1,720,974 research outputs found
The future of Thermoeconomics: from industrial cost minimization toward cumulative resources accounting and sustainability assessment
No full textThermoeconomics has been developed with the main object of first identifying, and then reducing the costs of the energy produced by industrial power plants. More recently, the same approach formalized in the Exergy Cost Theory has been recognized as a useful tool also in a wider field, like industrial symbiosis and sustainability assesment. To do this, exergy supply chains have been tracked backward and backward, to include in the primary resource consumption a more and more complete inventory of the indirect consumption. In Authors' opinion, the future of Thermoeconomics is to go on in this directions. If a very complete inventory of all indirect consumption were obtained, the sustainability assessment of a production process could be performed (at least in principle) by applying the idea that the lower its consumption (direct and indirect) of scarce primary resources, the more sustainable a production process is. In this paper, the idea of the Thermoeconomic Environment (TEE) is summarized, to highlight as it is a consistent ultimate boundary of the exergy cost accounting, where the origin of the exergy supply chains can be properly placed. Then, the frame of the TEE is used to discuss some possible options for obtaining a more complete inventory of all indirect consumption, and to outline possible perspective connections with some relevant environmental models, coming from Biology, Dynamic of Populations, or Climatology
The Gouy-Stodola Theorem and the derivation of exergy revised
Full text linkThe Gouy-Stodola Theorem is the theoretical basis for allocating irreversibility and for identifying the maximum possible efficiency for any kind of energy conversion system. The well-known theorem is re-obtained in this paper, relaxing the hypothesis about a constant value for temperature and pressure of the reference environment. The equations that have been derived taking into account the variation of reference temperature and pressure show that two additional terms appear in both reversible and irreversible maximum useful work output, besides the well-known terms. These additional terms take into account the potential useful work (exergy) destruction related to the variation of the ambient condition during the considered time interval. In this way the Gouy-Stodola Theorem still holds, but the allocation of exergy destruction is generally different from that calculated in the usual hypothesis of constant temperature and pressure of the reference environment. The Gouy-Stodola Theorem is also used in various textbooks for defining the flow and the non-exergy of a control volume. The same approach is applied in this paper, highlighting the differences and the difficulties related to the variation of the reference pressure and temperature in the reference environment
Energy production through distributed urban cogeneration systems: preliminary definition of lay-out, units size and operation
No full textOptimal synthesis and operation of advanced energy supply systems for standard and domotic home
No full texthe paper deals with the optimization of an advanced energy supply systems for two dwellings: a standard home and an advanced domotic home, where some demand side energy saving strategies have been implemented. In both cases the optimal synthesis, design and operation of the whole energy supply system have been obtained and a sensitivity analysis has been performed, by introducing different economic constraints. The optimization model is based on a Mixed Integer Linear Program (MILP) and includes different kinds of small-scale cogenerators, geothermal heat pumps, boilers, heat storages, solar thermal and photovoltaic panels. In addition, absorption machines, supplied with cogenerated heat, can be used instead of conventional electrical chiller to face the cooling demand. The aim of the analysis is to address the question if advanced demand strategies and supply strategies have to be regarded as alternatives, or if they have to be simultaneously applied, in order to obtain the maximum energy and economic benefit
Exergy analysis with variable ambient conditions
No full textFor high temperature industrial processes, or usual thermo-mechanical energy conversion plants, the results of the
exergy analysis show very low differences if the higher or the lower, possible value for the ambient temperature T ° is
chosen. This is not true if energy processes at a temperature close to ambient temperature are considered, for instance
thermal solar systems, or low temperature district heating systems.
The paper revises the derivation of flow and nonflow exergy if T° and P° vary in time, highlighting the case of periodic
variations. As a result, besides the terms analogous to the well known ones, in the expression of the exergy balance of a
generic control volume, two additional terms appear, that take into account exactly the available work (exergy)
destruction related to the variation of ambient condition during the considered time interval. Then, the theoretical
opportunity of taking advantage of the effects of variable T° (like exergy increment of thermal storag es, or creation of
“hot” and “cold” reservoirs without work expense) are discussed and their physical limitations are outlined
Constructal Law and Thermoeconomic Optimization
No full textThe paper introduces the concept of Thermoeconomic Environment and discusses how the
Constructal Theory can be applied to the productive structure of an energy system. In this way, the
optimal criterion of minimum energy cost of the product, generally assumed by the Thermoeconomic
Optimization, can be regarded as derived from the Constructal Law, when the flow of useful product
through the productive structure is considered as the characteristic flow of the system. In consequence
of the evolution prescribed by the Constructal Law, it can be highlighted that recycling flows may arise
in the productive structure and that residues and sub-products cannot be indefinitely accumulated. In
this process, a crucial role is played by the framework of the Thermoeconomic Environment. In the
outlined context, the evolution of energy systems toward highly interrelated productive structures can
be regarded as a consequence of the Constructal Law
The Gouy-Stodola Theorem revised
No full textThe Gouy-Stodola Theorem is the theoretical basis for allocating irreversibility and for identifying the maximum possible efficiency for any kind of energy conversion system. The well-known theorem is re-obtained in this paper, relaxing the hypothesis about a constant value for temperature and pressure of the reference environment. The equations that have been driven taking into account the variation of reference temperature and pressure show that two additional terms appear in both reversible and irreversible maximum output work, besides the well-known terms. These additional terms take into account the available work (exergy) destruction related to the variation of the ambient condition during the considered time interval. In this way the Gouy-Stodola Theorem still holds, but the allocation of exergy destruction is generally different from that calculated in the usual hypothesis of constant temperature and pressure of the reference environment. The Gouy-Stodola Theorem is also used in various textbooks for defining the flow-exergy of a material stream crossing the boundaries of the control volume. The same approach is applied in this paper, highlighting the differences and the difficulties related to the variation of the reference pressure and temperature in the reference environment
The Thermoeconomic Environment Cost Indicator (iex-TEE) as a One-Dimensional Measure of Resource Sustainability
Full text linkThis paper presents a conceptual development of sustainability evaluation, through an exergy-based indicator, by using the new concept of the Thermoeconomic Environment (TEE). The exergy-based accounting methods here considered as a background are Extended Exergy Accounting (EEA), which can be used to quantify the exergy cost of externalities like labor, monetary inputs, and pollutants, and Cumulative Exergy Consumption (CExC), which can be used to quantify the consumption of primary resources embodied in a final product or service. The new concept of bioresource stock replacement cost is presented, highlighting how the framework of the TEE offers an option for evaluating the exergy cost of products of biological systems. This sustainability indicator is defined based on the exergy cost of all resources directly and indirectly consumed by the system, the equivalent exergy cost of all externalities implied in the production process and the exergy cost of the final product
Increasing the energy efficiency of an internal combustion engine for ship propulsion with bottom ORCS
Full text linkThe study examines the option of adding a bottom Organic Rankine Cycle (ORC) for energy recovery from an internal combustion engine (ICE) for ship propulsion. In fact, energy recovery from the exhaust gas normally rejected to the atmosphere and eventually from the cooling water circuit (usually rejected to the sea) can significantly reduce the fuel consumption of a naval ICE during its operation. In the paper, different possible bottom ORC configurations are considered and simulated using the Aspen® code. Different working fluids are taken into account, jointly with regenerative and two-temperature levels designs. The energy recovery allowed by each solution is evaluated for different engine load, allowing the identification of the most suitable ORC configuration. For the selected case, the preliminary design of the main heat exchangers is carried out and the off-design performance of the whole combined propulsion plant (ICE + ORC) is evaluated, leading to a preliminary analysis of cost saving during normal ship operation. The results of this analysis show an increase in power output of about 10% and an expected Payback Time of less than 6 years
The role of the Thermoeconomic Environment in the exergy based cost accounting of technological and biological systems
No full textThe paper introduces the Thermoeconomic Environment as a consistent ultimate boundary of the exergy
cost accounting, where various exergy reservoir, of limited content, are immersed in the zero-exergy matrix,
but they keep separated from it because of some confinement constraint. Starting from this very simple,
but meaningful frame, the following issues are reviewed and commented, highlighting limitations and some
possible new perspective: the exergy cost of mineral resources, the exergy cost of the products of biological
systems, the exergy evaluation of capital and human work, the exergy evaluation of polluting emissions
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