Exergy-based ecological optimal performance for a universal endoreversible thermodynamic cycle

Exergy-based ecological optimisation of a universal endoreversible thermodynamic cycle model is performed using finite time thermodynamics or entropy generation minimisation. The cycle consists of two constant thermal-capacity heating branches, a constant thermal-capacity cooling branch and two adiabatic branches. An ecological optimisation criterion is taken as the objective, which consists of maximising a function representing the best compromise between the power output and exergy loss rate of the heat engine. The analytical formulae for power, efficiency and ecological function of the universal endoreversible thermodynamic cycle with heat resistance loss are derived. The comparative performance analyses for Diesel, Otto, Atkinson, Brayton and Dual-cycles are carried out by a detailed numerical example, which show that the ecological criterion is more available.     

Heating load and COP optimisations for a universal steady flow endoreversible heat pump model

The heating load and coefficient of performance (COP) of a class of universal steady flow endoreversible heat pump cycle model, which consists of one heating branch, two cooling branches and two adiabatic branches, are optimised using the theory of finite time thermodynamics. The analytical formulae for heating load and COP versus temperature ratio as well as COP versus heating load of the cycle model are derived. Effects of the total heat exchanger inventory on performances of heat pump cycles are shown by detailed numerical examples. The results obtained herein include the optimal performances of endoreversible Otto, Brayton, Atkinson, Diesel, Dual and Carnot heat pump cycles.     

电压缩式制冷循环与吸收式制冷循环的热力学比较分析

采用效率与损失分析方法,计算比较了电压缩式制冷循环与单效吸收式制冷循环的效率及两种制冷循环在典型工况下各环节的损失。结果表明,当采用合适的发生器温度和热源温度时,两种制冷循环的效率基本相同;电压缩式制冷循环的主要损失发生在压缩机环节,吸收式制冷循环的主要损失发生在吸收器和发生器。讨论了两种制冷循环的改进途径。     

Exergetic performance optimization of an endoreversible intercooled regenerated Brayton cogeneration plant. Part 2: Exergy output rate and exergy efficiency optimization

The exergy output rate and exergy efficiency performances of an endoreversible intercooled regenerative Brayton cogeneration plant are optimized based on the model which is established using finite time thermodynamic in Part 1 of this paper. It is found that the optimal heat conductance allocation of the regenerator is almost zero. When the total pressure ratio and the heat conductance allocation of the regenerator are fixed, it is shown that there exist two optimal intercooling pressure ratios, and two optimal groups of the heat conductance allocations among the hot-, cold- and consumer-side heat exchangers and the intercooler, which correspond to a maximum dimensionless exergy output rate and a maximum exergy efficiency. When the total pressure ratio is variable, there exist two optimal total pressure ratios which correspond to a double-maximum dimensionless exergy output rate and a double-maximum exergy efficiency, also the corresponding exergy efficiency and exergy output rate are obtained. The effects of the total heat exchanger conductance and the consumer-side temperature on the double-maximum dimensionless exergy output rate and the double-maximum exergy efficiency are discussed. It is found that there exists an optimal consumer-side temperature which correspond to a thrice- maximum dimensionless exergy output rate, and the intercooling process is not necessary by taking exergy efficiency as the objective when the consumer-side temperature is high.     

Effect of a complex generalised heat transfer law on the ecological performance of an endoreversible Carnot heat pump

The effect of a complex generalised heat transfer law q ∝ (ΔTⁿ)^m on the ecological performance of an endoreversible Carnot heat pump is derived by taking as the objective function an ecological optimisation criterion representing the best compromise between the exergy output rate and exergy loss rate (entropy production rate) of the heat pump. The results obtained include the optimal ecological performance of an endoreversible heat pump with various heat transfer laws, as obtained in existing literature.     

Comparative thermodynamic analysis of compact cogeneration and triple-effect refrigeration cycles

The ‘compact cogeneration cycle’ and the ‘compact power and triple-effect refrigeration cycle’ have been compared and analysed on the basis of energy and exergy approaches under the same operating conditions. The exergy analysis of both the above cycles leads to a possible performance improvement. The cogeneration cycle has less ‘exergy destruction’ due to irreversibilities in the different components, ‘exergy and energy lost’ to the environment than that of the ‘triple-effect refrigeration cycle’, while the total useful exergy and energy outputs of the cogeneration cycle are greater. The used refrigerants and exhaust gas emissions samples of both cycles are more favourable than the fossil fuel-run engine for reducing the global environment-related problems. The calculation results also show that the associated cycles with the cogeneration cycle have significant higher effect on the exergy and energy efficiencies than that of the ‘compact power and triple-effect refrigeration cycle’.     

Internal irreversibilities’ influence on the new thermo-ecological criterion for real absorption refrigerators

Irreversibility is classified in two main types: internal and external irreversibilities. Internal irreversibility is due to turbulence, pressure gradients, mixing and diffusion processes within the system, which is represented by two irreversibility parameters indicating the deviation from an endoreversible case. This paper studies and analyses the effects of two internal irreversibility parameters (the internal irreversibility parameter for generator–absorber assembly and the internal irreversibility parameter for condenser–evaporator assembly) on the optimal ecological performances of an irreversible four-heat-source absorption refrigerator based on the ecological coefficient of performance (ECOP) criterion. The ECOP objective function is defined as the ratio of the cooling load to the loss rate of availability (or entropy generation rate). The results obtained show that the internal irreversibility parameter for condenser–evaporator assembly affects more the ecological performance of the system than the internal irreversibility parameter for generator–absorber assembly. This is of importance to the optimal design and performance improvement of absorption refrigeration cycles.     

冰蓄冷低温送风空调系统(火用)损因素分析

低温送风空调系统引进新型冰蓄冷设备,采用正丁烷作为制冷剂,制冷剂与水直接接触,换热更强烈且稳定。为了研究该系统相应损因素条件下的节能薄弱环节,实现系统性能优化,基于该系统及各表冷器分析模型,分析了热湿比、新风比、送风温差等损因素对系统效率和各表冷器损率的影响。结果表明：当热湿比变化时,处理二次混风的表冷器损率随之呈正比变化,其他表冷器损率及系统效率随之呈反比变化;当新风比变化时,处理新风的两级表冷器损率随之呈正比变化,其他表冷器损率及系统效率随之呈反比变化;当送风温差变化时,处理一次回风的表冷器损率随之呈正比变化,其他表冷器损率及系统效率随之呈反比变化。     

Comparative performance analysis for endoreversible simple air refrigeration cycles considering ecological,exergetic efficiency and cooling load objectives

On the basis of exergetic analysis, the performance analysis and optimisation of endoreversible simple air refrigeration cycles with constant-temperature heat reservoirs is carried out by using the finite-time thermodynamic method in this paper. The expressions for cooling load, ecological function and exergetic efficiency of the refrigeration cycle are derived. The influences of pressure ratio of the compressor and allocation of heat exchanger inventory on the optimal performance of the cycle are investigated by detailed numerical examples. Performance comparisons between ecological optimisation objective, exergetic efficiency optimisation objective and traditional cooling load optimisation objective are performed. The results may provide guidelines for the design and optimisation of practical refrigeration plants.     

Energy and exergy analysis of compression ignition engine fuelled with rice bran biodiesel blends

The present study aims to investigate a four-stroke single cylinder, water-cooled compression ignition (CI) engine coupled with an eddy current dynamometer. The rice bran oil biodiesel blends of B10, B20, B30 and pure diesel are tested for its performance in the engine. Energy and exergy analysis is carried out for the biodiesel blends and pure diesel. The experimental data were collected using steady-state tests which enable accurate measurements of air, fuel and cooling water flow rates, engine load and all the relevant temperatures. The performance parameters, energy and exergy efficiencies were computed for each fuel operation and compared with each other. The energy and exergy analysis has made to find input availability, brake power availability, cooling water availability and exhaust gas availability. From the exergy analysis, component of major exergy destruction was found. Balances of energy and exergy rates for the engine were also computed.     

燃气吸收式制冷机的最大制冷量及相应的性能系数

利用有限时间热力学理论,建立了工作于有限热源下的燃气吸收式制冷机的四热源模型.运用拉格朗日乘数法,以最大制冷量为优化目标,对该系统进行了优化,得到最大制冷量的一般表达式.同时,也给出了取得该最大制冷量所需的设计条件.所得结果对吸收式制冷机的优化设计及性能提高提供了理论指导.     

间接蒸发冷却方案的比较研究

根据数值模拟计算结果,比较了间接蒸发冷却器(IEC)和回热式间接蒸发冷却器(RIEC)的温度、换热效率火、用效比。结果表明RIEC的火用效比略低于IEC,但能得到更低的温度。这两种方案都有非常显著的节能潜力。     

压缩空气溶液除湿系统分析

为了祛除压缩空气中的水蒸气,采用溶液除湿系统对压缩空气进行干燥。建立了压缩空气溶液除湿系统的分析模型,进行了损率和效率计算。并和国内目前普遍使用的压缩空气冷冻除湿方法、冷冻-吸附除湿方法进行分析比较。结果表明,采用溶液除湿系统对压缩空气进行干燥的效率为62.5%,比常规的冷冻除湿系统57.4%和冷冻-吸附除湿系统57%更节能,具有较大的节能潜力。     

Thermodynamic studies and parametric effects on exergetic performance of a steam power plant

A comprehensive thermodynamic analysis is conducted for an existing 82?MW steam power plant. A detailed assessment on energy loss and exergy destruction for individual components of plants (including boiler sub-parts) is reported. A code is built in EES to evaluate the energy loss, energy efficiency, physical and chemical exergies, exergy efficiency and exergy destruction for each part of plant by considering the real values’ range of operating parameters. Analysis pointed out that the main sources of exergy destruction are boilers followed by the turbines, deaerators and then condensers. In boiler, combustor contributes about 50% in total exergy destruction. The maximum energy loss is reported in boilers followed by condensers, in piping, due to friction and in turbines. The exergy efficiency procured about 42% for boilers, 84% for turbines, 38% for condenser, and 60% for deaerators, respectively. The effects of crucial working parameters on plant performance are analysed.     

蒸发冷却与机械制冷复合空调机组分析

对蒸发冷却与机械制冷复合空调机组进行了(火用)分析,并根据实测数据计算出了机组各功能段进出口(火用)的大小,并通过(火用)效率和(火用)效比分析得出了复合空调机组能量利用效率低的薄弱环节,提出了节能改进方法.     

CO_2套管式气冷器用能效率的热力学第二定律分析

利用1台安装有套管式换热器的跨临界CO_2制冷系统实验台,改变CO_2质量流量、高压侧压力及气冷器冷却水流量,通过实验测得气冷器中CO_2和冷却水沿管长方向的温度分布,并计算气冷器沿管长方向的熵产、火用正文损和火积分布,对气冷器的用能效率进行分析。结果表明,在多种工况下,熵产、火用损和火积耗散均沿管长逐渐降低;熵产和火用损均随CO_2质量流量的增大而降低,而随高压侧压力的升高而增大;质量流量对火积耗散无明显影响。     

天然气低压间歇循环催化改制制气(火用)平衡分析

对天然气低压间歇循环催化改制制气装置及各个子系统的平衡进行了计算,得出了系统火用效率、子系统效率及损失,对计算结果进行了分析。结果表明,天然气低压间歇循环催化改制制气装置具有一定的节能潜力,各子系统的损失相差较大,反应器最大,其次为燃烧室。     

基于产品成本的冷热源优化设计软件

结合火用分析方法和热经济学开发的基于产品火用成本的冷热源优化设计软件,综合考虑了产品火甩成本、系统造价、技术先进性、机房占地面积、系统可靠性、维护管理难易程度、环保性等多种影响因素.软件采用Visual Basic和Access作为开发工具,界面友好、方便易用,可实现对冷热源方案进行优化选择.     

Thermodynamic investigation of an integrated DI diesel engine with waste heat operated rankine cycle

ABSTRACT

A DI Diesel Engine has been integrated with a Rankine Cycle for making a proposed ‘integrated power generation cycle’. The heat of engine’s exhaust gases and jacket’s water is as a single heat source to produce additional output power through the Rankine Cycle. In exergy analysis, destruction of input exergy is nearly 64.13% due to irreversibilities. The useful exergy output is about 30.3%. The exhaust exergy lost to atmosphere is 5.39%, which is smaller than 20.83% of exhaust energy loss of its input, whereas the useful energy output is almost 38.02%. Moreover, there is the reduction in the BSFC due to the recovery of the exergy from the waste heat. The average reduction in the BSFC is about 18.42%. The results of this proposed cycle also show that the integration of the Diesel Engine with the Rankine Cycle has drastic effect on the efficiencies based on exergy and energy.     

Exergetic analysis of closed Brayton thermal power cycle with reheater,regenerator and intercooler

Energy and exergy analysis of a Brayton cycle gas turbine power plant with regenerator, reheater and intercooler is carried out in this work. It has been found that the effects of the regenerator, intercooler and reheater are significant. Although, the energy analysis shows that the first law efficiency is more effective than the second law efficiency and there are significant losses in these components which cannot be neglected, and hence proper care should be taken for the size and operating conditions of these components. Efficiency of some components is 100% especially when energy balance is applied, while it is not 100% in the case of energy consuming/conversion systems like compressor, turbine, etc. The energy loss in reheater is zero while there is a small amount of exergy loss. The intrercooler has both energy and exery losses, so proper care should be taken in intercooler.