Dumas Relationships Applied to Two Italian Sites. A Comparison among Various Solar Energy Estimating Formulas

Abstract In this paper different methods for a predictive estimation of solar radiation are compard. The timeframe is 2007-2009. The comparison has been made on two sites, Manfredonia and Portici, both located in the south of Italy. Even if these sites are relatively near and subjected to a temperate climate, typical of Mediterranean region, they present some important differences in local micro- climate, which affects atmospheric behavior, particularly in the daily temperature variations. The method for estimating solar radiation proposed by Dumas (1984) has been tested and compared with various solar radiation empirical formulas, correlating solar radiation energy with temperature, as the well known Bristow-Campbell and Hardgreaves-Samani models. This preliminary study shows the potential of the Dumas method, even in the tested locations. It also shows that the Dumas relation actually performs better then the models mentioned above, in particular for sites with low values of daily temperature variations. In some cases it even offers a comparable accuracy with respect to the Angstrom-Prescott formula

PHOTOVOLTAIC PRODUCTION OF HYDROGEN AT STRATOSPHERIC ALTITUDES

This paper compares hydrogen production by photovoltaic powered electrolysis of water at sea level and at low stratospheric altitudes up to 21 km. All the hydrogen production process has been considered from catchable solar radiation to storage technologies. The evaluation has been performed for 1 m2 of flat horizontal plane. It has been considered the electric energy amount produced by considering the equilibrium temperature of PV modules and its evolution due to external temperature and solar radiation. Hydrogen production through electrolysis has been evaluated too. Two different methods of hydrogen storage have been evaluated: high pressure compression up to 20 MPa and liquefaction process. The energetic cost of both production processes has been evaluated. The comparison is presented in terms of effective energy deliverable to final users considered in terms of HHV. This evaluation considers also, in the case of liquefaction process the energy which can be recovered by the regasification process

Constructal Design of an Entropic Wall With Circulating Water Inside

An entropic wall with circulating water inside could be a solution for acclimatizing a new building with high-energy efficiency and high levels of internal comfort. If circulating water is thermally stabilized by exchanging in the ground such has it happens in geothermal plants, a thermal shield could be realized keeping walls in comfort conditions and minimizing energy needs for further temperature regulations. This paper presents optimization guidelines of such a wall with the objective of maximizing the performances of the wall for reaching optimal internal wellness conditions. Optimization has been realized by a constructal law based method, which has been personalized by a step-by-step process and has been named constructal design for efficiency (CDE). The optimization of the system has been produced at different levels. It starts from a preliminary analysis at system levels, which allow defining the best objectives that could be reached. After this preliminary process, the system has been divided into modules, and the critical ones which have higher influence on the performances of the system have been evaluated. This analysis has been coupled also with an industrial analysis with the goal of defining an effective layout, which could be also manufactured with acceptable costs. The result has produced a final solution with a very good compromise between energetic performances and minimization of costs at industrial level. The results open interesting perspectives for the constructal law to become the core of an effective methodology of an industrial design which can couple perfectly with the modular approach which is currently the major part of industrial companies

Ambiente e clima della Sicilia durante gli ultimi 20 mila anni

Environment and Climate in Sicily over the last 20, 000 years. (IT ISSN 0394-3356, 2010). A series of recent studies shed light on the central Mediterranean, and Sicily, climate and environment, starting from the last glacial maximum (about 20 ka cal BP). In the present paper, we examine most of these works, in order to unravel environmental changes of the past, mainly in terms of temperature, atmospheric pattern, precipitation, vegetation and faunal associations. The climate of the last glacial maximum was characterised by very low temperature and by repeated northerlies penetration, even during summer. Low precipitation values led to a steppe- or semisteppe-like vegetation pattern, dominated by herbs and shrubs. Episodes of climatic anomaly, characterised by lower temperature and strengthened wind activity, could have occurred during the Holocene, as testified by micropaleontological and geochemical investigations carried out on the southern Tyrrhenian Sea and in the northern Sicily Channel. In the terrestrial record, there is evidence of drought at 8.2 ka cal BP, from the isotopic composition of a stalagmite recovered near Palermo, and of prolonged drought intervals during the Little Ice Age in the Erice village (Trapani). The vegetation pattern shows the development of Mediterranean Maquis in coastal sites and deciduous forests in sub-montane and montane regions, approximately from the Holocene base. The human impact is the main factor that forced the present vegetation pattern, as a consequence of intensive land-use, which started about 2.7 ka cal BP, when Greek colonies were first established. Human activity is however superimposed on a natural trend towards aridity, with climatic forces still not fully understood

A new aircraft architecture based on the ACHEON Coanda effect nozzle: flight model and energy evaluation

Purpose Aeronautic transport has an effective necessity of reducing fuel consumption and emissions to deliver efficiency and competitiveness driven by today commercial and legislative requirements. Actual aircraft configurations scenario allows envisaging the signs of a diffused technological maturity and they seem very near their limits. This scenario clearly shows the necessity of radical innovations with particular reference to propulsion systems and to aircraft architecture consequently. Methods This paper presents analyses and discusses a promising propulsive architecture based on an innovative nozzle, which allows realizing the selective adhesion of two impinging streams to two facing jets to two facing Coanda surfaces. This propulsion system is known with the acronym ACHEON (Aerial Coanda High Efficiency Orienting Nozzle). This paper investigates how the application of an all-electric ACHEONs propulsion system to a very traditional commuter aircraft can improve its relevant performances. This paper considers the constraints imposed by current state-of-the-art electric motors, drives, storage and conversion systems in terms of both power/energy density and performance and considers two different aircraft configurations: one using battery only and one adopting a more sophisticated hybrid cogeneration. The necessity of producing a very solid analysis has forced to limit the deflection of the jet in a very conservative range (±15°) with respect to the horizontal. This range can be surely produced also by not optimal configurations and allow minimizing the use of DBD. From the study of general flight dynamics equations of the aircraft in two-dimensional form it has been possible to determine with a high level of accuracy the advantages that ACHEON brings in terms of reduced stall speed and of reduced take-off and landing distances. Additionally, it includes an effective energy analysis focusing on the efficiency and environmental advantages of the electric ACHEON based propulsion by assuming the today industrial grade high capacity batteries with a power density of 207 Wh/kg. Results It has been clearly demonstrated that a short flight could be possible adopting battery energy storage, and longer duration could be possible by adopting a more sophisticated cogeneration system, which is based on cogeneration from a well-known turboprop, which is mostly used in helicopter propulsion. This electric generation system can be empowered by recovering the heat and using it to increase the temperature of the jet. It is possible to transfer this considerable amount of heat to the jet by convection and direct fluid mixing. In this way, it is possible to increase the energy of the jets of an amount that allows more than recover the pressure losses in the straitening section. In this case, it is then possible to demonstrate an adequate autonomy of flight and operative range of the aircraft. The proposed architecture, which is within the limits of the most conservative results obtained, demonstrates significant additional benefits for aircraft manoeuvrability. In conclusion, this paper has presented the implantation of ACHEON on well-known traditional aircraft, verifying the suitability and effectiveness of the proposed system both in terms of endurance with a cogeneration architecture and in terms of manoeuvrability. It has demonstrated the potential of the system in terms of both takeoff and landing space requirements. Conclusions This innovation opens interesting perspectives for the future implementation of this new vector and thrust propulsion system, especially in the area of greening the aeronautic sector. It has also demonstrated that ACHEON has the potential of renovating completely a classic old aircraft configuration such as the one of Cessna 402

The Efficiency of an Electric Turbofan vs. Inlet Area: A Simple Mathematical Model and CFD Simulations

It is well known that electric engines with a large external helice presents an higher propulsive efficiency if compared to electric turbofans. This paper defines the general guidelines for enhancing the efficiency of an electric turbofan by CFD symulations. A mathematical model to design the intake nozzle has been presented in order to allign the performance of the two systems. The analysis has been realized by basic fluid dynamic principles only, using traditional actuator disk propeller model for the verification of the results

A Predictive Climatic Model for Ballast in a Fixed Volume Blimp

This paper presents a mathematical model of the vertical forces acting on an airship during vertical motion. The main effort is the definition of an airship model, which move only vertically by ballast, and buoyancy effects, with a much reduced energy consumption for take-off and landing operations. It has been considered a disc-shaped airship, which can operate using the open balloon airship architecture defined to operate safely with hydrogen. This architecture does not require internal ballonets, because of the connected increased fire dangers that they create even if vented. Several models of airship based on vertical forces have been presented in literature. They often consider only the US or International Standard Atmosphere models and they neglect effects of weather conditions. The latter are connected with the location and with the season. These environmental and climatic factors have a large influence on behaviors of the airship system, because it is well known that the internal buoyant gas changes pressure and density condition because of external temperature. This paper defines the lifting behavior in terms of speed and acceleration. It evaluates the load factor as a function of the buoyancy and the ballast on board as a function of climatic conditions. A very simple methodology has been also presented on daily basis, authors neglect the effect of overheating of the gas due to solar radiation on the surface of the balloon, which can support the predefinition of climatic effects. The proposed methodology corrects the International Standard Atmosphere model by considering climatic data such as temperature, density and pressure of the air dependent on seasonal factors and location on annual basis

Optimization of Airships with Constructal Design for Efficiency Method

It is possible to define a novel optimization method, which aims to overcome the traditional Multidisciplinary Design Optimization. It aims to improve Constructal design method to optimize complex systems such as vehicles. The proposed method is based on the constructal principle and it is articulated in different stages: 1. preliminary top-down design process to ensure that the full system has one of the best configurations for the specified goals (contour conditions for constructal optimization could be stated ensuring an effective optimization at full-system level). 2. constructal optimization of the elemental components of the system to maximize the system performances; 3. eventually a competitive comparison between different configurations choosing the better one. The definition of an optimized flying vehicle (an airship) has been produced an example of this improved design method with the objective of minimizing the energy consumption during flight. Following this method, this paper aims defining the guidelines for an effective energetic optimization of an airship. The produced results allow defining a novel airship concept, which optimizes the airship shape to reach three fundamental energetic goals: energy consumption minimization, photovoltaic energy production maximization, definition of the conditions for energetically self-sufficient flight. This paper also demonstrates that the resulting architecture can fit perfectly novel operating conditions such as effective point to point logistic without any airport infrastructure having a potential breakthrough impact on the aerial logistic models and allowing an effective and better integration with any other terrestrial, maritime and aerial transport mode