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Abstract In this study, the influence of compressor speed, ejector motive nozzle needle position and evaporator inlet metering valve opening on the oil circulation rates (OCRs) of an R744 transcritical standard ejector cycle was experimentally investigated. Significantly higher OCR (∼10%) was observed at the evaporator inlet of the ejector cycle than that at the high pressure side (∼1%) measured in the same cycle under the same conditions. It has been observed that evaporator OCR was increased with increasing compressor speed. When the motive nozzle needle moved towards the nozzle throat, both compressor discharge flow rate and evaporator OCR were observed to be significantly lowered. As the evaporator inlet metering valve opening was adjusted, the compressor mass flow rate did not vary significantly while the evaporator mass flow rate decreased with decreasing metering valve opening. The evaporator OCR decreased from 6.5% to 2.2% as the metering valve opening varied from 86% to 27%. High evaporator OCR results in large evaporator pressure drop and low heat transfer coefficient. In addition to the standard ejector cycle, several alternative ejector cycles were theoretically analyzed to see if there is similar problem of high OCR in the evaporator. In ejector liquid recirculation cycle and multi-stage multi-ejector supermarket refrigeration cycle, similar high OCR problem in the evaporator may exist, while in two evaporator ejector cycle, evaporator OCR is equal to compressor OCR at steady state.

Abstract This paper deals with the problem of an infinite cylindrical heat source embedded into a saturated porous medium and subject to a cross-axial Darcian flow. Only forced convection is considered. We derived the transient dimensionless solution through a combined analytical – numerical method consisting of four steps: (a) a preliminary dimensional analysis of the constitutive equations of the problem in order to find the dimensionless groups governing the solution; (b) the identification of the validity range of the model as a function of the just-mentioned dimensionless groups; (c) the numerical resolution of the problem; (d) the synthesis of the numerical results in a general dimensionless form. Specifically, we provide several dimensionless maps of the 2D thermal field evolution for six different orders of magnitude of the Peclet number ( 10 - 3 – 10 2 ) . The evolution of the temperature of the heat source is fully illustrated and discussed through plain dimensionless criteria. Then, we discuss the time, space and fluid velocity scales in which the solution is practically equivalent to the ones given by a linear heat source and a purely conductive model. We conclude that the present model has to be employed to evaluate the temperature in proximity of the heat source when the reference Peclet number is greater than 0.5. On the contrary, the linear model can be successfully used for radial distances 5–10 times greater that the heat source radius, depending on the reference Peclet number.

In the present work an equilibrium model (gas-solid), based on the minimization of the Gibbs energy, has been used in order to estimate the theoretical yield and the equilibrium composition of the reaction products (syngas and char) of biomass thermochemical conversion processes (pyrolysis and gasification). The data obtained from this model have also been used to calculate the heating value of the fuel gas, in order to evaluate the overall energy efficiency of the thermal conversion stage. The proposed model has been applied both to partial oxidation and steam gasification processes with varying air to biomass (ER) and steam to carbon (SC) ratio values and using different feedstocks; the obtained results have been compared with experimental data and with other model predictions obtaining a satisfactory agreement.

Abstract The life cycle of a pavilion built for an international exhibition was investigated to understand the role that the design phase may play in the environmental sustainability of buildings. The limited life span of the structure allowed for a complete life cycle assessment (LCA) based on primary data to be undertaken, including the end of the first life. A methodology that considered an extension of the service life was applied to estimate the environmental impacts of distinct end-of-life scenarios. Results confirmed the paramount importance of the design phase in improving the life cycle sustainability of buildings. Accurate selection of materials allowed to markedly reduce the impact of the product stage (e.g. 37% fewer greenhouse gas emissions). Design for disassembly proved to be a necessary but not a sufficient condition to minimise the end-of-life impacts: design phase should not be limited to the appropriate selection of materials and components’ connections but must also foresee a second use for the structure or the materials at the end of the first life. Forecasting an after-life for the structure could reduce the life cycle burden up to 40% for several environmental impact categories. Conversely, if the second use is not predefined, the economic cost in the dismantling operation could become the priority rather than the salvaging of the components. Results of the present study may be used by future (temporary) building designers to improve the sustainability of their structure and to avoid the errors identified in the present case.

The passive approach to the themes of energy savings is essentially based on the morphologic articulations of the constructions. The experience of Studio Nicoletti in low energy building is exemplified by five groups of designs based on different typologies. Cool air stored in the heart of buildings. Tall buildings: energy savings based on minimization of the structural materials and bioclimatic systems. Double skin for cooling the external envelope of the buildings. Urban climate: climatization of large urban fragments, protected either by a glass envelope or a bioclimatic pergola. Integration of various methods including extensive use of natural lighting, like in the design for the New Acropolis Museum in Athens.

Driven by the search for the highest theoretical efficiency, in the latest years several studies investigated the integration of high temperature fuel cells in natural gas fired power plants, where fuel cells are integrated with simple or modified Brayton cycles and/or with additional bottoming cycles, and CO2 can be separated via chemical or physical separation, oxy-combustion and cryogenic methods. Focusing on Solid Oxide Fuel Cells (SOFC) and following a comprehensive review and analysis of possible plant configurations, this work investigates their theoretical potential efficiency and proposes two ultra-high efficiency plant configurations based on advanced intermediate-temperature SOFCs integrated with a steam turbine or gas turbine cycle. The SOFC works at atmospheric or pressurized conditions and the resulting power plant exceeds 78% LHV efficiency without CO2 capture (as discussed in part A of the work) and 70% LHV efficiency with substantial CO2 capture (part B). The power plants are simulated at the 100 MW scale with a complete set of realistic assumptions about fuel cell (FC) performance, plant components and auxiliaries, presenting detailed energy and material balances together with a second law analysis.

Abstract Energy poverty is broadly associated with the more general concept of income poverty. However, this phenomenon is more rarely linked to socio-economic inequalities. Recent works in the related literature are pursuing this line of research to explore if energy poverty is associated with a social vulnerability status with roots in structural inequities (Simcock et al. 2018). These factors are unevenly distributed in space and therefore, determine a geographical variability of energy poverty. Following Galvin (2019), in this paper we study if a relation between economic inequality and energy poverty exists also in the highly heterogeneous context of the Italian territory. We test this relationship on households living in Italian regions controlling for other variables influencing between-regions variation in energy poverty. Moreover, in the empirical analysis we use both consensual and expenditure-based indicators – and also a combination of them – to verify the extent to which the two methods to measure energy poverty contribute to understanding this complex phenomenon, as claimed in some of the literature. Our multivariate analyses confirm that income inequality significantly correlates with energy poverty indicators when Italian regions are the units of analysis. This suggests that strategies to address energy poverty should be comprehensive and spatially implemented.

A new modeling technique based on neural networks as a universal function approximator has been applied to study the local representation of flow boiling heat transfer at varying fluid dynamics conditions along the tube, i.e., moving through different flow pattern regions. After subdivision of the experimental data into subsets homogeneous for flow conditions, specific heat transfer equations have been heuristically got. Such specific equations have been validated and compared with the global MLFN heat transfer coefficient representation for the same target fluid as from a former work. The study has been extended to four fluids for which suitable data were available from the literature. The representation accuracies of the specialized heat transfer models are very high, even if such a method is not in general suggested due to the greater complication for both the equations development and for their practical use. It was furthermore shown that a global high accuracy flow boiling heat transfer equation can be developed also without any relation with local fluid dynamics conditions. A new modeling technique has been furthermore proposed for the fluid dynamics conditions along the tube. The linking of the picture of the actual flow condition directly with a conventional continuous real number, the so-called SF factor, allows to convert the flow condition into a numerical variable which can be turned into a continuous fluid specific function through a further MLFN technique. Limitedly to the few available literature SF data the method presents high performance and coherence for the whole SF surface. The present SF MLFN equation and the more advanced literature flow pattern model get comparable results, in spite of the limited data base. It is also shown that a flow boiling heat transfer model is not intrinsically flow pattern dependent, because a flow condition representation is never required for a global heuristic heat transfer coefficient modeling.