Stability analysis of inclined stratified two-phase gas-liquid flow

The present investigation involves the modeling of gas-liquid interface in a two-phase stratified flow through a horizontal or nearly-horizontal circular duct. The most complete and fundamental model used for these calculations is known as the one-dimensional two-fluid model. It is the most accurate of the two-phase models since it considers each phase independently and links both phases with six conservation equations. The mass and momentum balance equations are written in dimensionless form. The dimensionless mass and momentum balance equations are combined with the method of characteristics and an explicit method to simulate the flow. At first, the linear stability of the flow is investigated by disturbing the liquid flow with a small perturbation. An improved version of the one-dimensional two-fluid model for horizontal flows is developed as a set of non-linear hyperbolic governing equations. The importance of this research lies in obtaining a model that accounts for the effects of flow and geometrical conditions (such as liquid viscosity, surface tension). It is shown that, for positive values of the slope angle (upward inclination), the slug flow becomes more probable, whereas negative values of the slope angle (downward inclination) induce a more stable stratified flow.     

On the coefficient for bulk recombination of vacancies and interstitials

Bulk recombination in the rate theory of void swelling and irradiation creep is a significant process at low temperatures. The rate of recombination is proportional to the recombination radius which is evaluated in the present paper. The computed radius is in good agreement with measured values for dilute copper alloys at cryogenic temperatures. The theoretical results can therefore be extended to the temperature range for void swelling, and it is found that the recombination radius is about two times the lattice parameter.     

Numerical Simulation of Taylor–Couette Flows with Rotating Outer Wall Using a Hybrid Spectral/Finite Element Method

Theoretical Foundations of Chemical Engineering - Taylor–Couette flow between independently rotating cylinders with a relatively small aspect ratio Γ = 2.4 has been investigated...     

Simplified numerical model for defining Ledinegg flow instability margins in MTR research reactor

Establishment of safety margins and the corresponding operating condition limits will ensure achievement of a safe operation of nuclear installations. For this purpose, several critical phenomena have been analyzed theoretically and experimentally and a great number of models and correlations are made available. Among these critical issues the well-known flow instability has been intensively investigated by several authors especially for nuclear power plants' (NPPs) operating conditions. However, limited published work is available for research reactor operation conditions. In general, the Whittle and Forgan correlation is widely used to define the margin to static flow instabilities in narrow parallel heated channels for research reactors.In the framework of verification and assessment of the capabilities of the RELAP5/Mod 3 system code to determine the onset of flow instability in research reactor conditions, a simple model based on steady-state equations adjusted with drift-flux correlations has been developed. The program is used to draw the pressure drop characteristic curves and to establish the conditions of the Ledinegg instability in a uniformly heated channel subject to constant outlet pressure. The model is assessed by using experimental data from a thermal hydraulic test loop by Siman-Tov and numerical results from RELAP5/Mod 3. The model presents acceptable estimation of the target mass flow that would induce flow instability and the latter could be then used to establish a conservative margin to the Ledinegg instability.     

Analysis of loss of coolant accident in MTR pool type research reactor

In MTR research reactors, heat removal is, safely performed by forced convection during normal operation and by natural convection after reactor shutdown for residual decay heat removal. However, according to the duration time of operation at full power, it may be required to maintain the forced convection, for a certain period of time after the reactor shutdown. This is among the general requirements for the overall safety engineering features of MTR research reactors to ensure a safe residual heat removal. For instance, in safety analysis of research reactors, initiating events that may challenge the safe removal of residual heat must be identified and analyzed.In the present work, it was assumed a total loss of coolant accident in a typical MTR nuclear research reactor with the objective of examining the core behavior and the occurrence of any fuel damage.For this purpose, the IAEA 10 MW benchmark core, which is a representative of medium power pool type MTR research reactors, was chosen herein in order to investigate the evolution of cladding temperature through the use of a best estimate thermalhydraulic system code RELAP5/mod3.2.     

Single and two-phase flows in a horizontal pipe with a Kenics static mixer: Effect of pressure drop on mixing

Single and two-phase flows pressure drops through a Kenics static mixer were investigated, for liquid and gas Reynolds numbers ranging from 8110 < Re_L < 18 940 to 1730 < Re_G < 8680, respectively. New friction factor correlations were established for single and two-phase flows, showing better agreement than those available in the literature. Dissipated energy and characteristic time constants were estimated from experimental data. For instance, a dissipated energy with a maximum value of 510 W/kg was calculated in two-phase flow with the drift-flux model. The dispersed phase reduced the characteristic mixing times and its influence was more important than the continuous phase for all the characteristic mixing time investigated. Furthermore, the macroscopic characteristic mixing time was shown to be the governing mixing process for almost all gas and liquid flow rates explored.