First generation ethanol (1G) contributes to the majority of the ethanol produced worldwide, predominantly centered on corn and sugarcane. Nevertheless, several issues are regularly highlighted concerning the long-term sustainability of this technology, including its intensive water and land use, potential contamination of soils through the distillation residues, as well as the balance between fuel and food crops. Accordingly, in this study, a process design approach for biomass to ethanol production (1G ethanol technology) from sugarcane was performed by using Aspen Plus® software, based on the autonomous distillery (AUT, ethanol production) and the annexed plant (ANX, joint ethanol and sugar production) configurations. In addition, a performance comparison in respect to the exergy efficiency and the irreversibility as quality indicators of the conversion processes is carried out to identify potential improvements in the production facilities. Hence, the shortcomings of the techno-economic assessment of ethanol production can be overcome by using exergy efficiency as a suitable indicator for process performance. Moreover, the technical/sustainability aspects related to the process design of the sugarcane biorefineries are discussed in light of the renewability exergy index (λ). In general, the ANX plant has a saving in the process irreversibility rate of about 6%, whereas the average unitary exergy cost is 10% lower (AUEC= 2.41 kJ/kJ), in contrast to the AUT distillery. Moreover, a techno-economic analysis was carried out to assess the annexed plant and the autonomous distillery systems, considering the estimated capital expenditure. The results indicated that the ANX biorefinery has higher capex than the AUT distillery. It is noted that the higher investments are associated with sugarcane reception, ethanol production (juice extraction) and the combined heat and power sub-systems. Concerning system performance, the ANX plant presented a better overall exergy efficiency, with 41.39 %. Although this multi-criteria analysis is applied to 1G ethanol technology; it may be well-matched for various biorefineries/bioprocesses as a methodology to support decision-making as concerns potential improvement, well ahead of detailed process design.
The engine simulations have become an integral part of engine design and development. They are based on approximations and assumptions. The precision of the results depends on the accuracy of these hypotheses. The simplified models of frozen composition, chemical equilibrium and chemical kinetics provide the compositions of combustion products for engine cycle simulations. This paper evaluates the effects of different operating conditions and hypotheses on the exergetic analysis of a spark-ignition engine. The Brazilian automotive market has the highest number of flex-fuel vehicles. Therefore, a flex-fuel engine is considered for simulations in order to demonstrate the effects of these different hypotheses. The stroke length and bore diameter have the same value of 80 mm. The in-cylinder irreversibility is calculated for each case at the closed part of the engine cycle. A comparative analysis of these hypotheses provides a comprehensive evaluation of their effects on exergetic analysis. Higher values of accumulated irreversibility are observed for the oversimplified hypothesis.
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In this work, the performance of a two-shaft industrial gas turbine engine inspired by SGT-750 , one of best technology at Siemens, is analyzed thermodynamically and economically. The modelling and analyzing process for the proposed system was executed through a software package called IPSEpro and validated with manufacturers’ published data. Exergy analysis, based thermodynamics laws with mass conservation, provides valuable information about locations, magnitudes and types of wastes energy in the thermal systems. Exergoeconomic analysis, the amalgamation of exergy with economics, is useful tool to appraise the gas turbine engine cost-effectiveness. The Specific Exergy Costing method is selected in exergoeconomic evaluation because it is the most widely used reported in the literature and provides reliable results. The performance of a gas turbine engine was investigated for different load variation and climatic conditions. The result shows that the main source of irreversibilities take place in the combustion chamber, compressor and high-pressure turbine, respectively, which constitute to about 96 % of total exergy destruction. The exergetic efficiency and exergy loss rate of the proposed system are about 38.4% and 11.8% respectively. The combustion chamber has the highest value of cost (1312.9 $/h) among other components and the source losses may attribute to the component performance. The production cost of the gas turbine engine based on exergoeconomic evaluation is 12.1 US$/GJ.
In this study a cooling ejector cycle coupled to a compression heat pump is analyzed for simultaneous cooling and heating applications. In this work, the influence of the thermodynamic parameters and fluid nature on the performances of the hybrid system is studied. The results obtained show that this system presents interesting performances. The comparison of the system performances with hydrofluorocarbons (HFC) and natural fluids is made. The theoretical results show that the a low temperature refrigerant R32 gives the best performance.
This paper presents mathematical modelling and numerical analysis to evaluate entropy generation analysis (EGA) by considering pressure drop and second law efficiency based on thermodynamics for forced convection heat transfer in rectangular duct of a solar air heater with wire as artificial roughness in the form of arc shape geometry on the absorber plate. The investigation includes evaluations of entropy generation, entropy generation number, Bejan number and irreversibilities of roughened as well as smooth absorber plate solar air heaters to compare the relative performances. Furthermore, effects of various roughness parameters and operating parameters on entropy generation have also been investigated. Entropy generation and irreversibilities (exergy destroyed) has its minimum value at relative roughness height of 0.0422 and relative angle of attack of 0.33, which leads to the maximum exergetic efficiency. Entropy generation and exergy based analyses can be adopted for the evaluation of the overall performance of solar air heaters.
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In the present work, influence of nozzle holes diameter is studied on the first and second law balance in DI Diesel engine. To this aim, the first law analysis is done by using the results of a three dimensional CFD model. The results show a good agreement with the experimental data. Also for the second law analysis, a developed in house computational code is applied. Behaviors of the results have a good accordance with the literature. The results show that increase in nozzle holes diameter increases both indicated work and heat loss to walls. Also about the second law terms, results declare that increase in nozzle holes diameter leads to increase in indicated work availability, heat loss availability, and entropy generation per cycle and decrease in combustion irreversibility and exhaust gas availability.
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In this paper, comparison of a dual-fuel internal combustion engine performance for CNG and gasoline fuels is evaluated at the steady-state condition by application of energy and exergy analysis using the experimental test results. The energy and exergy balances are calculated at different engine speeds. The results show that the energy and exergy of the heat rejection for gasoline and CNG fuels increases with increasing engine speed and the exergy efficiencies are slightly higher than the corresponding energy efficiencies. Moreover, the results show that the exergy efficiency for gas-fuel is higher than the gasoline-fuel exergy efficiency at all engine speeds. The results show that due to volumetric efficiency drop, power and torque of the gas-fuel engine is lower than gasoline-fuel one. Furthermore, the specific fuel consumption of the gas-fuel engine is lower than gasoline-fuel one. The results of this study have revealed that the most important source of the system inefficiency is the destruction of exergy by irreversible processes, mostly by the combustion. Moreover, it should be noted that liquid fuels like gasoline have many important advantages like much greater volumetric energy density, ease of transport and storage, which have made them as the preferred fuels for IC engines.
Dwa klasyczne sformułowania drugiej zasady termodynamiki, Clausiusa i Kelvina [4], zostały przyjęte jako postulaty, będąc efektem kontynuacji pracy Carnota i uogólnienia wyników obserwacji procesów natury [1, 2]. Postulaty Plancka są takimi sformułowaniami drugiej zasady termodynamiki, których ważność można jednoznacznie zweryfikować na podstawie eksperymentów [3]. Postulaty przyjmuje się bez ścisłego dowodu, możliwe jest jednak dowodzenie ważności jednego sformułowania, po przyjęciu założenia o ważności dowolnego innego. Powszechnie znane są dowody równoważności sformułowań Kelvina i Clausiusa [4, 5], pierwszego i drugiego postulatu Plancka i sformułowania Kelvina [4], a także postulatów Plancka i sformułowania Kelvina [3]. W artykule zaproponowano dowody równoważności pierwszego postulatu Plancka, o nieodwracalności procesów przebiegających z tarciem, i sformułowań drugiej zasady termodynamiki Clausiusa i Kelvina. W dowodzie równoważności pierwszego postulatu Plancka i sformułowania Kelvina uwzględniono nie tylko ciepło tarcia mechanicznego, jak w dowodach przedstawionych w pracach [3, 4], lecz również ciepło tarcia wewnętrznego czynnika termodynamicznego. Pierwszy postulat Plancka może mieć zastosowanie do opisu i doskonalenia tych procesów technologicznych, w których tarcie odgrywa istotną rolę. Im więcej ciepła tarcia jest związane z procesem technologicznym, tym bardziej jest on odległy od wyidealizowanego pojęcia procesu odwracalnego. Szczególnie jest to widoczne w procesach przeróbki plastycznej i obróbki mechanicznej.
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Multiplicity of the second law of thermodynamics statements [6] points out on a universal occurrence of its phenomenological aspects in the processes appearing in the nature [7]. Two classical statements of the second law, Clausius' and Kelvin's statements [4], were accepted as the postulates, while being an effect of the Carnot's work continuation and generalization of results of the observation of the processes in the nature [1, 2]. The Planck's postulates are such second law statements, whose validity may be unequivocally verified by the experiments. Three Planck's postulates are directly connected with an essence of the second law, pointing out on a fact of the existence of the irreversible processes in the nature [3]. The postulates are taken as valid without strict proof; however it is possible to prove any one of the statements, if any of the others is accepted as a postulate. It means that all of the statements of the second law are equivalent, however it seems that more proofs of it cause the better understanding of the second law sense. Commonly well-known there are proofs of equivalence of the Kelvin's and the Clausius' statements [4, 5], the first and second Planck's postulates and the Kelvin's statement [4], also the Planck's postulates and the Kelvin's statement [3]. In this paper the equivalence of the first Planck's postulate, about irreversibility of the processes being proceeded with friction, and the Clausius' and the Kelvin's statements of the second law of thermodynamics are proposed. In the proof of equivalence of the first Planck's postulate and the Kelvin's statement not only heat coming from mechanical friction was taken into account, like in proofs presented in works [3, 4], but also heat coming from internal friction of a thermodynamical agent. The first Planck's postulate could be used to describe and optimize such technological processes, in which friction plays a significant role. The more heat coming from friction is accompanying the technological process, the more far it is from idealized concept of reversible process. Particularly it is noticed in the plastic working and machining processes.
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We investigate the nature of heat transfer and entropy generation for natural convection in a two-dimensional circular section enclosure vibrating sinusoidally perpendicular to the applied temperature gradient in a zero-gravity field. The enclosure is assumed to fill with porous media. The Darcy momentum equation is used to model the porous media. The full governing differential equations are simplified with the Boussinesq approximation and solved by a finite volume method. Whereas the Prandtl number Pr is fixed to 1.0. Results are presented in terms of the average Nusselt number (Nuav), entropy generation number (Nsav), Bejan number (Beav), and kinetic energy (KEav).
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