基于热力学第二定律的一次能源折算方法研究

不同的一次能源具有不同的品质和做功能力,在第一定律框架下的基于燃料低位热值的折算标准煤的统计方法存在着理论的缺陷和现实性矛盾。在分析第一定律折算方法的基础上,提出了基于"等价"原则的热力学第二定律的一次能源折算方案,并对理想燃料和典型燃料的折算进行了计算和比较分析。该折算方案有利于揭示能源利用的本质过程,从而实现一次能源统计和核算上"质"和"量"的高度统一,并使得产品能源利用效率的考核和统计具备了现实可能性。     

Numerical analysis reliability control for a double‐pipe heat exchanger with virtual entropy generation method

There are two primary laws including the first and second laws of thermodynamics that should be used to assess a process. Generally, only the first law of thermodynamics is investigated in numerical solutions, so it is possible to exist some numerical results that do not satisfy the second law of thermodynamics because of numerical errors. To achieve reliable numerical outcomes, it is better to apply two indexes of HEAT BALANCE ERROR and VIRTUAL ENTROPY GENERATION, which come from the second law of thermodynamics. In other words, an approach to develop computational fluid dynamics investigations is to take second law of thermodynamics into consideration. In this study, two different models including counterflow double‐pipe heat exchanger and single‐pipe with constant wall temperature are simulated in various cases with different efficiencies and temperature ratios. It is found that 46 cases of total 523 double‐pipe models and 24 cases of total 402 simulations of single‐pipe models had unacceptable results regarding to two mentioned criteria. The results revealed that it is less likely to gain unreliable results in smaller efficiency and lower inlet temperature for double‐pipe heat exchanger and single‐pipe respectively.     

Determination of PAR configuration for PWR containment design: A hydrogen mitigation strategy

This paper deals with determination of the minimum number and identification of the best configurations of passive autocatalytic recombiners (PAR) for the effective design of the containment in a pressurized water reactor (PWR). It considers the current design of PAR in the containment of a PWR and for that tries to identify, through a large number of sensitivity analyses, the minimum required number of PARs in different compartments. In this regard, a qualified nodalization has been developed for best estimate modeling by MELCOR integrated code. The developed model includes primary and secondary systems, containment, and related safety systems. A large number of simulations including the plant specific probabilistic safety assessment and success criteria analysis are used to identify the accident scenario with the highest amount of hydrogen production and risk. We first screened postulated accidents based on the PSA results and then based on the deterministic severe accident computations. It is found that the large break loss of coolant accident (LB-LOCA) without emergency core cooling system (ECCS) actuation is the bounding case from the hydrogen hazard point of view. To find the optimal configuration with minimum number of PARs in the containment, 40 different configurations are analyzed for the selected accident for a Westinghouse type PWR. The main finding of this work is identification of the minimum required number of PARs and their best distribution among the associated compartments. The obtained configuration is equally effective for the hydrogen risk mitigation with 36% reduction in the number of PARs in comparison to the base case design. The methodology of the analysis can be used for other plants.     

燃气机热泵的热力学分析

燃气机热泵是以燃气机作为动力来驱动的压缩式热泵。对燃气机热泵的热力学第一定律、Yong分析和能级平衡理论分析结果表明：其一次能源利用率可达1.76，Yong效率为0.291，能级平衡系数为0.394。与电动热泵等其他供热装置相比，燃气机热泵有着较高的热力学完善性，是一项高效节能技术。由于能级平衡理论分析考虑了Wu的作用，而热泵供暖时其性能系数的提高主要是利用了环境热量，所以建议采用能级平衡理论来分析评价热泵的性能。     

The effects of momentum diffusers and flow guides on the efficiency of stratified hot water seasonal heat stores

Hot water seasonal heat stores (HWSHS) carry the solar thermal energy from energy‐rich seasons of the year over to energy‐poor seasons so as to ensure the availability of solar energy throughout the year. Momentum diffusers and flow guides are designed to charge and discharge the harvested solar thermal energy within HWSHS in a stratified manner to enhance the efficiency of the solar systems. To evaluate the efficiency of an HWSHS, a characterization scheme developed for general stratified thermal energy stores (TES) (Sol Energy 2007; 81 :1043–1054) is used. It addresses the First Law and Second Law concerns over a TES simultaneously. This study is confined to systems that use the same nozzles at fixed positions in both charging and discharging cycles. Different parameters related to axial, conical and radial diffusers as well as a variety of flow‐guide designs are studied. The results suggest that a nozzle that brings about better diffuser action by minimizing entropy generation may not necessarily improve the energy response and guarantee better overall efficiency of the HWSHS. Of all, the different nozzle designs experimented with the conical diffusers with smaller angles of diffusion produced the best overall efficiency. Copyright © 2008 John Wiley & Sons, Ltd.     

不可逆回热布雷顿CCHP装置FTT建模

应用有限时间热力学理论和方法(FTT)建立了闭式不可逆回热布雷顿热电冷联产(CCHP)装置模型,导出了装置无量纲可用能率、火用输出率、利润率、第一定律效率和火用效率的解析式。通过数值计算得到了各个性能指标与压比的关系,优化了压比。分析了设计参数对最优性能的影响,发现回热能够显著增大第一定律效率和火用效率;增大压气机和透平效率、压力恢复系数能够增大5个性能指标,但前者使相应压比增大,后者使相应压比减小;增大热电比能够显著增大可用能率和第一定律效率;分别存在最佳的供热温度使5个最优性能指标取得最大值;提高冷库温度能增大可用能率和第一定律效率,但会降低火用输出率、火用效率和利润率。     

Thermodynamic analysis of reheat cycle steam power plants

In this study, a thermodynamic analysis of a Rankine cycle reheat steam power plant is conducted, in terms of the first law of thermodynamic analysis (i.e. energy analysis) and the second law analysis (i.e. exergy analysis), using a spreadsheet calculation technique. The energy and exergy efficiencies are studied as 120 cases for different system parameters such as boiler temperature, boiler pressure, mass fraction ratio and work output. The temperature and pressure values are selected in the range between 400 and 590°C, and 10 and 15 MPa, being consistent with the actual values. The calculated energy and exergy efficiencies are compared with the actual data and the literature work, and good agreement is found. The possibilities to further improve the plant efficiency and hence reduce the inefficiencies are identified and exploited. The results show how exergy analysis can help to make optimum design decisions in a logical manner. Copyright © 2001 John Wiley & Sons, Ltd.     

Evaluation of a spark ignition engine cycle using first and second law analysis techniques

In the present work, a simulation model of the actual processes occurring during the thermodynamic cycle of a real spark ignition engine is developed. The model incorporates such important features as heat exchange of the cylinder gases with the chamber walls (during all phases), real spark ignition timings, real valve opening and closing timings, accurate simulation of the spherical flame front movement issuing from the spark plug and calculation of eight chemical species concentration during combustion, at every engine degree crank angle. The results from this first law analysis of the real cycle (for example pressure indicator diagrams, efficiencies) are compared favourably with the relevant experimental results obtained from a flexible, variable compression ratio, Ricardo E-6 spark ignition engine, located at the author's laboratory, forming thus a sound basis for moving towards a second law evaluation of this cycle. The thermodynamic state points, determined from the first law analysis, are used to determine the availability (second law analysis) at each engine crank angle and so lead to the effectiveness computation, as well as to the revelation of the magnitude of the work-potential lost during the various processes in a much more realistic way than the first law analysis can. The second law analysis results, for the actual engine in hand, are compared with the up-to-now existing ideal cycle Otto engine results. Also, a second law parametric investigation is performed over a wide range of design and operation conditions (compression ratio, fuel-air ratio, ignition advance), providing useful information for the cycle processes performance assessment by bringing state degradations and thermodynamic losses into perspective.     

Exergetic and performance analyses of two-layered packed bed latent heat thermal energy storage system

In concentrating solar power (CSP) plant, a novel method involving the use of thermocline can be employed to augment the capability of the thermal energy storage system (TES). The rate of thermocline degradation can be reduced by packing encapsulated phase change material (PCM) in the TES. The thermal performance of the packed bed latent heat thermal energy storage system (PBTES) can be further enhanced by employing different diameters of PCM capsules arranged in multiple layers. In this paper, the thermal and exergetic performance of single-layered and two-layered PBTES is evaluated for varying mass flow rate, PCM capsule diameter and bed height of larger PCM capsules using a dynamic model based on simplified energy balance equations for PCM and heat transfer fluid (HTF). The single-layered PBTES has a lower TES latent charging rate than the two-layered PBTES. The charging efficiency and charging time of two-layered PBTES are increased by 15.85% and 16.85%, respectively for reducing the HTF mass flow rate by 14.29%. A higher stratification number can be achieved by using a two-layered PBTES instead of a single-layered PBTES filled with the corresponding larger diameter PCM capsules. The second law efficiency of the two-layered PBTES is found to be less than that of the single-layered PBTES. A decrease in the bed height of larger PCM capsules decreases the exergetic efficiency of the two-layered PBTES by 3.27%. The findings from this study can be used in further designing and optimising the multi-layered PBTES.     

Simulated energy and exergy analyses of the charging of an oil-pebble bed thermal energy storage system for a solar cooker

Energy balance equations are used to model the solar energy capture (SEC) system and the thermal energy storage (TES) system of a proposed indirect solar cooker. An oil-pebble bed is used as the TES material. Energy and exergy analyses are carried out using two different charging methods to predict the performance of the TES system. The first method charges the TES system at a constant flowrate. In the second method, the flowrate is made variable to maintain a constant charging temperature. A Simulink block model is developed to solve the energy balance equations and to perform energy and exergy analyses. Simulation results using the two methods indicate a greater degree of thermal stratification and energy stored when using constant-temperature charging than when using constant-flowrate charging. There are greater initial energy and exergy rates for the constant-flowrate method when the solar radiation is low. Energy efficiencies using both methods are comparable whilst the constant-temperature method results in greater exergy efficiency at higher levels of the solar radiation. Parametric results showing the effect of each charging method on the energy and exergy efficiencies are also presented.     

热虹吸管传热过程中的熵增分析

以热力学理论为基础，对稳定操作条件下的热虹吸管的重要操作参数、工作特点及其内部工质循环过程进行详细分析，导出了由于存在温度差、工质流动摩擦损失、蒸气温度／压力降等因素而引起的熵增的表达式，并由此得到相应的最小熵增优化准则。所得到的热虹吸管重要操作条件，即蒸发段和冷凝段温度匹配关系以及其它重要影响参数的关系，可以为热管实际设计和应用提供重要的理论参考。     

Thermodynamic analysis and utilisation of wet ethanol in homogeneous charge compression ignition engine

In this study, our objective is to computationally analyse the wet ethanol operated homogeneous charge compression ignition (HCCI) engine to evaluate its first and second law efficiency and observe these results by varying effectiveness of regenerator. The paper concludes that the first and second law efficiency decreases due to the increase in the effectiveness of regenerator. This increase in effectiveness leads to an increase in the temperature of air coming out of the regenerator. It further results in increase of the fuel air mixture intake temperature which finally reduces the work output and efficiency of the engine. Furthermore, the method of exergy analysis has been applied and evaluated. This study indicates that due to domination of chemical exergy destruction in combustion reaction in these systems, maximum exergy is destroyed in HCCI engine and to a lesser extent in catalytic converter. These findings will help in the design of such system for optimum result.     

Analysis of total energy system based on solid oxide fuel cell for combined cooling and power applications

A total energy system (TES) incorporating a solid oxide fuel cell (SOFC) and an exhaust gas driven absorption chiller (AC) is presented to provide power, cooling and/or heating simultaneously. The purpose for using the absorption chiller is to recover the exhaust heat from the SOFC exhaust gas for enhancing the energy utilization efficiency of the TES. A steady-state mathematical model is developed to simulate the effects of different operating conditions of SOFC, such as the fuel utilization factor and average current density, on the performance of the TES by using the MATLAB softpackage. Parametric analysis shows that both electrical efficiency and total efficiency of the TES have maximum values with variation of the fuel utilization factor; while the cooling efficiency increases, the electrical efficiency and total efficiency decrease with increase in the current density of SOFC. The simulated results could provide useful knowledge for the design and optimization of the proposed total energy system.     

Energy and exergy analysis of a latent heat storage system with phase change material for a solar collector

Analysis of energy and exergy has been performed for a latent heat storage system with phase change material (PCM) for a flat-plate solar collector. CaCl₂·6H₂O was used as PCM in thermal energy storage (TES) system. The designed collector combines in single unit solar energy collection and storage. PCMs are stored in a storage tank, which is located under the collector. A special heat transfer fluid was used to transfer heat from collector to PCM. Exergy analysis, which is based on the second law of thermodynamics, and energy analysis, which is based on the first law, were applied for evaluation of the system efficiency for charging period. The analyses were performed on 3 days in October. It was observed that the average net energy and exergy efficiencies are 45% and 2.2%, respectively.     

Second law analysis of reverse osmosis desalination plants: An alternative design using pressure retarded osmosis

A second law analysis of a reverse osmosis desalination plant is carried out using reliable seawater exergy formulation instead of a common model in literature that represents seawater as an ideal mixture of liquid water and solid sodium chloride. The analysis is performed using reverse osmosis desalination plant data and compared with results previously published using the ideal mixture model. It is demonstrated that the previous model has serious shortcomings, particularly with regard to calculation of the seawater flow exergy, the minimum work of separation, and the second law efficiency. The most up-to-date thermodynamic properties of seawater, as needed to conduct an exergy analysis, are given as correlations in this paper. From this new analysis, it is found that the studied reverse osmosis desalination plant has very low second law efficiency (<2%) even when using the available energy recovery systems. Therefore, an energy recovery system is proposed using the (PRO) pressure retarded osmotic method. The proposed alternative design has a second law efficiency of 20%, and the input power is reduced by 38% relative to original reverse osmosis system.     

Optimal design of thermal-energy stores for boiler plants

In addition to the existing optimal design method of thermal-energy storage (TES) for industrial boiler plants, 2 new methods are put forward in this paper to achieve energy conservation. The 3 methods are based on minimization of TES capacity, optimization of load assignment, and minimization of the life-cycle cost (LCC) of a boiler plant equipped with TES, respectively. Modeling of the problems is introduced in the paper. A comprehensive computer program is completed, embodying 3 main modules corresponding to the 3 methods. The results of a computation example show that there are obvious differences between the 3 methods. The least initial investment in TES is obtained by the existing method, and the maximum energy saving results from the 2nd method, while the minimum LCC method is the most economic in over the life cycle. The program is useful in obtaining basic data necessary for decision making at the design stages of TES projects.     

The generalized thermodynamic temperature and the new expressions of the first and the second law of thermodynamics

The classical thermodynamics reflects the significant relationship between the heat and the temperature. On the basis of the relationships, according to the mathematical derivation, this paper structures the conceptions of generalized heat, generalized thermodynamic temperature, generalized entropy and so on. The series of conceptions in the classical thermodynamics is merely a special case of the generalized thermodynamics. Based on these conceptions of generalized thermodynamics, this paper presents the new expressions of the first law and the second law of thermodynamics. In other words, these expressions are endued with new explanations. The Eq. LZ = kTS given by this paper provides theoretical basis for these new expressions.     

Energy and exergy analyses in drying process of porous media using hot air

In this paper the energy and exergy analyses in drying process of porous media using hot air was investigated. Drying experiments were conducted to find the effects of particle size and thermodynamics conditions on energy and exergy profiles. An energy analyses was performed to estimate the energy utilization by applying the first law of thermodynamics. An exergy analyses was performed to determine the exergy inlet, exergy outlet, exergy losses and efficiency during the drying process by applying the second law of thermodynamics. The results show that energy utilization ratio (EUR) and exergy efficiency depend on the particle size as well as hydrodynamic properties. Furthermore, the results of energy and exergy presented here can be applied to other porous drying processes which concern effect of porosity as well as grain size.     

Thermodynamic performance assessment of an indirect intercooled reheat regenerative gas turbine cycle with inlet air cooling and evaporative aftercooling of the compressor discharge

This study provides a computational analysis to investigate the effects of cycle pressure ratio, turbine inlet temperature (TIT), and ambient relative humidity (φ) on the thermodynamic performance of an indirect intercooled reheat regenerative gas turbine cycle with indirect evaporative cooling of the inlet air and evaporative aftercooling of the compressor discharge. Combined first and second‐law analysis indicates that the exergy destruction in various components of gas turbine cycles is significantly affected by compressor pressure ratio and turbine inlet temperature, and is not at all affected by ambient relative humidity. It also indicates that the maximum exergy is destroyed in the combustion chamber; which represents over 60% of the total exergy destruction in the overall system. The net work output, first‐law efficiency, and the second‐law efficiency of the cycle significantly varies with the change in the pressure ratio, turbine inlet temperature and ambient relative humidity. Results clearly shows that performance evaluation based on first‐law analysis alone is not adequate, and hence more meaningful evaluation must include second‐law analysis. Decision makers should find the methodology contained in this paper useful in the comparison and selection of gas turbine systems. Copyright © 2006 John Wiley & Sons, Ltd.     

First and second law analyses to an energetic valorization process of biogas

The limitations in the world sources of energy are being mitigated by the exploitation of renewable forms and by increases in the efficiency of energy utilization. Exergy analysis is a useful method for the design, evaluation, and improvement of energy systems, that uses conservation of mass and conservation of energy principles, together with the second law of thermodynamics.This study covers first and second law analyses of a cogeneration system run with the biogas produced in a landfill. Such plant produces useful electrical and thermal energies, while protecting the environment from greenhouse emissions. The objectives were to identify locations where major irreversibilities occur, to evaluate their magnitudes, and to assess the energy and exergy efficiencies of the global system and of its constituent units.The results show that the overall-plant first law efficiency is 37.9% and the exergy efficiency is 36.2%, which is far from the thermodynamic ideal limit. The internal combustion engine and one of the radiators are the most inefficient units, as judged by the parameters degree of thermodynamic perfection and exergy destruction quotient. The main potential for improvement in the plant is the harnessing of the energy in the exhaust gases.