1,720,987 research outputs found
Prediction of radiative heat transfer in metallic foams
No full textA simplified analytical-numerical method to model radiation heat transfer in metallic foams is proposed. It modifies a model taken from the literature and allows to predict the radiative conductivity for high and low porosity foams. A simplified cubic representative elementary volume of the foam is assumed and radiative heat flux is evaluated by computing radiosities and view factors. The analytical approach proposed in this paper slightly modifies some coefficients of the original model. Test ray-tracing and numerical simulations based onto Monte Carlo method are carried out in order to consistently calculate some view factors. The comparison with experimental results shows that predictions of the proposed model are more accurate than those of the original one. © 2013 Elsevier Masson SAS. All rights reserved
The prediction of radiation heat transfer in open cell metal foams by a model based on the Lord Kelvin representation
No full textA theoretical approach proposed in the literature has been used to develop a new radiative heat transfer model based on the tetrakaidecahedric representation of open cell metal foams proposed by Lord Kelvin. The analytical approach has been combined with numerical simulations based onto ray-tracing Monte Carlo method. An iterative matrix algebra implemented procedure has been used to consistently calculate the coefficients involved in view factors. The radiative conductivity of foams has been evaluated by means of the proposed model. Predictions are compared both with experimental results from the literature, obtained on several metallic foams, and with predictions given by an existing simpler model based on a cubic representation of the foam unit cell. The agreement of experimental results with predictions derived by means of the proposed model is good and far better than that with predictions by the simpler model. � 2014 Elsevier Ltd. All rights reserved
Efficiency enhancement of a-Si and CZTS solar cells using different thermoelectric hybridization strategies
No full textThe 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 vacuum–sealed compound parabolic concentrator (CPC). As an alternative, PV and TEG devices are thermally coupled putting them directly in contact to each other. Single–junction a–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 to ≈ 57% for single-junction a-Si and up to ≈ 35% 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. © 2017 Elsevier Lt
LabZERO, an interdisciplinary living laboratory for the promotion of renewables and energy efficiency
No full textLabZERO is a multidisciplinary laboratory located at Politecnico di Bari and ENEA Centro Ricerche di Brindisi aimed to promote energy efficiency and renewables in both urban and industrial districts. The lab activities are oriented to provide fast-prototyping, instrumentation, methodologies and equipment for material characterization of new components in the field of energy efficiency, micro-generation, micro-grids, renewables, energy hubs, energy districts. © 2016 AEIT
Theoretical analysis of two novel hybrid thermoelectric-photovoltaic systems based on Cu2ZnSnS4 solar cells
No full textThe 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
Morphology of opencell foams: A critical review and geometric modeling
No full textTransport phenomena through open-cell foams are strongly affected by their complex microstructure. Morphological parameters, such as the diameter of pores and cells, the strut thickness, and the specific surface area, play key roles. Due to the intricate nature of an open-cell foam, its morphological models are very useful in engineering applications. We first review correlations in the literature of the morphological parameters that affect transport phenomena in foams. Then, with reference to the Kelvin’s foam model, we present a unique model for the characterization of morphological parameters of open-cell foams, accounting for different strut shapes. New correlations among morphological parameters are proposed. There is good agreement between the correlations obtained with the proposed model and the experimental results from the literature. The model, accounting for any shape of the struts cross section, predicts values of foam morphological parameters generally closer to those predicted by available models not valid for all strut shapes
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