波纹流道中流体流动特性的数值与实验研究

引　言翅片是紧凑式热交换器和化工设备的基本元件之一 ,对传热传质过程的强化起着重要作用[1～ 4].本文研究的波纹型翅片是翅片型式的一种 ,它是在平直翅片的基础上压成一定的波纹 ,横截面形状类似于平直翅片 .这种波纹形结构导致了很复杂的流动 ,使流体在弯曲流道中不断地改变流动方向 ,以促进流体的湍流 .有关波纹型翅片方面的研究报道很少 .波纹型流道的计算比较复杂 ,文献 [5,6]采用不同的方法、不同的网格生成技术对波纹形流道充分发展段的层流流场和温度场进行了数值模拟 .本文运用ＳＩＭＰＬＥ算法对波纹形流道的流场分布进行模拟计…     

LDV和CFD在流体混合中的应用进展

采用激光多普勒测速仪LDV (LaserDopplerVelocimetry)测试技术和计算流体力学CFD (ComputationalFluidDynamics)方法 ,可获取搅拌槽中的速度场、浓度场等。从更微观的角度研究混合 ,对于混合设备的优化设计、放大和混合的基础理论研究具有重要意义。综述了此领域的进展情况     

规整填料内单相流的LDV实验研究

To date, many models have been developed to calculate the flow field in the structured packing by the computational fluid dynamics （CFD） technique, but little experimental work has been carried out to serve the vali-dation of flow simulation. In this work, the velocity profiles of single-phase flow in structured packing are measured at the Reynolds numbers of 20.0, 55.7 and 520.1, using the laser Doppler velocimetry （LDV）. The time-averaged and instantaneous velocities of three components are obtained simultaneously. The CFD simulation is also carried out to numerically predict the velocity distribution within the structured packing. Comparison shows that the flow pattern, velocity distribution and turbulent kinetic energy （for turbulent flow） on the horizontal plane predicted by CFD simulation are in good agreement with the LDV measured data. The values of the x-and z-velocity components are quantitatively well predicted over the plane in the center of the packing, but the predicted y-component is sig-nificantly smaller than the experimental data. It can be concluded that experimental measurement is important for further improvement of CFD model.     

一种双扭转流换热器壳程传热性能与机理分析

双扭转流换热器是一种新型管壳式换热器,分别建立扭转流换热器和新型双扭转流换热器的周期全截面计算模型,利用计算流体力学（CFD）方法对壳体侧的传热系数、流动阻力和综合性能进行了数值研究。结果表明：在壳程同等质量流量下,双扭转流换热器传热系数与类梯形折流板换热器相比降低24.4%~27.9%,压降降低63.3%~71.0%,综合性能增加1.2%~4.1%。通过场协同原理对其传热和降阻机理进行了分析,表明双扭转流换热器速度与压力梯度协同较好,扭转流换热器速度与温度梯度协同性较好。对扭转流换热器进行冷模实验,采用激光多普勒测速仪（LDV）对线上速度进行测量,验证了仿真方法和结果的正确性和准确性。研究模型与结论可为换热器的结构开发与性能研究提供参考。     

三角形螺旋流道层流流动及换热特性模拟

应用CFD软件研究了直角三角形螺旋流道内层流流体的流动及换热特性,得到了充分发展条件下流体的速度场及温度场,分析了换热壁面局部努塞尔数Nuloc的分布及流道结构对三角形螺旋流道内流体流动及换热的影响。结果表明:层流状态内,流体在流道横截面上产生的二次涡为稳定的两涡结构;受二次流的影响,换热壁面上各点的努塞尔数并不一致,其峰值出现在靠近二次涡中心位置的换热壁面处。增大雷诺数及量纲一曲率,使得局部努塞尔数峰值明显增大,且会使换热面中心弱传热区增大。平均努塞尔数随着雷诺数或曲率的增大而增大,但相应的阻力系数也会随之增加。     

双波纹板束逆流传热与流动的数值模拟和实验研究

利用Fluent软件对一种全焊式双波纹板式换热器的板束传热与流动性能进行数值模拟,运用场协同原理进行强化传热机理分析的同时对双波纹板式换热器进行传热实验,验证数值模拟和理论分析的合理性。结果表明：双波纹结构使得流体在流道形成湍流,减薄板片的层流边界层并且改善了主流区域的速度与温度梯度的协同程度,强化传热。双波纹板束本身的传热系数受到板束热侧入口尺寸的影响,并且在固定尺寸上达到峰值,增大冷热流体入口速度可以提升板束的传热能力,同时也受到压降增大的影响。     

波纹内翅片管的管内对流换热特性研究

通过实验研究了波纹形内翅片换热管的对流换热和阻力特性,拟合了所测Re范围内对流换热和阻力实验关联式,并运用相同质量流量、相同泵功率、相同阻力降这三种准则比较了该翅片管与普通光管之间的传热效果。结果表明,这种波纹形内翅片管有较强的换热效果,特别是在低Re条件下,强化效果更加明显。     

规整波纹填料内气体流动和传质的CFD模拟

为了研究规整填料局部特征单元内流体的流动状况和传质效果,采用计算流体力学的方法对JKB-250Y交叉波纹填料以及增加隔板后的JKB-250Y交叉波纹填料进行了模拟计算比较。结果表明,加入隔板后有效改善了传质的局部均匀性,并且消除了两股气体交叉流动带来的阻力,降低了通道的单位压降。增加隔板后的交叉波纹填料压降比传统交叉波纹填料压降降低20%~50%,增加隔板后的交叉波纹填料传质系数比传统交叉波纹填料传质系数提高约20%,可见提高传质分布的局部均匀性是提高传质效率并且降低阻力的较为有效途径之一。     

波纹壁面上流动液膜涡的生成特性

针对液膜在非平整壁面上流动过程中生成涡的现象,基于VOF方法,采用FLUENT软件模拟了三维波纹壁面上的液膜流动。研究了波纹结构内涡结构的演化过程,分析入口Reynolds数、波纹结构、壁面倾角、流体黏度和表面张力对波纹结构内涡结构的影响。结果表明：随着时间的演化,涡的大小和形状不断变化,最终达到稳定。且涡结构变化对自由液面的波动影响显著。较低Re和波形度时,波纹结构内不易形成涡,随着Re和波形度增大,产生涡且涡呈增大趋势,涡的形态也随之改变,自由液面位置升高,其相位滞后于波纹壁面。当壁面倾角改变时,波纹结构内的涡特性变化较大,液膜厚度略有增加,而自由液面相位不明显。表面张力对涡结构有显著影响,液膜流动过程中不容忽视。流体黏性改变时,波纹结构内涡的大小和形状无明显的变化。黏度变小和忽略表面张力时,液膜厚度均变薄。以上结果为工业设备生产、运行和设计提供了一定参考依据。     

双阀重波纹导向浮阀塔板的流体力学性能

采用空气-水系统,在直径1 000 mm圆形塔内对3种不同配比的双阀重波纹导向浮阀塔板流体力学性能进行了实验研究。在开孔率15.25%,堰高30 mm,板间距600 mm,3种液流强度下,测定了不同配比的双阀重波纹导向浮阀塔板干板压降、湿板压降、雾沫夹带率和漏液率等流体力学性能参数,并与单阀重波纹导向浮阀塔板进行了相互对比。实验表明:双阀重波纹导向浮阀塔板能够有效地降低雾沫夹带以及漏液,尤其在液流强度较小的时候更加明显,但同时会造成压降升高。其中,配比为26.56%的双阀重波纹导向浮阀塔板在压降增加较小时能够大幅提高雾沫夹带性能,综合性能优越,具有一定工业使用价值。其压降、雾沫夹带率、漏液率的关联公式通过实验数据拟合得出。     

Experimental and computational fluid dynamics modeling of double-partition divided-wall column for flow hydrodynamics and wall heat transfer characteristics

The aim of this study is to investigate the flow hydrodynamics and wall heat transfer characteristics on the tray of a two-staggered walled region in a double-partition divided-wall column (DPDWC). An experimental setup of DPDWC is designed, and a theoretical temperature gradient (TG) model based on Fourier's equation, which describes the wall heat transfer, is proposed. A coupled computational fluid dynamics-TG model is developed to analyze the heat transfer characteristics across partitions of DPDWC. The effects of liquid velocity, gas velocity, and different wall thermal boundary conditions on the flow and temperature fields are studied. The results indicate that the lack of a gas cone near partitions led to few vertical backflows of the liquid phase on the tray. Furthermore, the TGs near the liquid phase outlet increased with an increase in the liquid phase velocity. This work provides a scope for design and operation of DPDWC for industrial implementation.     

三维槽道的周期性层流流动与传热

应用数值模拟方法分析了以周期性方式布置不同节距比(PR=L/H)、倾角为45°挡板槽道的流动特性与传热特性。挡板在槽道上下壁面对齐布置高度比(BR=b/H)为0.2,以便在槽道内部形成一对沿流向的反向旋涡。数值模拟计算Reynolds数范围为100~1000,流体介质为空气。计算结果表明:布置斜置挡板后,在槽道内诱导产生了沿流向的旋涡流,且在测试段中旋涡流冲击槽道上下壁面和槽道一侧壁面,结果使得传热效率提高;分析了范围内平均Nusselt数比Nu/Nu₀、摩擦系数比f/f₀及传热增强系数η随节距比PR和Reynolds数的变化关系,并建立了相应的准则关系式;当挡板间节距比为0.5时,传热增强系数可达最大值3.0。     

刚性波纹面与柔性波纹面传热及流动特性

采用大涡模拟方法,对流体在刚性及柔性波纹面上的流动与传热特性进行了数值研究。结果表明:对于刚性波纹面,当振幅与波长比值(a/λ)较小时,波谷区域无回流现象;当a/λ增大至0.03时,波谷区域出现回流区,且回流区域随波幅的增加而增大;波纹面上坡部位沿展向出现较高Nusselt数的斑块;当a/λ从0.01增至0.04时,时均Nusselt数提高了近63.5%,综合系数增加了0.5112。对于柔性波纹面,其压力分布也呈现周期性变化;且在上坡位置也出现较大Nusselt数斑块;当a/λ从0.01增至0.04时,时均Nusselt数值提高了173.1%,综合系数增加了1.1232。与刚性波纹面相比,在消耗相同流体输送泵功时,柔性波纹面具有更好的传热效果。     

An application of MACSYMA in solving the laminar flow of micropolar fluid in a meandering channel

Plane laminar micropolar fluid flow in a meandering channel of constant width is considered. A perturbation scheme based on the assumption of slow and slight curvature of the centreline is used to study the effect of curvature and various micropolar parameters on some flow properties. The symbol manipulation system MACSYMA is used to generate the successive perturbation equations. The effects of two different types of boundary conditions are investigated. The second approximation is given for a general centreline geometry. Results indicate that to the order of approximation considered, pressure gradient along the centreline is increased while shear stress on the walls is decreased for micropolar fluids and the effect of curvature becomes more pronounced with increasing micropolarity.     

螺旋折流板换热器壳程流动特性

可视化实验研究了透明螺旋折流板换热器的壳程速度分布特征,重点研究了轴向速度的分布规律及对应的机理。结果表明,轴向速度按照折流板的螺旋周期呈周期性变化,不同流量下同一测点的轴向速度分布规律相似。轴向速度在换热器壳程周边区域分布比较均匀,沿轴向变化幅度较小,流动相对稳定,湍流度较低。由于受三角区漏流的影响,管束中心区域轴向流速急剧增大,沿轴向变化幅度较大,稳定性差,湍流强度较高。中心区域轴向速度平均值明显高于外围区域,离换热器中心越近,轴向速度越大。随着壳程流量的增大,中心区域轴向速度的增幅高于外围区域。管束中心处轴向速度波动剧烈,壳程流量较小时,中心处轴向流速平均值最大,随着流量的增加,湍流度增大,流体返混现象明显,中心处轴向流速平均值逐渐减小。     

Study on the flow characteristics and mixing performance of multi-blade combined agitator

Developing an agitator suitable for wide viscosity range is of great significance to the energy saving and efficiency improvement by the intensification of fluid flow and mixing process. The power characteristics, flow field distribution, turbulence characteristics and mixing performance of multi-blade combined (MBC) agitator under laminar to turbulent flow state were studied experimentally and numerically at the level of large eddy simulation. The predicted power curve is consistent with the experimental results. Tangential flow is the main flow in laminar flow. With the increase of Reynolds number (Re), axial and radial flows in the vessel gradually increase. When Re reaches 486, the velocity field distribution is basically the same as that in the turbulent flow. At the same energy consumption level, MBC agitator is superior to the commercial Maxblend agitator in mixing high viscosity fluid. The intensification of axial and radial flows is due to the dispersed arrangement of the blades, enabling the MBC agitator to achieve larger axial and radial flows from the transitional flow to the turbulence state. Moreover, the turbulent kinetic energy is evenly distributed and the mixing process is significantly accelerated.     

多叶片组合式搅拌桨釜内流动特性和混合性能研究

开发可适用于较宽黏度范围的搅拌桨,强化釜内的流体流动和混合过程对于搅拌釜的节能增效具有重要的意义。实验与数值模拟相结合,在大涡模拟层面研究了多叶片组合式搅拌桨(MBC桨)从层流到湍流状态下,釜内的功率特性、流场分布、湍流特性和混合性能。结果表明:预测的功率曲线与实验结果一致;层流状态下釜内以切向流动为主,随着Reynolds数(Re)的增大,釜内轴向和径向流动逐渐增强,当Re达到486时,速度场分布与湍流状态下基本一致;在相同的能耗水平下,MBC桨对高黏度流体的混合性能优于商业Maxblend桨。桨叶的分散组合布置,强化了釜内的轴向和径向流动,使得MBC搅拌桨在从过渡流到湍流状态下均可实现较大的轴径向流动,湍动能分布较为均匀,混合过程显著加快。