Influence of aspect ratio on the flow above the free end of a surface-mounted finite cylinder

The flow above the free end of a surface-mounted finite-height cylinder was studied in a low-speed wind tunnel using particle image velocimetry (PIV). Velocity measurements were made in vertical and horizontal measurement planes above the free end of finite cylinders of aspect ratios AR = 9, 7, 5 and 3, at a Reynolds number of Re = 4.2 × 10⁴. The relative thickness of the boundary layer on the ground plane was δ/D = 1.7. Flow separating from the leading edge formed a prominent recirculation zone on the free-end surface. The legs of the mean arch vortex contained within the recirculation zone terminate on the free-end surface on either side of the centreline. Separated flow from the leading edge attaches onto the upper surface of the cylinder along a prominent attachment line. Local separation downstream of the leading edge is also induced by the reverse flow and arch vortex circulation within the recirculation zone. As the cylinder aspect ratio is lowered from AR = 9 to AR = 3, the thickness of the recirculation zone increases, the arch vortex centre moves downstream and higher above the free-end surface, the attachment position moves downstream, and the termination points of the arch vortex move upstream. A lowering of the aspect ratio therefore results in accentuated curvature of the arch vortex line. Changes in aspect ratio also influence the vorticity generation in the near-wake region and the shape of the attachment line.     

Soot studies of laminar diffusion flames with recirculation zones

This paper describes the unusual sooting structure of three flames established by the laminar recirculation zones of a centerbody burner. The vertically mounted burner consists of an annular air jet and a central fuel jet separated by a bluff-body. The three ethylene fueled flames are identified as: fully sooting, donut-shape, and ring-shape sooting flames. Different shapes of the soot structures are obtained by varying the N₂ dilution in the fuel and air jets while maintaining a constant air and fuel velocity of 1.2 m/s. All three flames have the unusual characteristic that the soot, entrained into the recirculation zone, follows discrete spiral trajectories that terminate at the center of the vortex. The questions are what cause: (1) the unusual sooting structures and (2) the spiral trajectories of the soot? Flame photographs, laser sheet visualizations, and calculations with a 2D CFD-based code (UNICORN) are used to answer these questions. The different sooting structures are related to the spiral transport of the soot, the spatial location of the stoichiometric flame surface with respect to the vortex center, and the burnout of the soot particles. Computations indicate that the spiral trajectories of the soot particles are due to thermophoresis.     

非胶结含水合物沉积物修正等效介质速度模型及其地震波场特征研究

通过数值分析,发现对应于悬浮模式、颗粒接触模式的等效介质模型A,B预测的含水合物沉积物纵波速度、横波速度及泊松比存在物理认识上的缺陷,单独考虑水合物微观模式为悬浮模式或颗粒接触模式并不合理.认为非胶结水合物的微观模式与其饱和度存在关联,并运用拉格朗日插值方法建立了新的非胶结含水合物沉积物修正等效介质速度模型.该模型体现了水合物饱和度对于水合物微观模式的影响,数值分析结果表明新模型预测结果更合理.基于新模型对非胶结含水合物沉积物的地震波场进行了数值模拟,探讨了似海底反射及空白带的形成机理,对实际水合物地震勘 关键词： 水合物 等效介质模型 似海底反射 空白带     

非球面检测中衍射光学补偿器的校准定位研究

在非球面检测中,为了消除衍射光学补偿器的位置偏差.在补偿器的外围设计、制作了位相型反射式菲涅耳波带板作为衍射光学校准器.利用微细加工手段,将补偿器和校准器整体集成在同一片基上.通过位相型反射式菲涅耳波带板的自校准功能,使其衍射光波与参考光波干涉,形成校准干涉条纹.测量时,调节校准干涉条纹成为最简单的形式,即可校正补偿器的离焦、偏心和倾斜误差,实现位置的精确校准.实验中,得到了近似零校准干涉条纹,有效地消除了补偿器的装调误差对测量的影响.     

太阳池非对流层最佳厚度及最大效率数值模拟

本文对现有的太阳池辐射透射模型及稳态热效率模型进行了改进,改进的模型既考虑了池水浊度的影响又考虑了池内多重反射的影响,更接近实际情况。在改进的稳态热效率模型基础上,通过数值模拟的方法,对太阳池非对流层最佳厚度及其最大效率的相关影响因素作了较为详细的分析和讨论。认为太阳池非对流层最佳厚度及其最大效率取决于太阳池尺寸和结构、太阳辐射强度、储热层和上对流层的温差、太阳辐射在水中的透射率、池底反射率、水浊度、池水的物理特性以及池深度等综合因素,其中,△T/I0(储热层和上对流层的温差与水面太阳辐射强度的比值)是影响太阳池非对流层最佳厚度的主要因素,这为太阳池高效运行提供了理论指导。     

毛细管区带电泳的离子交换在柱预富集技术研究

提出了离子交换固相萃取的毛细管区带电泳在柱预富集技术。预富集毛细管和分离毛细管的端面靠紧,二者通过一段带侧孔的聚四氟乙烯（PTFE）套管固定。预富集毛细管内壁键合羧基阳离子交换基团,进样时分析离子被保留在预富集管的固定相上,用2mol／L的氯化铵溶液洗脱,再进行毛细管区带电泳分离。方法成功富集和分离了两种低浓度的药物阳离子,普萘洛尔和美托洛尔的灵敏度比常规电动进样分别提高4200和3400倍,其浓度检出限分别为0．02μg/L和0．14μg/L。     

毛细管区带电泳分离硝基苯胺位置异构体的研究

采用毛细管区带电泳(CZE)技术,在极端pH值条件下分离了邻、间、对硝基苯胺位置异构体;研究了背景缓冲溶液、pH值、分离电压、温度及进样时间等因素对分离的影响,得出了3种样品的标准曲线、线性范围及加样回收率。在选定的实验条件下15min内实现了上述3种苯胺类化合物的分离。该方法快速,准确,重现性好。     

毛细管电泳氨类手性药物对映体拆分机理研究

手性药物及其对映体在药理上可表现出较大的差异,对它们进行研究将具有重要的理论意义和实用价值[1,2].毛细管区带电泳因其分离效率高、药品和试剂用量少、方法简单而成为目前手性拆分鉴定的重要方法之一[3].     

Silica nanoparticle-templated methacrylic acid monoliths for in-line solid-phase extraction–capillary electrophoresis of basic analytes

Polymeric ion-exchange monoliths typically exhibit low capacities due to the limited surface area on the globules of the monoliths. The ion-exchange binding of protonated weakly basic analytes on deprotonated carboxylate sites on methacrylate polymer monoliths has been increased by templating the monoliths with silica nanoparticles. The templating method is achieved by adding the nanoparticles as a suspension to the polymerisation mixture. After polymerisation, the nanoparticles are removed by washing the monolith with strong base. Monolithic columns prepared using this procedure have exhibited a 33-fold increase in ion-exchange capacity when compared to untemplated monoliths prepared and treated under similar conditions. The templating procedure does not alter the macroporous properties of the polymer monolith, confirmed through scanning electron microscopy and BET surface area analysis, but provides increased capacity predominantly through the re-orientation of more carboxylic acid groups. The resulting increase in ion-exchange capacity has proven to be useful for the preconcentration and separation of neurotransmitters by in-line solid-phase extraction–capillary electrophoresis. The increased capacity of the templated monolith allowed the injection time to be increased 10 times over that of an untemplated monolith, allowing 10 times more sample to be injected with the efficiencies and recoveries remaining unaffected. The enhancement in sensitivity for the test mixture of neurotransmitter (dopamine, norepinephrine and metanephrine) ranged 1500–1900 compared to a normal hydrodynamic injection in capillary electrophoresis. Efficiencies obtained for the neurotransmitters were 100 000–260 000 plates, typical of those obtained in capillary zone electrophoresis. The applicability of the increased capacity silica nano-templated polymer monolith was demonstrated by analysing trace levels of caffeine in biological, food and environmental samples.     

On-column liquid–liquid–liquid microextraction coupled with base stacking as a dual preconcentration method for capillary zone electrophoresis

A simple and efficient dual preconcentration method of on-column liquid–liquid–liquid microextraction (LLLME) coupled with base stacking was developed for capillary zone electrophoresis (CZE) in this paper. Four N-methyl carbamates were used as target compounds to evaluate the enrichment means. The carbamates in sample solutions (donor phase) were extracted into a dodecanol phase immobilized on a porous hollow fiber, hydrolyzed and back extracted into 0.20 μL running buffer (acceptor phase) of 30 mmol/L methylamine hydrochloride (pH 11.6) containing 0.5 mmol/L tetradecyltrimethylammonium bromide inside the hollow fiber, stacked further with 0.5 mol/L NaOH injected at −10 kV for 60 s, and separated by CZE. Analytical parameters affecting the LLLME, base stacking and CZE were investigated, including sample solution volume, pH and temperature, extraction time, stirring rate, buffer component, buffer pH, NaOH concentration, stacking time, etc. The enrichment factors of the carbamates were higher than 1100. The relative standard deviation (RSD) of peak height and limits of detection (LODs) were 4.5–5.5% (n = 6) and 2–4 ng/mL (S/N = 3) for standard solutions, respectively. The proposed method was applied to the analysis of vegetable and fruit samples with the RSD less than 6.0% (n = 3) and LODs of 6–10 ng/g (S/N = 3). The calibration solutions were prepared by diluting the stock solutions with blank sample solutions, and the calibration concentrations ranged from 0.012 to 1.0 μg/mL (r > 0.9951). The analytical results demonstrated that the LLLME coupled with base stacking was a simple, convenient and reliable on-column sample pretreatment method for the analysis of anionic analytes in CZE.