流延辊出水腔结构优化仿真研究

为了获得高质量的薄膜,需对流延膜的冷却机理、流延辊的工作原理、流延辊内部流道结构等进行研究。对现有单向螺旋流动式流延辊内部冷却水流动情况进行了仿真研究,发现在现有结构条件下流延辊内部有多个影响流动的旋涡区,特别是在流延辊出水腔处有一较大环流流动,严重影响了冷却水快速流动。为了降低流延辊流动阻力,首先提出在出水腔添加导流叶片的初始优化方案,结果表明,在出水腔添加导流叶片的优化方式可有效改善现有流延辊的送水能力;随后对导流叶片进一步优化,采用"扇形"结构的导流叶片,使得优化结果更好。最后"扇形"导流片的优化方案相比于原有结构,其进出口总压损失降低了6.1%,每小时送水量增加了66.3 t。     

边界条件和结构尺寸对提升管内气固流动特性的影响

引言提升管是非均匀结构显著的气固两相流动体系,其流动特性主要表现为轴向空隙率的S形分布、径向的"环-核"结构以及团聚物的生成和破碎等。近年来,有关数值计算方法的研究增多,其中双流体模型的应用最为广泛,颗粒动理学则是目前封闭控制方程的最合理有效的方法。     

循环流化床气体-颗粒团聚物两相流体动力特性的研究

基于气固两相流体动力学,建立循环流化床内气体-颗粒团聚物两相流动模型,模拟计算循环流化床内气固两相流动.理论预测得到循环流化床内颗粒团聚物的形成,得到颗粒"环-核"流动结构,模拟计算颗粒相浓度和速度以及气相速度分布与前人实验结果的趋势基本吻合.     

板间距对三角槽道脉动流流动阻力的影响

以水为工质对不同板间距的三角槽道脉动流流动阻力特性进行了研究。基于受力平衡方程,建立了适用于三角槽道脉动流压降的数学模型,用于理论分析流动阻力的影响因素。通过实验测试与数值模拟,校验数学模型的合理性,并且对三角槽道脉动流流动阻力进行分析。结果表明,流动阻力主要受板间距、涡旋拟"能"两方面因素影响,且与板间距呈反比,与涡旋拟"能"呈正比;板间距的缩小,会使流动阻力增加,当缩小到板间距与槽深比值为1.0时,出现流动阻力的阶越式增长,上升1个数量级;造成流动阻力骤升的主要原因在于:随着板间距的缩小,流场结构逐渐变化,三角槽道内涡旋的影响区域由"三角槽内部"逐渐转变为"整个流道",且主流区壁面出现流动分离,出现涡旋流动与波状流共存现象,使流动阻力大幅提升。     

多溢流大型塔板的计算传质学

利用计算传质学方法研究了直径12.6 m的四溢流大型塔板上液相流动结构对塔板效率的影响,建立了描述多溢流塔板上液相流动和传质状况的理论化计算模型。应用该模型,研究了传统等鼓泡面积设计方法条件下单块塔板的速度场和浓度场。结果表明,所模拟四溢流塔板的左侧翼塔板出现返流区,而右侧翼塔板流动结构相对均匀未出现返流区。为进一步优化塔板结构,提高传质效率,对左侧翼塔板提出了加设导流板的改进结构。计算结果表明,改进的塔板结构在一定程度上改善了塔板上液相的流动结构,使得塔板效率较传统设计方法提升了4.53%～9.22%（当Q₁/Q₂=［0.5,1.5］时）。     

底吹气连铸中间包内气液两相流的数值模拟

以宝钢集团梅山钢厂1台连铸中间包为原型,进行底吹气中间包水模型研究. 实测结果表明,底吹气在中间包内形成"鼓泡流"形式的流动结构;"鼓泡流"的形成一方面能够破坏中间包内"层流"形式的短路流动,增强混合,另一方面能在中间包内形成"气幕挡墙",有利于夹杂物去除. 针对中间包内气-液两相"鼓泡流"特征,建立了底吹气中间包内气-液两相欧拉多流体模型,模型中考虑了气泡的存在对湍流增强的影响,考虑了相间滑移、气泡浮力及湍流分散力. 采用所建立的模型对底吹气中间包内气液两相流动和混合特性进行了模拟和分析,结果与水模型实测结果一致.     

一种新型微流动混合圆通道装置的制作、数值模拟和初步应用

微混合通道是微流控芯片实现功能的重要结构。微丝模塑法制作的微流动混合圆通道,具有特殊"立体"结构的侧壁沟通式通孔。通过数值模拟方法,定性描述了沟通通孔处的流场特征,以此来辅助设计微混合通道,并初步探索了微流动混合圆通道的粒子合成能力。结果表明,微丝模塑法制作的微混合圆通道较相同条件下的软光刻通道具有更好的流场特征,并为粒子合成提供了一条新的途径。     

循环流态化：（Ⅲ）气,固流动模型

根据气、固两相流动的基本特征,循环流态化气、固两相流动模型可分为局部流动结构模型及整体流动结构模型两类。局部流动结构模型主要描述床内稀相及絮状物相的局部分布及变化,而整体流动结构模型主要描述床中空隙率。颗粒速度以及气体速度轴、径向分布及变化,其中根据实用层次不同,整体流动结构模型可分为一维、一维两区及两维模型。本文对循环流态化气、固流动模型进行了分类评述,供循环流化床反应器设计时参考。     

连铸"三大件"生产线专用设备的研制与应用

本文简要介绍了为连铸"三大件”生产线研制的专用设备.对其中的关键设备,如混练机、流动干燥床的结构形式和工作原理,及其主要技术参数做了较为详细的介绍.     

水银电解槽的阴极和槽底设计

本文综合国内外氯碱生产先进技术和本厂氯碱生产实践经验,论述了水银电解槽如阴极和槽底设计中的几个问题.(1)水银电解槽的容量与阴极电流密度的确定;(2)水银电解槽的几何尺寸(长宽比)与流动的水银阴极,处于稳定流动状态的水力学条件的关系及电槽长宽比的选择;(3)槽底结构设计原则及本厂首创的"挠性槽底"水银电槽的结构特点;(4)锦化水银电槽与国内外同等容量水银电槽的结构、性能比较.     

湍动流化床过渡段固含率分布特征的实验及数值模拟

在湍动流化床中,过渡段对于包括甲醇制烯烃在内的气固催化快反应有着重要的作用。采用PV6D反射型光纤探针对内径95 mm的湍动流化床内过渡段的固含率分布和脉动参数进行了测量,分别考察了表观气速和静床高的影响,并采用修正的基于颗粒动力学的三段曳力双流体模型进行模拟。实验表明,湍动流化床过渡段中固含率的轴向分布呈现S型和指数型两种类型,固含率轴向与径向分布都在过渡段内出现最大梯度,表明过渡段中固体浓度分布比稀相段和密相段更不均匀。表观气速和静床高的变化将导致S型和指数型分布的相互转变,并且对过渡段底部与壁面附近的固体高浓度区影响最为显著。局部固含率脉动概率密度分布表明,在静床高较小时,随着气速的增大,床层下部气含率最大值位置将从中心区移动至环隙区,呈现气含率的双峰型分布。本文提出的修正三段曳力模型考虑了颗粒团聚的影响,对过渡段中分布板影响区之外的固含率分布均能较好地模拟。     

网格尺寸对循环流化床内气固两相流动的影响

将基于能量最小多尺度方法(EMMS)的曳力模型耦合到双流体模型中,并针对循环流化床内的气固两流动进行了模拟研究。采用全滑移壁面边界条件处理颗粒相,考察了3种网格尺度对轴向空隙率和出口颗粒循环量等气固流动特性的影响。计算结果表明,应用EMMS曳力模型处理相间作用力,同时在采用全滑移壁面边界条件处理颗粒相时,双流体模型能够正确预测轴向空隙率分布。采用网格尺寸为2.325 mm×20 mm时,模拟结果和实测数据吻合较好,表明在循环流化床的数值模拟中选择恰当的网格尺度是极为重要的。     

循环流化床中颗粒团聚物性质的PDPA测量

提出了一种利用相位多普勒粒子分析仪（PDPA）来测量气固循环流化床中颗粒团聚物性质的方法,并运用此方法初步考察了操作条件对循环流化床稀相区中颗粒团聚物性质的影响.在本实验操作条件下,颗粒团聚物的时间分率、频率、内部空隙率以及轴向速度等性质都存在轴径向的不均匀分布,具有较明显的环核特征;固体循环速率对颗粒团聚物性质径向分布影响不大,表观气速的变化可引起其轴向分布规律发生显著改变,但其径向的环核特性仍然存在.     

Microstructural aspects of the flow behaviour in a liquid—solids circulating fluidized bed

The local instantaneous and time‐average suspension densities were determined in a 76 mm diameter by 3 m tall liquid‐solids circulating fluidized bed riser using a fibre‐optic probe. Attempts were made to qualify the microflow structure through statistical analysis of the local bed voidage fluctuations obtained under different operating conditions for the first time. The results show that local microflow structure is uniform in the axial direction but non‐uniform in the radial direction with more flow fluctuation near the wall than in the core of the column for a given axial position. The standard deviation and intermittency index tend to increase with increasing solids circulating rates. Comparing with the gas—solids CFB, the liquid—solids CFB shows much more homogeneous flow structure in both the axial and radial microscopic flow behaviours. The microflow behaviours in the conventional liquid—solids fluidization, liquid—solids circulating fluidization and dilute‐phase liquid transport regimes are also characterized by examining the probability distribution and the intermittency index of the solids holdup.     

非均匀气固两相系统中多尺度传质模型

建立了适用于气固循环流化床的多尺度传质模型 .从过程与尺度的角度出发 ,将非均匀气固两相流中的传质过程分解为静态与动态的过程 ,并将前者分解为稀相内、密相内以及稀密相间 3个尺度下的传质 ;在用多尺度能量最小 (EMMS)模型求解已知物系性质和操作条件的非均匀气固两相流体动力学参数的基础上 ,借助于前人的研究结果 ,利用相对滑移速度、空隙率等参数求解传质系数 ,求得轴向的浓度场分布 ,并讨论非均匀两相流动结构对传质效率的影响     

Chaotic characteristics of local voidage fluctuation in a circulating fluidized bed

Local voidage fluctuations have been measured by using an optical transmittance probe at various axial and radial positions in a circulating fluidized bed riser with a 0.1 m i. d. and 10 m height. The chaotic time series analysis of the local voidage fluctuations has been adopted to characterize the nonlinear dynamics of the circulating fluidized bed riser. The variations of the correlation dimension and the Kolmogorov entropy of the voidage fluctuation were found to depend on the local time-average voidage. The axial and radial distributions of the correlation dimension and the Kolmogorov entropy were strongly affected by the solids flow structures (e.g. core-annulus flow) in various operating conditions. The correlation dimension of local voidage fluctuations increases along the riser, except the position near the distributor. Both, the correlation dimension and the Kolmogorov entropy of local voidage fluctuations near the wall, were found to be smaller than those at the center of the riser, independent of the solids circulation rate and the axial position.     

Searching for a mesh-independent sub-grid model for CFD simulation of gas-solid riser flows

This work aims to examine the effects of grid size in applying the two-fluid model (TFM), and thereby attempts to search for a mesh-independent sub-grid model for simulating gas-solid riser flows. To this end, we performed a series of TFM simulations over a periodic domain with various grid resolutions and drag closures. Of these drag models, EMMS/matrix model in its simplified version was chosen to be the focus of discussion. It was found that TFM simulation with a homogeneous drag model reaches its numerically asymptotic solution when the grid scale is as small as 10 times the particle diameter, but it still fails to capture the characteristic S-shaped axial voidage profile and highly over-predicts the solids flux. By comparison, EMMS/matrix model seems to reach a mesh-independent solution of the effect of sub-grid structures on the drag force, and predict successfully the axial voidage profile and the solids flux with even coarse grid. Therefore, the fine-grid TFM simulation is inadequate for gas-solid riser flows. We need sub-grid modeling of the heterogeneous structure.     

负压差立管内的气固两相流

在φ800 mm×12000 mm流化床实验装置上对150 mm×11500 mm负压差立管内气固两相流的轴向压力、空隙率和气体流动特性进行了测量和分析.立管出口无约束淹没在密相流化床内,颗粒质量流率范围G_s<1200 kg&#8226;m^-2&#8226;s^-1.立管内气固两相流态有两种存在形式,当颗粒质量流率G_s<200～250 kg&#8226;m^-2&#8226;s^-1时,流态是稀密两相共存形式;当G_s>200～250 kg&#8226;m^-2&#8226;s^-1时,流态是浓相输送流态.两种流态之间可以相互转换,主要取决于颗粒质量流率的变化.影响立管内气固两相流的轴向压力、空隙率分布、气相的流动特性和气固流态存在形式的主要参数是颗粒质量流率G_s、旋风分离器入口速度V_i、下端流化床流化速度u_f,质量流率G_s是主要的影响因素.     

Voidage characteristics and prediction of bed expansion in liquid-solid inverse fluidized bed

Studies on voidage fluctuations, axial voidage profile and bed expansion are carried out by measuring the local void fraction using particles of wide ranging characteristics in liquid-solid inverse fluidized bed. The quality of fluidization is elucidated by the local voidage fluctuations. The RMS voidage fluctuation depicts a maximum with respect to average bed void fraction and increases with increase in Archimedes number. The fluidization quality has been quantified using average normalized RMS voidage fluctuation in terms of Transition number. The axial void fraction is almost uniform throughout the bed except for particles with size distribution. All the literature and present experimental data on bed expansion are unified in terms of Richardson and Zaki equation using experimental terminal velocities. A new correlation is proposed for predicting the wall effect corrected experimental terminal velocities, as a substitute for standard drag equation. The bed expansion data are also predicted using the drift flux model.