Sensitivity analyses of convective and diffusive driving potentials on combined heat air and mass transfer in hygroscopic materials

ABSTRACT

The focus of this paper was to examine the contribution of two key mechanisms—moisture convection and diffusion–on heated air and moisture transfer in porous building envelopes and to define the validity of the sub-models. A numerical simulation was performed and is focused on the one-dimensional problem for drying test boundary conditions. Thereafter, a detailed parametric analysis was carried out in order to investigate the influence of typical nondimensional parameters. Results show that convection is a prominent driving potential with respect to the diffusion process when the hygric state is stable between the environment and the envelope.     

Characterization and modeling of sintering of polymer particles

An experimental study of simultaneous sintering of several particles has been carried out using spherical polymer grains. Considering rotational molding condition, coalescence of several grains in contact, happens simultaneously on internal surface of the mould. Theoretical model based on the effect of surface tension and viscosity can accurately predict the coalescence of a pairs of grains. However, it was observed in this study that coalescence rate changes with presence of neighboring grains and their position and the theoretical model proposed for two grains, is not able to predict the coalescence rate of mutli‐grains. Based on this finding, we have modified this model with taking into account the effect of neighboring particles in the sintering rate of multi‐grains. Obtained modified model is capable of predicting the multi‐grains sintering rate observed in this study. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Estimation and fault diagnosis for non-linear system with time-varying faults and measurement noises: Application on two CSTRs in series

A continuously stirred tank reactor (CSTR) is largely used in water treatment and in chemical and biological processes. It is characterized by a complex non-linear behaviour. Operating large reactors in industry can be expensive, so a common trick used to reduce costs is to operate multiple CSTRs in series. Consequently, the CSTR is usually exposed to faults and noises. This paper addresses the design of a robust observer for estimation and fault diagnosis strategy on two CSTRs in series. The considered system is affected simultaneously by time-varying actuator and sensor faults with measurement noises. The Takagi-Sugeno multimodel approach is proposed to transform the non-linear model into an interpolation of several linear sub-models with non-measurable premise variables. The purpose of this brief is to provide the state and the fault estimation for the considered system using a proportional multiple integral (PMI) unknown input observer. The exponential stability conditions are studied with the Lyapunov theory and L2 optimization and formulated in terms of linear matrix inequalities. In addition, a comparative study with a PMI observer is conducted. Finally, the proposed observer is used for time-varying fault detection and isolation.     

Photovoltaic properties of M-phthalocyanine/fullerene organic solar cells

Photovoltaic devices made from M-phthalocyanine and fullerene have been fabricated and characterized by current–voltage response, lateral time-of-flight photoconductivity, UV-visible absorption and scanning electron microscopy. The effect of varying the central moiety on the photovoltaic performance is examined, and demonstrates that the monovalent and divalent phthalocyanines tend to yield higher efficiencies in blended structures, whereas the trivalent and tetravalent phthalocyanines tend to yield higher efficiencies in a bilayer structure. The apparent reason for the disparity is the measured decrease in the hole transport efficiency in trivalent and tetravalent phthalocyanine upon blending with C₆₀. Furthermore, the open circuit voltages of M-phthalocyanine/fullerene solar cells are grouped together according to the valency of the central moiety.     

Frequency,thermal and voltage supercapacitor characterization and modeling

A simple electrical model has been established to describe supercapacitor behaviour as a function of frequency, voltage and temperature for hybrid vehicle applications. The electrical model consists of 14 RLC elements, which have been determined from experimental data using electrochemical impedance spectroscopy (EIS) applied on a commercial supercapacitor.     

Two-dimensional hygrothermal transfer in porous building materials

A two-dimensional mathematical model for evaluating the simultaneous heat and moisture migration in porous building materials was proposed. Vapor content and temperature were chosen as the principal driving potentials. The numerical solution was based on the control volume finite difference technique with fully implicit scheme in time. Two validation experiments were developed in this study. The evolution of transient moisture distributions in both one-dimensional and two-dimensional cases was measured. A comparison between experimental results and those obtained by the numerical model proves that they are fully consistent with each other. The model can be easily integrated into a whole building heat, air and moisture transfer model. Another main advantage of the present numerical method lies in the fact that the required moisture transport properties are comparatively simple and easy to determine.     

Recent oil price shock and Tunisian economy

The objective of this paper is to study the oil prices–macroeconomy relationship by the analysis of the role of subsidy policy. The vector autoregression (VAR) method was employed to analyze the data over the period 1993 Q1 2007 Q3. The results of the model using both linear and non-linear specifications indicate that there is no direct impact of oil price shock on the economic activity. The shock of oil prices affects economic activity indirectly. The most significant channel by which the effects of the shock are transmitted is the government's spending.     

Removal of phosphorus from aqueous solution by Posidonia oceanica fibers using continuous stirring tank reactor

The present study aims to develop a new potentially low-cost, sustainable treatment approach to soluble inorganic phosphorus removal from synthetic solutions and secondary wastewater effluents in which a plant waste (Posidonia oceanica fiber: POF) is used for further agronomic benefit. Dynamic flow tests using a continuous stirred tank reactor (CSTR) were carried out to study the effect of initial concentration of phosphorus, amount of adsorbent, feeding flow rate and anions competition. The experimental results showed that the removal efficiency of phosphorus from synthetic solutions is about 80% for 10 g L(-1) of POF. In addition, the variation of the initial concentration of phosphorus from 8 to 50 mg L(-1) increased the adsorption capacity from 0.99 to 3.03 mg g(-1). The use of secondary treated wastewater showed the presence of competition phenomenon between phosphorus and sulphate which could be overcoming with increasing the sorptive surface area and providing more adsorption sites when increasing the adsorbent dosage of POF. Compared with columns studies, this novel CSTR system showed more advantages for the removal of soluble phosphorus as a tertiary treatment of urban secondary effluents with more adsorption efficiency and capacity, in addition to the prospect use of saturated POF with nutriment as fertilizer and compost.     

Nutrient composition of the marine snail (Hexaplex trunculus) from the Tunisian Mediterranean coasts

BACKGROUND: Marine snail (Hexaplex trunculus) presents increasing nutritional, commercial and economical importance, being widely consumed in northern Africa, particularly in Mediterranean countries. From a nutritional point of view there is still limited information on the chemical composition of edible tissues (meat and hepatopancreas) of this species. Therefore, the aims of the present work were to study the proximate chemical composition, fatty acid and amino acid profiles of H. trunculus from the Tunisian Mediterranean coasts. RESULTS: Fatty acid profiles showed that the polyunsaturated fatty acids (PUFA) content is higher than the saturated fatty acids (SFA). The yields of PUFA and SFA present in the meat fat were 68.2% and 33.4% of the total fatty acids, respectively. Similar values were obtained in the hepatopancreatic lipidic fraction. Snail tissues contain valuable concentrations of PUFA, especially n‐6 and n‐3 with chain lengths of 20 and 22 carbons. All edible tissues were valuable sources of essential amino acids. Aspartic acid is the major amino acids present in the meat and hepatopancreas. The concentrations of nutrients were also determined in the hepatopancreas and meat of H. trunculus. Significantly high concentrations of minerals and trace elements were found in these tissues. CONCLUSION: This study suggests that H. trunculus is an important source of protein and essential amino acids. Furthermore, the snail lipidic fraction contains high proportions of polyunsaturated fatty acids benefical for human health. Copyright © 2011 Society of Chemical Industry     

Process dependence of BTI reliability in advanced HK MG stacks

Bias temperature instabilities (BTI) reliability is investigated in advanced dielectric stacks. We show that mobility performance and NBTI reliability are strongly correlated and that they are affected by the diffusion of nitrogen species N at the Si interface. PBTI, more sensitive to bulk oxide traps, is strongly reduced in very thin dielectric films. Reducing the metal gate thickness favors the reduction of mobility degradations and NBTI, but, also strongly enhances PBTI, due to a complex set of reactions in the gate oxide. Trade off must be found to obtain a great trade off between device performance and reliability requirements.