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Abstract An attractive path to the production of hydrogen from water is a two-step thermo chemical cycle powered by concentrated sunlight from a solar tower system. In the first process step the redox system, a ferrite coated on a monolithic honeycomb absorber, is present in its reduced form while the concentrated solar energy hits the ceramic absorber. When water vapour is fed to the honeycomb at 800 °C, oxygen is abstracted from the water molecules, bond in the redox system and hydrogen is produced. When the metal oxide system is completely oxidised it is heated up for regeneration at 1100–1200 °C in an oxygen-lean atmosphere. Under those conditions and in the second process step, oxygen is set free from the redox system, so the metal oxide is being reduced and after completion of the reaction again capable for water splitting. Since the overall process consists of two core reaction steps, which need to be carried out sequentially in a reactor unit at two different temperature steps, a special process and plant concept had to be developed enabling the continuous supply of product regardless of the alternating nature of the solar reactor operation. The challenge of the process control is to keep the two core reaction temperatures constant and to ensure regular temperature switches after completion of the individual process steps, independent of the weather conditions, like DNI fluctuation, clouds and wind speed. Also start-up, the fast switching after completion of half-cycles and the shutdown must be controlled. State of the art is the manual switching of heliostats to fulfil those control tasks. This paper describes the development and use of a system model of this process. The model consists of three main parts: the simulation of the solar flux distribution at the receiver aperture, the simulation of the temperatures in the reactor modules and the simulation of the hydrogen generation. It can be used for the analysis of the operational behaviour. The model is intended to be used in the future for the control of the whole process.

We combined profiling of the bloom-forming and potentially toxigenic cyanobacterium Planktothrix rubescens using a multiparameter probe equipped with a phycoerythrin sensor (in vivo fluorometry, IVL) in Lake Mondsee, Austria, with flow cytometric live analyses of discrete samples taken from several depths in the upper 20 m of the water column. Results obtained by IVL and acoustic flow cytometry (AFC) were compared to microscopic analyses of integrated (0-21 m) water samples using fixed material. This comparison was made because the integrated samples are used for the Austrian monitoring programme according to the EU Water Framework Directive. We demonstrate that AFC provides quantitative analyses of the filaments of P. rubescens that are significantly correlated to IVF and microscopic analyses, allowing rapid (within hours) and more precise calculation of P. rubescens biomass than estimates derived from IVL. Our analysis shows that vertically integrated water samples provide unreliable information on the concentration of P. rubescens in the upper surface waters and on the peak concentration of P. rubescens within the water column. We conclude that the protocol that we developed is superior to the current monitoring practice.

This paper proposes a study about the feasibility to modulate the indoor artificial lighting, taking into account both achievable energy savings and comfort conditions, in order to reduce lighting electric loads. In particular, it focuses on the possibility, on one hand, to decrease the luminous flux and, on the other hand, to change the Correlated Colour Temperature (CCT), in order to decrease the absorbed power. Moreover, the impact of daylight-linked control systems was considered. Finally, the possibility to combine the different technical solutions was analysed. The paper proposes the definition of daily scheduling referred to lighting energy management, in order to modulate the maximum load value, maintaining a minimum during the rest of the time for an office end use.

Computed tomography of chemiluminescence (CTC) is one kind of volumetric tomography which can recover 3D flame structures and has found extensive applications for spatiotemporally resolved measurements of flames. However, the existing CTC techniques rely on the pinhole model and fail when the flames are confined within a cylindrical glass due to image distortion caused by the refraction on both the internal and external surfaces of the glass. In this work, a refined camera model was developed by combining the pinhole camera model with Snell's laws using a reverse ray-tracing method to incorporate the effects of refraction. A proof-of-concept demonstration of CTC based on the refined camera model was conducted on a swirl flame confined within a 20-mm-thick K9 glass. The results proved the superiority of such technique against the existing version in terms of reconstruction accuracy. This work is expected to be especially useful for the study of combustion phenomena such as combustion instability for which the flames are typically confined within cylindrical combustors.

Abstract The contamination of water bodies by heavy metals is one of the main concerns for environmental protection, due to the intrinsic toxicity and long lifetime of these compounds. Consequently, there is a pressing need to reduce emissions of heavy metals in wastewater, using efficient and cost-effective remediation techniques, which at the same time will not produce toxic residues, e.g. adsorption on activated carbon. The present work deals with the optimal design and operation of adsorption columns for the removal of cadmium and nickel from synthetic aqueous solutions, both in single-compound and binary systems. Thermodynamic experimental tests were carried out on activated carbon samples (GAC), produced starting from a commercial carbon by chemical oxidation with either nitric acid or hydrogen peroxide, to support the dynamic study and to identify the sample with higher adsorption capacity. Subsequently, the dynamic behavior of Cd and Ni adsorption was studied by means of software simulations in order to attain an optimized column design. Several working configurations were explored, investigating the effects of GAC physical and chemical properties, pollutant concentration and flow rate, for a wide application in process operations. Moreover, the intertwining between thermodynamic and dynamic parameters in the performance of a fixed-bed was highlighted. All the transport phenomena that can affect the overall performance, i.e. axial dispersion, external film diffusion and intraparticle mass transport were considered. In particular, for the internal transport, both pore and surface diffusions were taken into account and considered to occur in parallel; moreover the contribution of pollutant surface diffusivity, which is usually neglected in the commonly adopted model because difficult to estimate, was isolated and its influence on the overall adsorption rate was elucidated. The general formulation of the kinetic model allowed estimating the contribution of each adsorption rate controlling parameter and the effect exerted by the main fluid dynamic parameters, hence representing a fundamental tool for the design and optimization of an adsorption column.

Abstract This paper reports a study on the enlargement of particles, produced by a model ethylene/air flame, by heterogeneous condensation of water vapour. This was carried out in an instrumented lab-scale facility based on the use of a growth tube. Tests were performed by varying the temperature of the condensing vapour and the gas residence time in the growth tube. Particle enlargement was favoured by increasing the vapour temperature and the residence time. Experiments can be proficiently described using consolidated models for heterogeneous condensation, provided that the contact angle between the liquid embryo of condensing vapour and the particle surface is considered as an adjustable parameter, variable with temperature.

AbstractClonal plants from poor habitats benefit less from morphologically plastic responses to heterogeneity than plants from more productive sites. In addition, physiological integration has been suggested to either increase or decrease the foraging efficiency of clonal plants. We tested the capacity for biomass production and morphological response in two closely related, rhizomatous species from habitats that differ in resource availability, Carex arenaria (from poor sand dunes) and C. disticha (from nutrient‐richer, moister habitats). We expected lower total biomass production and reduced morphological plasticity in C. arenaria, and that both species would produce more ramets in high nutrient patches, either in response to signals transported through physiological integration, or by locally determined responses to nutrient availability. To investigate mineral nutrient heterogeneity, plants were grown in boxes divided into two compartments with homogeneous or heterogeneous supply of high (H) or low (L) nutrient levels, resulting in four treatments, H‐H, H‐L, L‐H and L‐L. Both C. arenaria and C. disticha produced similar biomass in high nutrient treatments. C. disticha responded to high nutrients by increased biomass production and branching of the young parts and by altering root:shoot ratio and rhizome lengths, while C. arenaria showed localised responses to high nutrients in terms of local biomass and branch production in high nutrient patches. The results demonstrated that although it has a conservative morphology, C. arenaria responded to nutrient heterogeneity through morphological plasticity. An analysis of costs and benefits of integration on biomass production showed that young ramets of both species benefited significantly from physiological integration, but no corresponding costs were found. This suggests that plants from resource‐poor but dynamic habitats like sand dunes respond morphologically to high nutrient patches. The two species responded to nutrient heterogeneity in different traits, and this is discussed in terms of local and distant signalling of plant status.