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A subchannel void sensor (SCVS) acquires the two-phase flow in a rod bundle as the time-series data of cross-sectional distributions. Herein, the temperature and pressure ranges of an SCVS were extended to include the rated conditions of boiling water reactors. The improved SCVSs were installed in a 5 × 5 heated rod bundle at eight height levels. In a boiling experiment using the rod bundle, the three-dimensional distributions of the boiling two-phase flow were measured over a wide pressure range (up to 7.2 MPa). The new experimental data were compared with existing experimental data and the results of a subchannel analysis. Experimental results were consistent with those of a high-energy X-ray computed tomography study of a heated rod bundle with the same geometry and under the same heat and flow conditions as those used in our study. The subchannel analysis code reproduced the experimental results fairly well, and the obtained database is applicable for validating and improving thermal-hydraulic analysis codes. [ABSTRACT FROM AUTHOR]

A novel approach for the solution of Stefan problem within the framework of the multi-fluid model supplemented with Volume of Fluid (VOF) method, i.e. two-fluid VOF, is presented in this paper. The governing equation set is comprised of mass, momentum and energy conservation equations, written on a per-phase basis and supplemented with closure models via the source terms. In our method, the heat and mass transfer is calculated from the heat transfer coefficient, which has a fictitious function and depends on the local cell-size and the thermal conductivity, and the implementation is straightforward because of the usage of the local value instead of a global parameter. The interface sharpness is ensured by the application of the geometrical reconstruction scheme implemented in VOF. The model is verified for three types of computational meshes including triangular cells, and good agreement was obtained for the interface position and the temperature field. Although the developed method was validated only for Stefan problem, the application of the method to engineering problems is considered to be straightforward since it is implemented to a commercial CFD code only using a local value; especially in the field of naval hydrodynamics wherein the reduction of ship resistance using boiling flow can be computed efficiently since the method handles phase change processes using low-resolution meshes. [ABSTRACT FROM AUTHOR]

In this work, argon flow within different microchannels with square cross-section is simulated by the molecular dynamics simulation (MDS) method. The first simulation is done within ideal microchannel and then, internal surfaces of this microchannel are roughened by cone, cubic and spherical barriers respectively to report influences of roughness with different geometries on the distribution of fluid flows. It is reported that cone and spherical geometry of barriers do not strongly affect flow characteristics of argon fluid within the microchannel, while the cubic geometry of barriers delays density distribution of argon flow in the middle region of the microchannel due to their destructive role against translocation of fluid particles between lateral and central layers of the microchannel. For the density results, it is reported that two physical phenomenon of thermal and external energies play important roles on the distribution of fluid particles in different sections of microchannel due to their different applying directions. Moreover, it is observed that the temperature profile of fluid flow within microchannel with cubic barriers touched a maximum temperature of 420 K at the central layers which are in the highest temperature level among all cases studied. Results of this study are applicable for practical application in small scale designs such as medical probes to inject destructive fluid for destroying tumors in cold surgeries. [ABSTRACT FROM AUTHOR]

A homogenous phase change model (HPCM) based on the mass conservation law is pro-posed to analyze the flow field of a two-phase mechanical seal with 3D face structures. The two-phase flow domain is governed by the simultaneous partial differential equation set containing a mass transfer governing equation for each phase with a source term derived from the Rayleigh-Plesset model and a Reynolds equation for the mixture, where the pressure and the liquid fraction are unknowns. A numerical solution is developed based on finite element method (FEM). The results from the present model are in good agreement with those from the previous two-phase mechanical seal models. A two-phase mechanical seal with wavy-tilt-dam face structure is calculated. The results indicate that the 3D face structure affects the phase distribution by altering the film pressure field. The present model is especially useful to analyze the two-phase film flow field bounded by the complex solid suif aces. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical integrity of heat exchangers is the result of an interplay of many physical phenomena. A full, albeit simple, model, that covers mixture phase thermodynamics, heat transfer, flow dynamics, and the thermal and pressure stresses has been created. Using this simulation model it is now possible to quantify the magnitude of different effects. The focus has been on internal instabilities under stationary operations. [Copyright &y& Elsevier]