Thermal and technical analyses of solar chimneys

An analysis for the solar chimneys has been developed, aimed particularly at a comprehensive analytical and numerical model, which describes the performance of solar chimneys. This model was developed to estimate power output of solar chimneys as well as to examine the effect of various ambient conditions and structural dimensions on the power output. Results from the mathematical model were compared with experimental results and the model was further used to predict the performance characteristics of large-scale commercial solar chimneys. The results show that the height of chimney, the factor of pressure drop at the turbine, the diameter and the optical properties of the collector are important parameters for the design of solar chimneys.     

Natural rubber/leather waste composite foam: A new eco‐friendly material and recycling approach

This article describes a new approach of recycling the leather waste (shavings) using it as filler in natural rubber foams composites. The foams were prepared using different amounts of leather waste (0–60 parts per hundred of rubber) and submitted to morphological (SEM microscopy) and mechanical analyses (cyclic stress–strain compression). The increase of leather shavings on the composite causes an increase of viscosity in the mixture, which reflects in the foaming process. This results in smaller and fairly uniform cells. Furthermore, expanded rubber has the biggest cell size, with more than 70% of cell with 1000 µm, while the composite with the higher concentration of leather has around 80% of total number of cells with 100–400 µm. The mechanical parameters were found to depend on the leather dust concentration. Moreover, the stiffness rises with the increase of leather shavings; consequently, the compression force for expanded rubber was 0.126 MPa as well as the composite with higher concentration of leather was 7.55 MPa. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41636.     

Influence of rotational speed on the microstructure and mechanical performance of friction-riveted thermosetting composite joints

Facing the actual demand for efficient joining technologies for multi-materials structures, friction riveting was shown to be an alternative joining technology for thermoset composite profiles in civil infrastructure. This process is based on plasticizing and deforming the tip of a rotating metallic rivet within a polymeric component through frictional heating. The feasibility of friction-riveted hybrid joints of Ti-6Al-4 V/glass-fibre reinforced thermoset polyester was already demonstrated in a separate work. This paper complements this study by analyzing the rivet rotational speed effect on the process temperature, joint microstructure and the local and global mechanical properties of the joint. Joints were produced using two different levels of rotational speed: 9000 and 10,000 rpm (the other parameters were kept constant). The results showed process temperatures (655–765 °C) up to 96% higher than the onset decomposition temperature of the polyester matrix (370 °C); this led to severe degradation of the composite in the joint area. The increase in rotational speed, and therefore in heat generation, led to a statistically insignificant increase of the rivet penetration depth and the rivet diameter widening. However, the extension of the degraded composite area increased 47% which was responsible to deteriorate in 50% the joint tensile strength (from 4.0 ± 1.2 kN to 2.0 ± 0.7 kN). Moreover, the microhardness map of the joined rivet evidenced possible phase transformations in the alloy, favouring the material hardening by increasing in rotational speed. However, no correlations could be established between the changes in hardness and the joint tensile strength since the joints majority failure by full rivet pull-out. Thereby, for the improvement of friction-riveted Ti-6Al-4 V/ glass-fibre reinforced thermoset polyester joints, the optimization of rotational speed is essential. This can guarantee the formation of efficient anchored joints and wider rivet tip deformation, concomitantly with the minimizing of the extension of the matrix degradation and finally leading to better tensile strength of the joints.     

Microstructure and Thermal Profile of Structured Lipids Produced by Continuous Enzymatic Interesterification

Enzymatic interesterification has been shown to be an alternative for the production of structured lipids resembling human milk fat. The knowledge of the physical properties of fat is an important tool for the implementation of this fat in a food matrix. The enzymatic interesterification reaction modifies the composition of triacylglycerols changing the crystallization properties and polymorphic form of fats. Blends containing different proportions of lard and soybean oil (80:20, 70:30, 40:60, 30:70 and 20:80) were enzymatically interesterified in a continuous flow tubular reactor and analyzed for crystalline structure by polarized light microscopy, the polymorphic form using X-ray diffraction and thermal properties by differential scanning calorimetry. The structural modifications resulting from continuous enzymatic interesterification changed the crystallization behavior and thermal profile of the samples, reducing enthalpy values. Structural changes were also evident on polarized light microscopy images, disclosing an increase in the crystallization rate among the samples after the continuous enzymatic reaction.     

Increasing the elongation at break of polyhydroxybutyrate biopolymer: Effect of cellulose nanowhiskers on mechanical and thermal properties

Bionanocomposites based on polyhydroxybutyrate (PHB) and cellulose nanowhiskers (CNWs) were prepared by dispersing CNWs in poly(ethylene glycol) (PEG) plasticizer subsequently incorporating the CNWs/PEG suspensions in the matrix. The thermal properties of the nanocomposites indicate an enlargement in the processing window in comparison to the neat PHB. The nanocomposites showed a remarkable increase in the strain level (50 times related to the neat PHB), without a significant loss of the tensile strength with the incorporation of small concentrations of CNWs in the final nanocomposite (up to 0.45 wt %). This behavior was explained in terms of a considerable chain orientation promoted by the presence of CNWs in the same direction of the applied load, which activated shear flow of the polymer matrix. The results described here can be explored to extend the applications of this biopolymer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Nonlinear identification using a B-spline neural network and chaotic immune approaches

One of the important applications of B-spline neural network (BSNN) is to approximate nonlinear functions defined on a compact subset of a Euclidean space in a highly parallel manner. Recently, BSNN, a type of basis function neural network, has received increasing attention and has been applied in the field of nonlinear identification. BSNNs have the potential to “learn” the process model from input–output data or “learn” fault knowledge from past experience. BSNN can be used as function approximators to construct the analytical model for residual generation too. However, BSNN is trained by gradient-based methods that may fall into local minima during the learning procedure. When using feed-forward BSNNs, the quality of approximation depends on the control points (knots) placement of spline functions. This paper describes the application of a modified artificial immune network inspired optimization method − the opt-aiNet − combined with sequences generate by Hénon map to provide a stochastic search to adjust the control points of a BSNN. The numerical results presented here indicate that artificial immune network optimization methods are useful for building good BSNN model for the nonlinear identification of two case studies: (i) the benchmark of Box and Jenkins gas furnace, and (ii) an experimental ball-and-tube system.     

FricRiveting of aluminum 2024-T351 and polycarbonate: Temperature evolution,microstructure and mechanical performance

Friction Riveting (FricRiveting) is an innovative, fast and energy-efficient spot joining process used to join lightweight hybrid metal–polymer and metal–composite structures. In this process, a cylindrical metallic rivet is used to join one or more thermoplastic components by means of plasticizing and deforming the tip of a metallic rivet through frictional heating and pressure inside the polymeric parts. This work studies the feasibility of the FricRiveting technique for polycarbonate/aluminum 2024-T351 alloy spot joints by investigating the temperature development (measured by infrared thermography), microstructure (evaluated by optical microscopy) and mechanical properties (investigated by tensile testing) of the joints. The thermographic temperature investigation indicated that the average peak process temperatures were from 280 to 360 °C, from 56% to 72% of the AA 2024 eutectic point and below the temperature range of extensive thermal degradation of polycarbonate (480–550 °C). Furthermore, the typical deformed tip of the rivet – the anchoring zone – was attained for all joints investigated in this study, as induced by thermo-mechanical processing. The anchoring efficiency represented by the aspect ratio of the deformed rivet was evaluated by optical microscopy. Aspect ratio values were compared with the process temperatures and the tensile strengths of the joints. Increases in process heat input resulted in larger aspect ratios. High average values of ultimate tensile forces varying from 6659 ± 62 N to 8540 ± 182 N (68.4–87.8% of the ultimate tensile strength of the metallic rivet) were achieved, with final ductile fracture occurring in the metallic rivet for joints with aspect ratios of 0.88 ± 0.02 and in the polymeric base plate for joints with aspect ratios of 0.61 ± 0.03 and 0.68 ± 0.04. The volumetric ratio – a recent, more complex three dimensional approach for evaluating the mechanical performance of the joints – was also investigated, revealing similar interactions with process temperatures and tensile strengths as the aspect ratio. The results of this work proved that FricRiveting is a feasible method for use on the PC-AA 2024-T351 material combination, as it yields strong joints.     

Ethylene Polymerization under high pressure and temperature using Nickel-α-diimine catalyst

The combination of 1,4–bis(2,6-diisopropylphenyl)-acenaphthenediimine-dichloronickel (II) (1) and methylaluminoxane (MAO) has been shown as being highly active in ethylene polymerization under high pressure and temperature. Herein we describe the effects of ethylene pressure and reaction temperature on polymer properties and reaction performance. The polyethylenes synthesized with the system 1/MAO are highly branched, with 105 to 277 branches per 1000 backbone carbon atoms, depending on the reaction conditions. The branching index increases with the rise of temperature or with the decrease of ethylene pressure. These branches go from methyl to hexyl, or even farther, and present a pattern in which 1,4; 1,5 and 1,6 methyl groups appear mainly and isolated methyl groups are not present. These branches are generated by a chain-walking system. The polyethylenes produced with these systems have a molecular weight (Mw) between 44,000 and 105,000 Daltons and polydispersions from 2,0 to 4,0, depending on reaction conditions. The polymer molecular weight tends to decrease with the increasing temperature of polymerization.