http://www.mdpi.com/journal/entropy/special_issues/exergy/ Dear Colleagues, Exergy analysis is a powerful thermodynamic technique for assessing and improving the efficiency of processes, devices and systems, as well as for enhancing environmental and economic performance. As a multidisciplinary concept, exergy applications are observed in various fields, including mechanical and chemical engineering as well as economics, management, physics and biology. Consequently, exergy analysis is used increasingly by industries and governments throughout the world, particularly with the aim of improving energy sustainability. Research and review articles on all facets of exergy and its applications, and on exergy-related topics, are sought for this special issue. Marc A. RosenGuest Editor http://www.mdpi.com/1099-4300/12/7/1696/ For ecological economic evaluation based on the unified biophysical matrix this research illustrates an updated emergy synthesis in terms of embodied cosmic exergy instead of embodied solar energy, which successes the foundation of systems ecological theory but changes the starting point for the estimation from simply the sun to the cosmos. According to the modified definition implicating explicit scarcity and strict additivity based on the fundamental thermodynamics laws, the updated emergy approach overcomes the confusable and intractable deficiencies of traditional one and shows firmer theoretical basis as well as better applicability. As a case study for the regional socio-economic ecosystem, a cosmic emergy based ecological economic evaluation of the Beijing urban ecosystem during the period 1978-2004 is presented. The local and external resources supporting the concerned ecosystem are accounted and analyzed in a common unit, i.e., cosmic Joule, according to which a series of indicators are applied to reveal its evolutional characteristics through five aspects as emergy structure, emergy intensity, emergy welfare, environmental impacts, and degree of exploitation and economic efficiency. During the analyzed period, the major emergy source sustaining the operation of the ecosystem had changed from the renewable resources exploited locally to the nonrenewable resources purchased from outside. Emergy intensity for the Beijing urban ecosystem kept rising owing to the continuous investment of resources, which not only improved the living standard but also intensified the environmental pressure. Moreover, the increase of exploitation degree was accompanied with the decline of economic efficiency, while the rising emergy investment ratio implicates that Beijing was at the risks of resources shortage and high dependence on external resources http://www.mdpi.com/1099-4300/12/7/1696/ Tue, 29 Jun 2010 00:00:00 CEST Entropy 2010-06-29 12 7 Article 1696 1720 1099-4300 Ecological Economic Evaluation Based on Emergy as Embodied Cosmic Exergy: A Historical Study for the Beijing Urban Ecosystem 1978–2004 2010-06-29 doi: 10.3390/e12071696 Ming Zhan-Ming Bo Cheng Hua Yi Bo http://www.mdpi.com/1099-4300/12/5/1006/ A multi-criteria approach is presented for the assessment of alternative means for covering the energy needs (electricity and heat) of an industrial unit, taking into consideration sustainability aspects. The procedure is first described in general terms: proper indicators are defined; next they are grouped in order to form sub-indices, which are then used to determine the composite sustainability index. The procedure is applied for the evaluation of three alternative systems. The three systems are placed in order of preference, which depends on the criteria used. In addition to conclusions reached as a result of the particular case study, recommendations for future work are given. http://www.mdpi.com/1099-4300/12/5/1006/ Tue, 27 Apr 2010 00:00:00 CEST Entropy 2010-04-27 12 5 Article 1006 1020 1099-4300 Multi-Criteria Evaluation of Energy Systems with Sustainability Considerations 2010-04-27 doi: 10.3390/e12051006 Frangopoulos Keramioti http://www.mdpi.com/1099-4300/12/4/902/ Exergy is demonstrated to be a useful measurable parameter reflecting the state of the ecosystem, and allowing estimation of the severity of its anthropogenous damage. Exergy is shown to have advantages such as good theoretical basis in thermodynamics, close relation to information theory, rather high correlation with others ecosystem goal functions and relative ease of computation. Nowadays exergy is often used in ecological assessment. This paper reviews the application of exergy in ecology in the fields of ecological modeling and natural ecosystem monitoring. Special attention is paid to the use of exergy for aquatic ecosystem studies, particularly, assessment of the lake Baikal ecosystem state. http://www.mdpi.com/1099-4300/12/4/902/ Tue, 13 Apr 2010 00:00:00 CEST Entropy 2010-04-13 12 4 Review 902 925 1099-4300 Exergy as a Tool for Ecosystem Health Assessment 2010-04-13 doi: 10.3390/e12040902 Silow Mokry http://www.mdpi.com/1099-4300/12/4/859/ In this paper exergy analysis is used to assess the performance of the three most common air conditioning plant schemes: all-air, dual-duct and fan-coil systems. The results are presented in terms of flow diagrams to provide a clear picture of the exergy flow across the systems. The most relevant outcomes are that the air cooling and dehumidification is the process most responsible for the exergy loss and that the exergy efficiency of the overall systems is rather low; thus the quest for more appropriate technologies. Solar-assisted air-conditioning is also discussed, outlining the possibilities and the constraints. http://www.mdpi.com/1099-4300/12/4/859/ Tue, 13 Apr 2010 00:00:00 CEST Entropy 2010-04-13 12 4 Article 859 877 1099-4300 Air Conditioning Systems from a 2nd Law Perspective 2010-04-13 doi: 10.3390/e12040859 Marletta http://www.mdpi.com/1099-4300/12/3/591/ Industrial Ecology involves the transformation of industrial processes from linear to closed loop systems: matter and energy flows which were initially considered as wastes become now resources for existing or new processes. In this paper, Thermoeconomics, commonly used for the optimization and diagnosis of energy systems, is proposed as a tool for the characterization of Industrial Ecology. Thermoeconomics is based on the exergy analysis (Thermodynamics) but goes further by introducing the concepts of purpose and cost (Economics). It is presented in this study as a systematic and general approach for the analysis of waste flow integration. The formulation is based on extending the thermoeconomic process of the cost formation of wastes in order to consider their use as input for other processes. Consequently, it can be applied to important Industrial Ecology issues such as identification of integration possibilities and efficiency improvement, quantification of benefits obtained by integration, or determination of fair prices based on physical roots. The capability of the methodology is demonstrated by means of a case study based on the integration of a power plant, a cement kiln and a gas-fired boiler. http://www.mdpi.com/1099-4300/12/3/591/ Mon, 22 Mar 2010 00:00:00 CET Entropy 2010-03-22 12 3 Article 591 612 1099-4300 Application of Thermoeconomics to Industrial Ecology 2010-03-22 doi: 10.3390/e12030591 Valero Usón Torres Valero http://www.mdpi.com/1099-4300/12/3/445/ Fluid flow, heat transfer and entropy generation characteristics of micro-pipes are investigated computationally by considering the simultaneous effects of pipe diameter, wall heat flux and Reynolds number in detail. Variable fluid property continuity, Navier-Stokes and energy equations are numerically handled for wide ranges of pipe diameter (d = 0.50–1.00 mm), wall heat flux (q''= 1000–2000 W/m2) and Reynolds number (Re = 1 – 2000), where the relative roughness is kept constant at e/d = 0.001 in the complete set of the scenarios considered. Computations indicated slight shifts in velocity profiles from the laminar character at Re = 500 with the corresponding shape factor (H) and intermittency values (γ) of H = 3.293→3.275 and γ = 0.041→0.051 (d = 1.00→0.50 mm). Moreover, the onset of transition was determined to move down to Retra = 1,656, 1,607, 1,491, 1,341 and 1,272 at d = 1.00, 0.90, 0.75, 0.60 and 0.50 mm, respectively. The impacts of pipe diameter on friction mechanism and heat transfer rates are evaluated to become more significant at high Reynolds numbers, resulting in the rise of energy loss data at the identical conditions as well. In cases with low pipe diameter and high Reynolds number, wall heat flux is determined to promote the magnitude of local thermal entropy generation rates. Local Bejan numbers are inspected to rise with wall heat flux at high Reynolds numbers, indicating that the elevating role of wall heat flux on local thermal entropy generation is dominant to the suppressing function of Reynolds number on local thermal entropy generation. Cross-sectional total entropy generation is computed to be most influenced by pipe diameter at high wall heat flux and low Reynolds numbers. http://www.mdpi.com/1099-4300/12/3/445/ Tue, 09 Mar 2010 00:00:00 CET Entropy 2010-03-09 12 3 Article 445 472 1099-4300 Combined Effects of Pipe Diameter, Reynolds Number and Wall Heat Flux and on Flow, Heat Transfer and Second-Law Characteristics of Laminar-Transitional Micro-Pipe Flows 2010-03-09 doi: 10.3390/e12030445 A. Alper Ozalp http://www.mdpi.com/1099-4300/12/3/434/ The transport equation of entropy is introduced in large eddy simulation to perform exergy analysis of turbulent combustion systems. The sources of exergy destruction can be evaluated by analyzing entropy generation terms, which appear in unclosed forms in this equation. The closure is based on the filtered density function (FDF) methodology. The primary advantage of FDF is that chemical reaction and its entropy generation effects appear in closed forms. This methodology involves a stochastic model, which is being developed to account for the subgrid scale transport of entropy. http://www.mdpi.com/1099-4300/12/3/434/ Mon, 08 Mar 2010 00:00:00 CET Entropy 2010-03-08 12 3 Article 434 444 1099-4300 Entropy Transport Equation in Large Eddy Simulation for Exergy Analysis of Turbulent Combustion Systems 2010-03-08 doi: 10.3390/e12030434 Mehdi Safari M. Reza H. Sheikhi Mohammad Janbozorgi Hameed Metghalchi http://www.mdpi.com/1099-4300/12/3/375/ This work applies the second-law analysis of thermodynamics to quantify the exergy destruction of the components of screw liquid chiller, and to identify the potential for each component to contribute to improve the overall energy efficiency of the system. Three screw liquid chiller units were built to demonstrate the feasibility of the model presented herein. Unit A was a 100 RT water-cooled screw liquid chiller. Unit B was modified from Unit A by switching the old condenser for a new one with a greater heat transfer, and Unit C was modified from Unit B by exchanging the compressor for a more efficient one. The results indicate that the compressor has the largest potential to improve energy efficiency, followed in order by the condenser, and then the evaporator. The second law analysis may help engineers to focus on the components with higher exergy destruction and quantify the extent to which modifying such components can influence, favorably or unfavorably, the performance of other components of the screw liquid chiller. http://www.mdpi.com/1099-4300/12/3/375/ Thu, 04 Mar 2010 00:00:00 CET Entropy 2010-03-04 12 3 Article 375 389 1099-4300 Second-Law Analysis to Improve the Energy Efficiency of Screw Liquid Chillers 2010-03-04 doi: 10.3390/e12030375 Tzong-Shing Lee http://www.mdpi.com/1099-4300/12/2/243/ Exergy analysis is a powerful and systematic tool for the improvement of energy systems, with many possible applications in both conversion and utilization of energy. Here we present selected applications, with a special attention to renewable energy systems (solar), covering both design and operation/control. After these applications to non-reactive systems, potential ways of reducing the large irreversibilities connected to reactive systems (combustion) are considered, with special reference to chemically-recuperated gas turbine cycles and topping high-temperature fuel cells. http://www.mdpi.com/1099-4300/12/2/243/ Fri, 05 Feb 2010 00:00:00 CET Entropy 2010-02-05 12 2 Article 243 261 1099-4300 Improvement of Energy Conversion/Utilization by Exergy Analysis: Selected Cases for Non-Reactive and Reactive Systems 2010-02-05 doi: 10.3390/e12020243 Daniele Fiaschi Giampaolo Manfrida http://www.mdpi.com/1099-4300/11/4/820/ The benefits are demonstrated of using exergy to understand the efficiencies of electrical power technologies and to assist improvements. Although exergy applications in power systems and electrical technology are uncommon, exergy nevertheless identifies clearly potential reductions in thermodynamic losses and efficiency improvements. Various devices are considered, ranging from simple electrical devices to generation systems for electrical power and for multiple products including electricity, and on to electrically driven. The insights provided by exergy are shown to be more useful than those provided by energy, which are sometimes misleading. Exergy is concluded to have a significant role in assessing and improving the efficiencies of electrical power technologies and systems, and provides a useful tool for engineers and scientists as well as decision and policy makers. http://www.mdpi.com/1099-4300/11/4/820/ Fri, 06 Nov 2009 00:00:00 CET Entropy 2009-11-06 11 4 Article 820 835 1099-4300 Using Exergy to Understand and Improve the Efficiency of Electrical Power Technologies 2009-11-06 doi: 10.3390/e11040820 Marc A. Rosen Cornelia Aida Bulucea http://www.mdpi.com/1099-4300/11/4/798/ It is known that mechanical work, and in turn electricity, can be produced from a difference in the chemical potential that may result from a salinity gradient. Such a gradient may be found, for instance, in an estuary where a stream of soft water is flooding into a sink of salty water which we may find in an ocean, gulf or salt lake. Various technological approaches are proposed for the production of energy from a salinity gradient between a stream of soft water and a source of salty water. Before considering the implementation of a typical technology, it is of utmost importance to be able to compare various technological approaches, on the same basis, using the appropriate variables and mathematical formulations. In this context, exergy balance can become a very useful tool for an easy and quick evaluation of the maximum thermodynamic work that can be produced from energy systems. In this short paper, we briefly introduce the use of exergy for enabling us to easily and quickly assess the theoretical maximum power or ideal reversible work we may expect from typical salinity gradient energy systems. http://www.mdpi.com/1099-4300/11/4/798/ Thu, 05 Nov 2009 00:00:00 CET Entropy 2009-11-05 11 4 Article 798 806 1099-4300 Exergy as a Useful Variable for Quickly Assessing the Theoretical Maximum Power of Salinity Gradient Energy Systems 2009-11-05 doi: 10.3390/e11040798 Raynald Labrecque http://www.mdpi.com/1099-4300/11/4/702/ All real processes generate entropy and the power/exergy loss is usually determined by means of the Gouy-Stodola law. If the system only exchanges heat at the environmental temperature, the Gouy-Stodola law gives the correct loss of power. However, most industrial processes exchange heat at higher or lower temperatures than the actual environmental temperature. When calculating the real loss of power in these cases, the Gouy-Stodola law does not give the correct loss if the actual environmental temperature is used. The first aim of this paper is to show through simple steam turbine examples that the previous statement is true. The second aim of the paper is to define the effective temperature to calculate the real power loss of the system with the Gouy-Stodola law, and to apply it to turbine examples. Example calculations also show that the correct power loss can be defined if the effective temperature is used instead of the real environmental temperature. http://www.mdpi.com/1099-4300/11/4/702/ Fri, 30 Oct 2009 00:00:00 CET Entropy 2009-10-30 11 4 Article 702 712 1099-4300 Determination of the Real Loss of Power for a Condensing and a Backpressure Turbine by Means of Second Law Analysis 2009-10-30 doi: 10.3390/e11040702 Henrik Holmberg Pekka Ruohonen Pekka Ahtila http://www.mdpi.com/1099-4300/11/4/529/ This paper reviews how ideas have evolved in this field from the pioneering work of CARNOT right up to the present. The coupling of thermostatics with thermokinetics (heat and mass transfers) and entropy or exergy analysis is illustrated through study of thermomechanical engines such as the Carnot heat engine, and internal combustion engines. The benefits and importance of stagnation temperature and irreversibility parameters are underlined. The main situations of constrained (or unconstrained) optimization are defined, discussed and illustrated. The result of this study is a new branch of thermodynamics: Finite Dimensions Optimal Thermodynamics (FDOT). http://www.mdpi.com/1099-4300/11/4/529/ Mon, 28 Sep 2009 00:00:00 CEST Entropy 2009-09-28 11 4 Review 529 547 1099-4300 Optimal Thermodynamics—New Upperbounds 2009-09-28 doi: 10.3390/e11040529 Michel Feidt http://www.mdpi.com/1099-4300/11/3/443/ In the present paper, the thermoeconomic optimization of an endoreversible solardriven heat engine has been carried out by using finite-time/finite-size thermodynamic theory. In the considered heat engine model, the heat transfer from the hot reservoir to the working fluid is assumed to be the radiation type and the heat transfer to the cold reservoir is assumed the conduction type. In this work, the optimum performance and two design parameters have been investigated under three objective functions: the power output per unit total cost, the efficient power per unit total cost and the ecological function per unit total cost. The effects of the technical and economical parameters on the thermoeconomic performance have been also discussed under the aforementioned three criteria of performance. http://www.mdpi.com/1099-4300/11/3/443/ Tue, 25 Aug 2009 00:00:00 CEST Entropy 2009-08-25 11 3 Article 443 453 1099-4300 Thermoeconomic Optimum Operation Conditions of a Solar-driven Heat Engine Model 2009-08-25 doi: 10.3390/e11030443 Marco A. Barranco-Jiménez Norma Sánchez-Salas Marco A. Rosales http://www.mdpi.com/1099-4300/11/3/334/ An experimental design is presented for an optical method of measuring spatial variations of flow irreversibilities in laminar viscous fluid motion. Pulsed laser measurements of fluid velocity with PIV (Particle Image Velocimetry) are post-processed to determine the local flow irreversibilities. The experimental technique yields whole-field measurements of instantaneous entropy production with a non-intrusive, optical method. Unlike point-wise methods that give measured velocities at single points in space, the PIV method is used to measure spatial velocity gradients over the entire problem domain. When combined with local temperatures and thermal irreversibilities, these velocity gradients can be used to find local losses of energy availability and exergy destruction. This article focuses on the frictional portion of entropy production, which leads to irreversible dissipation of mechanical energy to internal energy through friction. Such effects are significant in various technological applications, ranging from power turbines to internal duct flows and turbomachinery. Specific problems of a rotational stirring tank and channel flow are examined in this paper. By tracking the local flow irreversibilities, designers can focus on problem areas of highest entropy production to make local component modifications, thereby improving the overall energy efficiency of the system. http://www.mdpi.com/1099-4300/11/3/334/ Thu, 23 Jul 2009 00:00:00 CEST Entropy 2009-07-23 11 3 Article 334 350 1099-4300 Imaging Velocimetry Measurements for Entropy Production in a Rotational Magnetic Stirring Tank and Parallel Channel Flow 2009-07-23 doi: 10.3390/e11030334 Greg F. Naterer Olusola B. Adeyinka