Numerical Investigation of Forced Convection Nonequilibrium Effects on Heat and Mass Transfer in Porous Media

A numerical investigation is performed to analyze the coupled heat and mass transfer in porous media with a strong exothermic reaction. Similar problems have received great attention due to their relevance in a wide variety of engineering applications, such as heat pipes, drying technologies, nuclear reactors, catalytic reactors, environmentally clean utilization of energy, and many others. The momentum transfer in the porous substrate is modeled with the Darcy–Brinkman–Forchheimer law, while the temperature and concentration fields are obtained subsequently from the energy and diffusion equations. The considered configuration consists of a cylindrical duct where a first-order reaction is supposed to occur. The governing equations are solved by using the finite-volume method. The SIMPLER algorithm is applied to solve the momentum and continuity equations. The power-law scheme is used to model the interaction between convection and diffusion terms. The effect of the main governing parameters, such as permeability, aspect ratio, solid-to-fluid conductivity ratio, Reynolds number, Biot number, and the modified Frank-Kamenetskii number, are studied. The comparison with previously published work shows excellent agreement.     

Fire behaviour and external flames in corridor and tunnel‐like enclosures

This work investigates how the inflow, the burning and the outflow develop in a corridor open to one end having a fire at either the closed or open end. The situation of a corridor fire having a fire source at the close end is a situation similar to a tunnel having a fire source at the centre of the tunnel without ventilation. A gaseous propane burner is used to produce the fire at a prescribed fuel flow rate in a long corridor of aspect ratio up to 6:1 having a rectangular cross section and varying door‐like openings. Gas temperatures using thermocouple trees, heat fluxes in the corridor and on its façade, flame heights of emerging flames and total heat release rates (HRRs) are measured as the fuel flow rate of propane increases gradually and linearly with time to a preset maximum value. For over‐ventilated conditions, the flames remain near the fire source at the closed end of the corridor. Unexpectedly, it is established for under‐ventilated conditions that the inflow of air is not affected by the aspect ratio of the corridor or the location of the burner in the corridor and that the vertical distribution of gas temperatures inside the enclosure is nearly uniform with height everywhere. In addition, the flame heights and heat fluxes on the façade are the same as those for aspect ratios of the corridor from 1:1 to 3:1 examined in previous work. Moreover, as the conditions changed from over‐ventilated to under‐ventilated conditions, the flames migrated in a ghostly manner from the closed end to the open end of the corridor as soon as under‐ventilated conditions were established. The speed of migration of the flames from the back to the front has also been inferred from the thermocouple tree measurements, which also indicate that the flow conditions ahead and after the passing of the front are changed. These results can be applied to interpret some of the observed behaviours of fires in long corridors or tunnels without ventilation. Copyright © 2012 John Wiley & Sons, Ltd.     

A Knowledge Transfer Framework: the PFI context

The UK's Private Finance Initiative market is predicted to rise to over £8 billion a year and there are indications of growing opportunities. PFI creates a long‐term income stream and provides valuable opportunities for portfolio diversification. PFI has evolved at a fast pace and the momentum is set to continue. However, there are major challenges facing construction organisations. These include the lack of PFI experts, longer negotiation periods and tight time schedules to deliver large‐scale schemes, high levels of investment and risks involved and limited knowledge transfer between PFI projects. Concerns over the level of knowledge sharing have prompted the development and evaluation of a Knowledge Transfer Framework that encourages construction organisations to transfer PFI knowledge between projects. It achieves this by building on a questionnaire survey of PFI clients and construction companies, case studies of companies involved in PFI, and research workshops to validate the framework developed.     

One-pot lithium bromide-catalyzed reaction of polyoxyethylene diglycidyl ether with carbon disulfide: synthesis of new polyoxyethylene epoxyoxathiolane-2-thione

A simple and highly efficient regio- and chemio-specific synthesis of polyoxyethylene epoxyoxathiolan-2-thione was realized from a one-pot reaction of polyoxyethylene diglycidyl ether and carbon disulfide using lithium bromide as a catalyst. The unsymmetrical obtained products were fully characterized by ¹H, ¹³C NMR and high-resolution mass spectra data.     

Tracking control of trim trajectories of a blimp for ascent and descent flight manoeuvres

A blimp is a small airship that has no metal framework and collapses when deflated. It belongs to family of unmanned aerial vehicles (UAVs). In this paper we address the problem of designing tracking feedback control of an underactuated autonomous UAV. The ascent and descent flight conditions as one in which the rate of change (of magnitude) of the airship's state vector is zero and the resultant of the applied forces and moments is constant lead to trimmed flight trajectories. The subject of the tracking control is to stabilize the engine around the planned flight. Using a combined integrator backstepping approach and Lyapunov theory, the stability results are local and overcome the minimum number of actuators (inputs) with respect to the blimp's six degrees of freedom. Considering physic limits in UAVs, other trimmed flights are investigated and compared.     

Use of hydroxytelechelic cis-1,4-polyisoprene (HTPI) in the synthesis of polyurethanes (PUs). Part 1. Influence of molecular weight and chemical modification of HTPI on the mechanical and thermal properties of PUs

New telechelic cis-1,4-polyisoprene oligomers bearing an hydroxyl group at the end of the polyisoprene backbone and possessing controlled molecular weights were used as soft segments in the elaboration of polyurethane elastomers. Besides, the well defined hydroxytelechelic cis-1,4-polyisoprene (HTPI) structure obtained through a controlled methodology, was chemically modified leading to hydrogenated and epoxidized oligomers based polyurethanes. The influence of the structural changes of these precursors on the polyurethanes properties have been studied. Thus, mechanical parameters as well as glass transition and mechanical transition temperature measurements indicated an increase in PUs hardness when the length of soft segment decreases and when the degree of epoxidized and hydrogenated isoprenic moieties increases. Moreover, based on thermogravimetric analysis (TGA), a linear relationship was established between the weight loss in the urethane stage degradation and the amount of hard segments in the PUs. Otherwise, the hydrogenated soft segments were found more thermally stable than the epoxidized and the non modified ones. By comparison with similar investigations developed from commercial oligodienes (PBHT R20 LM^® and EPOL^®), this study mainly showed that the PUs based on hydrogenated hydroxytelechelic cis-1,4-polyisoprenes were more thermally stable and softer than the EPOL^® based analogues.     

On the Use of Real-Time Video to Forecast Fire Growth in Enclosures

The potential of the concept of combining video data analysis and numerical simulations for numerical fire forecasting is illustrated for the case of a burning sofa in an ISO room. The fire is monitored by means of a video camera. The temporal evolution of smoke layer height, flame height and flame width are obtained from the real-time video data analysis. The fire heat release rate, estimated from the flame height and width, serves as input for the numerical simulations. The two-zone model approach is adopted, because the calculations are very fast. This is necessary for forecasting: time scales in fire development are in the order of seconds (minutes), not hours (which are typical calculation times in CFD simulations). Data assimilation with real-time adjustments according to sudden changes in the fire development as observed, improves the predictions by the two-zone model and allows to make a forecast of the fire development and possible subsequent hazards, in terms of evolution of smoke layer height and temperature.     

Accurate closed-form formulas for the electromagnetic parameters of squared coaxial lines

This article presents a set of accurate closed-form formulas for the electromagnetic parameters (inductance (L), capacitance (C) and characteristic impedance (Z_c)) for squared coaxial lines with circular and square inner conductor. The analytical expressions, deduced from rigorous analysis by the finite element method (FEM), method of moments (MoM) and curves fitting techniques, can be easily implemented in CAD simulation tools, to design components for wireless communication. This study presents accurate and suitable general expressions for all squared coaxial lines with a wide range of outer to inner conductors ratio between 1.2 and 10. As an application, we present the design of 60 GHz branch line couplers.