Investigations of mixing in a fluid Jet agitated tank

Mixing can be achieved in a variety of ways including mechanical agitation, agitation by a fluid jet impingement or by static mixers. This article is concerned with mixing by a fluid jet impingement. Jet mixing can be described as a fast-moving stream of liquid being injected into a slow-moving or stationary liquid. In this study, computational fluid dynamics (CFD) is used to investigate the performance of a jet mixer. The degree of mixing has been evaluated by monitoring mixing of a hot volume of fluid in the larger tank until criteria for 95% mixing are met at a number of monitoring points. A wide range of jet injection rates has been investigated. Good agreement was shown between numerical and published experimental results. Moreover, the need to monitor mixing at more than one point, and especially at points in zones with little liquid motion, is shown to be necessary. Numerical results provided detailed plots of velocity and temperature fields and clearly showed the locations of zones with very low velocities, which require the longest time to become well mixed.     

Sedimentation behavior of mixed solid particles

During the material relocation phase of core-disruptive accidents in sodium-cooled fast reactors, the sedimentation behavior of fragmented debris discharged from the reactor core into the lower plenum region leading to a debris-bed formation is crucial in regard to in-vessel retention and safety concerns. The height of the beds formed may influence both the cooling of the bed from the decay heat in the fuel and the neutronic characteristics. To develop an experimental database of bed formation behavior, a series of experiments using simulant materials, namely, Al₂O₃, ZrO₂, and stainless steel, were performed under gravity-driven discharge of solid particles from a nozzle into a quiescent cylindrical water pool. The bed height was measured for particles of different size, density, and sphericity, and an injection nozzle with varying diameter, injection velocity, and injection height. From these experiments, an empirical correlation was established to predict the bed height for both homogeneous and mixed particles for the different properties. This correlation reproduces reasonably well the experimental trend in bed height with critical factors, which were identified in this and previous experiments.     

A study on inspection schemes in optimal design of control charts for deteriorating processes

The non-uniform inspection scheme obtained by the constant integrated hazard procedure overcomes the uniform scheme economically in optimal design of control charts. The comperative study is generalized in this paper to an optimization problem which looks for the optimal sampling points among all possible sampling schemes. The objective function is simplified here by modelling sequential time intervals as a family of functions of the first sampling interval, which also has been induced by the constant integrated hazard approach. The study demonstrates the model implementation through the economic design of $\overline{X}$ and T²-Hotelling control charts, both under the two widely used process failure mechanisms, that is, Weibull and Chen distributions. A comprehensive numerical investigation illustrates the possibility of existence of sampling schemes which outperform the constant integrated hazard approach and emphasizes the necessity of further investigation into the solution procedure.