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1.
利用流体力学计算软件F luen t建立平板式阳极支撑固体氧化物燃料电池(SOFC)的三维数学模型。在阳极与阴极多孔电极中使用尘气模型模拟气体质量传输并采用B rinkm an-Forschhe im er-D acy模型来模拟多孔电极中黏性与惯性效应对气体流动的影响。研究给出了燃料气与空气在同向流与反向流情况下组分浓度、电压与温度分布。结果显示在同向流情况下,电池的最大功率密度较大与温度分布较均匀合理。研究给出了多孔电极结构参数(孔隙率、曲折因子与孔径尺寸)对电池性能的影响。结果表明比较计算的极化性能与文献的实验数据两者较好的吻合。  相似文献   

2.
基础理论的创新与计算机性能的大幅度提升为高精度与多尺度的计算模拟提供了可能,这些方法也在锂离子电池的研究中得到了广泛的应用。本文介绍了第一性原理、密度泛函理论、分子动力学、蒙特卡罗、相场模拟、分子力场、有限元等不同时间与空间尺度上的模拟方法的基本原理,并探讨了这些方法在锂离子电池基础研究中的应用,如计算电池电压、电极材料的电子结构、能带结构、迁移路径、缺陷生成能、离子在材料体相及不同微观结构中的输运、材料中温度场分布、应力场分布等。  相似文献   

3.
基础理论的创新与计算机性能的大幅度提升为高精度与多尺度的计算模拟提供了可能,这些方法也在锂离子电池的研究中得到了广泛的应用。本文介绍了第一性原理、密度泛函理论、分子动力学、蒙特卡罗、相场模拟、分子力场、有限元等不同时间与空间尺度上的模拟方法的基本原理,并探讨了这些方法在锂离子电池基础研究中的应用,如计算电池电压、电极材料的电子结构、能带结构、迁移路径、缺陷生成能、离子在材料体相及不同微观结构中的输运、材料中温度场分布、应力场分布等。  相似文献   

4.
利用综合传热性能实验台,研究对比旋向自交叉转子、同向转子的换热器和光管的传热性能。结果发现:通过Webb性能比较方法,在同样面积和同等泵功率情况下,同向转子比光管换热器的换热量最大可提高为6.99%,而旋向自交叉转子比光管的换热量最大可提高8.11%,并计算推导了旋向自交叉转子与同向转子、光管之间的准则关联式;同时研究了换热量与转子外径的关系,结果发现换热量随转子外径变大而增多。  相似文献   

5.
为深入研究质子交换膜燃料电池内电荷传递的规律,发展了一个三维的单相流、非等温数学模型,模型考虑了电子在催化层和扩散层、质子在催化层和质子交换膜中的传递。通过计算得到了电池内电位和电流密度的空间分布,分析了不同电极结构参数下电流密度的分布和最终造成的性能差异。结果表明,欧姆电位的下降主要发生在膜相电位,而碳相电位的下降几乎可以忽略不计;电流密度在流道与集电极交界处出现"火焰形"累积效应;改变电池的结构对电池性能影响不大,应结合加工成本和电流密度分布综合考虑。  相似文献   

6.
建立了直接甲醇燃料电池垂直流道方向电池单元的二维稳态数学模型,考虑了电化学动力学、多组分传递和甲醇渗透影响.计算了流道布置密度、扩散层、催化层和质子交换膜等组件尺度对电池内物料传质特性、化学反应组织和电池输出性能的影响.研究发现,增加流道布置密度、增加催化层厚度能有效提高电极反应均匀性和电池性能.其中催化层和质子膜的厚度影响最为显著,在该文研究范围内分别可提高电池的平均电流密度131.0%和17.8%.而扩散层和质子交换膜厚度都存在一个最佳值,需要与以上流场板设计尺寸和膜电极尺寸匹配.  相似文献   

7.
电池在充放电过程中内部温度的分布特征对于锂离子电池热管理系统的设计十分重要。根据电池的物理结构,将圆柱型电池内部平均分成若干等温层,建立了电池沿径向的产热和传热模型,将测试获得的电池表面温度和热流密度作为边界条件,假设热量从中心向外传递过程中等温层之间的热流密度线性增加,提出了一种计算电池沿径向内部温度分布的方法,并在电池内部中心放置热电偶,验证了该方法的准确性。计算结果表明,电池内部温度并非线性分布,在靠近电池中心位置处相邻等温层之间的温度梯度较小,而在靠近电池表面区域附近相邻等温层之间的温度梯度较大。该计算方法在20~40 ℃环境温度区间内具有较高的精度,而在−10 ℃环境温度下误差会偏大些。  相似文献   

8.
通过建立海底电缆芯线、护层及铠装的电流分布方程,分析了正常运行情况下,接地方式、接地电阻、铠装材质对护层、铠装的返流效果的影响。计算结果表明,海底电力电缆的返流性能与其两端的接地状态密切相关。在平行距离较近、长度较长的情况下,海底电力电缆对临近信号电缆的磁感应影响不可忽略。  相似文献   

9.
在三维、两相、非等温模型的基础上,分析了阴极参考体积交换电流密度和阴极传递系数对电池内传递过程(包括气体传递特性、局部电流密度及膜中水传递)的影响。分析结果表明,随着阴极参考体积交换电流密度和阴极传递系数的增加,电池性能不断提高;低电压时,阴极参考体积交换电流密度或阴极传递系数的增加,均可改善电池的气体传递特性及局部电流密度分布。阴极参考体积交换电流密度或阴极传递系数的增加,使膜中含水量的分布不再均匀。  相似文献   

10.
建立了一个具有蛇形通道,采用Nafion117膜单体质子交换膜燃料电池的三维数学模型,该模型同时考虑了流动、传热、传质、电化学动力学和多组分传输现象。通过求解传输方程组,并耦合电化学动力学方程,获得了电池的极化性能曲线和电池内部的反应物浓度、温度、速度分布。计算结果表明,增加电极孔隙率、提高电池运行温度和压力有助于改善电池性能。估算的极化性能与献中的实验数据基本符合。分析了运行条件对电池性能的影响。  相似文献   

11.
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.  相似文献   

12.
13.
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%.  相似文献   

14.
Performance assessment of some ice TES systems   总被引:1,自引:0,他引:1  
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.  相似文献   

15.
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.  相似文献   

16.
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.  相似文献   

17.
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 (NOx) 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 NOx emissions. High NOx 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 NOx 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.  相似文献   

18.
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.  相似文献   

19.
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.  相似文献   

20.
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. σred = σ1 β + (1 − β)σi, where: σ1-maximal principal stress, σi-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.  相似文献   

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