Exergy analysis for greener gas turbine engine arrangements

Exergy analysis is a method that uses the conservation of mass and conservation of energy principles together with the second law of thermodynamics for the analysis, design, and improvement of energy and other systems. The exergy method is a useful tool for furthering the goal of more efficient energy-resource use, for it enables the locations, types, and magnitudes of wastes and losses to be identified and meaningful efficiencies to be determined. The exergy analysis of two-shaft gas turbine arrangements is presented and discussed in this paper. Two configurations (in parallel and series free turbine) are presented here and analyzed separately to identify and quantify the energy and exergy losses. Comparison between the two configurations is presented in terms of work output, efficiency, SFC, exergy destruction, and second-law efficiency for the design conditions. The percentage ratio of the exergy destruction in the individual components to total exergy destruction was found maximum in the combustion chambers (above 90%). The second-law efficiency of series configuration is found to be higher than parallel.     

Exergy Analysis of a Bio-System: Soil–Plant Interaction

This paper explains a thorough exergy analysis of the most important reactions in soil–plant interactions. Soil, which is a prime mover of gases, metals, structural crystals, and electrolytes, constantly resembles an electric field of charge and discharge. The second law of thermodynamics reflects the deterioration of resources through the destruction of exergy. In this study, we developed a new method to assess the exergy of soil and plant formation processes. Depending on the types of soil, one may assess the efficiency and degradation of resources by incorporating or using biomass storage. According to the results of this study, during different processes from the mineralization process to nutrient uptake by the plant, about 62.5% of the input exergy will be destroyed because of the soil solution reactions. Most of the exergy destruction occurs in the biota–atmosphere subsystem, especially in the photosynthesis reaction, due to its low efficiency (about 15%). Humus and protonation reactions, with 14% and 13% exergy destruction, respectively, are the most exergy destroying reactions. Respiratory, weathering, and reverse weathering reactions account for the lowest percentage of exergy destruction and less than one percent of total exergy destruction in the soil system. The total exergy yield of the soil system is estimated at about 37.45%.     

涡流管性能的热力学分析

涡流管是一种新型的能量分离装置,热力学参数和几何参数对其的性能影响很大。该文依据热力学第一、第二定律,建立了涡流管能量分离过程热力学模型,将不可逆过程可用能损失归结为热量火用收益和压力损失两部分,获得了一种基于热力学火用分析的涡流管性能优化新途径。结合不同进气压力、喷嘴数和冷端出口直径的涡流管能量分离性能实验,得到上述诸因素对涡流管能量分离过程中火用变化的影响,通过对能量分离过程中热量火用收益和压力损失的比较,实现了涡流管能量分离性能的优化设计。     

Thermodynamic Irreversibility Analysis of Dual-Skin Chest-Freezer

In this work, a transient analysis of a dual-skin chest-freezer refrigeration system, operating with R290, is studied numerically with the purpose of performing the characterization of the system through the second law of thermodynamics. A mathematical model which accounts for refrigerant mass distribution inside the system is used. In addition, this work addresses the calculation of entropy generation and exergy destruction for characterizing the system performance during its operations. In order to validate the model, a comparison with measured experimental data is performed for both pull-down and on-off operations. The characterization of the system through the second law of thermodynamics is conducted using two different methods. One consists of a direct calculation of the entropy generation rate and the second one in the calculation of exergy destruction rate. The equivalence of these two methods is used as an indicative of the “correctness” of the performed calculations. The model results agree near 97% with the experimental data used in the comparisons. Entropy generation and exergy destruction results along time for the whole system and in its individual components are characterized with the second law. These results are very useful for improving refrigeration system design.     

Numerical Investigation of Exergy Loss of Ammonia Addition in Hydrocarbon Diffusion Flames

In this paper, a theoretical numerical analysis of the thermodynamics second law in ammonia/ethylene counter-flow diffusion flames is carried out. The combustion process, which includes heat and mass transfer, as well as a chemical reaction, is simulated based on a detailed chemical reaction model. Entropy generation and exergy loss due to various reasons in ammonia/ethylene and argon/ethylene flames are calculated. The effects of ammonia addition on the thermodynamics efficiency of combustion are investigated. Based on thermodynamics analysis, a parameter, the lowest emission of pollutant (LEP), is proposed to establish a relationship between the available work and pollutant emissions produced during the combustion process. Chemical reaction paths are also analyzed by combining the chemical entropy generation, and some important chemical reactions and substances are identified. The numerical results reveal that ammonia addition has a significant enhancement on heat transfer and chemical reaction in the flames, and the total exergy loss rate increases slightly at first and then decreases with an increase in ammonia concentration. Considering the factors of thermodynamic efficiency, the emissions of CO₂ and NOx reach a maximum when ammonia concentration is near 10% and 30%, respectively. In terms of the chemical reaction path analysis, ammonia pyrolysis and nitrogen production increase significantly, while ethylene pyrolysis and carbon monoxide production decrease when ammonia is added to hydrocarbon diffusion flames.     

单耗分析理论与结构系数法的对比分析

本文简要阐述了结构系数法和能源利用的单耗分析理论,并针对链式系统进行了初步的对比分析;尽管都是基于热力学第二定律的分析方法,并且它们的结果有一定的相似性,但结构系数法存在某些错误。比较而言,单耗分析理论显得更全面,也更实用。本文以锅炉供热系统为对象进行了详细的单耗分析,对系统中间子系统的(火用)耗损变化所带来的影响进行了详细的分析,结果证明结构系数法所作的“某一子系统(火用)效率变化,其他子系统(火用)效率不变”的假设是不恰当的, 其结论也是不准确的。     

两级中冷回热再热布雷顿热电联产装置的性能

应用有限时间热力学理论和方法建立了恒温热源不可逆两级中冷回热再热布雷顿热电联产装置模型,基于分析的观点,导出了装置无量纲输出率和效率的解析式。在给定总压比的情形下,通过数值计算分别研究了输出率和效率与两个中冷压比和两个再热压比的关系,当总压比变化时,发现输出率和效率对总压比存在最大值,并分别求出了两个相应的最佳的中冷压比和再热压比。分析了回热度、中冷度、再热度、压气机和涡轮机效率、压降损失等特征参数对装置性能的影响。最后发现分别存在最佳的用户侧温度使输出率和效率取得双重最大值。     

Energy,Exergy, Exergoeconomic and Exergoenvironmental Impact Analyses and Optimization of Various Geothermal Power Cycle Configurations

Energy, exergy, and exergoeconomic evaluations of various geothermal configurations are reported. The main operational and economic parameters of the cycles are evaluated and compared. Multi-objective optimization of the cycles is conducted using the artificial bee colony algorithm. A sensitivity assessment is carried out on the effect of production well temperature variation on system performance from energy and economic perspectives. The results show that the flash-binary cycle has the highest thermal and exergy efficiencies, at 15.6% and 64.3%, respectively. The highest generated power cost and pay-back period are attributable to the simple organic Rankine cycle (ORC). Raising the well-temperature can increase the exergy destruction rate in all configurations. However, the electricity cost and pay-back period decrease. Based on the results, in all cases, the exergoenvironmental impact improvement factor decreases, and the temperature rises. The exergy destruction ratio and efficiency of all components for each configuration are calculated and compared. It is found that, at the optimum state, the exergy efficiencies of the simple organic Rankine cycle, single flash, double flash, and flash-binary cycles respectively are 14.7%, 14.4%, 12.6%, and 14.1% higher than their relevant base cases, while the pay-back periods are 10.6%, 1.5% 1.4%, and 0.6% lower than the base cases.     

Weak cosmic censorship conjecture and thermodynamics in quintessence AdS black hole under charged particle absorption

Considering the cosmological constant as the pressure, this study addresses the laws of thermodynamics and weak cosmic censorship conjecture in the Reissner-Nordstr?m-AdS black hole surrounded by quintessence dark energy under charged particle absorption. The first law of thermodynamics is found to be valid as a particle is absorbed by the black hole. The second law, however, is violated for the extremal and near-extremal black holes, because the entropy of these black hole decrease. Moreover, we find that the extremal black hole does not change its configuration in the extended phase space, implying that the weak cosmic censorship conjecture is valid. Remarkably, the near-extremal black hole can be overcharged beyond the extremal condition under charged particle absorption. Hence, the cosmic censorship conjecture could be violated for the near-extremal black hole in the extended phase space. For comparison, we also discuss the first law, second law, and the weak cosmic censorship conjecture in normal phase space, and find that all of them are valid in this case.     

Quantum heat engine cycle working with a strongly correlated electron system

A new model of a quantum heat engine(QHE) cycle is established,in which the working substance consists of an interacting electrons system.One of our purposes is to test the validity of the second law of thermodynamics by this model,which is more general than the spin-1/2 antiferromagnetic Heisenberg model since it would recover the spin model when the on-site Coulomb interaction U is strong enough.On the basis of quantum mechanics and the first law of thermodynamics,we show no violation of the second law of thermodynamics during the cycle.We further study the performance characteristics of the cycle by investigating in detail the optimal relations of efficiency and dimensionless power output.We find that the efficiency of our engine can be expressed as η = 1 - t22/t12 in the large-U limit,which is valid even for a four sites QHE.     

复合冷凝空调机组的分析

以家用分体式空调作为节能改造对象,将传统单一冷凝改进为复合冷凝,即在压缩机排气管路上串联一个水冷冷凝器,吸收部分冷凝热制备生活热水。并在此基础上建立了分析模型。模拟计算结果表明,复合冷凝空调的目的效率得到了大大的提高,当空调的蒸发温度为0℃、冷凝温度为30℃时,空调目的效率由单一冷凝时的52%上升到70%。     

The Second Law of Thermodynamics in a Quantum Heat Engine Model

The second law of thermodynamics has been proven by many facts in classical world. Is there any new property of it in quantum world? In this paper, we calculate the change of entropy in T.D. Kieu's model for quantum heat engine (QHE) and prove the broad validity of the second law of thermodynamics. It is shown that the entropy of the quantum heat engine neither decreases in a whole cycle, nor decreases in either stage of the cycle. The second law of thermodynamics still holds in this QHE model. Moreover, although the modified quantum heat engine is capable of extracting more work, its efficiency does not improve at all. It is neither beyond the efficiency of T.D. Kieu's initial model, nor greater than the reversible Carnot efficiency.     

Exergy analysis of radial inflow expansion turbines for power recovery

The paper presents an exergy analysis of the performance of a single-stage, radial-inflow expansion turbine. The analysis considers the effect of the design controlling parameters on the power output, and the first law and second law efficiencies of the turbine. The design parameters include: inlet temperature, wheel tip speed, exhaust Mach number and expansion pressure ratio. Limitations imposed by the second law of thermodynamics are presented and discussed, and the admissible ranges of variation of the controlling parameters are outlined and discussed. The analysis enables the process designer to quickly and realistically estimate the amount of power available from the exhaust gases of a process stream, the maximum effective pressure ratio and the temperature drop across the turbine and the exit Mach number.     

Thermal Relativity

The group G of general coordinate transformations on the thermodynamic configuration space E spanned by all the extensive variables keeps the first law of thermodynamics invariant. One can introduce a metric with Lorentzian signature on the space E, with the corresponding line element also being invariant under the action of G. This line element is identified as the square of the proper entropy. Thus the second law of thermodynamics is also formulated invariantly and this lays down the foundation for the principle of thermal relativity.     

Fractional Action Cosmology: Emergent,Logamediate, Intermediate,Power Law Scenarios of the Universe and Generalized Second Law of Thermodynamics

In the framework of Fractional Action Cosmology (FAC), we study the generalized second law of thermodynamics for the Friedmann Universe enclosed by a boundary. We use the four well-known cosmic horizons as boundaries namely, apparent horizon, future event horizon, Hubble horizon and particle horizon. We construct the generalized second law (GSL) using and without using the first law of thermodynamics. To check the validity of GSL, we express the law in the form of four different scale factors namely emergent, logamediate, intermediate and power law. For Hubble, apparent and particle horizons, the GSL holds for emergent and logamediate expansions of the universe when we apply with and without using first law. For intermediate scenario, the GSL is valid for Hubble, apparent, particle horizons when we apply with and without first law. Also for intermediate scenario, the GSL is valid for event horizon when we apply first law but it breaks down without using first law. But for power law expansion, the GSL may be valid for some cases and breaks down otherwise.     

Thermodynamics in Higher Dimensional Vaidya Space-Time

In this work, we have considered the Vaidya spacetime in null radiating fluid with perfect fluid in higher dimension and have found the solution for barotropic fluid. We have shown that the Einstein’s field equations can be obtained from Unified first law i.e., field equations and unified first law are equivalent. The first law of thermodynamics has also been constructed by Unified first law. From this, the variation of entropy function has been derived on the horizon. The variation of entropy function inside the horizon has been derived using Gibb’s law of thermodynamics. So the total variation of entropy function has been constructed at apparent and event horizons both. If we do not assume the first law, then the entropy on the both horizons can be considered by area law and the variation of total entropy has been found at both the horizons. Also the validity of generalized second law (GSL) of thermodynamics has been examined at both apparent and event horizons by using the first law and the area law separately. When we use first law of thermodynamics and Bekenstein-Hawking area law of thermodynamics, the GSL for apparent horizon in any dimensions are satisfied, but the GSL for event horizon can not be satisfied in any dimensions.     

A New Perspective on Cooking Stove Loss Coefficient Assessment by Means of the Second Law Analysis

The chimney effect taking place in biomass cooking stoves results from a conversion process between thermal and mechanical energy. The efficiency of this conversion is assessed with the stove loss coefficient. The derivation of this quantity in cooking stove modelling is still uncertain. Following fluid mechanics, this loss coefficient refers to an overall pressure drop through stove geometry by performing an energy balance according to the first law of thermodynamics. From this approach, heat-transfer processes are quite ignored yet they are important sources of irreversibilities. The present work takes a fresh look at stove loss coefficient assessment relying on the second law of thermodynamics. The purpose in this paper is to identify the influence of operating firepower level on flow dynamics in biomass natural convection-driven cooking stoves. To achieve that, a simplified analytical model of the entropy-generation rate in the flow field is developed. To validate the model, experiments are conducted first on a woodburning stove without cooking pot to better isolate physical processes governing the intrinsic behaviour of the stove. Then, for the practical case of a stove operating with a cooking pot in place, data from published literature have served for validation. In particular, mass-flow rate and flue gas temperature at different firepower levels have been monitored. It turns out that losses due to viscous dissipations are negligible compared to the global process dissipation. Exergy analysis reveals that the loss coefficient should rather be regarded from now as the availability to generate flow work primarily associated with the heat-transfer Carnot factor. In addition, the energy flux applied as flow work has to be considered as pure exergy that is lost through consecutive energy-transfer components comprising the convective heat transfer to the cooking pot. Finally, this paper reports a satisfactory agreement that emerged between the exergy Carnot factor and the experimental loss coefficient at different fuel-burning rates.     

An Exergoeconomic Analysis of a Gas-Type Industrial Drying System of Black Tea

The performance evaluation and optimization of an energy conversion system design of an energy intensive drying system applied the method of combining exergy and economy is a theme of global concern. In this study, a gas-type industrial drying system of black tea with a capacity of 100 kg/h is used to investigate the exergetic and economic performance through the exergy and exergoeconomic methodology. The result shows that the drying rate of tea varies from the maximum value of 3.48 g_water/g_{dry matter} h to the minimum 0.18 g_water/g_{dry matter} h. The highest exergy destruction rate is found for the drying chamber (74.92 kW), followed by the combustion chamber (20.42 kW) in the initial drying system, and 51.83 kW and 21.15 kW in the redrying system. Similarly, the highest cost of the exergy destruction rate is found for the drying chamber (18.497 USD/h), followed by the combustion chamber (5.041 USD/h) in the initial drying system, and 12.796 USD/h and 5.222 USD/h in the redrying system. Furthermore, we analyzed the unit exergy rate consumed and the unit exergy cost of water removal in different drying sections of the drying system, and determined the optimal ordering of each component. These results mentioned above indicate that, whether from an energy or economic perspective, the component improvements should prioritize the drying chamber. Accordingly, minimizing exergy destruction and the cost of the exergy destruction rate can be considered as a strategy for improving the performance of energy and economy. Overall, the main results provide a more intuitive judgment for system improvement and optimization, and the exergy and exergoeconomic methodology can be commended as a method for agricultural product industrial drying from the perspective of exergoeconomics.     

Theoretical analysis on the exergy destruction mechanisms and reduction under LTC relevant conditions

Low temperature combustion (LTC) is a potential thermodynamic pathway to maximize the thermal efficiency of internal combustion (IC) engines. However, high exergy loss is also observed within this combustion concept. The present study focuses on the homogeneous combustion process and examines the detailed exergy destruction mechanisms under representative LTC engine conditions. By varying both equivalence ratios (φ) and temperatures (T) at initial pressure of 50?bar, it is found that the decreased total exergy destruction fraction (f_ED) with increasing initial temperature mainly results from the decreased exergy destruction in the high temperature heat release stage, while using rich mixture can significantly reduce the f_ED in the ignition delay stage, which is dominated by the reactions involving large molecules (C7 species). Reaction pathway analysis reveals that the detailed exergy destruction sources are significantly affected by the reaction pathways. Furthermore, a qualitative exergy loss φ-T map was created to illustrate the exergy loss reduction potential. It is concluded that the combustion pathway that reforming the rich fuel/air mixtures before ignition followed by the low temperature combustion of lean reforming products offers the potential to simultaneously reduce exergy destruction and avoid soot and NOx formation. However, the potential advantages of this exergy reduction combustion concept still require further work.