cfd optimization of cpc solar collectors

Abstract The use of solar energy for industrial purpose at medium-low temperature is receiving attention. As a matter of fact, this temperature range, usually between 80-200°C, requires low cost devices to convert solar energy into useful heat. In particular, the use of CPCs collectors has been suggested in literature because they can be operated without the use of a tracking system, at least within certain limits. The thermal losses of these devices are often reduced by using an evacuated pipe, but this solution increases the manufacturing costs and reduces the reliability and the optical efficiency of the receiver. A series of alternative methods for the thermal losses reduction has been proposed in this paper, for working temperature up to 200°C. Their effectiveness was evaluated by means of a previously validated CFD model. A cylindrical receiver and a concentration ratio of 2 were taken into account. The results were analyzed in terms of temperature contours and thermal efficiency. In particular, the optical efficiency was focused as a key parameter in the performances of a CPC. As conclusion, it was found that a proper arrangement of the absorber with a baffle may entail an improvement of the thermal efficiency without significantly increasing the complexity of the system

an experimental and numerical analysis of the performances of a wankel steam expander

Abstract In the last decades, the energy market increased its interest towards the smart grids and electrically isolated systems. These systems utilize small size power generators in which volumetric expanders may be employed for a wide range of operative conditions, because of their robustness and reliability. In this work a study on a volumetric expander based on the Wankel mechanism was carried out. The aim of this study was to develop a lumped parameters numerical model able to predict the brake effective torque and working fluid consumption of the expander. This model was validated by comparison with experimental results obtained using steam as working fluid. This model allowed to trace the trends of mechanical and thermal losses versus rotating speed and inlet pressure. The experimental results encouraged the need for a further development of this expander, and showed the capability of the numerical model to predict the effective performances of the device

experimental results of a wankel type expander fuelled by compressed air and saturated steam

Abstract The work presented in this paper deals with the experimental tests which were carried out on a prototype of a rotary volumetric expansion device based on the Wankel mechanism. This expansion device is addressed to small size power plants (in the range 5-50 kW) for distributed micro-generation using various sources of thermal energy, such as sun, biomass and waste heat. The prototype was built using an internal combustion Wankel engine, employing the shaft, the rotor, the bearings, while the statoric case was newly built on the design of the University of Pisa. Firstly, the tests were carried out with the compressed air produced by a compressor, then the prototype was fed with the saturated steam produced by a biomass boiler. In the first case, the exhaust back-pressure was the atmospheric one, in the second case vacuum conditions were employed thanks to a condenser. The inlet pressure was between 4 and 8 bar. The results showed the capability of the prototype to rotate regularly at 3000 rpm, and allowed the validation of numerical models presented in previous papers. Moreover, the expansion device showed the capability of developing the expected power

Synthesis and antibacterial effects of cobalt–cellulose magnetic nanocomposites

© The Royal Society of Chemistry. Green synthesis is employed to prepare cobalt/cellulose nanocomposites with cubic (α-cobalt) cobalt as a main component with antibacterial and magnetic properties. An in situ reduction of aqueous solutions of cobalt ions on a model cellulose substrate surface using hydrogen gas affords spherical, cellulose-stabilised cobalt nanoclusters with magnetic properties and an average diameter of 7 nm that are distributed evenly over the surface of the cellulose fibres. These cobalt/cellulose nanocomposites exhibit good antibacterial action against opportunistic pathogens both Gram-positive (S. aureus) and Gram-negative (E. coli, A. baumannii and P. aeruginosa), with zones of inhibition up to 15 mm, thereby encouraging the deployment of these advanced materials for the treatment of wastewater or within medical dressings. This method of preparation is compared with the analogous in situ reduction of cobalt ions on a cellulose surface using sodium borohydride as reducing agent

HIV-1 Tat alters neuronal intrinsic excitability

Objective: In HIV+ individuals, the virus enters the central nervous system and invades innate immune cells, producing important changes that result in neurological deficits. We aimed to determine whether HIV plays a direct role in neuronal excitability. Of the HIV peptides, Tat is secreted and acts in other cells. In order to examine whether the HIV Tat can modify neuronal excitability, we exposed primary murine hippocampal neurons to that peptide, and tested its effects on the intrinsic membrane properties, 4 and 24 h after exposure. Results: The exposure of hippocampal pyramidal neurons to Tat for 4 h did not alter intrinsic membrane properties. However, we found a strong increase in intrinsic excitability, characterized by increase of the slope (Gain) of the input-output function, in cells treated with Tat for 24 h. Nevertheless, Tat treatment for 24 h did not alter the resting membrane potential, input resistance, rheobase and action potential threshold. Thus, neuronal adaptability to Tat exposure for 24 h is not applicable to basic neuronal properties. A restricted but significant effect on coupling the inputs to the outputs may have implications to our knowledge of Tat biophysical firing capability, and its involvement in neuronal hyperexcitability in neuroHIV

Doping of inorganic materials in microreactors – preparation of Zn doped Fe₃O₄ nanoparticles

Microreactor systems are now used more and more for the continuous production of metal nanoparticles and metal oxide nanoparticles owing to the controllability of the particle size, an important property in many applications. Here, for the first time, we used microreactors to prepare metal oxide nanoparticles with controlled and varying metal stoichiometry. We prepared and characterised Zn-substituted Fe₃O₄ nanoparticles with linear increase of Zn content (ZnxFe₃−xO₄ with 0 ≤ x ≤ 0.48), which causes linear increases in properties such as the saturation magnetization, relative to pure Fe₃O₄. The methodology is simple and low cost and has great potential to be adapted to the targeted doping of a vast array of other inorganic materials, allowing greater control on the chemical stoichiometry for nanoparticles prepared in microreactors

Prenatal and childhood adverse life events, inflammation and depressive symptoms across adolescence

Background No study has investigated the role of inflammation in explaining the association between early exposures to adverse life events and depressive symptoms in adolescence. Method Using data from the Avon Longitudinal Study of Parents and Children, we tested if inflammatory markers [serum C-reactive protein (CRP) and interleukin 6 (IL-6)] at age 9 years mediate the association between adverse life events, measured separately for the prenatal (since the beginning of pregnancy) and the childhood (ages 0–9 years) periods, and the development of depressive symptoms at ages 10–17 years. Data (n = 4,263) were analyzed using mediation analysis in a latent growth curve modeling framework. Results Depressive symptoms at the beginning of adolescence (age 10) were associated with the number of prenatal events, the number of events around birth and the increase in events over time in childhood (ages 0–9), even after adjustment for confounders. IL-6 partially mediated the association between increasing exposure to events over time in childhood and depressive symptoms at the beginning of adolescence. IL-6 did not mediate any other association between events and symptoms. There was no evidence for mediation by CRP, which was generally unrelated to exposure to events. Limitations The small size of the mediation effect and the robust direct effects of events prenatally and around birth suggest there are multiple routes from early stressors to adolescent depression. Conclusions In the general adolescent population, increasing exposure to psychosocial stressors over time during childhood is associated with the early onset of depressive symptoms, partly via increasing levels of plasma IL-6

Ground-based NO2 measurements at the Italian Brewer stations: A pilot study with Global Ozone Monitoring Experiment (GOME)

Ground-based NO2 total column measurements have been collected since 1992 using Brewer spectrophotometry at Rome, an urban site, and Ispra (semirural). These are the only ground-based stations regularly monitoring NO2 in Italy. The methodology of measurement together with the procedure to control its quality is described. From the analysis of the time series it was found that the mean value of the NO2 column is 1.63 DU atRome and 1.60 DU atIspra. A firstat tempt to compare NO2 vertical column densities (VCD) from GOME with those derived from ground-based Brewer measurements, under different atmospheric conditions and measurement time lags is here presented. The results of this pilot study showed unsatisfactory agreement because different atmospheres are probed by GOME and Brewer instruments. The GOME space resolution resulted insufficient to fully characterize the Rome and Ispra highly localized polluted areas

Ground-based NO2 measurements at the Italian Brewer stations: A pilot study with Global Ozone Monitoring Experiment (GOME)

Ground-based NO2 total column measurements have been collected since 1992 using Brewer spectrophotometry at Rome, an urban site, and Ispra (semirural). These are the only ground-based stations regularly monitoring NO2 in Italy. The methodology of measurement together with the procedure to control its quality is described. From the analysis of the time series it was found that the mean value of the NO2 column is 1.63 DU atRome and 1.60 DU atIspra. A firstat tempt to compare NO2 vertical column densities (VCD) from GOME with those derived from ground-based Brewer measurements, under different atmospheric conditions and measurement time lags is here presented. The results of this pilot study showed unsatisfactory agreement because different atmospheres are probed by GOME and Brewer instruments. The GOME space resolution resulted insufficient to fully characterize the Rome and Ispra highly localized polluted areas

Nanoparticulate Pd-Sn Compounds Supported on Metal Oxides: Synthesis, Material and Catalytic Properties

The manufacture of chemicals requires innovation at the catalyst frontier so that processes can be developed with higher energy efficiency and increased facility of separation and recovery of products. Catalysts with high selectivity and activity control the overall efficiency of a process by avoiding unwanted side-reactions and increasing the conversion per unit time. Although processes catalysed by homogeneous catalysts have the advantage of offering better control and understanding of the reaction mechanism, their frequent dependence on expensive metals which are difficult to recover, often precludes their employment in large-scale applications. Heterogeneously catalysed reactions on the other hand, are not associated with problems regarding recycling and reuse of catalyst, contamination of products or intermediates. This work reports the synthesis, characterization and testing of Pd-Sn nanoalloy catalyst in the selective hydrogenation of 2-methyl-3-butyn-2-ol. Our results show that the Pd-Sn nanoalloy, of composition Pd2.8Sn, supported on ZnO (Pd2.8Sn/ZnO), offers very high activity and selectivity in the semi-hydrogenation of 2-methyl-3-butyn-2-ol to 2-methyl-3-buten-2-ol in the liquid phase. Under identical reaction conditions, Pd2.8Sn/ZnO shows activity, both turnover frequency and activity normalized by Pd content, significantly higher than Pd/CaCO3 (the Lindlar catalyst), with TOF of 137.6 s−1 compared to 79.2 s−1 for Pd/CaCO3 with approximately equal selectivity. The preparation of Pd2.8Sn/ZnO is achieved using a one-pot polyol procedure with the addition of a capping agent (polyvinylpyrrolidone) to control the particle size distribution. TEM shows nanoparticles evenly dispersed on the support, with a size distribution of 4.06 ± 0.75 nm. Single phase Pd2.8Sn was also prepared without the ZnO support, via the polyol method. Powder X-Ray diffraction data from the unsupported nanoalloy shows that the unit cell of Pd2.8Sn is face centred cubic with the Pd and Sn atoms occupying randomly the same crystallographic position. The chemical formula was calculated from a combination of ICP and PXRD analyses