气液降膜流动厚度及流速分布特性

对洗涤冷却管内垂直降膜的流动特性进行了研究,采用超声波多普勒测速仪,对气相影响下液膜的厚度和速度进行了无接触式的测量,实验液膜雷诺数为2.04×10~4,气相雷诺数范围0~6.83×10~4。结果表明:液膜在洗涤冷却管流动发展过程中明显存在中央液膜向两边铺展的现象,铺展规律受气相雷诺数及出口槽缝尺度影响显著。管内周向角8和16°处局部液膜波动较其余周向位置剧烈并有增厚的趋势,且气相雷诺数和槽缝宽度的增大均使这两处液膜增厚位置向后延迟,使得管内初始段膜厚变薄。此外,气相雷诺数增大加强气液两相间的剪切作用,整体上加剧了液膜波动幅度,液膜速度波动趋势更加显著。     

管内垂直下降液膜速度与厚度分布特性

对洗涤冷却管内垂直降膜的流动特性进行研究,采用超声波多普勒测速仪对管内不同周向以及轴向位置的液膜厚度和速度进行了无接触式的测量,液膜Reynolds数范围为1.0×10⁴~3.1×10⁴。结果表明:在0°周向位置上液膜厚度与速度均达到最大值,导致该位置局部液膜厚度过大而不能保持稳定,部分液体脱离液膜表面,此外还造成了8°和16°位置的液膜厚度激增。在轴向上,当Reynolds数小于2.0×10⁴时,液膜速度在重力作用下随流动距离增加而增加,反之,液膜速度因为流动阻力会随距离增加而减小。随着Reynolds数的增大,液膜平均厚度和速度呈增大趋势。此外,Reynolds数的增大还会使得液膜更加不稳定。     

单螺杆膨胀机螺旋槽道内液膜分布均匀特性

螺旋槽道内均匀分布的液膜厚度对减小气体泄漏,保证膨胀机高效稳定运行至关重要。本文采用VOF两相流数值模型,主要探讨螺旋槽道结构参数对y方向液膜膜厚均匀度分布的影响规律。根据前期试验获得的螺旋槽内两相环状流的试验数据验证了数值模型的准确性,给出了入射角度η=0.90β时,液膜沿螺旋槽道内的演变过程。可以看出,当η=0.90β时,扭转效应对螺旋槽液相分布的影响基本可以忽略不计,螺旋槽外侧液膜厚度沿y方向基本呈均匀分布。理论分析不同无量纲节距和曲率比对y方向液膜厚度均匀度的影响规律,结果表明：随着螺旋槽道无量纲节距的增大,液膜厚度均匀度有所增加,随着曲率比的增大,液膜厚度均匀度降低。     

洗涤冷却管出口处的射流深度和界面波动特性

采用压差传感器和高清摄像仪对洗涤冷却管出口处射流深度和洗涤冷却室内气液界面波动特性进行了冷模实验研究,研究发现,随着表观气速的增大,射流深度呈指数式增大,由此提出了主流射流深度与洗涤冷却管出口处动量通量的经验式,其最大射流深度可达2.51 cm,同时采用VOF模型和RNG κ-ε 湍流模型对其进行了模拟计算,模拟结果与实验结果吻合良好。研究结果还表明,洗涤冷却管出口处液面波动对床层内气液两相环流脉动的影响较为显著。     

洗涤冷却环内液体冷态流动行为数值模拟

为了研究洗涤冷却环内冷却水流动的情况,借助计算流体力学软件Fluent建立了洗涤冷却环流体冷态流动的数学模型,同时为了验证模型的可靠性,对洗涤冷却环出口处的流动情况进行了实验研究,实验结果与模拟结果基本吻合。结果表明：因为洗涤冷却环的结构限制,其内部存在多处涡旋区域;内室入水口周向位置处的涡旋运动最为剧烈;受其影响,入水口周向位置的射流孔出口平均速度最小,两入水口之间周向位置的射流孔出口平均流速最大;槽缝出口的平均流速在周向上的分布与射流孔出口平均流速分布相同。     

洗涤冷却环内液体冷态流动行为数值模拟

为了研究洗涤冷却环内冷却水流动的情况,借助计算流体力学软件Fluent建立了洗涤冷却环流体冷态流动的数学模型,同时为了验证模型的可靠性,对洗涤冷却环出口处的流动情况进行了实验研究,实验结果与模拟结果基本吻合。结果表明:因为洗涤冷却环的结构限制,其内部存在多处涡旋区域;内室入水口周向位置处的涡旋运动最为剧烈;受其影响,入水口周向位置的射流孔出口平均速度最小,两入水口之间周向位置的射流孔出口平均流速最大;槽缝出口的平均流速在周向上的分布与射流孔出口平均流速分布相同。     

管内垂直下降液膜速度与厚度分布特性

对洗涤冷却管内垂直降膜的流动特性进行研究,采用超声波多普勒测速仪对管内不同周向以及轴向位置的液膜厚度和速度进行了无接触式的测量,液膜Reynolds数范围为1.0×10~4~3.1×10~4。结果表明:在0°周向位置上液膜厚度与速度均达到最大值,导致该位置局部液膜厚度过大而不能保持稳定,部分液体脱离液膜表面,此外还造成了8°和16°位置的液膜厚度激增。在轴向上,当Reynolds数小于2.0×10~4时,液膜速度在重力作用下随流动距离增加而增加,反之,液膜速度因为流动阻力会随距离增加而减小。随着Reynolds数的增大,液膜平均厚度和速度呈增大趋势。此外,Reynolds数的增大还会使得液膜更加不稳定。     

电导法测量新型旋风分离器内液膜的分布规律

根据电导率变化原理设计了双平行电导探针,并采用该探针对新型旋风分离器内的液膜分布进行了研究。通过对不同结构参数和操作条件的研究发现,液膜沿筒体呈不对称分布,入口附近截面上的液膜随着轴向距离的增大其最厚值点沿圆周后移,液膜呈螺旋带状下行;发展后的液膜厚度在不同截面的最大值在160°左右的圆周角度处。研究还表明,随着处理负荷的增加,切向速度增大,液膜的分布区域变大,有利于分离效率的提高,但整体液膜厚度变薄,不利于减缓筒壁的磨损;入口角度的变化对撞击区附近的液膜分布影响较大,入口角度越大,切向力在径向上的分量越小,液膜的分布范围越小;另外,随着升气管直径的增加,由于分离空间变小,整体液膜厚度增加。     

高雷诺数下管内垂直降膜瞬时厚度空间分布及波动特性

研究了高雷诺数条件下(Rel=2.04×104)洗涤冷却管内下降液膜的空间分布及波动特性。采用超声波多普勒测速仪对不同轴向和周向位置的下降液膜瞬时厚度进行了无接触测量。结果表明:在高雷诺数条件下,管内液膜处于高湍动状态,液膜表面波动剧烈,平均参数无法准确描述液膜空间分布及波动特性。随着轴向和周向距离的增加,膜表面波动幅度及大波频率减少,小波频率增加。轴向上,液膜瞬时厚度概论密度分布函数(PDF)曲线波峰高度随轴向距离增加而增高;周向上,PDF曲线呈单峰-双峰-单峰分布。     

水平烧结管降膜蒸发器管外流动分析

烧结管由光滑圆管外表面烧结铝合金或铜合金粉末制备，用于水平管蒸发器传热元件，实现高效传热。模拟分析烧结层材质、喷淋孔流量和烧结层孔隙率对烧结管管外液膜分布的影响。结果表明：比较液柱截面及波峰截面的平均液膜厚度，铝合金烧结层减薄了52.22%,而铜合金烧结层减薄了56.12%,故铝合金烧结层液膜流动较稳定。当烧结层为铝合金时，在喷淋孔流量Q_v=140—200 L/h,液膜厚度随着流量增大而增大，增大幅度达到了16.52%。当Q_v=160 L/h时，流速随着液膜厚度增大逐渐减小；随着孔隙率增大，液膜厚度在周向角度θ=0°—160°时增大，在θ=160°—170°时减小。当孔隙率n=50%时，平均液膜厚度减薄率较小，表明液膜厚度均匀性较好。2种烧结管表面均可形成连续的流动液膜，烧结层增大了工质接触管壁的传热面积。     

Identification of Flow Regimes in Slot‐Rectangular Spouted Beds using Pressure Fluctuations

Pressure fluctuation data recorded in slot‐rectangular spouted beds of 1.44 mm diameter glass beads were analyzed with the aid of statistical and chaotic tools. The column width was maintained at 150 mm, while the thickness and slot width were both varied. It is shown that there are significant shifts in both statistical and chaos measures as the gas flow rate is increased. The results suggest that pressure fluctuations can be used to provide diagnostics of flow regime transitions in spouted beds when viewing is impossible.     

波纹板填料表面液体降膜流动的特性分析

基于降膜流动实验台,结合计算流体力学方法(Computational Fluid Dynamics, CFD)研究了波纹板表面液体的平均液膜厚度和有效润湿面积等定量信息,并通过三维模拟进一步分析了喷淋密度和波纹倾斜角度β对降膜流动特性的影响。结果表明,液体在波纹板表面的流动并非均匀,分为沟流和溪流两种形式;当喷淋密度较小时,液体在波谷内形成沟流,当喷淋密度达到400 m3/(m2?h),液体跨越相邻波纹进行溪流流动;两种形式波纹板整体的润湿性能均较差,且液膜厚度分布不均;波纹倾斜角度对降膜流动特性影响较大,90°时更有利于提高有效润湿面积。     

丝网板液膜流动及传质

采用液膜流动测定及CO₂吸收实验较为系统地考察了固体壁面与丝网壁面液膜流动差异, 以及网孔尺寸对降膜流动及传质影响, 结果表明:在较低Re下, 丝网结构对液膜波动存在一定抑制作用。两种结构的壁面液膜波动振幅整体上随Re及距进口位置的增加而有所增加, 相比于固体壁面, 丝网壁面在沿流动方向不同位置处平均膜厚及波动振幅差异更小, 且在较低Re(<80)下, 液膜波动对液量更为敏感。不同孔径丝网板液膜流动观测结果表明, 液膜瞬时波动振幅及波动频率随丝网孔径的增加均出现了先增加后减小的变化趋势;在不同物系下, 当网孔尺寸≤2 mm时, 膜厚随网孔尺寸的增加逐步增大, 后随着网孔尺寸的进一步增大, 膜厚逐步减小。此外, CO₂吸收实验结果显示, 随着丝网孔径的减小, 测试板传质性能提升明显, 但单位面积网丝对传质贡献减少。     

Computational Fluid Dynamics Modeling of Gas‐Liquid Two‐Phase Flow around a Spherical Particle

Microscale studies, which can provide basic information for meso‐ and macroscale studies, are essential for the realization of flow characteristics of a packed bed. In the present study, the effects of gas velocity, liquid velocity, liquid‐solid contact angle, and liquid viscosity on the flow behavior were parametrically investigated for gas‐liquid two‐phase flow around a spherical particle, using computational fluid dynamics (CFD) methodology in combination with the volume‐of‐fluid (VOF) model. The VOF model was first validated and proved to be in good agreement with the experimental data. The simulation results show that the film thickness decreases with increasing gas velocity. This trend is more obvious with increasing operating pressure. With increasing liquid velocity, the film thickness tends to be uniform on the particle surface. The flow regime can change from film flow to transition flow to bubble flow with increasing contact angle. In addition, only at relatively high values does the liquid viscosity affect the residence time of the liquid on the particle surface.     

Polymer melt differential electrospinning from a linear slot spinneret

Preparation of melt electrospun fibers with high efficiency and high productivity remains a big challenge. A polymer melt differential electrospinning system with linear slot spinneret (LSSP) was proposed in this work. Under a high electric field, multiple jets distributed at the tip of LSSP were self-organized from the polymer melt film with controlled thickness. The spinning parameters were investigated, and the electric filed between spinneret and collector was analyzed. The results showed that the interjet distance decreased significantly with the decrease of the thickness of polymer melt film and the Tayler cone size. The smallest average interjet distance of 1.9 mm with deviation of 0.5 mm was obtained under the condition of applied voltage of 45 kV, collecting distance of 9 cm, temperature of 250 °C, and slot thickness of 0.2 mm. The high output of 75.6 g/h was achieved and could be increased just by increasing the slot width. It was demonstrated that the proposed technology was a promising way to fabricate melt electrospun fibers with high efficiency. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48922.     

Effect of counter current gas phase on liquid film

Liquid film flow is very important in many industrial applications. However, there are few reports about its characteristics on structured packings. Therefore, in this paper, liquid film phenomena were investigated experimentally to exploit new approaches for intensifying the performance of the structured packings. All experiments were performed at room temperature. Water and air were the working fluids. The effect of counter current gas phase on the liquid film was taken into consideration. A high speed camera, a non-intrusive measurement technique, was used. It is shown that both liquid and gas phases have strong effects on film characteristics. In the present work, liquid film width increased by 57% because of increasing liquid flow rate, while it decreased by 25% resulting from the counter current gas phase.     

Computational fluid dynamic simulations on liquid film behaviors at flooding in an inclined pipe☆

The complex liquid film behaviors at flooding in an inclined pipe were investigated with computational fluid dynamic (CFD) approaches. The liquid film behaviors included the dynamic wave characteristics before flooding and the transition of flow pattern when flooding happened. The influences of the surface tension and liquid viscosity were specially analyzed. Comparisons of the calculated velocity at the onset of flooding with the available experimental results showed a good agreement. The calculations verify that the fluctuation frequency and the liquid film thickness are almost unaffected by the superficial gas velocity until the flooding is triggered due to the Kelvin–Helmholtz instability. When flooding triggered at the superficial liquid velocity larger than 0.15 m·s?1, the interfacial wave developed to slug flow, while it developed to entrainment flow when it was smaller than 0.08 m·s?1. The interfacial waves were more easily torn into tiny droplets with smaller surface tension, eventual y evolving into the mist flow. When the liquid viscosity increases, the liquid film has a thicker holdup with more intensive fluctuations, and more likely developed to the slug flow.     

螺旋槽液膜密封端面空化发生机理

液膜中空化的发生直接影响着密封流体动压润滑性能,基于质量守恒的JFO边界条件,建立考虑表面粗糙度的螺旋槽液膜密封物理模型,经坐标变换将不规则物理域转换成规则计算域,采用有限控制体积法离散控制方程并求解,分析了膜厚、表面粗糙度、螺旋槽功用（上游泵送和下游泵送）、螺旋槽开槽位置及空化压力对液膜中空化发生的影响。结果表明：较小膜厚工况易促生空穴,而较大膜厚易削弱空穴,且随着膜厚增大,表面粗糙度的影响降低甚至被忽略;当密封为上游泵送型时,空穴区周向宽度明显大于下游泵送型,而螺旋槽位置对空化的影响与螺旋槽功用密切相关;选取较小空化压力使空穴缩减,而较大者反之,且后者对提升液膜承载有利。     

Numerical study on falling film flowing characteristics of R113 inside vertical tube under different structural conditions

To develop an appropriate falling film evaporation device for organic fluid cogeneration, a numerical study on the gas–liquid two-phase counter-current flow characteristics of R113 inside a vertical tube under different structural conditions was conducted using the Fluent software. The effects of the tube length, tube diameter, and annular gap on the falling film flow characteristics were determined, respectively. The results indicated that under a certain spray density, the falling film thickness in the region of the steady section was almost constant with different structural parameters for the tube diameter, tube length, and annular gap. In addition, a smaller tube diameter resulted in a steadier film flow. When the tube diameter decreased to a specific value, the film thickness showed a uniform distribution along the wall surface. This indicated that a best falling tube diameter exists. Meanwhile, the film fluctuation was enhanced with an increase in the tube length. When the tube length was greater than 1.2 m, the falling film splashed and could not completely wet the wall surface. The film fluctuation was enhanced by decreasing the annular gap, and the film could not be formed when the annular gap was smaller than 1.2 mm.