环形进出口旋流燃烧室内有回流的湍流旋流流动的数值模拟

对环形进出口旋流燃烧室内有较强回流的湍流旋流流动进行了数值模拟。计算中分别采用了完整形式与简化形式的新的代数Reynolds应力模型及κ－ε模型。模拟结果与实验测量数据在气体轴向与切向时均速度和轴向、切向与径向湍流脉动速度均方根值分布上的对比表明，新的代数应力模型可预报出旋流燃烧室内范围较大的中心回流区，气体切向速度分布的Rankine涡结构，以及湍流脉动的各向异性。     

旋流燃烧器出口湍流流场的数值模拟

对旋流燃烧器出口的湍流流场进行了深入的数值模拟研究，经过对不同旋流强度的旋转射流的计算，比较了对目前应用较多的k-ε模型、重正化群(RNG)的k-ε模型及雷诺应力模型在实际求解中的优劣。在弱旋气相流动时，RNG k-ε模型可以满足工程上的精度需求。在强旋流动中，基于“有效粘性”的各个模型的计算结果和实验相差很远，只有采用雷诺应力模型才能得到较为满意的结果。图4表3参5     

带钝体的旋流燃烧器出口气相流场数值模拟

应用重整化群k-ε模型和雷诺应力模型,在弱旋和强旋两种状态下,对带钝体的旋流燃烧器进行了冷态气相数值计算,弱旋流动以重整化群k-ε模型计算结果为参考,强旋流动以雷诺应力模型计算结果为参考,对比了燃烧器出口轴向平均速度和切向平均速度变化.模拟结果可以为燃烧器的设计和运行提供依据.     

一种离心力修正的湍流模型及其在数值模拟中的应用

通过分析强旋流场中离心力的作用，提出了考虑湍流脉动中离心力作功的湍流模型(k-ε-cf模型)。模型的特征参数根据大涡参数和小涡参数的几何平均得到，其中旋涡的频率与热线测量实验结果一致。运用k-ε-cf模型对一同轴旋转分层流燃烧器空气动力场进行了数值模拟，计算结果与实验数据吻合良好，比标准k-ε模型结果有较大改进。图4参4     

轴向叶片式旋流煤粉燃烧器出口区域两相流场的数值模拟

采用ｋ－ε－ｋｐ两相湍流模型模拟了轴向叶片式旋流煤粉燃烧器出口区域的冷态两相流场,并将计算结果与ＰＤＰＡ的实验结果作了详细的比较。计算和实验结果都表明该燃烧器能产生较大的回流区,但回流区中大部分区域煤粉浓度较低。ｋ－ε－ｋｐ模型预报的两相速度场、湍流度和煤粉浓度场有的在定量上、也有的在定性上合理。因此ｋ－ε－ｋｐ模型可以满足工程上的需求     

内燃机缸内几种湍流流动涡粘度模型的比较

将几种湍流涡粘度模型 ,即压缩修正的 k-ε模型、RNG- k-ε模型和修正的非线性三方程模型用于计算内燃机缸内的湍流流动 ;对计算结果进行了分析 ,并与实验数据作了对比。结果表明 :RNG- k-ε湍流模型的计算结果较 k-ε模型有所改进 ,而修正的非线性三方程模型则克服了涡粘度模型不能反映平顶活塞压缩上止点处雷诺应力各向异性的缺点 ,在定量和定性上明显优于各种 k-ε模型。     

入口旋流数对煤粉低尘燃烧器流场的影响

以液排渣旋风燃烧过程为基础的煤粉低尘燃烧器可在燃烧过程实现捕渣,为工业加热提供低含尘浓度的高温火焰,是工业加热过程实现以煤代油的先进燃烧技术。根据旋流燃烧流动特点,采用能考虑非均向湍流应力的雷诺应力模型,对旋流煤粉低尘燃烧器内气流流动过程场进行数值模拟计算,计算结果与流场实验测试相吻合。研究表明,气流进入燃烧器时的旋转强度（旋流数）对燃烧器内的流动特性有很大影响,在冷态模型条件下,当旋流数在7以上时,环室回流在轴向贯穿燃烧器整个流场,有利于增加煤粉颗粒在燃烧室内的循环次数,提高灰渣捕获率;低于7时,环室回流出现阻断,不再连续,易造成煤粉颗粒直接逸出,对燃烧及灰渣捕获不利。随旋流数增加,燃烧器出口处中心回流率增大,对炉膛高温烟气的抽吸作用增强。     

有旋燃烧器的数值模拟

采用κ-ε双方程模型模拟计算了冷态燃气在轴对称渐扩燃烧器内的有旋流动状态;分析了不同旋流强度对速度分布、回流区形状大小的影响及旋流强度与出口速度之间的相互关系;预报了有旋流和无旋流下燃烧器内的流场分布;给出了燃烧器出口速度随旋流强度的变化趋势,为燃烧器设计提供理论依据。     

受浮力作用的湍流扩散火焰的数值模拟

应用浮力修正的k-ε模型和EDC湍流燃烧模型对旋流燃烧室内具有较低燃料/空气初始动量的甲烷湍流扩散火焰进行了数值模拟，得到了两组工况下的气体时均速度场、温度场、组分浓度场和湍流脉动速度均方根值分布等．并与实验数据进行了比较，二者基本相符．同时，还将计算结果与标准k-ε模型的模拟结果进行了对比，揭示了浮力对具有较低初始动量的湍流扩散火焰的影响．     

低浓度瓦斯脉动燃烧过程的数值模拟

选取k-ε湍流双方程模型、概率密度方程(PDF)湍流燃烧模型及部分预混燃烧模型,利用流体分析软件Fluent对煤矿低浓度瓦斯在Helmholtz型脉动燃烧器中的燃烧过程进行了数值模拟。通过对燃烧室内低浓度瓦斯脉动燃烧压力场和速度场的分布进行模拟研究,并与理论燃烧过程相比较,其结果表明:低浓度瓦斯脉动燃烧数值模拟结果符合实际脉动燃烧规律,说明脉动燃烧这一燃烧方式适合低浓度瓦斯的研究利用,并为以后的研究提供参考。     

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.     

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.     

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.     

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.     

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.     

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。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.