界面物性对液滴聚结的影响

推导了分散相液滴运动轨迹模型和分层二相流基本流模型,并优化了计算方法。直接数值模拟结果表明：当层膜厚度和板宽变化时,流场的密度、黏度以及界面张力对界面处的液滴的作用方式不相同;黏度始终对液滴聚结产生明显的影响,而密度和界面张力对聚结的影响却因流场结构的变化而有所不同;密度、黏度及界面张力的变化使得液滴的顺时针或逆时针旋转运动更加具有倾向性。因此,密度和黏度在一定程度上可用于改善流场的聚结条件。数值模拟的结果与已知的实验结果吻合较好,而且,基本流的介入使得该模型能较好地反映液滴在分层二相流流场中的运动特性。     

新型液-液分离设备——斜板沉降器

介绍了斜板沉降器的结构和操作特性，并对液滴在斜板层膜上的聚结过程以及影响液滴聚结的因素进行了分析；提出了液滴在斜板上有效聚结作为斜板沉降器的设计依据，最后对斜板沉降器的进一步研究重点提出了建议。     

重力式油气分离器内聚结元件分离流场的数值模拟

应用标准к-ε模型和多相混合模型,对重力式油气分离器内聚结元件分离流场进行了三维数值模拟,通过改变进入分离器液滴粒径来模拟其在加装了蛇形相向平行板型和田字型聚结板的分离器中的流场,研究粒径对于聚结板聚结性能的影响,研究结果表明:聚结板并非能够聚结沉降所有粒径下的液滴,对于粒径在50μm以下的液滴,蛇形相向平行板型聚结板无法有效使之聚结并沉降下来;对于粒径在75μm以下的液滴,田字型聚结板无法有效使之聚结并沉降下来。对于粒径在175μm以上的液滴,在模拟用边界条件下,上述两种聚结板也无法使之有效聚结沉降。而粒径在75μm至175μm之间的液滴,现有边界条件下,蛇形相向平行板型聚结板和田字型聚结板可以有效的使之聚结并沉降下来。相比而言,蛇形相向平行板型聚结板的聚结性能优于田字板型聚结板,该分析结果为分离器的设计提供了科学的参考依据。     

斜板沉降器处理负荷的计算

依据双膜模型和液滴在斜板层膜上的有效聚结 ,对层膜层流的临界雷诺数进行了关联 ,得出了斜板沉降器处理负荷的计算式。经实验数据验证 ,处理负荷的计算误差在 8%以内。     

斜板沉降分离器分离模型

在斜板沉降分离器的液滴动力模型基础上,建立了关于斜板分离器的分离过程数学模型,并分析了分离直径的范围,从而为斜板分离器的设计提供了理论依据。该模型不仅考虑了液滴的上升时间、液滴的聚结时间,还考虑了液膜的稳定时间,这对提高斜板分离器的分离效率具有重要的指导作用。     

液—液两相聚结分离原理及实际应用

对非均相液—液两相的聚结分离机理进行了阐述,以纤维类聚结介质为例,将聚结过程分为液滴捕集、液滴聚结和液滴沉降三个阶段。在聚结原理基础之上,对液—液聚结分离用的聚结材料进行分类,在此基础之上,详细介绍了目前应用比较广泛的液—液两相分离设备。最后指出液—液两相聚结分离技术及设备的发展方向。     

高效复合聚结板式油水分离器数学模型

通过对油水分离过程中油滴在聚结板间浮升和在聚结板表面聚结的过程机理的研究,建立了关于聚结板式油水分离器的油水分离过程数学模型,求得分散相液滴分离所需的时间。该模型充分考虑了油水两相的物性以及两相分层流动对分离过程的影响。     

液液体系界面上的液滴聚结特性

<正>众所周知,分散相液滴的大小影响液液萃取设备的处理能力和传质效率.Garg和Pratt对脉冲筛板柱的研究及Hamilton和Pratt对填料柱的研究均表明,液滴大小受液滴聚结和破碎速率控制.聚结速率对混合澄清槽的澄清室设计极为重要,并已成为许多科学工作者的研究课题.如Jeffreys等对连续澄清器性能的宏观研究及水平界面上单液滴聚结特性的研究等.单液滴研究有助于判别聚结时作用在液滴上的一些重要的作用力.一般说,聚结过程包括以下步骤:     

液液聚结分离器原理及石油化工中的应用

对非均相液-液两相的聚结分离机理,以纤维类介质为例,将聚结过程分为液滴捕集、液滴聚结和液滴沉降,同时也对影响聚结分离的因素进行了阐述.在此基础之上,介绍了目前在石油化工行业中应用比较广泛的高效的液-液两相分离设备:单级聚结器和二级聚结分离器,重点论述滤芯式聚结分离设备.为在石油化工领域中液-液分离提供指导和借鉴作用,为实现经济、有效的分离操作提供理论和实践支持.最后指出液-液两相聚结分离技术及设备的发展方向.     

液膜分离技术脱除废水中的醋酸——外相边界层及膜相扩散控制模型

本文导出了无再分散、无内循环、乳液滴直径均匀的液膜系统中的扩散控制模型。此模型同时考虑了外相边界层及膜相传质阻力。采用摄动法求得了非线性方程组的近似解。解中所含参数M,代表外相边界层中的传质阻力与乳液滴内最大传质阻力之比。当M等于零时,此解与渐进前沿模型的解相同。实验数据与模型计算值能很好吻合。通常,零级解(即拟稳态解)即可描述液膜传质。乳液溶胀可分为渗透溶胀与夹带溶胀。渗透溶胀速率随表面活性剂及内相试剂浓度的增加而增加。多次聚结再分散及增加搅拌强度加速了夹带溶胀。当内相试剂浓度较高时,渗透对溶胀的影响较大。本文提出了夹带溶胀机理。     

Particle velocity in a stratified two-phase flow between inclined parallel plates

Fundamental investigations of coalescence processes in settlers with plate packages for the separation of liquid-liquid dispersions prompted an analysis of the drop motion on the interface of a stratified two-phase flow. Therefore, a physical model was developed, which permits the calculation of drop velocity along the interface of an inclined trickling film. Starting from a balance of forces around a single particle, the model provides the equation of motion for a steady motion of single particles in a stratified two-phase flow. Several assumptions and considerations were necessary to solve this equation, such as taking into account the influence of the wall and of flow resistance. The model calculation assumes Newtonian liquids and laminar, smooth trickling films. A comparison with experimental results confirms that the drop motion behaviour is well reproduced.     

滴流床中持液量及流型转变的一维流体力学模型

针对滴流床中均匀球形填料,在颗粒尺度上分析气液两相在颗粒空隙中的流动.从基本的流体力学方程出发,建立了微观流动模型,求得滴流区液相在填料表面上的分布,进而计算液相总持液量,并通过对液膜波的稳定性分析,提出了滴流区向脉动区转变的判据.模型与实验结果及文献值作了比较,符合程度较好.     

Measurements and modeling of heat generation in a trickling biofilter for biodegradation of a low concentration volatile organic compound (VOC)

The experimental and theoretical heat generation behavior of a trickling biofilter treating toluene is discussed. The experimental results show that the temperature of the packed bed has a significant effect on the purification performance of the trickling biofilter and that an optimal operation temperature exists between 30 and 40 °C. During the gas–liquid co-current flow, the temperature in the packed bed gradually rises along the direction of the gas and liquid flow due to the exothermic biodegradation of toluene. The temperature rise between the inlet and outlet of the trickling biofilter increases with an increase in the gas flow rate and inlet toluene concentration. In addition, a larger liquid flow rate leads to a smaller temperature rise. The heat generation process occurring in the trickling biofilter is modeled by representing the packed bed as an equivalent set of parallel capillary tubes covered by the biofilm. The temperature profile in the packed bed during the liquid–gas co-current flow is analyzed by simultaneously solving the problem of gas–liquid two-phase flow and heat and mass transfer through the liquid film and biofilm. It is shown that the model agrees well with the experimental data, predicting the variations of the temperature rise between the inlet and outlet of trickling biofilter with the increasing gas and liquid flow rates.     

生物膜填料床内含有生化反应的多相传输模型

废气处理生物膜滴滤塔的多孔填料床内是带有气液两相流动、有机污染物扩散、生物膜内生化反应的复杂生化反应体系.在平行平板理论模型基础上,建立了生物膜多孔填料床内含生化反应的多元多相流动及传输特性的多相混合模型,获得了废气处理生物膜滴滤塔净化效率的理论计算方法.模型的理论预测值与生物膜滴滤塔净化低浓度甲苯废气的实验结果基本吻合.     

Bubble mechanisms and characteristics at pore scale in a packed-bed reactor

An image processing technique was used to study dominant bubble mechanisms in a two-dimensional packed-bed at pore level under the bubbly flow regime. Bubble breakup and coalescence were identified as dominant mechanisms using a large number of image samples. Two types of coalescence mechanisms were identified that occur due to compression and deceleration associated with the bubbles and three breakup mechanisms were identified that are result of liquid shear force, bubble acceleration, and bubble impact. Data on various two-phase parameters, such as local void fraction, bubble velocity, size, number, and shape were obtained from the images. Results indicated that when a flow regime changed from bubbly to either trickling or pulsing flow, the number of average sized bubbles significantly decreased and the shape of the majority of the bubbles was no longer spherical. Although a mean bubble velocity of all sized bubbles was uniform for given gas and liquid superficial velocities, individual bubble velocities were quite different depending on the bubble location in the pore. The present bubble size distributions were compared with previous studies and the results on bubble size are in general agreement.     

陶瓷球填料生物滴滤塔降解甲苯废气

The Purification experiments of waste gas containing low concentration toluene were made in trickling biofilter with ceramic spheres. The effects of liquid flow rate,gas flow rate,pH of circulation liquid, and toluene concentration in inlet gas on the purification efficiency of trickling biofilter were investigated. The pressure drop of the trickling biofilter was also measured during experiments.Increasing liquid flow rate and gas flow rate resulted in the decrease of purification efficiency of trickling biofilter. The highest purification efficiency of trickling biofilter was found at the circulation liquid pH of 7. The porosity of the packing material at the inlet of gas was higher than that at the outlet of gas in biofilter after continuous operation in 50 days. The decrease in the porosity of packing material caused a great increase in the pressure drop of the biofilter.     

Drop coalescence on inclined plates in liquids

Inclined plates are often installed as mechanical separation aids in gravity settlers for the separation of liquid-liquid systems. The authors investigated the process of coalescence of single drops on trickling films flowing off inclined plates. The method of investigation was developed by Blass and Rautenberg. It ensures that, under certain conditions, only hydrodynamic parameters influence the coalescence process to any significant extent. The coalescence time of the drops characterizes the process of coalescence. Short time between 1 and 3 seconds provide favourable conditions for coalescence whereas long times, often ten times as long or even longer are unfavourable. This contribution introduces a criterion for clear demarcation between these two ranges and also a determination of separation parameters for favourable conditions for coalescence. Furthermore, the function of the plates is described, which is determined by hydrodynamic and wetting processes. The characteristic operating regions of a plate are shown in a working diagram.     

生物膜滴滤床内温度及其分布特性对废气净化性能的影响

对不同温度下,陶瓷球填料生物膜滴滤塔净化低浓度有机废气的降解性能以及填料床内温度分布进行了实验研究,实验结果表明：填料床内微生物生长环境温度对微生物酶活性影响很大,从而造成温度对滴滤塔净化性能的显著影响.微生物酶活性最高时的温度为30℃,最高滴滤塔净化性能所对应的温度在30～40℃.在滴滤塔顺流操作条件下,滴滤床内温度沿气液流动方向升高;在进口碳源浓度一定时,滴滤床内沿气液流动方向的温升随着液体流量的减小和气体流量的增大而升高;废气进口浓度及系统操作方式对滴滤床温度分布也有显著影响.     

An investigation of liquid maldistribution in trickle beds

The influence of liquid maldistribution at the top of the packing on flow characteristics in packed beds of gas and liquid cocurrent downflow (trickle beds) is experimentally investigated. Particular attention is paid to the effect of gas and liquid flow rates on flow development. Tests are made in the trickling and pulsing flow regimes. A uniform, a half-blocked and a quarter-blocked liquid distributor is tested. Packings of various sizes and shapes are employed. Data are presented on pressure drop and liquid holdup as well as trickling to pulsing flow transition. Diagnosis of radial and axial liquid distribution is made by means of conductance probes. The effects of liquid foaming, bed pre-wetting, top-bed material, and blockage midway the bed on liquid distribution are also examined. Overall, liquid waves in the pulsing flow regime have a beneficial effect, promoting uniform liquid distribution in the bed cross section.