Natural ageing of tri-layer polyethylene film: Evolution of properties and lifetime in North Africa region

The effects of natural ageing in the north Algeria of tri-layer films lay down hot greenhouse made of low-density polyethylene are presented in this work. Ageing was monitored by observing the changes of physical, mechanical and structural effects on the various greenhouse faces. It has been shown that the structural change occur on the outside face of the films, while the inside faces are protected by the dye. The study shows that the measured parameters are directly related to the criteria of evaluation of the greenhouse effectiveness. The lifetime of these films under natural conditions in north Algerian was estimated to be 10 months.     

Validation of the Langevin particle dispersion model against experiments on turbulent mixing in a T-junction

The fluctuating fluid velocities seen by particles entrained in a turbulent fluid have recently been modeled using a stochastic model based normalized Langevin Continuous Random Walk (CRW). This model has been quite successful in predicting particle dispersion in mildly complex flows. In the present study, we aim at validating the CRW model further against data collected in a challenging 3D geometry. We consider turbulent fluid mixing downstream of a T-junction using a hybrid Euler-Lagrange approach whereby tracer particle trajectories are computed and mixing of the streams deduced from the relative concentration of particles originating from the two inlet branches of the Tee. In a first simulation, RANS Reynolds Stress Model (RSM) is used to obtain the mean flow field, whereas the fluid fluctuations are specified from a CRW. Simulation results are compared to experimental data on mixing of two isothermal streams consisting of tap and de-ionized water, respectively. It is found that RSM-CRW yields strong under-prediction of the mixing. Closer look at the results shows that the Reynolds stresses, which are required inputs to the CRW, are poorly predicted with RSM. Detached Eddy Simulations (DES) are subsequently performed to provide the mean flow field, and the DES-CRW model predictions are found to compare quite well with the experimental data.     

A NOTE: A MODEL OF STEAM INJECTOR PERFORMANCE

A simple, mathematical model of the steady state performance of a condensing steam injector is developed based on one-dimensional conservation equations. The model involves two distinct flow regions-a stratified annular flow and a downstream dispersed flow. The former regime is modeled using a two fluid, non-equilibrium formulation while the latter is described by a homogeneous non-equilibrium model. The flow regime transition point is not calculated from first principles but must be described empirically. The model is applied to the simulation of experimental data. Good accuracy is achieved especially in cases where a significant condensation potential exists. The major modeling deficiencies are the lack of a predictive flow transition and the need for empirical closure relations for interphasial exchanges and shock calculations. More fundamental experiments are required before qualitative analytical model improvements are possible.     

Failure mechanisms and qualification testing of passive components

New electronic architectures and mechatronic integration in automotive and oil-field applications lead to increasing requirements concerning operating temperatures and vibration levels. At the same time, reliability and lifetime have to fulfil strong demands.In the European funded project PROCURE (Program for the development of passive devices used in rough environments) a generic spectrum of passive components needed for electronic control units has been developed. The failure mechanisms, the technological challenges, and the test requirements are highlighted below.     

Steam generator tube rupture (SGTR) scenarios

The steam generator tube rupture (SGTR) scenarios project was carried out in the EU 5th framework programme in the field of nuclear safety during years 2000–2002. The first objective of the project was to generate a comprehensive database on fission product retention in a steam generator. The second objective was to verify and develop predictive models to support accident management interventions in steam generator tube rupture sequences, which either directly lead to severe accident conditions or are induced by other sequences leading to severe accidents. The models developed for fission product retention were to be included in severe accident codes. In addition, it was shown that existing models for turbulent deposition, which is the dominating deposition mechanism in dry conditions and at high flow rates, contain large uncertainties. The results of the project are applicable to various pressurised water reactors, including vertical steam generators (western PWR) and horizontal steam generators (VVER).     

CFD simulation of particle deposition on an array of spheres using an Euler/Lagrange approach

The Generation IV Pebble Bed Modular Reactor (PBMR) is being considered as a promising concept to produce electricity or process heat with high efficiencies and unique safety features. The PBMR is a high-temperature, helium-cooled, graphite moderated reactor. The fuel elements consist of 6 cm diameter spherical graphite “pebbles” containing each thousands of uranium dioxide microspheres.As the pebbles continually rub against one another in the core, a significant quantity of graphite dust can be released in the reactor coolant system. These dust particles, which contain some amounts of fission products, are transported and deposited on pebbles as well as primary circuit surfaces. It is therefore of great safety interest to develop and benchmark numerical approaches for predicting deposition of dust particles in the various locations of the PBMR primary circuit.In this investigation, we use the ANSYS-Fluent CFD code to simulate particulate flows around linear arrays of spheres and compare deposition rates against experiments. It is found that the Reynolds Stress Model (RSM) combined with the Continuous Random Walk (CRW) to supply fluctuating velocity components predicts deposition rates that are generally within the scatter of the data. The methodology developed here can therefore be used to predict to first order the graphite dust deposition rates on pebbles in PBMR-type reactors.     

High temperature reliability testing of aluminum and tantalum electrolytic capacitors

Nowadays, many innovations in the automobile are enabled by electronics. Ambient requirements can be very stringent especially when the temperature reaches 150 °C or even more. Especially electrolytic capacitors are known to be critical devices at high temperatures.Therefore, it is necessary to validate the performance of such components and check their reliability during high temperature operation. In this paper we discuss how to predict the lifetime of both aluminum and tantalum electrolytic capacitors. In that aim we first review state of the art qualification tests that allow a life prediction.We describe a test setup that we have built in order to investigate electrolytic capacitors by LCR and leakage current measurements at temperatures above current manufacturer's specifications. Results for different capacitors after variation of tests conditions will be presented.     

Defect detection in multilayer ceramic capacitors

Cracks in Multilayer Capacitors are often latent defects, which are not recognized in production, but can cause substantial problems in field. Therefore it is important to find possibilities to detect those candidates before delivering electronic equipment.In this work, cracked capacitors were characterized by electrical parameter testing and by piezoelectric spectroscopy. As a new method, sound emission spectroscopy was employed as indicator for latent defects and correlated with electrical data and physical analysis. The results show that sound emission used on a statistical basis and piezoelectric response might be effective to screen latent defects in electronic control units.     

Transition from natural to mixed convection for steam–gas flow condensing along a vertical plate

An analysis method based on two-phase boundary layer analysis has been developed to study the effects of superimposed forced convection on natural convection steam–gas flow condensing along a vertical plate. The mechanism by which superimposed forced convection enhances heat transfer is evaluated: the bulk flow blows away non-condensable gases accumulating near the interface, resulting in an elevated condensation driving force. Further, this bulk flow blowing capability may be characterized by a conventional mass transfer driving potential. Results of the new model are shown to be consistent with experimental data. Finally, a simple criterion was developed to identify transition to mixed convection from natural convection steam–gas flow.     

Progress in understanding key aerosol issues

The 6th FWP SARNET project launched a set of studies to enhance understanding and predictability of relevant-risk scenarios where uncertainties related to aerosol phenomena were still significant: retention in complex structures, such as steam generator by-pass SGTR sequences or cracks in concrete walls of an over-pressurised containment, and primary circuit deposit remobilization, either as vapours (revaporisation) or aerosols (resuspension). This paper summarizes the major advances achieved.Progress has been made on aerosol scrubbing in complex structures. Models based on empirical data (ARISG) and improvements to previous codes (SPARC) have been proposed, respectively, for dry and wet aerosol retention, but, further development and validation remains, as was noted during the ARTIST international project and potential successors. New CFD models for particle-turbulence interactions have been developed based on random walk stochastic treatments and have shown promise in accurately describing particle deposition rates in complex geometries. Aerosol transport in containment concrete cracks is fairly well understood, with several models developed but validation was limited. Extension of such validation against prototypic data will be feasible through an ongoing joint experimental program in the CEA COLIMA facility under the 6th Framework PLINIUS platform.Primary deposit revaporisation has been experimentally demonstrated on samples from the Phebus-FP project. Data review has pinpointed variables affecting the process, particularly temperature. Available models have been satisfactorily used to interpret separate-effect tests, but performing integral experiments, where revaporisation is likely combined with other processes, still pose a difficult challenge. Further experimental data as well as modelling efforts seem to be necessary to get a full understanding. Resuspension, sometimes referred to as mechanical remobilization, has been recently addressed in SARNET and although a set of models were already available in the literature (i.e., Rock'n Roll model, CESAR, ECART), further work is needed to extend current capabilities to multi-layer deposits and to produce simplified, but sufficiently accurate, models. A major remaining uncertainty is the particle-to-particle/wall adhesion and its dependence on microscale roughness. Data from the previous EU STORM project have been retrieved and further experiments designed for code validation are being used to benchmark the models.