1,721,202 research outputs found
Emergy, Empower and the Eco-Exergy to Empower Ratio: a Reconciliation of H.T. Odum with Prigogine?
No full textThis paper presents the theory behind and the possible uses of the ratio of eco-exergy to empower. This orientor originates from the comparison of S.E. Jrgensens and H.T. Odums approaches to ecosystems theory. The former proposed as orientor the maximization of stored eco-exergy, that is the extension of the thermodynamic function exergy of ecosystems. The latter, the maximization of empower, is the flow of emergy (solar energy directly and indirectly required to obtain a certain item). The use of the ratio of eco-exergy to empower enables one to understand what is the order that the two maximization criteria follow during the evolution of an ecosystem. A possible analogy between the maximization of eco-exergy to empower ratio and the minimization of specific dissipation is discussed. The use of this orientor for the comparison of the same system at different times or of different systems provides a possible holistic measure of the effects of the use of a certain pattern of inputs in a system. This can help comparisons within the framework of life cycle assessment
A definition of pollution based on thermodynamic goal functions
No full textSeveral functions, called 'goal functions', have been introduced at the interface between ecology and thermodynamics. Two have been chosen to study the effect of pollution on ecological systems: Exergy is related to the degree of organization of a system and represents the biogeochemical energy of a system; Emergy is defined as the total amount of solar energy directly or indirectly required to generate a product or a service. They represent two complementary aspects of a system. We previously introduced the ratio of exergy to the emergy flow to indicate the efficiency of an ecosystem in producing or maintaining its organization. If we consider the variation in time of exergy and emergy, their ratio indicates the effect of the change of available inputs in the level of organization of the system under study. This can lead to a definition of 'pollution' based on thermodynamics: we can define pollutant for a system as an input for which to an increase (decrease) in the emergy flow corresponds a loss (rise) in the exergy content of the system. A two dimensional diagram is shown in which all the possible situations are represented and discussed. (C) 1998 Elsevier Science B.V. All rights reserved
Use of Thermodynamic Orientors to Assess the Efficiency of Ecosystems: A Case Study in the Lagoon of Venice
Full text linkSo-called orientors have been introduced at the interface between ecology and thermodynamics. Two have been chosen here to compare the characteristics of five ecological systems: exergy, which is related to the degree of organization of a system and represents the biogeochemical energy of a system, and emergy, which is defined as the total amount of solar energy directly or indirectly required to generate a product or a service. They represent two complementary aspects of a system: the actual state and the past work needed to reach that state. The ratio of exergy to the emergy flow indicates the efficiency of an ecosystem in producing or maintaining its organization
Analisi termodinamica e valutazione della sostenibilità ambientale di un sistema territoriale: lo studio della Provincia di Modena
No full textEco-exergy to Emergy flow ratio
No full textThe ratio of eco-exergy to emergy flow is a conceptual tool derived from two orientors, emergy and eco-exergy. Orientors have been developed in the last years to give an holistic framework to ecological studies. The study of thermodynamics produced a number of functions that measure the distance from thermodynamic equilibrium of a system under study with respect to the outside environment. This index has been used in the field of ecology to indicate the solar (direct and indirect) flow required by the ecosystems to produce or maintain a unit of their organization or structure. On the other hand, the ratio of the variation of eco-exergy and emergy flow can be used to express, from an holistic point of view, the concept of pollution in an ecosystem. © 2008 Elsevier B.V. All rights reserved
Exergy and extended exergy accounting of very large complex systems with an application to the province of Siena, Italy
No full textThis paper describes the application of exergy and extended exergy analyses to large complex systems. The system to be analysed is assumed to be at steady state, and the input and output fluxes of matter and energy are expressed in units of exergy. Human societies of any reasonable extent are indeed Very Large Complex Systems and can be represented as interconnected networks of N elementary “components”, their Subsystems; the detail of the disaggregation depends on the type and quality of the available data. The structural connectivity of the “model” of the System must correctly describe the interactions of each mass or energy flow with each sector of the society: since it is seldom the case that all of these fluxes are available in detail, some preliminary mass- and energy balances must be completed and constitute in fact a part of the initial assumptions. Exergy accounting converts the total amount of resources inflow into their equivalent exergetic form with the help of a table of “raw exergy data” available in the literature. The quantification of each flow on a homogeneous exergetic basis paves the way to the evaluation of the efficiency of each energy and mass transfer between the N sectors and makes it possible to quantify the irreversible losses and identify their sources. The advantage of the EEA, compared to a classical exergy accounting, is the inclusion in the system balance of the exergetic equivalents of three additional “Production Factors”: human Labour, Capital and Environmental Remediation costs. EEA has an additional advantage: it allows for the calculation of the efficiency of the domestic sector (impossible to evaluate with any other energy- or exergy-based method) by considering the working hours as its product. As implied in the title, an application of the method was made to a model of the province of Siena (on a year 2000 database): the results show that the sectors of this Province have values of efficiency close to the Italian average, with the exception of the commercial and energy conversion sectors that are more efficient, in agreement with the rather peculiar socio-economic situation of the Province. The largest inefficiency is found to be in the transportation sector, which has an efficiency lower then 30% in EEA and lower than 10% in classical exergy accounting
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