气液逆流洗涤器内两相流场的实验研究与数值模拟

采用RNG k-ε湍流模型和欧拉双流体多相流模型模拟了气液逆流接触洗涤器内的两相流场,将计算结果用实验验证.通过考察两相流速、湍流强度、压降、气含率等参数验证了模型的可靠性,对不同喷嘴结构和操作条件下的泡沫区流场特性进行了模拟分析.结果表明,气液撞击形成的泡沫区湍流强度高,气液两相径向与切向速度较大,轴向速度较小,可用湍流强度大小表征泡沫区的大小.泡沫区占整个洗涤器的体积分数β随气液质量流量比增大先增大后减小,气液质量流量比为0.0096时达峰值;随进液轴/切流量比增大β先增大后减小,流量比为0.66时达峰值.喷口直径为8 mm、切向进液倾斜角为60°时气液传质效果最好.     

气体分布器对气升式反应器内流场和传质特性的影响

在气升式反应器冷模实验装置中,研究了气体分布器类型及结构参数对流场和传质的影响规律。结果表明：与环形分布器和四喷嘴分布器相比,采用半球形分布器时平均气含率更高、气含率径向分布更均匀、气泡直径更小、比表面积更大、下降段液速更大、液相体积传质系数更高。气升式废水处理反应器中选用半球形气体分布器可获得更好的混合和传质效果。进一步考察了半球形分布器开孔率和开孔角度对气含率、下降段液速和体积传质系数的影响,确定了最优开孔率为0.457%、最优开孔角度为45o。研究结果可为气升式反应器的工业设计和操作优化提供依据。     

一种新型自吸式喷嘴喷射性能初步研究

建立实验装置,研究一种带凸形圆环结构的新型自吸式气液二相喷嘴的吸气溶氧性能。以吸上真空度和溶解氧为目标,考察喷射口直径、凸形圆环缩颈直径与喷射口直径比、锥形喷射口与凸形圆环缩颈上端间距离等参数对喷嘴喷射性能的影响,并与普通喷嘴对比。结果表明:上述3个参数均能影响溶氧能力,而喷射口直径、凸形圆环缩颈直径与喷射口直径比则主要影响吸上真空度;相同液体流量下,新型喷嘴吸上真空度和溶氧能力均好于普通喷嘴;较优的结构参数是喷射口直径D、凸形圆环缩颈直径与喷射口直径比为1.2、锥形喷射口与凸形圆环缩颈上端间距离则为4D。     

气体搅动的筛板萃取塔性能实验研究

在筛板萃取塔中引入气体搅动,既能明显提高装置的传质效率,又能大幅提高装置处理能力。筛板塔的通量随气速的变化规律与填料塔有显著区别,其性能研究有重要意义。利用煤油(苯甲酸)-水-空气体系,考察了气体搅动和筛孔直径对萃取塔流体力学和传质性能的影响。结果表明,随着表观气速的增加,气含率、分散相含率、液泛速率和传质效率均明显增加。但过高的气速也会导致分散相的过于分散和乳化,传质性能下降,直至液泛。不同直径的筛孔相比,较小的筛孔使分散相停留时间延长,分散相含率和传质效率提高,但液泛速率和处理能力降低。     

三相强制浆料环流反应器的局部传质行为

提出了一种新型的强制外循环三相环流反应器结构,根据结构特点及流动状态的不同,将反应器分为6个不同的流动区域. 在f300 mm′1700 mm的实验装置内,采用氧气气提-空气解吸法,详细考察了内环表观气速0.006~0.19 m/s、外循环液速0.03, 0.05 m/s、固含率5%, 10%, 15%时不同流动区域的体积传质系数. 发现外循环液流影响区体积传质系数最大,最高可达0.754 s-1,外环环隙区最小,不超过0.043 s-1,环流反应器整体体积传质系数与气液分离区体积传质系数接近. 适当扩大内、外环截面积比有利于提高环流反应器的传质性能. 环流反应器整体体积传质系数随内环表观气速和外循环液速的增加而增加,随颗粒浓度的增加略有降低.     

喷嘴结构对射流鼓泡反应器混合和传质性能的影响

喷嘴结构对射流鼓泡反应器的混合和传质性能具有重要的影响。以空气-水作为模拟介质,使用双探头电导探针、电解质示踪法和动态溶氧法,对比研究了缩径式圆形喷嘴和旋扭三角形喷嘴对射流鼓泡反应器中气泡尺寸分布、平均气含率、液相混合时间和气液传质系数的影响规律。实验发现,随着气速或液体射流Reynolds数的增大,两种喷嘴对应的平均气含率、液相混合时间和气液传质系数具有相同的变化规律;与缩径式圆形喷嘴相比,采用旋扭三角形喷嘴的射流鼓泡反应器中气泡尺寸更小,平均气含率更高,宏观混合时间更短;当气体输入功占总输入功比例超过20%时,喷嘴结构对气液传质系数的影响较小,当气体输入功占总输入功比例小于20%时,旋扭三角形喷嘴的气液传质性能优于缩径式圆形喷嘴。研究结果可为工业射流鼓泡反应器喷嘴结构的优化提供理论指导。     

喷嘴结构对射流鼓泡反应器混合和传质性能的影响

喷嘴结构对射流鼓泡反应器的混合和传质性能具有重要的影响。以空气-水作为模拟介质,使用双探头电导探针、电解质示踪法和动态溶氧法,对比研究了缩径式圆形喷嘴和旋扭三角形喷嘴对射流鼓泡反应器中气泡尺寸分布、平均气含率、液相混合时间和气液传质系数的影响规律。实验发现,随着气速或液体射流Reynolds数的增大,两种喷嘴对应的平均气含率、液相混合时间和气液传质系数具有相同的变化规律;与缩径式圆形喷嘴相比,采用旋扭三角形喷嘴的射流鼓泡反应器中气泡尺寸更小,平均气含率更高,宏观混合时间更短;当气体输入功占总输入功比例超过20%时,喷嘴结构对气液传质系数的影响较小,当气体输入功占总输入功比例小于20%时,旋扭三角形喷嘴的气液传质性能优于缩径式圆形喷嘴。研究结果可为工业射流鼓泡反应器喷嘴结构的优化提供理论指导。     

循环浆态床气液传质系数的研究

以空气-水-玻璃微珠和空气-石蜡油-玻璃微珠两种三相系统为研究对象,在常温常压下分别考察了液体介质的粘度等物性因素,表观气速、固含率、液体循环量等操作因素,气体分布器、分隔板等结构因素对循环浆态床反应器气液传质特性的影响.实验结果表明,气液传质系数随表观气速的增加而增加,随液体粘度和固含率的增大而减小,当表观气速和固含率增加到一定程度后,传质系数趋于稳定;低气速下,玻璃烧结板的传质效果较好,而较高气速时,多孔板和新型锐孔分布器的传质效果较好;分隔板能显著增大气液传质系数.对多孔板分布器实验数据进行了拟合,得出气液传质系数的经验关联式,关联式计算值与实验结果吻合良好.     

静止非牛顿流体中气泡生成过程的传质

气泡生成过程中气液传质是气液接触设备的设计、优化的重要参考指标。以二氧化碳气泡在羧甲基纤维素钠(carboxymethyl cellulose,CMC)溶液中生成过程中的传质为研究对象,分别考察了气速、CMC溶液浓度、针头直径对气泡生成过程气液传质的影响,采用具有CCD显微相机的动态接触角分析仪测量了气泡形状、表面积和体积的变化,进而获得气泡生成过程气液传质系数k_l。实验结果表明,CMC浓度从0.2%增加到0.8%,黏度逐渐增大,传质系数随CMC浓度的增大而增大;针头直径从2.5 mm增加到4 mm,传质系数也随之增大;气速从1 ml·min^-1增加到9 ml·min^-1,传质系数也逐渐增大。     

面积比及筛网对环流反应器流动与传质的影响

通过实验考察了具有不同上升区与下降区面积比的内循环气升式环流反应器气含率、循环液速以及循环流量等,确定了具有较高气含率、循环液速及循环流量的环流反应器结构。随后在环流反应器的上部布置筛网,改变气泡进入下降区的流动形态,考察筛网对于环流反应器流体力学以及传质性能的影响。结果表明:上升区与下降区面积比接近为1的反应器流动性能最好;在内套筒上部布置筛网会改变气泡由上升区进入到下降区的流动形态,流动形态分为3种,无气泡进入下降区、仅有小气泡进入下降区以及全部小气泡以及部分大气泡进入下降区。筛网孔径会影响环流反应器中的气含率、循环液速、循环流量以及传质系数,可以通过优化筛网孔径而提高流动与传质性能。     

Theoretical and experimental studies of confined vortex flow

A study of the air flow characteristics is reported for a vortex chamber 122 cm in diameter consisting of an upper cylindrical section 61 cm high and of a lower conical section 108 cm high. Measurements were made with a five-channel pressure probe of the radial profiles of tangential and axial velocities, with varying inlet air velocity and axial distance from the top of the chamber. Measurements of the static pressure profiles were made simultaneously. Finally, the angle of flow of the air entering through the single tangential inlet could be adjusted, and its effects on the flow recorded. From these results and from a theoretical analysis, generalized expressions for the tangential velocity profiles were obtained for the two regions of flow, forced-vortex and quasi-free vortex, which prevail in a confined vortex chamber, as a function of the entrance air velocity and of the radius at the point considered only. The angle of entering air was found to have no effect on the tangential velocity and only a minor effect on the static pressure distribution. The outlet diameter of the chamber was found to have a large effect on the profile of the axial velocities, reflecting the influence of the chamber static pressure on the latter.     

Theoretical and experimental studies of confined vortex flow

A study of the air flow characteristics is reported for a vortex chamber 122 cm in diameter consisting of an upper cylindrical section 61 cm high and of a lower conical section 108 cm high. Measurements were made with a five-channel pressure probe of the radial profiles of tangential and axial velocities, with varying inlet air velocity and axial distance from the top of the chamber. Measurements of the static pressure profiles were made simultaneously. Finally, the angle of flow of the air entering through the single tangential inlet could be adjusted, and its effects on the flow recorded. From these results and from a theoretical analysis, generalized expressions for the tangential velocity profiles were obtained for the two regions of flow, forced-vortex and quasi-free vortex, which prevail in a confined vortex chamber, as a function of the entrance air velocity and of the radius at the point considered only. The angle of entering air was found to have no effect on the tangential velocity and only a minor effect on the static pressure distribution. The outlet diameter of the chamber was found to have a large effect on the profile of the axial velocities, reflecting the influence of the chamber static pressure on the later.     

Numerical Simulation of the Two‐Phase Fluid Field in a Gas‐Around‐Liquid Spray Nozzle

A new gas‐around‐liquid spray nozzle (GLSN) was designed, and the two‐phase flow fluid field in this nozzle was simulated numerically. Flow characteristics under different structural parameters were obtained by changing the L/D ratio of the premixing chamber, incident angle, and inlet pressures. Increasing the L/D ratio and incident angle improved flow characteristics such as atomization flow, outlet velocity, and turbulence intensity. The nozzle performed optimally at an L/D ratio of 0.5 and incident angle of 60°. The atomization flow decreased with higher gas pressure and increased with higher liquid pressure. The outlet velocity mainly depended on the inlet gas pressure, not on the inlet liquid pressure. These results provide an indication for optimum structures and parameters of the GLSN.     

Overall mass transfer in the swirling flow induced by a tangential inlet between coaxial cones

An electrochemical method is used to measure mass transfer coefficients between an electrolytic solution and the inner core of a system formed by stationary coaxial cones of the same apex angle. A swirling decaying flow is induced by means of a tangential inlet at the system base. The average mass transfer coefficients are measured at three axial positions from the tangential inlet for both laminar and turbulent flow regimes. Pressure drops between the inlet and the outlet of the experimental device are also investigated. Flow visualization revealed the existence of axially fixed toroidal vortices. The overall mass transfer coefficients along the conical gap are found to be greater than those measured in annular swirling decaying flow for the same values of the annular gap thickness, of the tangential inlet diameter and of the Reynolds number based on the mean axial velocity at the bottom of the conical gap. The enhancement in mass transfer, up to 50% compared with that measured in a cylindrical arrangement, is not counter-balanced by an increase in pressure drop, which remains of the same order of magnitude as that measured in a classical annular configuration.     

Mass transfer and hydrodynamic characteristics in a co‐current downflow contacting column

Hydrodynamic and mass transfer characteristics of water–air system in a co‐current downflow contacting column (CDCC) were studied for various nozzle diameters at different superficial gas velocities and liquid re‐circulation rates. Gas hold‐up and liquid‐side mass transfer coefficient increased with increasing superficial gas velocity and liquid flow rate but decreased with increasing nozzle diameter. It is shown that correlations developed, which are based on liquid kinetic power per liquid volume present in the column, and superficial gas velocity explains gas hold‐up and the mass transfer coefficient within an error 20% for all gas and liquid flow rates and nozzle diameters used. The constants of correlations for gas hold‐up and mass transfer coefficient were found to be considerably different from other gas–liquid contacting systems. © 2003 Society of Chemical Industry     

蜗壳式旋风分离器内气相流场非轴对称特性分析

采用Fluent软件对蜗壳式旋风分离器内气相流场进行了数值模拟,并在此基础上对流场的非轴对称特性进行了机理分析。蜗壳式旋风分离器入口结构的非轴对称以及气相旋流的不稳定性造成了气流的旋转中心与旋风分离器的几何中心不重合,从而导致了气相流场三维速度的非轴对称分布以及速度分量由于基准不同而产生的大小和方向变化。环形空间流场的非轴对称性主要是非轴对称入口结构影响的结果,分离空间流场的非轴对称性主要是旋流的不稳定性造成的。根据Rayleigh准则,旋风分离器内旋流流场的不稳定性是固有的,提高流场的旋流数可使流场的不稳定性降低,流场的非轴对称性降低。入口速度的变化不影响旋流数,也不影响流场的非轴对称性,但增加入口截面积比或减小量纲1升气管内径均可提高流场的旋流数,使流场的非轴对称性降低。旋风分离器的非轴对称性可以用角动量参量来描述。     

A new liquefaction method for natural gas by utilizing cold energy and separating power of swirl nozzle

A swirl nozzle with a central body was newly designed to make full use of the cold energy and separating power, and the coupling of swirling flow and condensation was realized based on a condensation model, a droplet surface tension model and a Reynolds stress model turbulence model. The flow and condensation characteristics of methane gas under supersonic swirling flow conditions were studied. The results show that the flow and condensation parameter distribution in the swirl nozzle are similar under varying swirling intensities, but the swirling performance improves with the increase in swirling intensity, and a tangential velocity is beneficial before the gas enters the nozzle. As the inlet temperature decreases or the inlet pressure increases, the liquefaction efficiency increases, and the gas condensation process can be promoted. With the advancement of the initial nucleation position and the increase in the droplet radius, the separation efficiency of the swirl nozzle increases.     

三相下喷式环流反应器的传质性能

在三相非牛顿型流体体系中，对下喷式环流反应器传质特性进行了实验研究。讨论了表观气速、能量耗散速率、导流筒直径与反应器直径比、喷嘴直径、导流筒下端距反应器底部的距离、固体装填量、羧甲基纤维素钠（ＣＭＣ）溶液浓度及其流变特性对它的影响。实验结果表明，容积传质系数随表观气速和能量耗散速率的增加有所增加，在实验条件下，发现最优的导流筒直径与反应器直径比在０．４～０．４５这一范围、固体装填量大约为３％（体积百分比）、导流筒下端距反应器底部的距离为０．０８ｍ左右。同时提出了容积传质系数的经验关联式。     

Bubble formation in cocurrently upward flowing liquid

The effects of liquid velocity, nozzle diameter, gas chamber volume and gas flow rate on volumes, shapes and growth curves of bubbles formed at a nozzle submerged in a cocurrently upward flowing liquid in a bubble column were experimentally investigated. The bubble volume decreases with increasing liquid flow velocity. The effect of liquid flow velocity on the volume of bubble increases with an increase in the gas flow rate. To simulate bubble formation at a nozzle submerged in cocurrently upward flowing liquid, a revised non-spherical bubble formation model was proposed. Bubble volumes, bubble growth curves and shapes experimentally obtained in this study, as well as in previous experimental studies, are well predicted by the present model.     

Flow field in the freeboard of vortexing fluidized bed

A systematic investigation on the flow field in a vortexing fluidized bed cold model was reported. The gas velocity profiles within the freeboard with diameters of 0.19 m and 0.29 m were measured by using a five-hole pitot tube. A new parameter, called vortex number, V_or defined as the ratio of tangential velocity to axial velocity of the swirling gas stream, was proposed for representing the swirl intensity. V_or is found to be increased with secondary air velocity, and decreased with primary air velocity and diameter of secondary air nozzles. It is also found that the profile of swirl flow is significantly affected by the arrangement of the secondary air nozzles. The effects of inserted length of secondary air nozzles and geometric structure of expansion section on the swirl flow are also studied. Based on the experimental data, a correlation is presented to estimate the vortex number. Vortex number is found to be a function of the geometric structure of exhaust tube, diameter of secondary air nozzle and tangential air flow rate.