煤的燃料(火用)分析

作为重要的一次能源,对煤的燃料(火用)进行分析以确定其最大做功能力,具有重要的理论和现实意义.通过对有关专家研究的总结和分析,认为Rant对燃料(火用)的估算方法既具有科学性,又与实际情况相符.根据电与(火用)的等效性,用发电能力来反映燃料的做功能力,使得基于第二定律的统计更加有效,并能准确揭示其潜力的大小.     

煤的燃料(火用)分析

作为重要的一次能源,对煤的燃料(火用)进行分析以确定其最大做功能力,具有重要的理论和现实意义.通过对有关专家研究的总结和分析,认为Rant对燃料(火用)的估算方法既具有科学性,又与实际情况相符.根据电与(火用)的等效性,用发电能力来反映燃料的做功能力,使得基于第二定律的统计更加有效,并能准确揭示其潜力的大小.     

单相逆流换热器温度分布及(火用)传递特性的研究

借鉴无相变逆流换热器对数平均温度的推导方法,导出了无相变换热器中流体及换热管内、外壁的温度分布,并基于热力学第一、第二定律及非平衡热力学理论,以某高压加热器过热段为例,分别求出了换热过程中蒸汽至管外壁和管内壁至给水的传(火用)系数,从(火用)传递的角度分析了无相变管壳式换热器的换热性能,为优化换热器结构提供了理论参考依据.     

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。     

单耗分析理论与能源利用的效率问题

<正>1引言能源利用的效率问题是一个重要而不容易说清楚的问题。在很多时候,人们喜欢用效率来描述能源利用,但又时常面临着热力学第一定律效率失效或不科学的尴尬境地。众所周知,热力学第二定律是分析能源利用的有力武器,但是由于第二定律和(火用)概念抽象性和复杂     

基于热力学第二定律的余热资源定量分析方法

应用热力学基本原理分析了余热回收的热量和热量(火用)的定量计算问题.基于能源利用的单耗分析理论,推导出基于第二定律的余热利用节煤量的定量计算公式,并对比分析了燃气轮机、水泥窑炉和电厂锅炉烟气余热回收及余热发电的节能特性.结果表明:余热回收的节能量不仅取决于余热的绝对量,还取决于其温度水平,温度水平越低,节能量越小.     

普适传热定律下广义不可逆卡诺制冷循环火用经济最佳性能

应用有限时间热力学理论,以广义不可逆卡诺制冷循环为对象,以(火用)烟经济性能为优化目标,研究了普适传热定律下循环的最佳性能,导出了循环有限时间(火用)经济性能界限以及优化目标之间的最佳关系,并分析了不同传热定律、各种损失和价格比因素对最佳(火用)经济性能的影响.所得结果具有普适性并可以为实际制冷机进行改良提供一种参考.     

电站锅炉(火用)传递描述

能量的传递和转换必然伴随其"质"--(火用)的传递和转换.能量在传递和转换过程中其量守恒,而炯在传递和转换过程中其量不守恒,因此(火用)必有其独特的传递和转换规律.常规(火用)平衡分析综合热力学第一定律和第二定律,以(火用)效率为评价指标,属于静态热力学研究.参照工程(火用)传递评价准则,提出了堋传递系数、(火用)流密...     

加氢裂化装置的流程模拟及用能分析

科学地分析评价炼油过程用能状况是节能工作的基础.以某炼油厂加氢裂化装置为例,利用PRO/Ⅱ软件模拟加氢裂化装置,运用过程系统三环节能量结构理论,依据热力学第一定律和热力学第二定律进行了装置的能量平衡和(火用)平衡计算及分析,并根据分析结果指出了装置的节能方向.     

搅拌液体风力致热装置的热力学分析

依据热力学第一定律和热力学第二定律,对搅拌液体致热装置进行能量分析和火用分析,建立搅拌液体致热装置的能量平衡分析模型和火用平衡分析模型,并分析搅拌液体致热装置各环节的能源利用状况,从而给出提高搅拌液体致热装置的能量效率和火用效率的途径,对搅拌液体致热装置今后的节能设计具有重要的指导作用。     

Exergy analysis of solar assisted double effect absorption refrigeration system

Exergy or the available energy is based on the second law of thermodynamics and goes back to Maxwell and Gibbs. It is the exergy content and not the energy content, that truly represents the potential of the substance to cause change. Exergy is the only rational basis for evaluating the system performance. The aim of this project is to study in detail the exergy variation in the solar assisted absorption system. The influence of the cycle parameters are analysed on the basis of first law and second law effectiveness and the results indicated various ways of improving system performance by better design. Also a better quality of the evaporator has more effect on the system performance than the better quality of other components. It was shown that second law analysis quantitatively visualizes losses within a system and gives clear trends for optimization.     

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.     

Energy and exergy analyses in convective drying process of multi-layered porous packed bed

This paper is concerned with the investigation of the energy and exergy analyses in convective drying process of multi-layered porous media. The drying experiments were conducted to find the effects of multi-layered porous particle size and thermodynamics conditions on energy and exergy profiles. An energy analysis was performed to estimate the energy utilization by applying the first law of thermodynamics. An exergy analysis was performed to determine the exergy inlet, exergy outlet, exergy losses during the drying process by applying the second law of thermodynamics. The results show that the energy utilization ratio (EUR) and the exergy efficiency depend on the particle size as well as the hydrodynamic properties and the layered structure, by considering the interference between capillary flow and vapor diffusion in the multi-layered packed bed.     

Experimental study on heat and exergy balance of a dual-fuel combined injection engine with hydrogen and gasoline

In this paper, a dual-fuel engine test rig with gasoline injected in the intake port and gasoline (or hydrogen) injected directly into the cylinder is built up; therefore, two injection models are realized. One is port fuel injection + gasoline direct injection (PFI + GDI), the other is port fuel injection + hydrogen direct injection (PFI + HDI). And the effects of two injection models on heat and exergy balance are investigated experimentally. The results show that, from the perspective of the first law of thermodynamics (heat balance), no matter what the injection mode is, the heat proportion of cooling water is the largest, the exhaust heat ratio and brake power are the second, which two are roughly equivalent, and the uncounted loss is the least. In PFI + GDI mode, the local mixture is too dense due to the increase of mixing ratio, which leads to insufficient combustion and a slight decrease of brake power ratio. However, due to the special characteristics of hydrogen, the increase of direct injection ratio improves the brake power ratio in PFI + HDI mode. Moreover, because of the short quenching distance of hydrogen, the cooling loss rises up with the increase of hydrogen ratio. The engine speed and load also have great impacts on heat distribution, but on account of the different physical and chemical properties between gasoline and hydrogen, resulting in varying degrees of impact and trends. On the basis of the second law of thermodynamics (exergy balance), it is found that no matter what injection mode is, the ratio of exergy destruction is always the highest, accounting for half of the total fuel energy, and the exhaust exergy ratio is lower than the brake power ratio. However, the proportion of exergy contained in cooling water is the smallest, which is quite different from the result of the first law of thermodynamics. The influences of several factors on engine energy balance are analyzed, and the differences and similarities between heat balance and exergy balance are compared. The two analytical methods are interrelated and complementary, and the purpose is to find a reasonable and comprehensive energy balance analysis method for internal combustion engine.     

Thermodynamical analysis of human thermal comfort

Traditional methods of human thermal comfort analysis are based on the first law of thermodynamics. These methods use an energy balance of the human body to determine heat transfer between the body and its environment. By contrast, the second law of thermodynamics introduces the useful concept of exergy. It enables the determination of the exergy consumption within the human body dependent on human and environmental factors. Human body exergy consumption varies with the combination of environmental (room) conditions. This process is related to human thermal comfort in connection with temperature, heat, and mass transfer. In this paper a thermodynamic analysis of human heat and mass transfer based on the 2nd law of thermodynamics in presented. It is shown that the human body's exergy consumption in relation to selected human parameters exhibits a minimal value at certain combinations of environmental parameters. The expected thermal sensation also shows that there is a correlation between exergy consumption and thermal sensation. Thus, our analysis represents an improvement in human thermal modelling and gives more information about the environmental impact on expected human thermal sensation.     

Energy and exergy analyses of drying of red pepper slices in a convective type dryer

In this paper, the energy and exergy analyses of the drying process of thin layer of red pepper slices are investigated. Drying experiments were conducted at inlet temperatures of drying air of 55, 60 and 70 °C and at a drying air velocity of 1.5 m/s in a convective type dryer. Using the first law of thermodynamics, energy analysis was carried to estimate the ratios of energy utilization. However, exergy analysis was accomplished to determine type and magnitude of exergy losses during process by applying the second law of thermodynamics.     

Comparison of the theoretical performance potential of fuel cells and heat engines

Fuel cells have decided advantages including compatibility with renewable fuels such as hydrogen, methanol and methane. It is often claimed that they have greater potential for efficient operation than heat engines because they are not restricted by the Carnot limitation. However, in this paper a generalized (exergy analysis) approach is utilized to clarify the comparison of the theoretical performance potential of heat engines and fuel cells, in particular, to show that fuel cell conversion is restricted by the second law of thermodynamics in the same way as heat engines. The Carnot efficiency is simply a manifestation of the second law for the heat engine excluding the combustion process. It is shown that the maximum work obtainable from the conversion device is related to the change in flow exergy between reactants and products, that is in general, not equivalent to the change in Gibbs free energy. For equivalent reactant and product temperatures, the difference between the change in Gibbs free energy and the change in flow exergy is equal to the exergy flux of heat transfer that must be rejected by the device due to absorption of entropy from the reactant-product flow. The importance of exergetic (second-law) efficiencies for evaluating performance is demonstrated. Also, exergy analysis is utilized to resolve a number of efficiency related issues for endothermic reactions.     

燃气轮机与混合装置的(火用)性能比较

燃气轮机中的燃烧反应是一种高度不可逆的过程,因此效率较低。燃气轮机-燃料电池混合装置则由于绝大部分燃料通过电化学反应来释放能量,只有未完全利用的燃料参加燃烧反应。用热力学第一定律和热力学第二定律对燃气轮机和它与燃料电池构成的混合装置进行了比较分析,研究了循环的效率和各部件的性能对整个系统的影响,给出了混合装置中对提高系统性能具有重要影响的部件。图4表2参8。     

Comparative exergy analyses of gasoline and hydrogen fuelled ICEs

Comparative exergy models for naturally aspirated gasoline and hydrogen fuelled spark ignition internal combustion engines were developed according to the second law of thermodynamics. A thorough analysis of heat transfer, work, thermo mechanical, and chemical exergy functions was made. An irreversibility function was developed as a function of entropy generation and graphed. A second law analysis yielded a fractional exergy distribution as a percentage of chemical exergy of the intake. It was found that the hydrogen fuelled engine had a greater proportion of its chemical exergy converted into work exergy, indicating a second law efficiency of 41.37% as opposed to 35.74% for a gasoline fuelled engine due to significantly lower irreversibilities and lower specific fuel consumption associated with a hydrogen fuelled ICE. The greater exergy due to heat transfer or thermal availability associated with the hydrogen fuelled engine occurs due to a greater amount of convective heat transfer associated with hydrogen combustion. However, this seemingly high available thermal energy or thermal ‘exergy’ is misleading due to the higher cooling load which decreases the power of a hydrogen fuelled ICE. Finally, a second law analysis of both hydrogen and gasoline combustion reactions indicate a greater combustion irreversibility associated with gasoline combustion. A percentage breakdown of the combustion irreversibilities were also constructed according to information found in literature searches.