Results 1 - 10 of 2040
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[en] Application of exergy analysis methodology for encapsulation of photochromic dyes by spray drying was presented. Spray drying system was investigated considering two subsystems, the heater and the dryer sections. Exergy models for each subsystem were proposed and exergy destruction rate and exergy efficiency of each subsystem and the whole system were computed. Energy and exergy efficiency of the system were calculated to be 5.28% and 3.40%, respectively. It was found that 90% of the total exergy inlet was destroyed during encapsulation by spray drying and the exergy destruction of the heater was found to be higher. (paper)
[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] Entropy is an extremely important physical quantity in thermodynamics. However, students studying thermodynamics commonly find it difficult to understand entropy. In most thermodynamics textbooks, there is only a microscopic explanation of the physical meaning of entropy, with a lack of a macroscopic interpretation. This lack is far from sufficient for people who are more concerned about the macroscopic engineering applications of entropy. In this study, we comparatively analyse entropy and exergy to explain the macroscopic physical meaning of entropy based on the concept of exergy. That is, entropy is a measure of the unavailable energy of a system during reversible heat interaction with the environment. Based on this physical interpretation of entropy, we have answered three questions that students may raise when learning about the concept of entropy. In addition to theoretical derivation, we also try to use several examples from daily life to help readers better understand the macroscopic physical meaning of entropy. Finally, through a questionnaire survey, we learned about students’ evaluations and their understanding of an engineering thermodynamics course. We have also learned whether the students prefer entropy or exergy and the reasons for their preference, as well as what aspects regarding the contents and methods the students would prefer the lecturer to improve upon when teaching entropy and exergy. The results of this work can make it easier for students to understand the physical quantity of entropy. Additionally, the results of the questionnaire analysis can be of a certain reference value for the instructions of an engineering thermodynamics course. (paper)
[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