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In this work we analyse the features of the unsteady breaking of two dimensional free surface waves induced by a submerged hydrofoil at steady forward speed. The study is conducted by means of numerical simulations with OpenFOAM: interFoam and swenseFoam solvers being used as a computational framework for the free-surface treatment with the Volume Of Fluid (VOF) and Level Set (LS) techniques respectively. Due to the strongly unsteady behaviour of the flow, the interest is here focused on the spectral content of the free surface elevation. The results from two interface-capturing methods, VOF and LS are discussed and compared with experimental data from the literature. The influence of the turbulence models on the free surface shape and spectral content is also discussed. The final goal of the entire research work is the simulation of complex two-phase flows for robust and fast engineering applications in the ship hydrodynamics and wave loads fields, including wave breaking phenomena.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 910-912, Key issues for the wide diffusion of compact devices for sunlight exploitation are both reduction of costs and increase in efficiency. A promising device should reach a good tradeoff between these two requirements. We studied the possibility to approximate a Compound Parabolic Concentrator (CPC) by simpler shapes, while maintaining as much as possible the level of sunlight collection efficiency. We investigated several approximation approaches, with a common characteristic being the use of truncated conic surfaces that are easy to optically manufacture by cheap and widely available machining techniques. All the considered configurations were compared and quantitatively evaluated using lighting simulation software (Lambda Research Trace-Pro), considering the collected power of obtained sunlight distributions.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 448-452, All concentrator devices, both photovoltaic and thermal, are designed to collect only some predetermined direct portion of the solar radiation; so, the correct measurement of the direct solar radiation incident on a C-system is requested to calculate properly its efficiency. The focus of this paper is to describe a novel, and simple, method to measure the CSR (CircumSolar Ratio) [1-5] and a measurement apparatus, put under Italian patent [6], developed at this aim. It is composed of a lens, a diaphragm on the lens focus, a measurement device (e.g. a photodiode, a thermopile, etc) on axis with the lens, everyone assembled on a stiff mechanical support. The whole system is installed on a solar tracker so that the perfect alignment between lens and solar radiation is guaranteed. Thanks to optical simulations we have concluded that, when a suitable achromatic lens is used, a good one-to-one correspondence exists - from practical point of view - between the diaphragm aperture and the maximum angular divergence of the solar radiation collected by the instrument on the detector. So, in principle, increasing the diaphragm aperture, the solar irradiances corresponding to the growing values of solar radiation angular divergences can be measured. Then, on the basis of the measurements of the solar divergence yearly average value, it is possible to understand when a C-system works at its best for a fixed site in connection to the CSR measured value.

Recently, high-dose rate intracavitary irradiation has been used as a boost therapy or a palliative therapy in the treatment of the esophageal carcinoma. The new intraesophageal device is based on a modified Sengstaken-Blackemore tube. On the surface of the esophageal balloon of the S-B tube Cyponil tubes are fixed as iridium containers. The device is placed at the level of the neoplastic lesion. Treatment tolerance is good.

A 4 × non-imaging optically concentrated solar thermoelectric generator (STEG) was simulated and its layout was optimized depending on materials characteristics. The performances of seven state-of-the-art thermoelectric materials were realistically compared considering direct normal irradiances (DNI) between 400 and 900 W/m2 and temperature dependence of the thermoelectric parameters. The model was tested with experimental data from literature and leg aspect ratios, fill factor (or thermal concentration), and leg number per STEG unit area were also used as variables. Due to the high values of thermal concentrations at maximum efficiency, different materials filling the gap among STEG legs were also considered. Maximum efficiency weakly decreases for filler thermal conductivities typical of common insulating materials, opening novel opportunities for STEGs not requiring vacuum. Results of the analysis show that skutterudites, lead telluride and bismuth telluride exhibit the highest efficiencies (≈7%) in the studied range of thermal concentrations and for a DNI equal to 900 W/m2. However, skutterudites and lead telluride were found to be very sensitive on the DNI level, differently from bismuth telluride, which therefore qualifies as the best solution for energy conversion. Moreover, optimal layouts for STEGs based on bismuth telluride more easily meet manufacturing constraints.

The development and commercialization of Photovoltaic (PV) cells with good cost-efficiency trade-off not using critical raw materials (CRMs) is one of the strategies chosen by the European Community (EC) to address the Energy Roadmap 2050. In this context Cu2ZnSnS4 (CZTS) solar cells are attracting a major interest since they have the potential to combine low price with relatively high conversion efficiencies. Although a ≈9% lab scale efficiency has already been reported for CZTS this technology is still far from being competitive in terms of cost per peak-power (€/Wp) with other common materials. One possible near-future solution to increase the CZTS competiveness comes from thermoelectrics. Actually it has already been shown that Hybrid Thermoelectric-Photovoltaic Systems (HTEPVs) based on CIGS, another kesterite very similar to CZTS, can lead to a significant efficiency improvement. However it has been also clarified how the optimal hybridization strategy cannot come from the simple coupling of solar cells with commercial TEGs, but special layouts have to be implemented. Furthermore, since solar cell performances are well known to decrease with temperature, thermal decoupling strategies of the PV and TEG sections have to be taken. To address these issues, we developed a model for two different HTEPV solutions, both coupled with CZTS solar cells. In the first case we considered a Thermally-Coupled HTEPV device (TC-HTEPV) in which the TEG is placed underneath the solar cell and in thermal contact with it. The second system consists instead of an Optically-Coupled but thermally decoupled device (OC-HTEPV) in which part of the solar spectrum is focused by a non-imaging optical concentrator on the TEG hot side. For both solutions the model returns conversion efficiencies higher than that of the CZTS solar cell alone. Specifically, increases of ≈30% are predicted for both kind of systems considered. Copyright © 2017 American Scientific Publishers All rights reserved.

The performances of two hybrid thermoelectric photovoltaic systems are compared. In the first instance, a photovoltaic (PV) device and a thermoelectric generator (TEG) are optically coupled using a vacuumâ sealed compound parabolic concentrator (CPC). As an alternative, PV and TEG devices are thermally coupled putting them directly in contact to each other. Singleâ junction aâ Si and heterojunction Cu2ZnSnS4 (CZTS) have been considered as PV systems. The two systems are studied by varying the heat transfer coefficient of the cooling system between the TEG cold side and the ambient, the TEG device fill factor, and the optical concentration. Hybridization, in both configurations, always enhances the efficiencies, up toÂâ Â57% for single-junction a-Si and up toÂâ Â35% for the heterojunction CZTS. It will be shown that while direct thermal contact enables larger efficiencies, optical coupling grants lower temperatures at the PV side, enhancing reliability and lifetime. Further advantages and limitations of both configurations will be discussed.

The increasing energy demand and the ever more pressing need for clean technologies of energy conversion pose one of the most urgent and complicated issues of our age. Thermoelectricity, namely the direct conversion of waste heat into electricity, is a promising technique based on a long-standing physical phenomenon, which still has not fully developed its potential, mainly due to the low efficiency of the process. In order to improve the thermoelectric performance, a huge effort is being made by physicists, materials scientists and engineers, with the primary aims of better understanding the fundamental issues ruling the improvement of the thermoelectric figure of merit, and finally building the most efficient thermoelectric devices. In this Roadmap an overview is given about the most recent experimental and computational results obtained within the Italian research community on the optimization of composition and morphology of some thermoelectric materials, as well as on the design of thermoelectric and hybrid thermoelectric/photovoltaic devices.