Numerical investigation of coupled natural convection and radiation in a differentially heated cubic cavity filled with humid air. Effects of the cavity size

A numerical study of natural convection with surface and air/H₂O mixture radiation in a differentially heated cubic square cavity is presented. The coupled flow and heat transfers in the cavity are predicted by coupling a finite volume method with a spectral line weighted sum of gray gase model to describe gas radiative properties. The radiative transfer equation is solved by means of the discrete ordinate method. Simulations are performed at Ra?=?10⁶, considering different combinations of passive wall and/or gas radiation properties and different cavity length. It was found that in presence of a participative medium representative of building, cavity length has a strong influence on temperature and velocity fields which affect the global circulation and heat transfers in the cavity. For each steady-state solution, the convective and radiative contributions to the global heat transfer are discussed. More specifically, boundary layer thickness, thermal stratification parameter, and three-dimensional effects are compared to pure convective case results. The results suggest that radiative effects, often considered as negligible in view of the relatively low optical thickness, may not be neglected when trying to predict regime transitions.     

Dynamic defect localization using FPGA to monitor digital values

Fault localization is a key step of the failure analysis flow on defective ICs. Recently, the development of parametric variation mapping (xVM) under dynamic laser stimulation has considerably increased the scope of soft defect localization.In this paper, we are presenting a FPGA-based real-time acquisition and processing unit for the variation mapping of a digital data. The FPGA-based solution is described and used on a real case of defective analog-to-digital converter (ADC). The advantages of our system are listed and future developments are considered.     

Convective heat transfer inside a rotating cylinder with an axial air flow

This article presents an experimental identification technique for the convective heat transfer coefficient inside a rotating cylinder with an axial airflow. The method consists in heating the outer face of the cylinder using infrared lamps, and acquiring the evolution of the external surface temperature versus time using an infrared camera. Heat transfer coefficients are identified via three methods. The first one is based on an inverse model, the second one assumes the wall of the cylinder as a thermally thin wall and the third one is based on an analytical method permitting to obtain the temperature field within the whole cylinder. The experiments were carried out for a rotational speed ranging from 4 to 880 rpm corresponding to rotational Reynolds numbers varying from 1.6×10³ to 4.7×10⁵ and an air flow rate varying from 0 to which corresponds to an axial Reynolds numbers ranging from 0 to 3×10⁴. Correlations connecting the Nusselt number to the axial and rotational Reynolds numbers are also proposed.     

Preliminary experiments on the control of natural convection in differentially-heated cavities

Aiming at the control of natural convection flows and heat transfer in air-filled differentially-heated cavities, experimental attempts were carried out in order to achieve the stability of such flows to various excitations. The mechanism of control chosen in these experiments introduces thermal disturbances via a thin pipe located inside the boundary layer at the bottom of the hot wall. Its temperature varies periodically due to alternating electrical heating and continuous water cooling. The effects of this disturbance in temperature are investigated for a Rayleigh number value chosen just greater than the first bifurcation value from a steady state flow to a monoperiodic state. The results show the distribution of the overall and local Nusselt numbers. The introduction of this obstacle induces a 10% decrease in heat transfer. Temperature oscillations of the actuator provoke modifications of the flow field. In particular, an amplification of unsteadiness in the outer borders of boundary layers is observed and a displacement of secondary vortices is encountered. Explanations are given by a detailed examination of flow structures, such as the spatial distribution of velocities and their fluctuations.     

Robust experiment design for the estimation of thermophysical parameters using stochastic algorithms

This numerical study deals with the design of experiments. It aims at optimizing thermocouple positions in order to reduce uncertainties in the estimation of thermophysical properties when an inverse method is applied. The 2D system under investigation is a squared sample of orthotropic material submitted to a constant heat flux on left and bottom edges. The temperature response is given by three sensors. The unknown parameters are the volumetric thermal capacity and the conductivities in the two principal directions. The experiment design is based on an original optimality criterion. Two stochastic algorithms are used to find its minimum and their efficiency is compared to a pure random search algorithm. To deal with the fact that the experiment design depends on the unknowns, a robust optimization approach is proposed.     

Practical knowledge in expert coaches: on-site study of coaching in sailing

The purpose of this study was to analyze the practical knowledge of expert sailing coaches of the French team preparing for the 1996 Olympic Games in Atlanta. Coaching knowledge was studied from a cognitive ergonomics perspective based on the task activity model. According to this model, a task is a set of constraints facing individuals. To meet the demands imposed by these constraints, an individual engages in an adaptative activity which can be studied from the point of view of his or her knowledge and cognitive operating modes. In-depth interviews were conducted after observation of five training sessions, and the verbal protocols obtained were coded inductively. The results showed that coaching tasks were considered by coaches as a set of interacting constraints which generate complex, contradictory, and ill defined problems. Coaches' operating modes appeared to be based on organization routines, cognitive anticipation on flexible plans, flexible on-site adaptation, joint control of training with athletes, and involvement in the training situation based on past experiences.     

Modelling of the coupling structure of a HTS DC SQUID amplifier

In order to estimate self- and mutual inductances of the input coil and the pick-up loop of a YBCO SQUID amplifier operating at 77 K, a simple method based on the determination of the current and flux distributions into the superconductors is presented. The cases of inductors (single loop and spiral) and induced circuits (closed and open loop) are considered. The authors stress the difference between a SQUID pick-up loop and a directly coupled magnetometer depending upon their action on the input inductance. Finally, the coupling efficiency and the ground plane effect are calculated and measured for various patterns     

Parametric defect localization on integrated circuits – From static laser stimulation to real-time variation mapping (RTVM)

Laser stimulation techniques have been intensively used in the last decades to localize defects on integrated circuits. Although static techniques are efficient in many cases, they are not appropriate to tackle complex macro failure modes such as parametric defects. Dynamic laser stimulation techniques overcome these limitations but their implementation requires inserting a tester between the device under test and the fault isolation equipment, which may result in quite long acquisition times.     

Description of dynamic shared knowledge: an exploratory study during a competitive team sports interaction

This exploratory case study describes the sharedness of knowledge within a basketball team (nine players) and how it changes during an official match. To determine how knowledge is mobilised in an actual game situation, the data were collected and processed following course-of-action theory (Theureau 2003). The results were used to characterise the contents of the shared knowledge (i.e. regarding teammate characteristics, team functioning, opponent characteristics, opposing team functioning and game conditions) and to identify the characteristic types of change: (a) the reinforcement of a previous element of shared knowledge; (b) the invalidation of an element of shared knowledge; (c) fragmentation of an element of shared knowledge; (d) the creation of a new element of shared knowledge. The discussion deals with the diverse types of change in shared knowledge and the heterogeneous and dynamic nature of common ground within the team. STATEMENT OF RELEVANCE: The present case study focused on how the cognitions of individual members of a team coordinate to produce a team performance (e.g. surgical teams in hospitals, military teams) and how the shared knowledge changes during team activity. Traditional methods to increase knowledge sharedness can be enhanced by making use of 'opportunities for coordination' to optimise team adaptiveness.     

Optimization of hydrogen vehicle refuelling requirements

The requirements regarding the refuelling process in order to prevent over-heating and over-filling significantly influence hydrogen fuelling station design and have a strong impact on potential fuelling performance. Consequently, refuelling station costs, reliability, and performance can be substantially improved by working on the way these requirements are formulated, in order to achieve shorter fuelling duration with a simpler process and less cooling. Two potential optimization opportunities were extensively investigated in the course of the EU funded HyTransfer project: (i) Application of the temperature limits to the tank material rather than to the gas inside the tank, (ii) Specification of the average delivery temperature rather than of the delivery temperature profile. Multiple research activities were carried out to this end. New models of various types were developed for predicting both the gas and material temperatures inside a vessel during filling and defueling. An experimental programme involving 82 filling and emptying tests of instrumented Type 4 and Type 3 vessels was performed for validating these models. New methods were developed and applied for determining the value of the gas-to-wall heat transfer coefficient from the temperature measurements. The balance of heat transferred from the gas to the liner and to the bosses in a type 4 vessel was reconstructed. CFD simulations were performed for analysing temperature disparities, and the thermal stratification observed in certain filling conditions reproduced. Criteria on gas injection conditions were identified for ensuring gas temperature homogeneity, a key assumption made by fuelling protocols. The temperature variations in the wall material were studied for future investigation of less conservative definitions of the maximum acceptable temperature in Hot Case situations. The effect of changing the delivery temperature profiles without changing the average delivery temperature was also analysed.