流动反转现象影响土壤内流场和温度场研究

为了保持植物内营养成份,使植物快速进入休眠状态,以含水土壤作为研究对象,采用数值计算方法,构造水的物性方程组,建立三维模型,采用有限容积法进行数值求解,分析土壤在不同高温壁面、不同Ra以及不同孔隙率条件下的流动反转现象。研究结果表明:含水土壤在3.98℃时水密度最大;在3.98℃时出现流动反转现象,此时流场和温度场均以中心呈轴对称;流动反转现象不会由于Ra大小的变化而变化,变化的只是流动的剧烈程度;在流动反转现象下,高温壁面的平均努谢尔特数与孔隙率存在非线性关系,其最小值出现在0.65左右。     

浙江省建筑与交通领域节能分析

对浙江省建筑领域和交通领域的能源利用及其效率的现状进行了深入的研究,并在此基础上,分析了浙江省建筑和交通这两大领域的节能潜力,并提出了关于节能措施的建议。     

水分迁移对地下土壤温湿度场分布的影响

建立了考虑水分迁移影响下的一维土壤热湿传递数学模型;计算分析了土壤高温蓄热过程中土壤温湿度场随时间和空间的动态变化规律;揭示了土壤热湿传递中含水率峰值现象及成因;探讨了地下土壤热湿传递特性及水分迁移规律。搭建了一维土壤高温蓄热热湿传递测试实验台,通过实验测试对数学模型进行了验证,实验结果与模拟值吻合得较好。     

电场作用下气泡的行为研究

为进一步揭示EHD强化沸腾换热机理，分析了电场作用下气泡的受力情况，综述了国内外对电场作用下气泡的行为研究成果，系统总结了电场对气泡行为及其动力学特性的影响，并对该领域的进一步研究提出了建议。     

Effect of pulsed magnetic field on superalloy melt

In order to investigate the magnetic force distribution, flow field distribution and Joule heat distribution under the pulsed magnetic field (PMF), transient numerical simulation was carried out. Results show that the magnetic pressure force appears in the inner of the melt, while the magnetic pull force and the magnetic pressure force appear alternately in the exterior of the melt, which is caused by the skin vortex current. The axial direction magnetic force results in the convection of the melt. The radial direction magnetic force produces vibration of the melt. The vibration will diffuse and superpose to produce the pressure wave. Finally, the fluctuation of the melt is caused by the pressure wave. The Joule heat produced by pulsed magnetic field concentrates near the surface of the melt in the pulse applying period.     

Simulation study on magnetic field distribution of PEMFC

As a promising next-generation energy source, proton exchange membrane fuel cell (PEMFC) still suffers from durability and reliability issues, where PEMFC performance will decay during its operation. In this study, a three-dimensional, multi-component and multi-physics PEMFC model is developed to investigate the effect of PEMFC performance degradation on its external magnetic field. By comparing simulation results and experimental data, the capability of the developed model in simulating magnetic field due to PEMFC current is demonstrated. With developed model, different PEMFC degradation mechanisms, including flooding, dehydration, PEMFC aging are simulated, and the amplitudes and distributions of magnetic field under different mechanisms are investigated. Moreover, considering local defects may happen in practical PEMFC systems, its influence on magnetic field distribution is also studied. From the results, the correlation between PEMFC performance degradation and its magnetic field distribution is clarified, which will be beneficial for researches utilizing PEMFC magnetic field for analyzing PEMFC performance variation.     

Nanogap plasmonic field enhancement on hydrogen-absorbing transition metals

The electromagnetic field enhancement factors by gap plasmons between two spherical metal particles are calculated for hydrogen-absorbing transition metals Pd, Ti, and Ni, and reference noble metals Au, Ag, and Cu, in air, H₂, or vacuum, and H₂O. The dependence of the field enhancement factors on the metal species, the field wavelength, the electric field polarization, the separation of the two metal particles, and the observing location is systematically investigated. Field enhancement is observed significantly large in the gap of two metal particles and sensitive to the particle separation, but insensitive to the position in the gap, indicating a geometric flexibility for applications. The spectral peak field enhancement factors for Pd, Ti, and Ni do not compete with those for Au, Ag, and Cu, but do in the microwave regime. For the electric field parallel to the bipartite alignment, the field enhancement factors in the gap for Pd, Ti, and Ni are observed as large as several hundred and ten thousand for the separation-to-radius ratios of 0.1 and 0.01, respectively, for a wide wavelength region spanning from the visible to the infrared. The large field enhancements in the nanogaps of hydrogen-absorbing transition metals observed in this study can potentially be utilized for various energy applications, such as hydrogen storage, sensing, and nuclear fusion. In practical metallic material systems, it is important to account for such a gap-plasmon effect because nanoscale gaps commonly exist, for instance, on rough metal surfaces and in metal particle aggregates.     

Electromagnetic field effects on transport through porous media

The effect of an imposed electromagnetic field on forced convection in porous media is analyzed in this work. The transient Maxwell’s equations are solved to simulate the electromagnetic field inside the waveguide and within a porous medium. The Brinkman–Forchheimer extended Darcy (generalized model) equations are used to represent the flow fluid inside a porous medium. The local thermal non-equilibrium (LTNE) is taken into account by solving the two-energy equation model for fluid and solid phases. Computational domain is represented for a range of Darcy number from 10^?5 to 10^?7 and dimensionless electromagnetic wave power P¹ from 0 to 1600, and dimensionless electromagnetic wave frequency f¹ from 0 to 8. The effect of variations of the pertinent electromagnetic field parameters in affecting the flow and thermal fields and the Nusselt number are analyzed. This investigation provides the essential aspects for a fundamental understanding of forced convection in porous media while experiencing an applied electromagnetic field such as applications in the material-processing field.     

Electric field effects on hydrogen/methane oxidation: A reactive force field based molecular dynamics study

In the study, molecular dynamics simulations associated with reactive force fields are performed to examine the effect of an imposed electric field at different strengths upon the reactive systems of hydrogen/methane mixture oxidation. Temporal evolution results regarding the initial species evidence the distinct alteration of external electric effects to the consumption rates and the reaction-starting time of the reactants in hydrogen/methane oxidation systems. Significantly, hydrogen molecules play contrasting roles under electric and electric-free reactions. The discoveries about the various categories of intermediate radicals and the differences in the temporal progress reveal that the introduction of an electric field to the reactive system modifies the diversities and generation trends of intermediate radicals and alters the reaction rates by affecting the reaction pathways. Different unique species are formed under electric fields of different strength. The current findings prove and support that molecular dynamics simulation associated with reactive force field is a feasible and promising technique for detailed investigation into combustion/oxidation reaction kinetics, involving high temperature and pressure.     

基于翼型帆理论的风场可用区域研究

基于大升力翼型风帆,完成风翼模型的风洞试验,并根据试验结果对该风翼空气动力参数进行了分析。计算和比较不同航速时,风翼辅助推力随绝对风场风向和风速的变化规律。根据船舶试航和营运数据设定各航速下的风翼辅助推力下限值,得出风场的可用区域。最后进行数学建模,提出了使用数学方程描述和求解风场的可用区域的方法。     

A review on why researchers apply external magnetic field on nanofluids

This paper reviewed the application of external magnetic field on nanofluids. So far, nanoparticles have been used in various areas such as manufacturing, electrical and electronics, automotive and recently biomedical applications. On the other hand, nanofluids with suspension of magnetic nanoparticles have attracted noteworthy attention due to its numerous applications in industries and engineering. In line with fast development of this type of nanofluid, the purpose of this paper is to further understand the effect of external magnetic field on nanofluids properties and fluid flow, which is a key issue that influenced both the nanofluid properties and control of fluid flow for application. The conclusions and important summaries were also presented according to the data collected.     

蛇形流场结构质子交换膜燃料电池的性能研究

建立包括催化层、扩散层、质子膜在内的三维质子交换膜燃料电池模型,通过Fluent软件模拟4种不同结构的蛇形流场,通过对速度、膜中水含量以及功率密度等分析得出蛇形流场的最优结构,并对最优结构进行参数优化。研究表明,4种不同蛇形流场结构中,Multi-serpentine II为最优,随着温度、压强的增加,这种流场结构的燃料电池呈现出良好的性能,从而为质子交换膜燃料电池双极板的设计提供依据。     

磁场效应对锂离子电池性能的影响

随着电动汽车行业的迅速发展,锂离子电池的性能对电动汽车的续航里程至关重要.磁场是由运动电荷或电场的变化产生的,当外部磁场作用于物质时,物质内部被磁化,会产生许多微小的磁偶极子.为了深入分析磁场对锂离子电池性能的影响,提出了一种在磁场效应下对锂离子电池进行性能测试的实验方法,在此基础上,搭建了由锂离子电池、电池充放电测试...     

Effect of field discharge resistors on turbine-generator shafttorsional torques

The possibility of reducing the torsional torques of turbine-generator shafts during disturbances by interrupting the generator excitation and switching in a field discharge resistor during the fault duration is discussed. The results of these investigations show that the use of such field discharge resistors reduces the turbine-generator torsional torques after the fault clearance. These results have been obtained through extensive parametric studies and are supported by simulation results     

Enhanced hydrogen sorption on carbonaceous sorbents under electric field

The effect of an applied electric field on hydrogen physisorption isotherm on carbonaceous sorbents was studied. Distinctive sorption enhancement was obtained by applying a positive electrical potential of 2000 V to platinum-supported carbon samples. The phenomenon was ascribed to stronger interactions between hydrogen and the sorbent. Theoretical studies suggested that, the interaction between hydrogen and neutral carbon is primarily the electrostatic attraction between the π-bonds of the aromatic rings and the σ-bonds of H₂, which is classified as van der Waals interaction and is weak. However, the interaction between electrically charged carbon and hydrogen might involve orbital interactions between hydrogen and carbon, an interaction stronger than van der Waals attraction. Experimental studies indicated that the presence of platinum would induce dissociation of hydrogen molecules in to hydrogen atoms. The easier accessibility of the atomic orbital might favor the electron transfer from the atomic hydrogen to charged carbon.     

Effect of an electric field on bubble growth rate

A uniform electric field elongates spherical bubbles to prolate spheroids. This results in a larger surface area to volume ratio for a given bubble size, and more efficient heat transfer from a superheated liquid to the bubbles during nucleate boiling. Hence bubbles should grow faster in an electric field. This paper studies the bubble growth rate in an electric field using the heat diffusion controlled growth model.     

Mofete geothermal field

This report deals with the Mofete geothermal field, which was discovered in southern Italy by AGIP, the Italian state-owned company for exploration of oil, gas and other alternative energy resources, such as geothermal. AGIP is the main operator in the Mofete geothermal field, in joint venture with ENEL, the National Electricity Board. Seven wells have been drilled, and two producing aquifers found at depths between 500 and 2000 m. The preliminary interpretation of a long-term test (three months), together with the model of the field, suggest that a 10 MW power-plant will operate in the near future in the limited area considered favourable so far for geothermal production.     

Effect of an axial electric field on detonation waves

The present study reports the results of an investigation of the effects of an axial electric field (200–8000 V/cm) on the propagation of detonation waves in mixtures of 2CO + O₂ and C₂H₂ + O₂ + 85%Ar. High speed streak camera and photodiodes were used for detonation velocity measurements. In addition, the voltage across the axial electrodes and the current are monitored as the detonation traverses the electric field region. The present results show that the neither the detonation structure nor its velocity are influenced by the electric field as it traverses the region between electrodes except when a breakdown occurs ahead of the detonation. The breakdown is due to the progressively increasing electric field between the detonation (which acts like a travelling quasi-neutral conducting plasma slug) and the downstream electrode. For a sufficiently strong electric field an arc discharge develops between the detonation and the charged electrode. When a discharge occurs in the unburned mixture ahead of the detonation wave, the mixture is ignited prior to the detonation arrival. This leads to the failure of the detonation since it now propagates into burnt products. Re-initiation of the failed detonation may occur downstream of the discharge section. The present results provide an explanation of the previous observations of Bone et al. [2].     

沟槽表面对翼型绕流流场的气动作用研究

基于大涡模拟(LES)技术对NACA6510翼型二维绕流流场进行数值模拟,研究吸力面圆弧型沟槽相对位置、相对深度对翼型气动特性与涡流结构的影响规律.研究表明:在小攻角下,沟槽表面对翼型的升、阻力系数影响很小,在大攻角下升、阻力系数明显减小.气体流经沟槽结构时会在内部形成反向二次漩涡,其脉动主频为上、下游主频的2倍,相对...