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[en] In the design and operation of energy intensive systems, the possibility of improving the system's efficiency is very important to explore. The main way of improving efficiency is through thermodynamic analysis and optimization. Methods are universal and make it possible to estimate the fluxes and balances of all energy flows for every element of the system using a common criterion of efficiency. The thermoeconomical approach allows to retain all advantages of exergy method and simultaneously estimate the investment and other monetary costs of a system. In this paper is developed the method of thermoeconomical optimization of a heating system for cottage complex. Example of real optimization is given. (author)
[en] A first model for a hydrogen liquefaction prototype laboratory unit has been developed. The process is based on using a mixed component refrigerant (MCR) process for pre-cooling. The process also includes an implementation of ortho para conversion. By simulations it has been shown that this process have potential to improve the exergy efficiency for the liquefaction process and thereby also the energy requirements for hydrogen liquefaction. One of the key points in the design work has been to find a refrigerant that is sufficiently wide-boiling and at the same time not freezing at the low temperature end. The goal has been to reach sub-cooling to below 75 K without freezing out any component of the MCR. (authors)
[en] Exergy analysis has been increasingly applied over the last several decades to systems of various sizes, ranging from nano-sized to planetary. Depending on the size of the application to which exergy analysis is directed, several considerations can be accounted for to ensure the analysis is applied in a manner that provides the information desired with appropriate levels of accuracy and effort. Six size categories are considered in this paper, in the form of a hierarchy. The examination has led to several conclusions: The various systems investigated with exergy analysis exhibit size-related trends regarding the manner in which exergy analysis is performed; The most appropriate way of applying exergy analysis appears to be dependent on the size of the application, whether nano-sized or large; A size categorization system can be formulated which helps identify the manner in which exergy analysis can most appropriately be applied for a given system; An understanding of these size considerations can help guide users of exergy analysis to the most suitable manner of application for a given system, avoiding confusion and wasted effort. It is anticipated that the results of this investigation of size considerations that affect applications of exergy analysis will improve the usability of exergy analysis and enhance its application in the assessment and improvement of energy systems. (author)
[en] Prediction models, based on ultimate analysis of biomass on dry basis (db) which is leveraged to predict chemical exergy, were proposed in this study. A new concept — chemical exergy per equivalent of available electrons transferred to oxygen (reductance degree) of model 1 was established. The result shows that chemical exergy per reductance degree of model 1 is relatively constant for the values of most biomass (db) beyond the±1% relative error range. A modified reductance degree of biomass was presented, whereas oxygen (O) content was neglected due to its inaccurate value and the high p-value for the coefficient of O variable. Chemical exergy per modified reductance degree of models 2 and 3 was approximated to be nearly a constant. Thus, two theoretical prediction models (model 2 and model 3) for the biomass (db) with and without sulfate (920.08(C/3 + H + S/8), 920.72(C/3 + H)) were established, respectively. The coefficients of the two models are of almost the same value, which indicates that the S content has also a negligible effect on chemical exergy. Model 3 (920.72(C/3 + H)) is also herein proposed for prediction of exergy of biomass. The average relative errors of model 1, model 2 and model 3 are 2.882%, 0.643% and 0.634%, respectively. - Highlights: • A new concept — chemical exergy per (modified) reductance degree is established. • Chemical exergy per modified reductance degree is approximately constant. • Estimation model of chemical exergy based on new concept provides higher accuracy. • Chemical exergy of biomass (db) can be easily estimated by simply using C and H.
[en] An ecosystem is a complex system in which biotic and abiotic factors interact and influence each other both directly and indirectly. Each of these factors has to comply with a specific function in the different processes that occur inside the ecosystem, whether transporting or transforming energy or both. When anthropogenic emissions are produced, part of the useful energy of the ecosystem is used to assimilate or absorb those emissions, and the energy spent, loses its function and becomes lost work in accordance with the Gouy-Stodola theorem. Thus, the work that an ecosystem can carry out varies as a function of the lost work produced by anthropogenic sources. The permanency or loss of the ecosystem depends on how many irreversibilities it can support. The second law of thermodynamics through a systematic use of the exergy and lost work is the basis of this paper where a general environmental impact index, based on exergy, is proposed. For the purpose of this work, the ecosystem is divided in subsystems--water, soil, atmosphere, organisms and society- -all of them inter-related. The ideal work variation can be obtained from each subsystem within the selected ecosystem, and a global index can be determined by adding the partial lost work of each subsystem. This global index is then used to determine the trend followed by the ecosystem from its pristine, original or environmental line base state. This environmental impact index applicability is presented for a simple combustion example
[en] A new approach for the calculation of the interactions among the components of a thermal system for application to the concept of advanced exergy-based analysis is presented. The approach can be used to determine the thermodynamic interactions of system components, and to evaluate alternative designs. The new approach puts the calculation of endogenous and exogenous exergy destruction on a proper thermodynamic basis and introduces a straightforward and time-saving calculation procedure in contrast to various approaches used in the past. When employed to the analysis of the CGAM-problem, the new approach complies with qualitative reasoning, resolves the shortcomings and shows comparable results with previous approaches. The top-down hierarchical approach assists in achieving the best system design possible by identifying the effects of design decisions and by stimulating the engineer's creativity in terms of design alternatives and optimization options. Furthermore, the generalization of the approach allows for any level of aggregation, thus, making the determination of improvement potentials easier. By providing profound thermodynamic understanding for processes, the advanced exergy-based analysis is a promising tool for designing, analyzing and optimizing processes for higher efficiencies and lower costs. - Highlights: • A new concept for the application in advanced exergy-based analysis is introduced and verified. • Problems with previous approaches for advanced exergy analysis are solved. • The concept easily integrates into existing process design methodologies. • Thermodynamic interactions among components are straightforwardly determined.
[en] A phenomenological equation of exergy transfer, which indicates the relation between exergy flux, exergy resistance and exergy driving forces, is derived by applying non-equilibrium thermodynamics to second law analysis, and simultaneously the expressions of the coefficients of exergy transfer are obtained. The results show that exergy transfers in different forms interact on each other. This study also proposes a simplified expression of exergy transfer coefficients by neglecting some minor engineering couplings in exergy transfers. Furthermore, a mixture consisting of two components is discussed. As an application of this result, thermal exergy transfer within a flat plate is studied
[en] In this study an energy and exergy analysis of a Ceiling-type residential air conditioning (CTRAC) system operating under different climatic conditions have been investigated for provinces within the different geographic regions of Turkey. Primarily, the hourly cooling load capacities of a sample building (Q_e_v_a_p) during the months of April, May, June, July, August and September were determined. The hourly total heat gain of the sample building was determined using the Hourly analysis program (HAP). The Coefficient of performance (COP), exergy efficiency (η) and exergy destruction (Ex_d_e_s_t) values for the whole system and for each component were obtained. The results showed that lower atmospheric temperature (T_a_t_m) influenced the performance of the system and each of its components
[en] The processes of power production and low temperature heat are analyzed on the basis of exergic energy production. The efficiency of exergic electric power varies as a function of the applied technology from 40 to 55 percent while the efficiency of combustion and heat transfer is as low as 22 percent. Higher efficiencies are obtained by heat power coupling and heat pumps. (A.S.)
[en] The concept of sustainability was developed from thermodynamic properties applied to complex adaptive systems. The origins of the perception about sustainable development and limitation in its application to analyze the interaction between a system and its surroundings were described. The properties of a complex adaptive system were taken as basis to determine how a system can to be affected by the resources restriction and irreversibility of the processes. The complex adaptive system was understood using the first and second law of thermodynamics, generating a conceptual framework to define the sustainability of a system. The contributions developed by exergy were shown to analyze the sustainability of systems in an economic, social and environmental context
[es]El concepto de sustentabilidad fue desarrollado a partir de propiedades termodinamicas aplicadas a sistemas adaptativos complejos. Los origenes de la percepcion sobre el desarrollo sustentable y la limitacion en su aplicacion para analizar la interaccion entre un sistema y su entorno fueron descritas. Las propiedades de un sistema adaptativo complejo fueron tomadas como base para determinar como un sistema puede ser afectado por la restriccion de recursos e irreversibilidad de los procesos. El sistema adaptativo complejo fue comprendido utilizando la primera y segunda ley de la termodinamica, generando un marco conceptual para definir la sustentabilidad de un sistema. Los aportes desarrollados por la exergia fueron mostrados para analizar la sustentabilidad de sistemas en un contexto economico, social y ambiental