发动机冷却水套设计及改进

针对某发动机设计了冷却水套并运用三维数值仿真技术对该水套冷却性能进行仿真分析发现,缸盖排气侧高温区的流场分布极不均匀,冷却液未能实现对缸体的完全绕流冷却,缸体水套存在局部低流速区。进一步分析发现,分水孔对流场分布具有很大的影响,并据此修改分水孔方案。仿真结果表明:改进方案缸盖高温区流场分布比较均匀,冷却液也实现了对缸体的完全绕流冷却,消除了原水套中的低流速区,高温区局部平均流速1.7 m/s,传热系数12 000 W/(m~2·K),水套平均流速大于0.5 m/s,冷却性能得到了改善。最后分析了金属纳米流体的强化换热效果,结果表明:浓度5%的铜水纳米流体局部传热系数比纯水提高了41%,效果明显的同时所需泵功也有所增加。     

六缸柴油机冷却系统流动与传热的数值模拟研究

冷却水的流动与传热直接影响柴油机的冷却效率、高温零件的热负荷、整机的热量分配和能量利用。在冷却系统传热计算时，利用流固耦合的方法，较为准确地确定了缸体水套的传热边界条件。采用CFD商用软件STAR—CD对直列六缸柴油机的冷却系统的流动与传热进行三维数值模拟，给出了整机冷却水套内冷却液的流场、换热系数及压力场分布，为柴油机冷却水腔的优化设计提供了理论依据。     

车用柴油机冷却水套的CFD分析与优化

利用三维造型软件Pro／E对某一六缸柴油机冷却水套建立模型,并用CFD软件Fluent进行模拟计算,得到整机冷却水套内冷却液速度分布、压力损失以及各缸流量分布等信息。分析结果表明：缸盖水套虽满足设计要求,但缸体水套存在冷却不足、均匀性差的缺陷。改进方案的模拟分析表明,改进后缸体水套冷却更为均匀,流动性能比原机水套有明显的改善。     

某汽油机冷却水套三维CFD分析

鉴于冷却水的流动与传热会直接影响发动机的冷却效率,高温零件的热负荷,整机的热量分配和能量利用,使用计算流体力学(CFD)软件对某汽油机冷却水套进行三维CFD分析,得到了冷却水套内冷却液的流场、换热系数分布、压力损失以及流量分布等信息,计算结果表明:该机冷却水套中流速和换热系数均能满足设计要求;气缸盖3缸冷却效果好于其它两缸。     

氧化铝纳米冷却液对发动机冷却性能影响的分析

利用AVL-Fire软件对氧化铝纳米冷却液在内燃机水套上的冷却性能进行模拟计算。研究结果表明:当Al_2O_3纳米粒子的浓度为2%时,冷却液的传热系数达到最大值,之后随着浓度的增加而减小;氧化铝纳米冷却液具有极高的沸点,其冷却性能随冷却液的温度升高而增加,并在90℃后急速提升,故氧化铝纳米冷却液适用于高温冷却。此外,纳米冷却液的传热系数在低温下比较低,有利于发动机起动时的暖机作业。     

基于CFD的柴油机冷却水套性能仿真分析优化

为保证柴油机可靠性和耐久性,必须进行有效冷却.冷却水套作为传热过程中的重要结构,直接影响柴油机的冷却效率和高温零部件的热负荷.本文对某四缸柴油机冷却水套进行了计算流体动力学(Computational Fluid Dynamics,CFD)数值模拟,分析了缸体和缸盖的关键区域流场状况,针对冷却液流速偏低的区域进行了优化...     

4102型柴油机冷却水套CFD分析

发动机冷却水套的CFD分析是目前发动机缸体开发有效计算分析手段,具有开发准确性高、速度快的特点。在设计开发过程中,可以先不用制造实体样机,而是先通过CFD分析,进行缸盖水套的优化。尤其是在处理发动机热负荷较高的燃烧室及排气道周围有良好的冷却液流动。尤其在设计开发过程中,在没有样机水流试验数据的条件下,手段为发动机结构设计提供了强大的技术支持。本文利用CFD分析设计4102型柴油机发动机冷却水套,成功分析并优化了发动机缸盖的水套结构,保证在发动机热负荷,而压力损失相对较低。确定出了流动性较好且压降低的水套,确保了发动机有良好的机内冷却。     

基于CFD的船用柴油机缸体水套设计

利用数值模拟对6170型船用柴油机的冷却水套进行了冷却性能研究,优化设计了缸体冷却水套.对原机缸体冷却水套内冷却水的流场分布、冷却水套内壁面换热系数、各缸冷却均匀性和压力损失进行了分析.计算结果表明：原机缸体水套上部存在冷却强度不足、冷却均匀性差的缺陷,不能满足缸套冷却要求.通过计算提出了提高缸体上部冷却强度及改善冷却均匀性的优化设计方案,从而满足了气缸套的冷却需要,确保了发动机工作的可靠性.     

欧-Ⅲ排放柴油机缸盖冷却水腔流动与传热的数值解析

本文利用CFD和FEM耦合计算的方法,较准确的确定缸盖冷却水腔的热边界条件,对普及型欧-Ⅲ排放柴油机的冷却水腔和缸盖温度场进行了模拟。文章对冷却水腔的整体流动均匀性和整机压力损失进行了分析评估,并对缸盖火力面、喷油器安装孔和排气道周围冷却水腔的冷却情况进行了详细分析。模拟计算结果表明:冷却水腔的流动均匀性和压力损失可以满足使用要求;流经火力面和排气道周围水腔的冷却液流量分配合理;缸盖火力面、喷油器安装孔和排气道周围水腔冷却良好。     

卧式柴油机冷却水流动特性的影响因素研究

针对卧式柴油机强制冷却闭式循环系统水套结构,试验研究了不同工况下水套入口流量及关键点的温度和压力。采用计算流体动力学(CFD)三维模拟的方法建立了冷却水流动仿真模型,并进行了试验验证。设计了冷却水套结构参数正交方案,通过CFD模拟分析了水泵出水流量、公共水腔截面形状和面积、缸体及缸盖入水孔的设置和分布等水套结构参数对冷却水流动的影响关系。研究结果表明:卧式柴油机缸体入水孔截面积和布置对缸体水套冷却水流动、冷却效果和冷却均匀性有很大的影响;卧式柴油机缸盖入水孔的位置、孔数和截面积等结构参数对缸盖水套的冷却水流动、冷却效果、冷却均匀性及进/排气侧的冷却分布等均有很大的影响。     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Contents in Volume 23,2014

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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.     

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.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.