Numerical study of the performance of multistage Scaba 6SRGT impellers for the agitation of yield stress fluids in cylindrical tanks

The 3-D flow fields and power consumption in a vessel stirred by multistage Scaba 6SRGT impeller have been investigated. The Xanthan gum solutions in water were used, which have a shear thinning behavior with yield stress. This study was carried out with the help of a CFD package(CFX 13.0, Ansys Inc.) which is based on the finite volume method to solve the momentum equations. The effects of stirring rate, fluid rheology, impeller number, impeller location and vessel size on the performance of such stirred system are presented. To validate the CFD model, our predicted results have been compared with other literature data and a satisfactory agreement has been found.     

Thermal Buckling Response of Functionally Graded Plates with Clamped Boundary Conditions

In this research work, an exact analytical solution for thermal buckling analysis of functionally graded material (FGM) plates with clamped boundary condition subjected to uniform, linear, and non-linear temperature rises across the thickness direction is developed. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory accounts for parabolic distribution of the transverse shear strains, and satisfies the zero traction boundary conditions on the surfaces of the plate without using shear correction factor. The material properties of FGM plate are assumed to be graded in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents. The governing equations are solved analytically for a plate with simply supported boundary conditions. Resulting equations are employed to obtain the closed-form solution for the thermal force resultant for each loading case. Numerical examples covering the effects of the plate aspect ratio, side-to-thickness ratio and gradient index on thermal force resultant are discussed.     

The influence of bleeding,extra water and superplasticizer on the SCC plastic shrinkage cracking: case of hot weather

Self-compacting concrete (SCC) is a new material able to be put in place without vibration. However, this advantage is offset by some drawbacks, such as plastic shrinkage, one of the causes of cracking in concrete. Furthermore, the presence of fines absorbs a large amount of water and therefore minimizes bleeding. This paper endeavours to provide a better understanding of the appearance of plastic shrinkage cracking, and to justify his relation with bleeding phenomena. Five SCC formulas with different W/C ratios were prepared and compared to the same range of ordinary concrete (OC) in terms of restrained shrinkage (cracking width). At the same time, a study of cracks’ propagation over time (cracking length) was conducted on the equivalent mortars (mOCe, mSCCe). Mixtures were placed in different hot environmental conditions. The results showed that bleeding significantly reduces cracking length and has no effect on cracking width. In the second part, extra water and superplasticizer was proposed as a solution to prevent SCC cracking and findings show the addition of 10% of water reduces cracking length and a slightly lower addition of superplasticizer reduces SCC’s crack width.     

Thermal Buckling of Functionally Graded Plates According to a Four-Variable Refined Plate Theory

In this article, a four-variable refined plate theory is presented for buckling analysis of functionally graded plates. The theory, which has strong similarity with classical plate theory in many aspects, accounts for a quadratic variation of the transverse shear strains across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. A power law distribution is used to describe the variation of volume fraction of material compositions. Equilibrium and stability equations are derived based on the present theory. The non-linear governing equations are solved for plates subjected to simply supported boundary conditions. The thermal loads are assumed to be uniform, linear and non-linear distribution through-the-thickness. The influences of many plate parameters on buckling temperature difference will be investigated. It is noticed that the present refined plate theory can predict accurately the critical temperatures of simply supported functionally graded plates.     

A new approach in tracking maximum power under partially shaded conditions with consideration of converter losses

The fact that photovoltaic panels are very sensitive to non-uniform insolation conditions, which can occur several times a day, causes a decrease of efficiency and so increases time for return on investment. This work presents a maximum power point tracking algorithm (MPPT) operating on the load characteristic in order to take the converters losses into account. In addition, the proposed MPPT deals with the problems of shadowing for which the power-load characteristic can present two or more local maximums close to each other. Considering the converters losses it can be shown that the maximum output power of the photovoltaic panels does not necessarily coincide with the maximum output power of the converters. The proposed MPPT algorithm tracks the maximum power with the intention of reducing the total losses including those of converters. Its performance is verified by simulation and confirmed by experimental results.     

Formulation and rheology of eco-self-compacting concrete (Eco-SCC)

This article presents the results of an experimental study on the rheology of eco-SCC, formulated on the basis of the modified Chinese method and on the new standard EN206/CN. The studied ecological concretes consist of Portland pozzolana cement, containing large amounts of limestone filler or natural pozzolana, which can replace cement up to 50%. In addition, the compactness of the granular mixture is optimized; therefore, the total amount of the incorporated binder is further reduced in the body of concrete. The study of the rheological behavior of these fluid concretes was carried out in the laboratory, using a coaxial vane-type rheometer. The results showed that both rheological models, i.e. modified Bingham and Herschel–Bulkley, describe satisfactorily the shear-thinning character of the formulations tested. However, the rheological parameters obtained with the modified Bingham model seem to have better correlations with the measurements of the slump test. These same results also indicated that replacing 30% of cement by one of the additions selected for our study, resulted in mixtures with yield stress and plastic viscosities that are within the validity range of SCC. This allowed reducing CO₂ emissions by about 40% for each cubic meter of concrete produced.     

Swellings due to alkali-silica reaction and delayed ettringite formation: Characterisation of expansion isotropy and effect of moisture conditions

This paper investigates the effect of different conditions on the development of concrete expansions due to alkali-silica reaction (ASR), delayed ettringite formation (DEF) and their combination. The presence of products of the two reactions has been observed during structure diagnosis. The aim of this research is to study the two reactions in concretes with close mix designs but with various types of aggregate and moisture conditions. Measurements performed in the three directions of stress-free specimens showed that DEF expansions could be considered as isotropic for stress-free material. DEF expansions were largely influenced by the storage conditions (immersed in water or in sealed conditions). The volume of storage water modified the kinetics. Under sealed conditions, no expansions were measured for mortar containing non-reactive aggregate, while small positive strains were obtained for mortar containing reactive aggregate. In all cases, new water supply caused fast, large expansions. The different effects of alkali leaching and moisture conditions on DEF and ASR expansions are discussed.     

Estimating probabilistic confidence for mixture components identified using a spectral search algorithm

Providing a confidence measure associated with the substance(s) identified in an unknown mixture by a spectral search technique is critical for non-expert users of devices and techniques based on spectroscopy. In this work, a technique for estimating probabilities associated with substances identified by spectral searching is described. In the proposed approach, a mixture analysis algorithm processes the spectrum of an unknown sample using a spectral library to generate a list of substances that may be present in the sample. The partial correlation of each of the substances in the list is then computed. The estimation of the probability is accomplished through a generalized linear model that converts the partial correlation values to a probability measure for each of the mixture components. The statistical properties of partial correlation allow probability estimation irrespective of whether a substance is present in a pure form or within a mixture. The technique was evaluated using both simulated and real Raman spectra of multi-component mixtures, and adequate performance was demonstrated.     

Effect of polymerization conditions on polyacetylene morphology

In an effort to optimize the synthesis of polyacetylene we have studied the evolution of its morphology by scanning electron microscopy (SEM) and also determined the density of the polymer. Both results are correlated and discussed.