广义不可逆布雷森循环生态学性能系数分析

以反映热机循环输出和损失之比的生态学性能系数(ECOP)为目标,用有限时间热力学理论,对广义不可逆布雷森循环进行性能分析。导出了在牛顿传热律下广义不可逆布雷森循环无因次功率、效率、无因次熵产率、无因次生态学函数和生态学性能系数的解析式;并通过数值算例得到它们之间的关系。结果表明,内不可逆性对该热机各种性能参数产生一定的影响,以ECOP为目标优化具有效率较高,熵产率较低的优势。     

具有热阻、热漏的不可逆布雷森循环生态学性能新析

以反映热机循环输出火用和火用损失之比的生态学性能系数为目标,用有限时间热力学的方法分析具有热阻、热漏的不可逆布雷森循环性能.导出了在牛顿传热律下布雷森循环无因次功率、效率、无因次熵产率和生态学性能系数的解析式;并通过数值算例得到它们之间的关系.结果表明:对比生态学目标E,循环在最大生态学性能系数ECOP下工作时,其相应的熵产率和热效率有明显优势.     

具有热阻、热漏和回热损失的不可逆斯特林循环生态学性能系数优化分析研究

利用有限时间热力学分析了具有热阻、热漏和回热损失的不可逆斯特林循环生态学经济性能优化ECOP评判标准,推导了不可逆斯特林循环关于功率输出、效率、经济学函数和ECOP优化分析的数学表达式,利用数字分析以及热漏、回热时间和回热器效率研究上述参数之间的相互关系.研究结果表明:在最大ECOP工作条件下工作的斯特林循环比在最大生...     

基于生态学准则对MCFC/AR混合系统的优化分析

基于生态学准则对稳定状态下运行的熔融碳酸盐燃料电池(MCFC)与吸收式制冷机(AR)组成的混合系统进行优化,考虑系统存在的电化学和热力学不可逆性,导出混合系统等效输出功率、效率以及生态学性能系数(ECOP)的表达式。应用数值模拟分析混合系统性能,得到功率密度、效率以及ECOP分别与电流密度的基本关系,从而确定工作参数的优化区间。结果表明:混合系统运行时的输出功率和效率相比于燃料电池单独运行时有所提升,并且通过生态学优化能得到更为精确的优化工作区间。最后分析燃料电池的工作温度、工作压力以及制冷机内部不可逆性对混合系统生态学性能的影响。     

太阳能驱动的联合卡诺热机循环生态学性能研究

用有限时间热力学的理论分析一个由太阳能驱动的具有热阻、热漏、内不可逆性和补燃的定常流联合卡诺型热机循环;研究其在补燃作用下功率、效率和生态学指标的性能,利用不可逆因子表征循环的内不可逆性,并在傅立叶导热定律下对其进行优化;得到功率、效率和生态学指标之间的优化关系。结果表明:以最大生态学指标为目标对模型进行优化,可比以功率为优化目标时获得更高的效率和更小的熵产率。     

太阳能驱动的联合卡诺热机循环生态学性能研究

用有限时间热力学的理论分析一个由太阳能驱动的具有热阻、热漏、内不可逆性和补燃的定常流联合卡诺型热机循环;研究其在补燃作用下功率、效率和生态学指标的性能,利用不可逆因子表征循环的内不可逆性,并在傅立叶导热定律下对其进行优化;得到功率、效率和生态学指标之间的优化关系。结果表明:以最大生态学指标为目标对模型进行优化,可以比以功率为优化目标时获得更高的效率和更小的熵产率。     

广义不可逆卡诺热机的生态学最优性能

以反映热机功率与熵产率之间最佳折衷的“生态学”准则为目标，综合考虑热阻、热漏及其它不可逆性对卡诺热机性能的影响，导出牛顿传热规律下循环的生态学最优性能，由数值计算分析比较了热漏、内不可逆性的影响特点。生态学优化以牺牲小部分输出功率为代价，较大地降低了循环的熵产率，而且在一定程度上提高了热机效率。因此，生态学目标函数不仅反映了输出功率和熵产率之间的最佳折衷，而且反映了输出功率和热效率之间的最佳折衷。     

工质非线性变比热比不可逆Dual-Miller循环生态学目标函数优化

考虑工质非线性变比热比特性,存在气缸传热损失、活塞摩擦损失和其他内不可逆性损失,应用有限时间热力学理论分析和优化空气标准Dual-Miller循环性能,推导出了功率、效率和生态学目标函数等性能参数表达式,并由数值计算得到功率和效率与压缩比、功率与效率、生态学目标函数与功率和效率的特性关系,分析升压比和活塞冲程对各性能指标的影响,并分析比较各种不同优化目标下的性能特点。     

恒温热源不可逆闭式中冷回热燃气轮机循环的生态学优化

考虑循环过程的内外不可逆性,以生态学函数为目标,优化了总压比和中间压比分配,分析了高低温侧换热器、中冷器和回热器的性能参数对最大生态学函数及其参数的影响,并与以功率为优化目标时的循环性能进行了比较.结果表明:以生态学函数为优化目标时比以功率为优化目标时具有更高的效率,但功率相差不太多,反映了输出功率和效率间的最佳匹配.     

燃气-蒸汽联合循环的生态学优化

建立了具有热阻、热漏的定常流布雷顿一朗肯联合循环模型,分析了联合循环功率、效率和生态学指标性能,并对其进行了优化;通过数值计算分析了功率、效率和生态学之间的优化关系,并讨论了热漏对联合循环优化性能的影响.结果表明:最大生态学指标下的效率十分接近联合循环可达到的最大效率,布雷顿一朗肯循环是燃气一蒸汽联合循环的一个特例.分析研究结果为燃气一蒸汽联合循环热机的设计提供了一定的依据.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

Decomposition of limestone in a solar reactor

The thermal decomposition of limestone has been selected as a model reaction for developing and testing an atmospheric open solar reactor. The reactor consists of a cyclone gas/particle separator which has been modified to let the concentrated solar energy enter through a windowless aperture. The reacting particles are directly exposed to the solar irradiation. Experimentation with a 60 kW reactor prototype was conducted at PSI's 90m² parabolic solar concentrator, in a continuous mode of operation. A counter-current flow heat exchanger was employed to preheat the reactants. Eighty five percent degree of calcination was obtained for cement raw material and 15% of the solar input was converted into chemical energy (enthalpy).The technical feasibility of the solar thermal decomposition of limestone was experimentally demonstrated. The use of solar energy as a source for high-temperature process heat offers the potential of reducing significantly the CO₂ emissions from lime producing plants. Such a solar thermochemical process can find application in sunny rural areas for avoiding deforestation.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Biohydrogen production by Anabaena sp. PCC 7120 wild-type and mutants under different conditions: Light, nickel, propane, carbon dioxide and nitrogen

Increasing awareness of environmental problems caused by the current use of fossil fuel-based energy, has led to the search for alternatives. Hydrogen is a good alternative and the cyanobacterium Anabaena sp. PCC 7120 is naturally able to produce molecular hydrogen, photosynthetically from water and light. However, this H₂ is rapidly consumed by the uptake hydrogenase.This study evaluated the hydrogen production of Anabaena sp. PCC 7120 wild-type and mutants: hupL⁻ (deficient in the uptake hydrogenase), hoxH⁻ (deficient in the bidirectional hydrogenase) and hupL⁻/hoxH⁻ (deficient in both hydrogenases) on several experimental conditions, such as gas atmosphere (argon and propane with or without N₂ and/or CO₂ addition), light intensity (54 and 152 ??Em⁻²s⁻¹), light regime (continuous and light/dark cycles 16 h/8 h) and nickel concentrations in the culture medium.In every assay, the hupL⁻ and hupL⁻/hoxH⁻ mutants stood out over wild-type cells and the hoxH⁻ mutant. Nevertheless, the hupL⁻ mutant showed the best hydrogen production except in an argon atmosphere under 16 h light/8 h dark cycles at 54 ??Em⁻²s⁻¹ in the light period, with 1 ??M of NiCl₂ supplementation in the culture medium, and under a propane atmosphere.In all strains, higher light intensity leads to higher hydrogen production and if there is a daily 1% of CO₂ addition in the gas atmosphere, hydrogen production could increase 5.8 times, related to the great increase in heterocysts differentiation (5 times more, approximately), whereas nickel supplementation in the culture medium was not shown to increase hydrogen production. The daily incorporation of 1% of CO₂ plus 1% of N₂ did not affect positively hydrogen production rate.     

Investigation of the thermodynamic and kinetic properties of La–Fe–B system hydrogen-storage alloys

La–Fe–B hydrogen-storage alloys were prepared using a vacuum induction-quenching furnace with a rotating copper wheel. The thermodynamic and kinetic properties of the La–Fe–B hydrogen-storage alloys were investigated in this work. The P–C–I curves of the La–Fe–B alloys were measured over a H₂ pressure range of 10⁻³ MPa to 2.0 MPa at temperatures of 313, 328, 343 and 353 K. The P–C–I curves revealed that the maximum hydrogen-storage capacity of the alloys exceeded 1.23 wt% at a pressure of approximately 1.0 MPa and temperature of 313 K. The standard enthalpy of formation ΔH and standard entropy of formation ΔS for the alloys' hydrides, obtained according to the van't Hoff equation, were consistent with their application as anode materials in alkaline media. The alloys also exhibited good absorption/desorption kinetics at room temperature.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

The Solar Office in context

The goal of sustainability in buildings can only hope to be realised if buildings are designed to both conserve and generate energy. The Solar Office at Doxford International is designed to minimise the use of energy while its external fabric is designed to replace such energy that is used. The recently completed building is now subject of a comprehensive monitoring programme. The programme covers both the performance of the 73 kW_p photovoltaic installation and the environmental conditions within the building as a whole. Hour by hour findings are posted on a dedicated web site. Photovoltaics could have the same impact on building form and layout as the invention of the passenger lift at the end of the last century.     

液压系统常见的故障诊断及处理

任何工程机械式液压设备使用时出现故障是不可避免的。但是怎样确定故障的原因及找到好的解决方法，这是使用者最关心的问题。讲述了液压系统常见的故障及其排除方法。     

Hydrogen recovery from the photovoltaic electroflocculation-flotation process for harvesting Chlorella pyrenoidosa microalgae

In this paper, an integrated process using photovoltaic power to harvest microalgae by electro-flocculation (EF) and hydrogen recovery is presented. It is mainly favorable in regions with high solar radiation. The electro-flocculation efficiency (EFE) of Chlorella pyrenoidosa microalgae was investigated using various types of electrodes (aluminum, iron, zinc, copper and a non-sacrificial electrode of carbon). The best results regarding the EFE, and biomass contamination were achieved with aluminum and carbon electrodes where the electrical energy demand of the process for harvesting 1 kg of algae biomass was 0.28 and 0.34 kWh, respectively, while the energy yield of harvested hydrogen was 0.052 and 0.005 kWh kg^?1, respectively. The highest harvesting efficiency of 95.83 ± 0.87% was obtained with the aluminum electrode.The experimental hydrogen yields obtained were comparable with those calculated from theory. With a low net energy demand, microalgae EF may be a useful and low-cost technology.