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Understanding the flow instabilities encountered by the turbocharger compressor is an important step toward improving its overall design for performance and efficiency. While an experimental study using Particle Image Velocimetry was previously conducted to examine the flow field at the inlet of the turbocharger compressor, the present work complements that effort by analyzing the flow structures leading to stall instability within the same impeller. Experimentally validated three-dimensional computational fluid dynamics predictions are carried out at three discrete mass flow rates, including 77 g/s (stable, maximum flow condition), 57 g/s (near peak efficiency), and 30 g/s (with strong reverse flow from the impeller) at a fixed rotational speed of 80,000 rpm. Large stationary stall cells were observed deep within the impeller at 30 g/s, occupying a significant portion of the blade passage near the shroud between the suction surface of the main blades and the pressure surface of the splitter blades. These stall cells are mainly created when a substantial portion of the inlet core flow is unable to follow the impeller's axial to radial bend against the adverse pressure gradient and becomes entrained by the reverse flow and the tip leakage flow, giving rise to a region of low-momentum fluid in its wake. This phenomenon was observed to a lesser extent at 57 g/s and was completely absent at 77 g/s. On the other hand, the inducer rotating stall was found to be most dominant at 57 g/s. The entrainment of the tip leakage flow by the core flow moving into the impeller, leading to the generation of an unstable, wavy shear layer at the inducer plane, was instrumental in the generation of rotating stall. The present analyses provide a detailed characterization of both stationary and rotating stall cells and demonstrate the physics behind their formation, as well as their effect on compressor efficiency. The study also characterizes the entropy generation within the impeller under different operating conditions. While at 77 g/s, the entropy generation is mostly concentrated near the shroud of the impeller with the core flow being almost isentropic, at 30 g/s, there is a significant increase in the area within the blade passage that shows elevated entropy production. The tip leakage flow, its interaction with the blades and the core forward flow, and the reverse flow within the impeller are found to be the major sources of irreversibilities. [ABSTRACT FROM AUTHOR]

This study investigates theoretically the effects of stroke/bore (s/b) ratio with availability (exergy) analysis in LPG (100% Propane) fuelled spark ignition (SI) engines. For this purpose, a two–zone quasi–dimensional cycle model of SI engines has been used. The combustion process is simulated as turbulent flame entrainment model, the intake and exhaust processes is simulated by using the simple empirical equations in the cycle model. The principles of the second law of thermodynamics were applied to the cycle model in order to perform the exergy analysis. In the exergy analysis, the exergetic terms such as the exergies transferred by heat, work and exhaust, irreversibilities, fuel chemical exergy, thermomechanical exergy and total exergy were calculated for the selected s/b ratios. In addition, the first and second law efficiencies and indicted specific fuel consumption were also calculated. Thus, the effects of s/b ratio on the exergetic terms, the first and second law efficiencies and indicated specific fuel consumption were determined for LPG fuelled SI engines. The results of the study showed that the increase of the s/b ratio reduces the values of the heat losses, irreversibility and indicated specific fuel consumption, increases the cycle work, exergy losses by exhaust gasses with the first and second law efficiencies in SI engines. The increasing of stroke/bore ratio from 0.7 to 1.3 in LPG fuelled SI engines decreases the heat losses by 10.67%, irreversibilities by 1.89% and indicated specific fuel consumption by 3.91%, while it increases exergy transfer with work by 4.12%, exergy losses with exhaust gasses by 2%, the first law efficiency by 4.07% and the second law efficiency by 4.08%, respectively. [ABSTRACT FROM AUTHOR]

A finite-time thermodynamics study and an exergetic optimisation for a four-temperature-level absorption heat pump have been performed. The maximum of the exergetic-performance coefficient (EPC) and the corresponding optimal ecological coefficient of performance (ECOP), ecological objective function (E), exergetic efficiency (ex), coefficient of performance (COP), specific entropy generation rate and heating load have been obtained. The effects of internal irreversibilities, external irreversibilities, heat leakages, ratio of the rejected heat of the absorber to the condenser and the heat-transfer coefficients of different components on the system performance have been analysed and discussed. It was noticed a greater harmful impact of heat losses in the generator-absorber assembly. Comparisons of EPC criterion with ECOP, COP, E and ex criteria have been provided. The results demonstrate that the four-temperature-level absorption heat pump working at maximum EPC conditions has a significant advantage in terms of entropy generation rate and coefficient of performance.

A finite-time thermodynamics study and an exergetic optimisation for a four-temperature-level absorption heat pump have been performed. The maximum of the exergetic-performance coefficient (EPC) and the corresponding optimal ecological coefficient of performance (ECOP), ecological objective function (E), exergetic efficiency (ex), coefficient of performance (COP), specific entropy generation rate and heating load have been obtained. The effects of internal irreversibilities, external irreversibilities, heat leakages, ratio of the rejected heat of the absorber to the condenser and the heat-transfer coefficients of different components on the system performance have been analysed and discussed. It was noticed a greater harmful impact of heat losses in the generator-absorber assembly. Comparisons of EPC criterion with ECOP, COP, E and ex criteria have been provided. The results demonstrate that the four-temperature-level absorption heat pump working at maximum EPC conditions has a significant advantage in terms of entropy generation rate and coefficient of performance. [ABSTRACT FROM AUTHOR]

Summary: Direct air capture of CO2 is often presented as a promising technology to help mitigate climate change, although proposed processes are highly energy intensive. We analyze Carbon Engineering’s 1 Mt-CO2/year natural-gas-powered direct air capture (DAC) process, which requires 273.2 MW per plant, where we find that 252 MW are irreversibly lost, corresponding to a second-law efficiency of 7.8%. Our component-level analysis details the mechanisms by which these losses of thermodynamic work potential occur in the most energy-intensive plant segments. Here, we emphasize the effects of chemical exergy dissipation in the air contactor, where stored chemical exergy is released as low-grade heat into the environment. Other major losses occur in the calciner and its preheat cyclones due to the high temperature demanded by its internal chemical reaction, as well as in the water knockout system, CO2 compression system, and power island. Finally, we illustrate the issues arising from the use of natural gas as a feedstock for heat and power, and suggest directions to pursue for further analysis and process improvements, which we consider imperative to make this DAC process a viable option for large-scale CO2 removal toward IPCC targets.

In this study, the performance of several gas turbine engines has been investigated using computational modelling based on the actual manufacturer's data. Further, the study focuses on evaluating the impact of varying the configuration of the compressor on overall engine performance based on the first and second laws of thermodynamics. The results confirm that the main source of irreversibilities occurs in the combustion chamber in all cases. The exergetic efficiency of the gas turbine engine significantly varies with compressor configurations, type of compressors, load variation, climatic condition, and isentropic efficiency. The engine capacity and high‐pressure turbine inlet temperature govern the gas turbine performance, and higher values are more favourable. The gas turbine exergetic efficiency drops off when the power setting adjusted at part‐load and at high ambient temperature. The most optimal gas turbine performance is located at the single axial compressor case, followed by the axial‐centrifugal compressor and then the centrifugal–centrifugal compressor. [ABSTRACT FROM AUTHOR]

The entropy generation analysis is an approach to optimize the performance of different thermal systems by investigating the related irreversibilities of the system. This paper provides a concise review of the entropy generation analysis performed for different solar thermal energy systems including solar collectors, solar heaters, solar heat exchangers, and solar stills. The mathematical formulation and the equations for calculating the entropy generation are briefly presented. Moreover, main passive techniques including the usage of nanofluids, porous materials, and inserts which are used to improve the efficiency of different solar systems are discussed. It is shown that using entropy generation minimization method is an efficient tool to find the optimal design of solar systems. The current review aims to motivate researchers in the field of solar energy for using entropy generation analysis to reduce the lost work and consequently improving the system performance. [ABSTRACT FROM AUTHOR]

The purpose of the present work is to investigate humidification–dehumidification desalination system and to explore the effect of pertinent parameters on the overall performance of the process taking in account the irreversibilities and energy losses. The system has been inspected using first and second laws of thermodynamics, and an optimization of the performance along with design development has been performed based on mathematical calculation and modeling for the fundamental equations associated with mass, energy, exergy and salinity balance incorporating the effects of irreversibilities and thermal losses which in turn helps in establishing an efficient desalination system by reducing these losses. The results show a good improvement compared to previous studies. The model target is to increase heat exchange in humidifier and dehumidifier compartment as well as augmenting pure water capacity and lessening energy consumption. Results expose that the inlet water temperature and flow rate represent the main factors affecting the system performance. It is found that the heater has the main part of exergy losses. Increasing the temperature of the water in the dehumidifier outlet allows minimizing the exergy losses in the dehumidifier. [ABSTRACT FROM AUTHOR]

A model for a pumped thermal energy storage system is presented. It is based on a Brayton cycle working successively as a heat pump and a heat engine. All the main irreversibility sources expected in real plants are considered: external losses arising from the heat transfer between the working fluid and the thermal reservoirs, internal losses coming from pressure decays, and losses in the turbomachinery. Temperatures considered for the numerical analysis are adequate for solid thermal reservoirs, such as a packed bed. Special emphasis is paid to the combination of parameters and variables that lead to physically acceptable configurations. Maximum values of efficiencies, including round-trip efficiency, are obtained and analyzed, and optimal design intervals are provided. Round-trip efficiencies of around 0.4, or even larger, are predicted. The analysis indicates that the physical region, where the coupled system can operate, strongly depends on the irreversibility parameters. In this way, maximum values of power output, efficiency, round-trip efficiency, and pumped heat might lay outside the physical region. In that case, the upper values are considered. The sensitivity analysis of these maxima shows that changes in the expander/turbine and the efficiencies of the compressors affect the most with respect to a selected design point. In the case of the expander, these drops are mostly due to a decrease in the area of the physical operation region.

This work presents an experimental energy and exergy analysis for the operation of a multi-cylinder four-stroke direct injection turbocharged and intercooled commercial diesel engine. A simplified model of an extended thermodynamic cycle over compressor-intercooler-engine and turbine was adapted, and then being calibrated with engine dynamometric bench measurements. For two representative engine operation modes - rated power and maximum torque - at full load, second law terms were assessed in function of chemical diesel fuel availability. The result was an integrated method for a reliable assessment of availability losses, which becomes a useful tool to evaluate the further improvement of process efficiency and of the energy harvesting potential. [ABSTRACT FROM AUTHOR]

• Thermodynamic study and analysis of an irreversible absorption heat pump with three-heat-reservoir. • Optimization by the thermo-ecological function is proposed. • We study the influences of both internal irreversibilities and external irreversibility on the system. • Heat losses have more effects on performance in the condenser-evaporator assembly. • The comparison between the thermo-ecological and exergy-based ecological criteria is established. The investigations carried out in this work concern the optimization and the thermodynamic analysis of an absorption heat pump with multi-irreversibilities and provided with three-heat-reservoir mainly using the thermo-ecological criterion as objective function. The thermodynamic analysis of the first and second laws of thermodynamics and the linear law of heat-transfer allowed us to evaluate and optimize the objective functions of performance such as: the specific heating load, the coefficient of performance, the specific entropy generation rate, the ecological coefficient of performance and the heat-transfer areas of the various components. These allowed us to study the variations of these criteria according to the design parameters and the temperatures of the working fluid in the components. From this study, it follows that the optimal system implies a maximum thermo-ecological coefficient, a minimum entropy production rate corresponding to a certain value of the specific heating load, while maintaining a system which limits the losses between the condenser and the evaporator. Moreover, the consideration of the two internal irreversibilities, the external irreversibility and the losses of the heat resistances is very close to a real absorption heat pump and allows a more precise and objective study rather than in the optimization and the design of an absorption system like an endoreversible system. [ABSTRACT FROM AUTHOR]

Thermoeconomic analysis allows for a deep understanding of the cost formation process within an energy system, providing insights into the possible routes for improvement. Several thermoeconomic approaches are well-established for application in systems with steady operating conditions, such as power plants, while a limited number of applications to air-conditioning systems in buildings have been proposed, due to the difficulties in dealing with very irregular load profiles and unsteady plant operating conditions. This study investigates the potential of Thermoeconomics as a support for decision making in building energy systems, proving its capability to identify trade-offs between cost fractions related to capital investment and efficiency. The proposed approach to thermoeconomic analysis of dynamic systems introduces some methodological novelties, such as the use of a preliminary dynamic simulation to calculate "averaged energy flows" on an arbitrary time basis and the adoption of a flexible super-structure, capable to reflect the different operating conditions throughout the year. That is then applied to a school dwelling, supplied with space heating and cooling and a mechanical ventilation Air Handling Unit. The sources of irreversibility are evaluated and the main targets for improvement are identified, calculating the trends of exergetic, exergoeconomic and exergoenvironmental costs on a monthly basis. • An innovative dynamic thermoeconomic analysis is performed for an air-conditioning system. • Symbolic Thermoeconomics is applied for exergetic and exergoeconomic cost accounting. • A novel flexible "productive superstructure" is defined for the dynamic operating conditions. • A simple guide workflow is given for Symbolic Thermoeconomics dynamic application. • Application to a school dwelling allowed to calculate average costs on a monthly basis. [ABSTRACT FROM AUTHOR]

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 Plusr 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. [ABSTRACT FROM AUTHOR]

This paper investigates the combined effects of using nanofluid, a porous insert and corrugated walls on heat transfer, pressure drop and entropy generation inside a heat exchanger duct. A series of numerical simulations are conducted for a number of pertinent parameters. It is shown that the waviness of the wall destructively affects the heat transfer process at low wave amplitudes and that it can improve heat convection only after exceeding a certain amplitude. Further, the pressure drop in the duct is found to be strongly influenced by the wave amplitude in a highly non-uniform way. The results, also, show that the second law and heat transfer performances of the system improve considerably by thickening the porous insert and decreasing its permeability. Yet, this is associated with higher pressure drops. It is argued that the hydraulic, thermal and entropic behaviours of the system are closely related to the interactions between a vortex formation near the wavy walls and nanofluid flow through the porous insert. Viscous irreversibilities are shown to be dominant in the core region of duct where the porous insert is placed. However, in the regions closer to the wavy walls, thermal entropy generation is the main source of irreversibility. A number of design recommendations are made on the basis of the findings of this study. [ABSTRACT FROM AUTHOR]

In an energy system, it is important to identify the origin of residue formation in order to implement actions to reduce their formation or to eliminate them as well as to evaluate their impact on the production costs of the system. In the exergetic cost theory, although there are several criteria to allocate the cost formation of residues to the productive components, no unique indication on the best choice has been defined yet. In this paper, the production exergy costs are determined by allocating the residue cost formation to the irreversibilities of the productive components from which they originate. This criterion, based on the Gouy−Stodola theorem, is an extension of the criterion of entropy changes, and unlike this, it avoids the existence of a negative production cost. This criterion is applied to a combined cycle of three pressure levels, and the production exergy costs are compared with the criteria of entropy changes, distributed exergy, and entropy. The results of the proposed criterion are in agreement with the compared criteria.

Surface enhancement in heat exchangers has been actively researched, but enhancements have been mainly on the tube side, involving optimization of the geometry. The effect of surface enhancement has been studied in great detail experimentally, but numerical studies are scarce and involve performance comparisons based on the friction factor and Nusselt number. However, true performance can be assessed based on entropy generation minimization. We performed a numerical study on tubes with helical groove formation to assess entropy generation minimization. The tube data were initially validated experimentally and tube performance was then examined via thermal enhancement factors and entropy generation minimization. The Reynolds number was taken as 5000 to 10000 in accordance with an experimental study. All the tubes had an enhancement factor greater than unity, meaning that they were thermally efficient. However, with regard to irreversibility, the tube with the minimum pitch-0.051 m-(GT02) produced the lowest value and hence the minimum entropy generation rate, and thus represented the optimal choice for heat exchangers. [ABSTRACT FROM AUTHOR]

Highlights • The presence of IHX in ERC causes a detrimental impact in the energy performance. • A novel configuration with IHX in ERC promotes an increase in the exergy efficiency. • Reduction of irreversibilities is produced by superheating of secondary flow in ERC. Abstract This paper presents the theoretical analysis of the influence of an internal heat exchanger (IHX) position, on an ejection-compression refrigeration system. The energy and the exergy performance are discussed by placing an IHX in two different positions: 1) Promoting the superheating in the compressor suction EC+IHX-1 and 2) promoting superheating in the suction nozzle EC+IHX-2, which is a novel configuration proposal. Both configurations are compared under air climatization conditions using the refrigerants R134a, R1234ze(E) and R290. The results show that the exergy efficiency is higher when EC+IHX-2 is used for an IHX effectiveness below 60%, and lower irreversibilities occur in the ejector with this configuration for an effectiveness value of IHX below 40%. In both cases, IHX presence promotes a decrease in the coefficient of performance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Endoreversible thermodynamics is a finite time thermodynamics ansatz based on the assumption that reversible or equilibrated subsystems of a system interact via reversible or irreversible energy transfers. This gives a framework where irreversibilities and thus entropy production only occur in interactions, while subsystems (engines, for instance) act as reversible. In order to give an opportunity to incorporate dissipative engines with given efficiencies into an endoreversible model, we build a new dissipative engine setup. To do this, in the first step, we introduce a more general interaction type where energy loss not only results from different intensive quantities between the connected subsystems, which has been the standard in endoreversible thermodynamics up to now, but is also caused by an actual loss of the extensive quantity that is transferred via this interaction. On the one hand, this allows the modeling of leakages and friction losses, for instance, which can be represented as leaky particle or torque transfers. On the other hand, we can use it to build an endoreversible engine setup that is suitable to model engines with given efficiencies or efficiency maps and, among other things, gives an expression for their entropy production rates. By way of example, the modeling of an AC motor and its loss fluxes and entropy production rates are shown.

While dual fuel low temperature combustion (LTC) has been studied before, a detailed second law analysis of dual fuel LTC is not yet available in the open literature. To address this gap, a previously validated, closed-cycle, multi-zone, simulation of diesel-natural gas dual fuel LTC was used to perform a second law analysis. For the present study, a 2.4-l single-cylinder research engine operating at a nominal load of 6 bar BMEP and 1700 rpm was used. Zone-wise thermodynamic irreversibilities as well as total cumulative entropy generated and lost available work over the closed cycle were quantified. Subsequently, two convenient second-law parameters were defined: (1) the “lost available indicated mean effective pressure” (LAIMEP), which can be interpreted as an engine-size-normalized measure of available work that is lost due to thermodynamic irreversibilities (analogous to the relationship between indicated mean effective pressure and indicated work); (2) fuel conversion irreversibility (FCI), which is defined as the ratio of lost available work to total fuel chemical energy input. Finally, parametric studies were performed to quantify the effects of diesel start of injection, intake manifold temperature, and intake boost pressure on LAIMEP and FCI. The results show that significant entropy generation occurred in the flame zone (52–61 percent) and the burned zone (31–39 percent) while packets account for less than 6 percent of the overall irreversibilities. Parametric studies showed LAIMEPs in the range of 645–768 kPa and FCIs in the range of 32.8–39.2 percent at different engine operating conditions. Although the present study focused on dual fuel LTC, the conceptual definitions of LAIMEP and FCI are generally applicable for comparing the thermodynamic irreversibilities of IC engines of any size and operating on any combustion strategy. [ABSTRACT FROM AUTHOR]

In this work, the stages of losses and lower exergetic efficiency are determined when the sugar production process is integrated with others for the production of products such as biogas, torula yeast and electricity. The study is carried out in three scenarios of integrated processes for obtaining the indicated products. A sugar factory in which sugar and electricity are produced is considered as the base scenario and from this; a second scenario is inferred in which alcohol is produced from the molasses of the sugar process and biogas from the vinasse of the alcohol distillation process. Finally, a third scenario is exergetically evaluated in which sugar, electricity, biogas and alcohol are produced, but this last one from juices and molasses of the sugar process. For the exergetic analysis the integrated scheme was divided into 8 subsystems. From the analysis of results, the major subsystems that generate irreversibilities are: cogeneration (64.36-65.98%), juice extraction (8.85-9.85%), crystallization and cooking, (8.48 - 9.02%), fermentation (4.12-4.94%) and distillation (2.74-3.2%). Improvements are proposed to minimize irreversibilities, including the thermal integration of processes, technological modifications in the fermentation process and the introduction of more efficient equipment for the generation of electricity. The exergetic efficiency is between 78.95-81.10%, obtaining greater exergetic efficiency in the scheme of joint operation to produce sugar, alcohol and biogas. [ABSTRACT FROM AUTHOR]

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Second Law efficiency is a useful parameter for characterizing the energy requirements of a system in relation to the limits of performance prescribed by the Laws of Thermodynamics. However, since energy costs typically represent less than 50% of the overall cost of product for many large-scale plants (and, in particular, for desalination plants), it is useful to have a parameter that can characterize both energetic and economic effects. In this paper, an economics-based Second Law efficiency is defined by analogy to the exergetic Second Law efficiency and is applied to several desalination systems. It is defined as the ratio of the minimum cost of producing a product divided by the actual cost of production. The minimum cost of producing the product is equal to the cost of the primary source of energy times the minimum amount of energy required, as governed by the Second Law. The analogy is used to show that thermodynamic irreversibilities can be assigned costs and compared directly to non-energetic costs, such as capital expenses, labor and other operating costs. The economics-based Second Law efficiency identifies costly sources of irreversibility and places these irreversibilities in context with the overall system costs. These principles are illustrated through three case studies. First, a simple analysis of multistage flash and multiple effect distillation systems is performed using available data. Second, a complete energetic and economic model of a reverse osmosis plant is developed to show how economic costs are influenced by energetics. Third, a complete energetic and economic model of a solar powered direct contact membrane distillation system is developed to illustrate the true costs associated with so-called free energy sources.

Se investigan las irreversibilidades de una bomba de calor, con análisis exergéticos y estructurales. Se utilizó una instalación experimental de una bomba de calor lográndose datos y cálculos de la eficiencia de la compresión, temperaturas medias de los focos caliente y frío del ciclo, diferencia de temperatura a la salida del condensador, media logarítmica del evaporador, caídas de presiones del condensador y el evaporador y un análisis exergético y estructural con las propiedades termodinámicas en los puntos clave del ciclo, coeficiente de comportamiento del ciclo, balances de masas, energías y entropía, entropía generada en cada componente, balance de exergía con las irreversibilidades en cada componente, eficiencia exergética, defecto de eficiencia y coeficientes de vínculos estructurales Se exploraron las potencialidades de mejora de cada componente para una posterior optimización termoeconómica. The irreversibility of a heat pump with exergy and structural analysis is investigated. An experimental installation of a heat pump and calculations achieving data compression efficiency, the average temperature of hot and cold spots in the cycle was used, The temperature difference output condenser, log mean evaporator , pressures drops condenser and evaporator and structural exergy analysis and thermodynamic properties at key points of the cycle, the cycle coefficient of performance, mass balances, energy and entropy, entropy generated in each component, the availability balance irreversibilities in each component , exergetic efficiency, default coefficients efficiency and structural links were obtained. The potential for improvement for each component for further thermoeconomic optimization were explored.

For a practical thermoelectric generator (TEG) system, the performance is affected by many irreversible processes. This study evaluates the effects of multi-irreversibilities on TEG performance using exergy analysis. Based on the exergy analysis, two performance indexes, the energy efficiency and exergy efficiency, are used. A finite element scheme is employed to model the TEG system. The heat loss from the TEG to the environment and temperature-dependent material properties are considered. The results suggest that when the application of the small electrical current is considered, decreasing the hot-reservoir temperature or increasing the cold-reservoir temperature can improve the TEG exergy efficiency. Although heat loss slightly decreases the maximum energy and exergy efficiency, it can improve energy and exergy efficiencies for a case with large electrical current. On the other hand, when the Seebeck coefficient or thermal conductivity is temperature-dependent, both the maximum energy efficiency and exergy efficiency increase with increasing hot-reservoir temperature. However, the temperature-dependence of the electrical resistivity reduces the maximum exergy efficiency when the hot-reservoir temperature increases even though the maximum energy efficiency is increased.

Organic Rankine Cycles (ORC) using toluene and hexamethyldisiloxane (MM) are put forward as a means of improving the efficiency of automotive heavy duty engines, and provide a reference for comparison in this study. Despite an efficiency improvement potential of 4–4.7%, the current ORC approach is not reaching the required fuel savings within the expected costs. As such, innovative pathways to improve the ORC performance and cost-effectiveness are of great importance to the research community. This paper presents a partial solution by means of a conceptual overview and simulation results for ORCs especially tailored for high-temperature applications. A fundamental revision of the heat transfer and expansion characteristics is presented, without increasing the system integration complexity. These characteristics are attributed to the use of formulated organic blends with toluene and MM as a significant blend component. The developed 22 criteria blend screening methodology is presented. Simulation results show that for an equivalent expansion volume flow ratio, and product of heat transfer coefficient and area, the blends offer a 22–24% improvement in the net power. This resulted in a 15–18% cost savings compared to the reference ORC. The simulations were conducted in Aspen HYSYS V8 using the Peng-Robinson and Wilson fluid property packages. [ABSTRACT FROM AUTHOR]

Cogeneration power plants connected to industrial processes have a direct impact on the overall efficiency of the plant and therefore on the economic results. Any modification to the thermal outline of these plants must first include an exergetic analysis to compare the benefits it can bring the new proposal. This research is performed to a cogeneration plant in operation with an installed electrical capacity of 24 MW and process heat demand of 190 MW, it shows a study made from the Second Law of Thermodynamics. Exergetic evaluation of each component of the plant was applied and similarly modified cogeneration scheme was evaluated. The results illustrate that the exergy losses and irreversibilities are completely different from one subsystem to another. In general, the total exergy destruction represented 70,7% from the primary fuel exergy. Steam generator was the subsystem with the highest irreversibility of the plant with 54%. It was demonstrated that the increase of the steam parameters lead to reduce exergy destruction and exergy efficiency elevation. The suppression of the reduction system and the adding of an extraction-condensing steam turbine produce the same effect and contribute to drop off the electrical consumption from the grid. [ABSTRACT FROM AUTHOR]

As part of the efforts to unify the various branches of Irreversible Thermodynamics, the proposed work reconsiders the approach of the Carnot engine taking into account the finite physical dimensions (heat transfer conductances) and the finite speed of the piston. The models introduce the irreversibility of the engine by two methods involving different constraints. The first method introduces the irreversibility by a so-called irreversibility ratio in the entropy balance applied to the cycle, while in the second method it is emphasized by the entropy generation rate. Various forms of heat transfer laws are analyzed, but most of the results are given for the case of the linear law. Also, individual cases are studied and reported in order to provide a simple analytical form of the results. The engine model developed allowed a formal optimization using the calculus of variations. [ABSTRACT FROM AUTHOR]

Analysis of thermal systems on the basis of the second law of thermodynamics has recently gained considerable attention. This is, in part, due to the fact that this approach along with the powerful tools of entropy generation and exergy destruction provides a unique method for the analysis of a variety of systems encountered in science and engineering. Further, in recent years there has been a surge of interest in the thermal analysis of conductive media which include solid structures. In this work, the recent advances in the second law analyses of these systems are reviewed with an emphasis on the theoretical and modeling aspects. The effects of including solid components on the entropy generation within different thermal systems are first discussed. The mathematical methods used in this branch of thermodynamics are, then, reviewed. This is followed by the conclusions regarding the existing challenges and opportunities for further research. [ABSTRACT FROM AUTHOR]

In the present study, environmental impact analysis is used for the optimization to an actual heat engine. Four new thermoenvironmental evaluation criteria called as thermoenvironmental function, ecological based thermoenvironmental function, ecologicoenvironmental function and finite time exergoenvironmental criteria are developed and compared with the each other. Ecologicoenvironmental function is used to determine environmental impact at the maximum ecological function. It is defined as the most suitable criteria for an actual heat engine. Because, it has lower irreversibilities compared with others, its work output is equal to 90% of the maximum work and 60% energy efficiency at the optimum point and exergy destruction is lower than others at the optimum point. [ABSTRACT FROM AUTHOR]

In this paper, a 1-D model of an half alpha type “double-acting” Stirling engine (made up of two double-acting pistons, two hot heat-exchangers, two cold heat-exchangers and a common recuperator-regenerator for the two separate gas circuits, all that giving two cycles with 180° phasing) is presented. In this architecture, two cylinders, containing, each one, a double-acting piston, are combined in order to operate like two parallel Stirling systems in opposition of phase. This model, derived from Andersen’s model, is used to describe the compressible flows in the half-engine, under energy transfers. A finite-volume numerical method is applied for the equations of energy, mass and momentum assessment. This modelling was carried out using the Matlab/Simulink software. The results of this dynamic modelling relate to one half engine. We obtain the evolution of the physical parameters (density, pressure and temperature), and the (p, V) cycle. The influence of the various assumptions was studied. A parametric study was carried out in order to obtain the optimal values of the geometry of the engine and its ideal speed of operation.

The energy efficient convection systems can be designed by reducing exergy losses. In this context, the analysis on the entropy generation during natural convection in the fluid-filled (Prandtl number, P r = 0.015 − 1000 ) rhombic enclosures with various inclination angles ( φ ) has been carried out for the efficient thermal processing in various applications such as the chemical reactor modeling, underground coal gasification, and nuclear reactors. The enclosure is subjected to the differential heating (case 1) and Rayleigh–Benard convection (case 2). The conduction based static solution occurs only for φ = 9 0 ∘ and it is observed that the conduction based static solution disappears with a slight perturbation of φ at Rayleigh number, R a ≥ 2 × 10 3 irrespective of P r in case 2. The active zones of the heat transfer irreversibility ( S θ ) and fluid friction irreversibility ( S ψ ) are found to occur near the isothermal walls for all φ s irrespective of P r in both the cases at R a = 10 5 . In addition, the active zones of S ψ are also found to occur near the adiabatic walls of the cavity for all φ s irrespective of P r in both the cases at R a = 10 5 . Also, the region between the fluid layers of primary circulation cells acts as the strong active zone of S ψ for all φ s in case 2 at lower P r ( P r = 0.015 ) and R a = 10 5 . The total entropy generation ( S t o t a l ) and maximum heat transfer rates ( N u ¯ ) are found to be significantly low for φ = 3 0 ∘ in both the cases at R a = 10 5 irrespective of P r . Analysis of heating patterns and geometrical orientations relates the exergy to irreversibilities which establishes that the rhombic cavity ( φ = 3 0 ∘ ) with the differential heating pattern may be the optimal design based on the energy efficient perspective. [ABSTRACT FROM AUTHOR]

In this paper, a nano scale irreversible Dual cycle working with ideal Bose and Fermi gases is examined. Degeneracy conditions and thermo-size effects on the quantum gases are researched. Thermodynamic analyses of the cycle are conducted by considering irreversibilities. Different thermodynamic assessment methods are applied and then compared to each other. The obtained results are presented numerically. It concluded that ECF is the most convenient method for the Bose gas under weak degeneracy condition and x should be chosen as biggest as possible for all other conditions. [ABSTRACT FROM AUTHOR]

Exergy analysis has gained significance in analysing thermal energy systems as it locates and quantifies the irreversibilities in the system. This paper investigates the thermoelectric heat pump systems through exergy analysis. Four thermodynamic models of the thermoelectric heat pump considering the internal and external irreversibilities are developed and analysed in MATLAB Simulink environment with temperature dependent material properties for various operating temperatures. Moreover, analytical expressions for exergy efficiency and irreversibilities for the thermoelectric heat pump are derived. The results show that the exergy efficiency of the thermoelectric heat pump increases with increase in Δ Th . For a typical operating condition in an irreversible thermoelectric heat pump with 31 thermocouples and when T H and T C of 313 K and 303 K respectively, the maximum energy and exergy efficiency obtained are 4.01 and 12.81% at same optimum current of 5.55A. The results also show that the effect of internal irreversibilities is more pronounced than the external irreversibilities in the performance of the thermoelectric heat pump. The effects of irreversible heat transfer and contact resistance in the exergy efficiency are also studied. This study will be helpful in designing the actual thermoelectric heat pump systems. [ABSTRACT FROM AUTHOR]

Homogeneous charge compression ignition (HCCI) combustion has shown the potential to improve gasoline engine efficiency, by integration into future dual-mode spark ignition/HCCI engines. With the current trend of downsizing and boosting, it is critical to implement HCCI combustion under elevated pressure, and assess its potential for high load and efficient operation. Thermodynamic analysis of such engines provides insight into the energy flows of the systems, and enables optimal design for efficiency. This study is focused on modeling a 4-cylinder boosted HCCI engine, and utilizing second law to describe the exergy flows of the system in order to identify areas of irreversibilities and inefficiencies. The implications of boosting and variable valve actuation on exergy flows are discussed and analyzed. Results from this modeling study indicated that light-duty boosted HCCI can be utilized up to 10-bar brake mean effective pressure (BMEP) with peak brake efficiency of 39%. [ABSTRACT FROM AUTHOR]

In last decades, nano technology developed. Since, nano scale thermal cycles will be possibly used in near future. In this study, a nano scale irreversible dual cycle was analyzed thermodynamically. Ideal Maxwell–Boltzmann gas is used for working fluid in the system. He 4 is chosen as working fluid. Results are obtained as numerically. In calculations, different thermodynamic performance evaluation methods are applied and these methods are compared each other to determine the most convenient optimization way. [ABSTRACT FROM AUTHOR]

Analytical analysis of unbalanced heat exchangers is carried out to study the second law thermodynamic performance parameter through second law efficiency by varying length-to-diameter ratio for counter flow and parallel flow configurations. In a single closed form expression, three important irreversibilities occurring in the heat exchangers-namely, due to heat transfer, pressure drop, and imbalance between the mass flow streams-are considered, which is not possible in first law thermodynamic analysis. The study is carried out by giving special influence to geometric characteristics like tube length-to-diameter dimensions; working conditions like changing heat capacity ratio, changing the value of maximum heat capacity rate on the hot stream and cold stream separately and fluid flow type, i.e., laminar and turbulent flows for a fully developed condition. Further, second law efficiency analysis is carried out for condenser and evaporator heat exchangers by varying the effectiveness and number of heat transfer units for different values of inlet temperature to reference the temperature ratio by considering heat transfer irreversibility. Optimum heat exchanger geometrical dimensions, namely length-to-diameter ratio can be obtained from the second law analysis corresponding to lower total entropy generation and higher second law efficiency. Second law analysis incorporates all the heat exchanger irreversibilities. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (). DOI 10.1002/htj.21109 [ABSTRACT FROM AUTHOR]

As part of the efforts to unify the various branches of Irreversible Thermodynamics, the proposed work reconsiders the approach of the Carnot engine taking into account the finite physical dimensions (heat transfer conductances) and the finite speed of the piston. The models introduce the irreversibility of the engine by two methods involving different constraints. The first method introduces the irreversibility by a so-called irreversibility ratio in the entropy balance applied to the cycle, while in the second method it is emphasized by the entropy generation rate. Various forms of heat transfer laws are analyzed, but most of the results are given for the case of the linear law. Also, individual cases are studied and reported in order to provide a simple analytical form of the results. The engine model developed allowed a formal optimization using the calculus of variations.

Low-temperature combustion has shown the potential to provide solutions for future clean and efficient powertrain systems. Traditional approaches using the first law of thermodynamics have been established for describing energy flows within engine systems and comparing losses between low-temperature and traditional combustion modes. An augmented approach, using the second law of thermodynamics, can be utilized to gain insight into the exergy flows within the system and thus identify areas of irreversibilities and inefficiencies. The present article aims at introducing the required framework for the second law analysis of low-temperature combustion concepts and demonstrating its application to boosted homogeneous charge compression ignition engines. The framework consists of a combination of the first law and second law expressions combined with the University of Michigan homogeneous charge compression ignition combustion model and was applied on a modeled light-duty four-cylinder boosted homogeneous charge compression ignition engine. It was found that combustion irreversibilities in homogeneous charge compression ignition were ∼25% more than traditional spark ignition or diesel engines and increased with dilution. On the other hand, exergy transfer to the walls was reduced with low-temperature combustion. It was also found that the combination of negative valve overlap and turbocharging is not beneficial for high-load operation. Exergy analysis of the exhaust system revealed that turbine useful work was lower than 50% of exergy at the exhaust ports and indicated that boosting performance may be improved by manipulating exergy transfer in the exhaust manifold. Results from the present study are focused on boosted homogeneous charge compression ignition, but the conclusions reached are applicable to other low-temperature combustion concepts as well. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Dimensionless equation that links COP, entropy rate variation and heat exchange. [•] Maximum COP as function of parameter controlling thermal exchanges. [•] Application at irreversible vapor compression refrigerator based on literature data. [•] Results show the analysis is useful in diagnostic and designing of refrigerators. [Copyright &y& Elsevier]

A mathematical model for a closed cylinder with a holed piston was established to investigate the operational characteristics of a gas spring. An ideal gas working fluid and an adiabatic process were assumed in the model. Simulation and experimental results for a typical design and operational condition showed good agreement. The model was then used to investigate the effects of the orifice diameter, the filling pressure, and the velocity of the piston on the applied force and operating pressures of two chambers in the gas spring. The results showed that the orifice diameter and the piston velocity had significant effects on the pressure difference between the two chambers. A 0.05-mm reduction in the orifice diameter led to an approximately two-fold increase in the pressure difference. A 10% increase in the piston velocity resulted in an approximately 25% increase in the pressure difference. The orifice diameter and the piston velocity had a greater effect on the chamber with lower pressure than on the chamber with higher pressure. The force applied to the piston also varied with the piston velocity, the orifice diameter, and the filling pressure due to irreversibilities including the throttling process through the orifice and friction between the wall and the piston. The present model and results are expected to supply useful information about a new gas spring design. [ABSTRACT FROM AUTHOR]

Abstract: An analysis of irreversibilities generated due to combustion in an adiabatic combustor burning wood was conducted. This was done for a reactant mixture varying from a rich to a lean mixture. A non-adiabatic non-premixed combustion model of a numerical code was used to simulate the combustion process where the solid fuel was modelled by using the ultimate analysis data. The entropy generation rates due to the combustion and frictional pressure drop processes were computed to eventually arrive at the irreversibilities generated. It was found that the entropy generation rate due to frictional pressure drop was negligible when compared to that due to combustion. It was also found that a minimum in irreversibilities generated was achieved when the Air–Fuel mass ratio was 4.9, which corresponds to an equivalence ratio of 1.64, which are lower than the respective Air–Fuel mass ratio and equivalence ratio for complete combustion with theoretical amount of air of 8.02 and 1. [Copyright &y& Elsevier]