套管式腔体在盐水淡化过程中的光热及产水性能研究

该文研究一种基于菲涅尔反射镜场和降膜方式相结合的多级套管式淡化系统,分析2种腔体结构,确定了光学性能更好的圆型腔体,并对其内部淡化过程进行仿真计算。建立两级淡化系统的能量流动模型,并进行稳态和瞬态加热实验,由稳态实验数据计算出月牙型有限空间内部自然对流传质经验关系式。瞬态试验结果表明,第1、2级的最高产水量分别为3.79和2.64 kg/h。     

Impact of volume fraction and fluid layer thickness on heat transfer effectiveness of water-based nanofluids

The heat transfer effectiveness of nanofluids is adversely affected by the delay in convection onset. The lesser effectiveness, when compared to that of base fluid, is observed in a range of nanofluid layer thickness. The heat transfer coefficient of water–Al₂O₃ nanofluid can be enhanced by sustaining the equilibrium between Rayleigh number, temperature, particle volume fraction, and enclosure aspect ratio. In this paper, the specific correlation of fluid layer thickness and the onset of convection, which can significantly dominate the heat transfer characteristics of nanofluids are investigated using the concept of critical Rayleigh number. The water layer thickness for convection onset is first experimentally assessed for different real-life heat flux densities. It is then performed for Al₂O₃–water nanofluid for varying volume fractions. With the increase in volume fraction even though thermal conductivity increases, the overall heat transfer enhancement of the nanofluid is reduced. Temperature involved (heat flux density), the volume fraction of the nanofluid used, nanofluid layer thickness (space availability for the cooling system), and mass of the nanoparticle influence heat transfer enhancement. A higher volume fraction may not always result in enhancement of heat transfer as far as nanofluids are concerned.     

双桥墩条件下冰塞发展临界条件试验初步研究

河流中的桥墩改变了附近原有的水流特征,冬季可能对其附近冰塞的形成和演变产生影响。基于水槽模型试验,通过改变墩心距、墩径、墩形、冰水流量比和水流弗劳德数,分析了双桥墩条件下冰塞发展通过桥墩的临界条件。试验表明：冰塞能否发展通过桥墩所在断面存在临界弗劳德数,其值受墩心距、墩径、墩形和冰水流量比等因素控制,随着墩心距的减小或冰水流量比、墩径的增大,冰塞发展通过桥墩所在断面难度增大,方形墩相较于圆柱形墩难度增大;试验范围内,随着墩心距的减小,桥墩所处河道断面输冰能力增强,初始冰塞厚度增加,但冰塞平衡厚度减小。     

结晶器铜管的失效分析

针对结晶器铜管在生产中出现的硬度不均、表面＂桔子皮＂、脱方现象,秦皇岛首钢长白结晶器有限责任公司采用调整加热温度和保温时间的方法,保证硬度符合标准,并解决了铜管裂纹和难以加工问题;控制铜管的变形量〉15%,消除了铜管的＂桔子皮＂现象;采取时效处理使铜管不在出现脱方现象。     

提高曲面铣削编程效率的步骤

数控铣床是模具制造的主导设备,能够完成较为复杂的曲面铣削,编程效率直接决定着生产进度和经济效益。本文以注射模中的虎齿盘工件为例,集中宏程序的优点,介绍曲面编程的思路与步骤。     

第二代催化裂化汽油选择性加氢脱硫（RSDS-Ⅱ）技术的中试研究及工业应用

对催化裂化汽油中硫化物及烃类分布进行详细分析,确立第二代催化裂化汽油选择性加氢脱硫（RSDS-Ⅱ）技术的工艺路线。中试试验结果表明,RSDS-Ⅱ技术对多种原料油具有较好的适应性。工业应用标定结果表明,以烯烃体积分数38.7%～43.3%、硫质量分数250～470 g/g的催化裂化汽油为原料,经过RSDS-Ⅱ技术处理后汽油产品硫质量分数小于50 g/g,满足沪Ⅳ/欧Ⅳ排放标准,RON损失0.3～0.6个单位,说明RSDS-Ⅱ技术具有较好的脱硫活性和较高的选择性,完全可以满足炼油厂汽油质量升级的需要。     

非达西渗流与采场底板突水防治

用Forcheimer型非Darcy渗流理论,从非线性动力学系统结构失稳的视角揭示了煤矿突水的机理。研究表明:矿井突水与岩层的孔隙率、颗粒直径、雷诺数及水流速度等因素有关;雷诺数Re随孔隙率ε的增大而减小;孔喉比b=0~10,雷诺数受孔喉比影响较大;孔隙率为0.2~0.5,孔喉比受孔隙率的影响较大。     

An analytical and numerical investigation of hetero-/homogeneous combustion with deficient reactants having larger than unity Lewis numbers

The heterogeneous combustion and the combined hetero-/homogeneous combustion of deficient reactants with Lewis numbers (Le) larger than unity was investigated analytically and numerically in two geometrical configurations, the flat plate and the planar channel, under the condition of infinitely fast catalytic chemistry. Analytical results based on similarity solutions for the catalytic flat plate and on heat and mass transfer solutions for the channel were complemented by detailed 2-D numerical simulations. The larger than unity Lewis number led to the underadiabatic surface temperatures, which in turn gave rise to gas-phase regions with local energy excess. For the flat plate case, the maximum gas-phase energy excess was a non-monotonic function of the Lewis number. The peak occurred at Le = 6.5 with a corresponding energy excess 6.4% above the total energy of the fresh reactants. In channel-flow combustion, the maximum gas-phase energy excess was a monotonically increasing function of Lewis number, approaching asymptotically the considerably higher value of 20.8% as Le → ∞. For current catalytic combustion methodologies, which include the fuel-lean hydrocarbon/air combustion (Lewis numbers of deficient hydrocarbon fuels up to ∼3.2) and the fuel-rich hydrogen/air combustion (Lewis number of deficient oxygen ∼2.3), the energy excess in the gas was significant and could reach up to 14%. Hetero-/homogeneous combustion simulations have shown that, upon homogeneous ignition, the gas-phase energy excess manifested itself with superadiabatic flame temperatures. However, the superadiabaticity in the gas was confined to the channel core, such that the surface temperature did not exceed the adiabatic equilibrium temperature. This behavior had key implications for the reactor thermal management and catalyst stability. Moreover, the gas-phase superadiabaticity led to peak prompt NO_x values 30% higher than those achieved by a diffusionally neutral deficient reactant (Le = 1).     

Lithium electrolytes based on modified imidazolium ionic liquids

In this study, new electrolytes for Li-ion batteries in the form of lithium salt solutions in room temperature imidazolium ionic liquids (RTIL) are reported. The ionic liquids applied, for higher reduction potential stability, were substituted at position C2 with oligooxyethylene groups of various length ([Im nEO]⁺X⁻; where: n = 0, 3, 7, 20 and X = Cl, BF₄, N(CF₃SO₂)₂). It was found that they are good solvents for lithium salts (LiBF₄, LiN(CF₃SO₂)₂, {[CH₃(OCH₂CH₂)₃O]₃BC₄H₉}Li) forming liquid solutions of low glass transition temperature (T_g in the −70 to −40 °C range). Ionic conductivity depends on the length of oxyethylene substituent in Im nEO and on the concentration of the salt applied, for 10 mol%, σ_RT is of the order of 10⁻⁴ S cm⁻¹. On the basis of polarization measurements by the variable-current method, the proportion of lithium cations in electric charge transfer (t₊) has been determined. The values obtained (typical for ionic liquids) are low and depend on n and lithium salt concentration but do not exceed a dozen or so percent.     

中学化学教学中2O3（催化剂∥或hν）3O2反应类型的探讨

高中化学教学中,大多教师对2O3(催化剂∥或hν)3O2的反应是非氧化还原反应深信不疑。文章从理论上对该反应进行了分析、探讨,认为该反应应该是氧化还原反应。