely, provides a better image of the complex topology of natural granular porous media. Although the generated medium is made up of spheres, it can be transformed, by changing the geometry of the grains through suitable domain mappings. The resulting threedimensional porous media provide a realistic boundary for the numerical solution of linearized Navier–Stokes equations. 相似文献
Two-dimensional phase-field simulations of void swelling in the Austenitic stainless steel were performed for irradiated materials. A numerical model was established for void swelling with an implementation of the elasticity effect, and we examined the roles of the applied stress and grain boundary sink strength and Frenkel defect recombination in determining the void swelling rate. The obtained results were compared with the existing experimental observations. 相似文献
Ferritic/martensitic steels show exceptional void-swelling resistance during neutron irradiation compared to conventional austenitic stainless steels, such as Types 316 and 304. Explanations for the difference have been proposed based on the different crystal structures and the different microstructures of the steels. In this paper, swelling behaviour of ferritic/martensitic steels HT9 and modified 9Cr–Mo are analysed to demonstrate how the complicated tempered martensite microstructure determines their excellent swelling resistance. The variation in steady-state swelling rate observed for different heats and different heat treatments is explained in terms of how chemical composition and heat treatment affect the microstructure. Microstructures of these steels are characteristically non-uniform, containing precipitate-rich and precipitate-deficient regions. Swelling resistance increases as number and size of precipitate-deficient regions are reduced by proper heat treatment. 相似文献