气隙取气汽轮发电机转子全隐式甩风斗甩风特性的数值研究

为提高全隐式甩风斗甩风能力,在分析全隐式甩风斗结构对其甩风性能影响的基础上,采用动态模型对全隐式甩风斗甩风特性进行了数值研究。通过对38个不同结构全隐式甩风斗流道内流场的分析与甩风量的比较,得到了结构参数出流角a、导流槽倾角b和槽深d对全隐式甩风斗甩风性能的影响规律。综合考虑全隐式甩风斗甩风性能与其结构强度,推荐在无导流槽时取a=70°;有导流槽时取a=65°~75°、b=30°~45°,在风斗及转子结构强度允许的条件下d越大越好。     

汽轮发电机转子气隙取气斜流通风系统试验研究

气隙取气斜流通风系统是大型汽轮发电机中应用较广的一种通风方式。槽楔的取风性能直接影响通风系统的冷却效果。对汽轮发电机转子气隙取气斜流通风系统进行试验研究,讨论槽楔结构形式、结构参数(槽楔入流角a、b、槽楔高度、槽楔出流角g )、斜流风沟阻力系数和来流风速对槽楔取风性能的影响。研究结果表明,通过改进槽楔结构设计,全隐式槽楔的取风性能可达到半隐式槽楔的取风性能;槽楔出流角也是影响取风系数的重要因素,出流角 g 为73°时取风性能优于 g 为90°;取风系数K不受来流风速的影响。本文的研究结果对汽轮发电机转子气隙取气斜流通风系统的设计具有指导意义。     

气隙取气转子风斗取风性能数值模拟与实验研究

气隙取气斜流通风系统是大型汽轮发电机中应用较广的一种通风方式.风斗的取风性能直接影响通风系统的通风冷却效果.对转子风斗的取风性能进行了CFD数值模拟研究,并进行了实验验证,获得了风斗结构参数对其取风性能的影响规律,可为汽轮发电机转子风斗的优化设计提供参考.     

气隙取气转子风斗取风性能的相互影响实验研究

气隙取气斜流通风系统是大型汽轮发电机中应用较广的一种通风方式。为了研究不同结构转子进、出风斗的取风能力和引风能力,对气隙取气通风系统进行了静态实验模拟研究,得到了进风斗和出风斗取风性能之间相互影响规律,为转子气隙取气通风系统的优化设计提供一定的参考。     

空调室外机的导风圈结构对风量噪音的影响研究

基于空调室外机提风量降噪音的设计需求,研究了前面板导风圈的结构对室外机风量噪音的影响因素,包括导风圈的高度、长度和弧形段结构。结果表明:在允许的外机空间尺寸范围内,随着导风圈长度增加,风量增加,当导风圈长度从a增加至c时,风量增加35~100方,且同风量下噪音可下降0.5d B~1d B。随导风圈弧形段增加,风量先上升,后下降,当弧形段从r到R风量上升30~140方,从R到RR风量下降30~80方,同风量下噪音先下降0.5~1d B,后增加约0.5d B,即弧形段为R时,室外机的风量噪音最佳。随导风圈高度增加,风量上升,当导风圈高度从h增加到H时,风量上升50方,同风量下噪音下降0.3~0.5d B。导风圈结构对空调室外机风量噪音的影响研究表明,导风圈的高度和长度对提升室外机的风量和降低噪音有正向作用,然而这种正向作用受到前面板钣金材质和加工工艺的限制。     

波状挡边带式输送机在火力发电厂中的应用

波状挡边带式输送机是一种灵活的物料输送机械,输送仰角可在0°~90°范围,并可在垂直输送过程中扭转180°。介绍了波状挡边带式输送机的结构、主要性能和特点,以及在火力发电厂输送煤炭的应用情况,并对波状挡边带式输送机的应用和国产化制造提出了建议。     

一种鲁棒的 2D 激光雷达和摄像机最小解标定方法

因为 P3P 问题固有的结构缺陷,二维激光雷达和摄像机的最小解标定方法存在数值稳定性差、精度较差等问题。 针对 上述问题,本文提出了一种鲁棒的最小解标定方法,对 P3P 问题的求解算法和最优解选择误差度量进行改进。 首先,根据 3 个 棋盘格构建的 P3P 问题,利用改进的 RP3P 算法进行求解,提高了解的稳定性。 然后,基于可信度加权观测概率设计了一种的 最优解选择策略,提高了所选解的准确性。 根据实验结果可知,本文的算法在标定结果的精度和有效性上得到明显改善。 仿真 实验中,在不同噪声水平下,相比于 Francisco 方法和 Hu 方法,本文方法的有效解概率提高了 5% ~ 41%和 2% ~ 20%,旋转矩阵 精度提高了 2° ~ 6°和 1. 5° ~ 2°,平移向量精度提高了 180~ 520 mm 和 150~ 180 mm,性能提高明显。     

对DZ15—40断路器触头扭簧的计算及探讨(Ⅱ)

三、断路器触头扭簧的计算3.对计算方法的探讨为了探讨文献的公式,采用其公式计算边相扭簧的M′.先求n=4+25°/360°=4.07算得M′=2.56N·mm/度当(?)_2=31°,M_2=79.4N·mm(?)_1=19.5°,M_1=49.9N·mm这样就得到了三种理论或计算的扭簧在相同的扭转角条件下的扭矩数值.同时也用一种使用中较符合实际触头压力中间值的扭簧,用它们检测出在相同的扭转角条件下的扭矩值.取其平均值列表对比见附表.     

360°风作用下线条风荷载分配系数特性

线条风荷载的准确计算是输电杆塔设计的关键一步,角度风荷载分配系数的选取是否合理将直接影响到设计指标的合理性。对常规线条风荷载（0.5Φ₁=0.5Φ₂=0）的计算原理进行梳理和分析,得到了0~90°范围内的角度风荷载分配系数。同时,通过对风向角θ和线路转角Φ的剖析,推导了线路前后侧360°风吹时的线条角度风荷载分配系数计算公式,并给出了前后侧挡距不同分配比例（0.5Φ₁=0.5Φ₂,0.5L₁∶0.5L₂=5∶5、4∶6、3∶7）时的线条角度风荷载分配系数,分析了分配系数的特点,并进行了对比研究。研究结果揭示了线条角度风荷载分配系数的特点,可作为输电杆塔抗风设计的一种参考。     

亚临界及近临界压力区倾斜管与垂直管中汽水沸腾传热特性比较

在亚临界及近临界压力下,对Φ32×3mm 不锈钢倾斜上升光管(倾角α=20°)及垂直上升光管中水的沸腾传热特性进行了试验研究。试验参数范围:压力 p=13~21.5MPa,质量流速 G=600~1200kg/(m2s),内壁热负荷 q=200~600kW/m2。试验结果表明:倾斜管比垂直管更容易发生第一类传热恶化(DNB),但倾斜管发生 DNB 后的壁温飞升峰值低于垂直管;倾斜管与垂直管类似,增加质量流速可以提高临界热负荷,在近临界压力区比亚临界压力区更容易发生DNB。提出了对超临界锅炉设计有重要参考价值的倾斜管临界热负荷、垂直管及倾斜管最小传热系数的计算关联式。     

基于普朗特类比的螺纹管内污垢分析模型

对冷却塔中的7根铜质内螺纹管进行了传热性能污垢试验,试验中流体流速为1.07 m/s,雷诺数为16 000。螺纹管几何参数范围为：螺纹数18~45,螺纹角25°~45°,螺纹高0.33~0.55 mm。污垢为颗粒污垢和析晶污垢的混合物,水的硬度为800 mg/L。引入普朗特类比法,以(Km/Kmp)/(f/fp) 和(j/jp)/(f/fp)1/3作为传热性能评价指标进行分析。与以往的研究相比,文中更加全面地考虑了内螺纹管参数的影响。同时建立了一系列关于螺纹管的污垢热阻与传热效能的半经验函数关系式,可用于评价和预测实际状态下冷却水的结垢情况。     

Investigation of Nozzle Cascades of a Turbine Stage

Two different nozzle cascades designed for an LP aircraft turbine have been investigated. The cascade had large convergence, a moderate curvature of the airfoils, and it flowed over so that the outlet subsonic velocity was high. It was designed for a flow inlet angle of α₀ = 63.5°, an outlet angle of α₁ = 28.6°, and a reduced isoentropic outlet velocity of λ₁ = 0.93. Having the same width of 41 mm, the first cascade was made up of 5.9 mm thick profiles, while the second one from 4 mm thick profiles. To improve the efficiency of the second cascade, the suction side curvature near the trailing edge decreased more sharply, which yielded a smoother velocity distribution over the suction side according to the design calculation. However, calculations of a viscous flow in the second cascade revealed no tendency towards a decrease in the profile losses. The experiments demonstrated that both cascades featured a high efficiency on the ranges of λ₁ = 0.80–0.98 and α₀ = 52°–69°. It is important that the design mode with respect to λ₁ coincided with the mode giving the lowest energy losses. The first cascade from thicker profiles was more efficient than the second cascade where, with the same overexpansion of the flow on the suction side, the critical velocity was attained just downstream of the throat while it was shifted to the trailing edge in the first cascade. A slight flow deceleration on the suction side did not result in a local velocity equal to the velocity downstream of the cascade, and a flow separation occurred near the trailing edge at λ₁ ≥ 0.93. It is these features of the flow in the second cascade that are responsible for an increase in the profile loss coefficient by 0.26% under the design operating condition.     

Effects of Magnetic Field on Synthesis and Thermoelectric Properties of NaCoO2

We synthesized polycrystalline sodium cobalt oxide (NaCoO₂) by using solid state reaction (SSR) method in a magnetic field. The powder of Na₂CO₃ and Co₃O₄ were mixed by ball milling and compacted in a magnetic field. The characterization of microstructure of powder size and crystal structure were analyzed through XRD. Thermoelectric properties and the lattice parameter of NaCoO₂ showed little change in magnetic field. The lattice parameters of NaCoO2 are a = 2.8443 Å, b = 2.8443 Å, and c = 10.8091 Å in the hexagonal structure (a = b ≠ c).     

Moment performance of photovoltaic/thermal hybrid panel (numerical analysis and exergetic evaluation)

A photovoltaic/thermal hybrid panel (PV/T) is a high‐efficiency energy converter which supplies electrical energy and thermal energy from solar energy. In this paper, we report characteristics of two PV/T types under various environmental conditions and fluid flow rates, using numerical analysis. We found photovoltaic efficiencies to be 9.61% for PV/T_A and 10.56% for PV/T_B at T _c = 25 °C; thermal ones were 52.11% for PV/T_A and 40.14% for PV/T_B at T_f = 40 °C, I_rr = 800 W/m². From these results, we propose some design points to construct the optimum structure of PV/T. Next, we adopted exergetic evaluation to study electrical energy and thermal energy quantitatively. As a result, we could confirm the existence of flow rate maximizing the total efficiency (optimum flow rate) on some environmental condition, and could define the optimum operating condition. Moreover, we compare exergetic efficiencies on optimum operating conditions (maximum exergetic efficiency) under various environmental conditions with PV, PV/T_A, and PV/T_B. A rise of maximum exergetic efficiency with increasing irradiance yielded –3.6%/kW ⋅ m^–2, +3.6%/kW ⋅ m², and +1.4%/kW ⋅ m², respectively. Nevertheless, we could confirm a hybridizing advantage of high irradiance. © 2000 Scripta Technica, Electr Eng Jpn, 133(2): 43–51, 2000     

Multilayer high gradient insulator technology

We are investigating a novel insulator concept that involves the use of alternating layers of conductors and insulators with periods on the order of <1 mm. These structures perform many times better (~1.5 to >4× higher breakdown electric field strength) than conventional insulators in long pulse, short pulse, and alternating polarity applications. A previously defined scaling law of d^0:5 , where d is the insulator length, appears to apply to these new structures when the scaling parameter d is replaced by the layer period d₁. This observation implies that each layer within the structure behaves independently in the breakdown process. We present our ongoing studies investigating the degradation of the breakdown electric field strength resulting from surface roughness, the effect of gas pressure, and the performance of the insulator structure under bipolar stress. Further, we present our initial work on scaling and modeling studies     

Optimized quadrature surface coil designs

Background Quadrature surface MRI/MRS detectors comprised of circular loop and figure-8 or butterfly-shaped coils offer improved signal-to-noise-ratios (SNR) compared to single surface coils, and reduced power and specific absorption rates (SAR) when used for MRI excitation. While the radius of the optimum loop coil for performing MRI at depth d in a sample is known, the optimum geometry for figure-8 and butterfly coils is not. Materials and methods The geometries of figure-8 and square butterfly detector coils that deliver the optimum SNR are determined numerically by the electromagnetic method of moments. Figure-8 and loop detectors are then combined to create SNR-optimized quadrature detectors whose theoretical and experimental SNR performance are compared with a novel quadrature detector comprised of a strip and a loop, and with two overlapped loops optimized for the same depth at 3 T. The quadrature detection efficiency and local SAR during transmission for the three quadrature configurations are analyzed and compared. Results The SNR-optimized figure-8 detector has loop radius r ₈ ~ 0.6d, so r ₈/r ₀ ~ 1.3 in an optimized quadrature detector at 3 T. The optimized butterfly coil has side length ~ d and crossover angle of ≥ 150° at the center. Conclusions These new design rules for figure-8 and butterfly coils optimize their performance as linear and quadrature detectors. This work is supported by NIH grant R01 RR15396.