不同工质对太阳能有机朗肯循环系统性能的影响

循环工质的特性是影响有机朗肯循环系统性能的重要因素之一,在不同的蒸发温度条件下,选取R600、R600a、R245fa、R236fa、R236ea、R601、R601a、RC318及R227ea共9种有机工质,基于热力学第一定律和第二定律对其热力循环特性进行了计算分析,并对各有机工质的蒸发压力、热效率、功比和不可逆损失等进行了比较.结果表明：R245fa作为太阳能低温热发电朗肯循环系统的循环工质具有较高的热效率和效率,并且产生的系统总不可逆损失较小,是一种较理想的有机工质;其次,R236fa和R236ea作为系统循环工质也具有较为良好的性能.     

基于遗传算法的有机朗肯循环系统参数优化

在有机朗肯循环系统中,汽轮机进口压力与进口温度是影响系统性能的重要因素.遗传算法在参数优化方面,具有显著的优点,广泛的应用于优化领域,是目前影响较广泛、应用较多、比较成熟的优化算法.本文采用遗传算法,对以R600,R600a,R245fa,R236fa,R236ea,R601,R601a,RC318,R227ea作为循环工质的有机朗肯循环系统进行参数优化,得出在特定的进口压力和进口温度的条件下,系统具有最小的总不可逆损失.     

地热驱动非共沸工质有机闪蒸循环的热性能分析

非共沸工质具有变温相变特性,可有效改善有机闪蒸循环系统与冷源温度匹配差的问题,进而提高系统的循环性能。文章构建了有机闪蒸循环系统模型,其中,循环工质为R245fa/R601a混合物,热源温度为150℃。文章以净输出功率作为目标函数对有机闪蒸循环系统进行优化,研究了R245fa/R601a混合物的组分变化对有机闪蒸循环系统的闪蒸压力、质量流量、净输出功率和热效率的影响,并比较了以非共沸工质与纯工质作为循环工质时,有机闪蒸循环系统的净输出功率。模拟结果表明:当R245fa/R601a混合物的摩尔组分为3∶7时,有机闪蒸循环系统的净输出功率最大,为25.21 kW,与纯工质R245fa和R601a作为循环工质的有机闪蒸循环系统相比,分别增大了4.39%和5.66%,但以非共沸工质作为循环工质的有机闪蒸循环系统的热效率并不一定大于以纯工质作为循环工质;当R601a的摩尔组分为0～0.6时,以非共沸工质作为循环工质的有机闪蒸循环系统的热效率大于以纯工质作为循环工质;当R601a的摩尔组分为0.7～1时,以R245fa作为循环工质的有机闪蒸循环系统的热效率大于以非共沸工质作为循环工质。     

回收低温余热的有机朗肯循环性能分析及优化

选取R113、R114、R141b、R123、R245fa、R245ca、R600、R600a作为回收120~200℃低温余热的有机朗肯循环工质,从净功量、热效率、不可逆损失等方面对有机朗肯循环系统性能进行分析和优化,得出系统最佳运行工况。     

用于高温热泵蒸汽系统的几种工质的循环性能

建立了高温热泵蒸汽系统的热力学模型。在蒸发温度为60℃,冷凝温度为120~140℃的工况下,进行经过初步筛选的4种高温热泵纯工质(R123,R141b,R245ca,R245fa)和传统高温热泵工质(R114)的循环性能对比研究。结果表明:R245fa的综合循环性能良好,单位容积制热量最高,其性能系数(COP)比R114平均高13.65%,压缩比与R114最接近;在符合干压缩要求的前提下,排气温度较低,而且环境友好,可作为高温热泵蒸汽系统的工质。     

应用热力学分析方法与AHP_熵值法对ORC的工质比较及优化

选取4种有机工质R245fa、R123、R600和R141b做为循环工质,采用火用分析方法在烟气入口温度为150℃、出口温度为75℃的条件下,在蒸发温度为80-140℃范围内对4种有机工质的亚临界有机朗肯循环进行分析,发现系统各设备的火用效率、系统总的火用效率、热效率、净输出功随蒸发温度的升高而升高,火用损失随蒸发温度的升高而降低。当蒸发温度达到140℃时,系统各设备的火用效率、系统总的火用效率、热效率、净输出功均达到最大值,而火用损失达到最小值。因此,4种有机工质蒸发温度在80-140℃范围内的最佳蒸发温度都为140℃,且4种工质中R141b的有机朗肯循环系统各设备的火用效率、系统总的火用效率、热效率、净输出功最大,火用损失最少,所以R141b为该系统的最适合工质,R123、R600和R245fa依次次之。以系统总火用损失、热效率、火用效率和净输出功为评价指标,采用层次分析法(The Analytic Hierarchy Process,AHP),通过熵值法确定权重因子,得到R600和R245fa的综合评价指标ξ,发现R600比R245fa更优。     

低温余热有机朗肯循环发电系统工质选择

对有机朗肯循环系统工质的优化选择已逐渐从单一优化目标向多目标发展,但所选的优化目标及优化方法普遍存在主观性较强的问题.针对上述问题,从环保性、安全性等方面对工质进行初选,得到了R123、R245fa、R245ca和R601等9种工质,然后采用主成分分析法对工质的热效率、循环净功和不可逆损失等7个热力性能指标进行了分析计算,得到了两个较为客观的综合评价指标,并在不同蒸发温度下对工质的综合热力性能进行了分析.结果表明:R601做功能力较强,综合效率较高,是该循环系统较为理想的工质.     

太阳能驱动的有机朗肯-喷气增焓（带二次吸气的增效）蒸汽压缩制冷系统性能分析

为有效利用太阳能,以有机朗肯−喷气增焓（带二次吸气的增效）蒸汽压缩式制冷系统为研究对象,建立了系统的热力学模型,分别选取R236fa、R245fa、RC318和R141b作为系统工质,研究了发生温度、凝结温度、冷凝温度、蒸发温度、膨胀机等熵膨胀效率及压缩机等熵压缩效率对系统性能的影响,并以系统性能最佳为目标对工质进行了优选。计算结果表明：对整个系统而言,R141b是最合适的工质,凝结温度和冷凝温度对系统性能有重要影响。以R141b为例,当发生温度在85℃、凝结温度为40℃、冷凝温度为40℃、蒸发温度为 −15℃时,系统COP_s达到0.2528,采用喷气增焓技术对于环境温度很低、太阳能资源丰富的北方地区具有很大的优势。     

利用中低温余热的回热有机朗肯循环性能分析

通过选取R227ea、R600和R141b 3种典型有机干流体作为工质,在热源流体进口温度设定为典型工业锅炉排烟温度423.15 K,冷却水进口温度和环境温度分别设定为283.15 K和293.15 K的条件下,分析蒸发温度、过热度和给水加热器出口处工质温度对回热有机朗肯循环性能的影响,比较回热有机朗肯循环与基本有机朗肯循环的性能。结果表明:随着蒸发温度的增大,循环总不可逆损失减小,循环热效率和第二定律效率增大,而循环输出净功率则先增大后减小;随着过热度的增大,循环总不可逆损失和循环输出净功率均减小,而循环热效率和第二定律效率的变化趋势则因工质而有所不同;随着给水加热器出口处工质温度的增大,循环总不可逆损失和循环输出净功率不断降低,而循环热效率和第二定律效率则先增后减;在相同工况下,回热有机朗肯循环的循环热效率和第二定律效率高于基本有机朗肯循环,但对于循环输出净功率和循环总不可逆损失,结果则相反。     

工质R123和R245fa的有机朗肯循环热力性能

在回收热量一定的条件下,运用热力学第一定律建立了有机朗肯循环热力分析模型,基于蒸发参数法展开了工质R123和R245fa的优选研究。计算结果表明:相同蒸发参数下,工质R123的循环热效率高于工质R245fa;相同蒸发温度下R123具有低压特性,这有利于系统的安全运行。从工质的环保性和热力性能来综合考虑,认为工质R123优于工质R245fa。     

Contents in Volume 23,2014

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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.     

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.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

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.     

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.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

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。     

汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。