氧在水中传质过程的探讨

曝气是污水处理厂的一个重要工艺环节,在实际应用中我们大多采用氧气传质速率方程来描述曝气池和设备的性能,但此公式不能预测工艺性能。文章将氧在水中的传质过程分为氧气和水接触界面过程与氧在水中的扩散过程两部分,分别进行分析,得出氧在水中传质的模型,最后结合现阶段对氧气在水中传质的各种研究,讨论了气泡半径、压力、温度、溶氧物质、悬浮物颗粒、粘度、水的紊动条件对氧气在水中传质的影响。     

新型气液混输型曝气增氧设备性能

介绍了水处理过程中曝气氧传质的基本原理以及几种传统曝气设备的优缺点,同时重点介绍了一种新型曝气增氧设备--离式螺旋曝气设备,并对该设备进行曝气性能试验研究。试验结果表明,该曝气装置具有良好的曝气性能,充氧能力良好,氧利用率较高可达30%以上,安装使用简便,可广泛应用于化工炼油等行业水处理过程。     

微孔扩散器在气液传质过程中的研究进展

阐述了微孔扩散器的定义及气泡传质理论,介绍了微孔扩散器在曝气、臭氧氧化、气浮、塔板、纳米材料制备等方面的研究现状和发展趋势。与其他技术相比较,以微孔介质为核心的微孔扩散技术具有混合、传质性能好,能耗低,操作简单,利于工程放大等优点。     

单个运动气泡近界面浓度场的研究

对单个气泡传质的近界面浓度场影响因素进行了实验和理论研究．实时激光全息干涉法测量结果表明,运动气泡近界面浓度是一个定态值,受流速、泡径、温度等因素影响显著;假设该传质过程达到局部平衡,进行热力学分析,得到的结论与实验结果一致．在实验测量结果的基础上,对单个O_2气泡在乙醇中吸收时的传质近界面浓度场进行了数值模拟,取得了良好的结果．     

析气界面上气泡滑移促进的传质模型探索

本文在充分研究析气界面上气泡行为的基础上，根据界面上析出气泡的动力学行为，结合界面附近流体及相间传质理论。导出了气泡滑移促进的传质模型     

液体中气泡上浮与传质过程的耦合模型

针对液体中气泡上浮与传质这一非稳态、强耦合过程,分析气泡的受力情况,考虑到非恒定Basset力的影响,得出了气泡瞬态加速度模型;利用绕球流动传质边界层模型,并引入非平衡传质理论,构建了气泡的瞬态非平衡传质模型;进而依据气泡质量变化率将两模型耦合,以此构建了完整描述这一过程的耦合模型。计算实例表明,Basset力对难溶性气泡的运动过程无明显影响,但对易溶性气泡影响显著;传质条件则对两类气泡都具有重要影响,且该模型中引入非平衡传质理论后,计算值与难溶性气泡的实验结果吻合更好。     

微曝氧化沟气液两相传质模型构建及传质影响因素分析

基于ANSYS Fluent软件建立了微曝氧化沟气–液两相流动和溶解氧输运模型,对比不同工况下氧体积传质系数的实验测量值和模拟结果,误差在7%以内。采用验证可靠性的模型模拟研究了气泡直径、曝气量和横向流动速度对微曝氧化沟内氧传质的影响。结果表明,气泡直径由1.5 mm增至3 mm时,氧体积传质系数由15.80 h?1降低至5.83 h?1;曝气量由0.5 m3/h增大至2 m3/h时,氧体积传质系数由4.21 h?1增至14.15 h?1,减小气泡直径和增大曝气量能明显提高氧体积传质系数。微曝氧化沟内气–液相间传质及溶解氧的分布受横向流动影响,开启单台和两台推流泵时,氧体积传质系数分别比无横向推流工况增大27.7%和42.4%,横向流动能有效提高气泡羽流内的气含率,增强氧传质效果。     

液体蒸汽向单气泡中传质过程的数值分析

<正>当气体通过液相介质时,由于气液界面和气相主体间存在液体蒸汽的浓度差,使液体迅速蒸发,可以大大强化对流传热及沸腾传热.此外,在鼓泡设备中,这种溶剂汽化现象亦可能对气含率及传质带来很大影响.因此,定量地分析液体蒸汽向气泡中传质的过程是很有意义的.此过程为具人体积变化的自由边界问题.对于核状沸腾过程的自由边界问题已有很多研究,其气泡长大的控制步骤为兴高采烈相可能提供的气化潜热速率,而由于气泡中质量传递控制的移动边界问题尚未见有研究.本文提出了液体溶剂向单气泡中传质的数学模型,获得了数值解.并且对各种影响因素进行了讨论.     

毛细管中泰勒流液侧传质特性及其强化机理的CFD模拟

采用计算流体力学（CFD）的方法,研究了圆管中泰勒流的液侧传质特性,分析了泰勒气泡上局部传质特性,并研究了气泡上升速度、液膜长度和液栓长度对液膜处和气泡半球帽处平均传质系数的影响。结果表明,泰勒气泡表面局部传质系数存在3个峰值,液膜处的平均传质系数随气泡上升速度增大显著增大,随液膜长度增大而减小,而半球帽处的平均传质系数随气泡速度和液膜长度的增大变化较小,即膜接触时间增加时,液膜处的传质系数降低,而半球帽处传质系数变化较小。另外,引入场协同原则对单元胞内速度场和浓度场进行分析,解释了局部传质特性及强化机理。最后,给出了分别预测短和长膜接触时间下泰勒流液侧体积传质系数的关联式,该式在较宽的管径尺度范围（0.25～3 mm）内的预测误差在±20%以内。     

臭氧微气泡处理有机废水的效果与机制

为解决臭氧氧化有机废水氧化效率差、臭氧利用率低这一问题,本文提出了臭氧微气泡处理有机废水的新技术。采用加压溶气法制备的臭氧微气泡处理苯酚配置的模拟废水,通过显微拍摄、动力学分析、紫外-可见吸收光谱、自由基屏蔽等手段对臭氧微气泡的形态大小、氧化效果、传质特性和氧化机制进行了研究,并对臭氧气泡直径和界面压力之间的关系进行了深入探讨。试验与数值计算表明,臭氧微气泡平均粒径为20.37μm,处理初始COD浓度为51.2mg/L的有机废水,COD去除速率分别是使用1μm曝气头和100μm曝气头曝气的1.59倍和3.61倍,臭氧利用率达到99.19%以上,氧化过程是自由基为主的间接氧化过程,污染物最终氧化产物为小分子烃和羧酸。微气泡影响下,臭氧分子传质速率和分解速率均有所提高,而臭氧微气泡表面较高的界面压力是其高效传质的原因之一。     

Bubble swarm behaviour and gas absorption in non-newtonian fluids in sparged columns

Mean relative gas hold up, slip velocity, bubble size distribution, and volumetric mass transfer coefficient of oxygen were measured in sparged columns of highly viscous non-Newtonian fluids (CMC solutions) as a function of the gas flow rate, and CMC concentration (fluid consistency index k, and flow behaviour index n).By comparison of the measured bubble swarm velocities with those calculated by relations for single bubbles the bubble swarm behaviour was investigated. It could be shown that small bubbles in swarm have higher rising velocities than single bubbles, expecially in highly viscous media. Large single bubbles rise with high velocity due to the change of their shape caused by the swarm of the smaller bubbles. No large bubbles with spherical cap shape could be observed. The volumetric mass transfer coefficient decreases rapidly with increasing CMC-concentration.A comparison of the volumetric mass transfer coefficients with those measured in mechanically agitated vessels indicates, that the performance of sparged columns is comparable with the one of agitated vessels. Because of their lower energy requirement sparged columns are more economical than mechanically agitated vessels. It is possible to improve the performance of sparged columns by the redispersion of large bubbles in a multistage equipment.     

搅拌槽内粘稠物系中气液相间氧传递

以发酵罐中气液相间氧传递为背景，考察了搅拌槽内搅拌器形式、物系流变性质、通气搅拌操作条件等对假塑性粘稠物系中氧传递过程的影响。结果表明，这些因素主要通过改变气体分散状态和相间传质面积来影响氧传递速率。根据气泡在搅拌槽内不均匀分布现象，多层搅拌下气液相间传质过程可以用气泡运动分区分布模型来描述。它说明了采用轴向流桨和涡轮桨组合的搅拌形式在氧传递方面的优越性，为强化发酵罐中供氧指明一条有效途径     

Evaluation of a novel self-aerating,oscillating baffle column

We describe the operation of a pilot scale oscillating baffle column using a self-aeration system for oxygenation of water. The top baffle has a high constriction ratio and is sufficiently near to the surface of the water such that gas bubbles are generated. This aeration plate is coupled with a series of equally spaced low constriction orifice baffles, which lead to uniform dispersion of entrained air bubbles throughout the liquid volume. Flow visualisation experiments using video and still photography were used to identify two mechanisms for bubble generation: bubble formation under the water surface by surface vortex suction, and bubble generation from the collapse of a surface fountain and subsequent entrainment of bubbles into the bulk. Mass transfer measurements have shown that under most conditions a uniform oxygen concentration could be obtained throughout the column as a result of efficient mixing, and that the sole limitation to mass transfer performance was determined by the aeration mechanism. Initial comparison on the basis of aeration efficiency with other devices reveals a modest oxygen transfer rate, but with low specific power consumption of order 0.3 kW/m³.     

Determination of oxygen transfer from single air bubbles to liquids by oxygen microelectrodes

For the investigation of mass transfer from gas bubbles into liquids the concentration gradient of oxygen migrating from air bubbles was measured by means of oxygen microelectrodes. For this purpose a single air bubble was fixed by a platinum wire spiral with the liquid flowing downward. Thus the ascent of the bubble in an aerated liquid was simulated. Liquid-side mass transfer coefficients determined from concentration gradients were higher than values calculated from theory. Sherwood numbers obtained from experimental results for bubbles of larger diameters were distinctly higher than those for smaller bubbles (diameter 1 mm); the difference corresponds approximately to that predicted theoretically between bubbles with mobile and those with rigid interfaces.     

Mass transfer from discrete gas bubbles in a reciprocating plate column

Measurements have been made of the uptake of oxygen in water from a series of discrete bubbles released into a 5 cm diameter reciprocating plate column. The rate of increase of dissolved oxygen in the water has provided data on the average mass transfer coefficients under the following conditions; (a) free rise in the absence of plates, (b) bubbles rising through a static plate assembly and (c) bubbles rising through moderately agitated plates (frequency up to 1.28 Hz). It was found that the mass transfer coefficients were higher under condition (b) than (a), and were further increased under condition (c). The results were compared with earlier data on mass transfer to agitated bubble dispersions.     

基于旋转浮阀的复合曝气器在曝气池中的应用及CFD模拟

基于气体通过阀片后能在阀盖四周形成旋转流场的特点，本文将旋转浮阀应用于曝气池中，以提高其充氧性能。在旋转浮阀四周均匀排布6个气泡石，即旋转浮阀-气泡石复合曝气器；在长宽高为800mm×600mm×910mm的透明有机玻璃池内，以空气-清水为体系，进行曝气实验。为了考察旋转浮阀形成的旋转流场对曝气的影响，以塔内件领域常见的F1浮阀以及气泡石为基准进行实验比较。结果表明，与F1浮阀-气泡石复合曝气器相比，旋转浮阀-气泡石复合曝气器的中心测量点与边界测量点的溶解氧浓度更接近，充氧均匀性指数也更小，说明了旋转浮阀能促进气泡分布均匀，减少传质死区。相比于F1浮阀-气泡石复合曝气器，旋转浮阀气泡石复合曝气器提高了氧总传质系数、氧传质速率、氧传质效率和曝气效率；相比于气泡石曝气器，旋转浮阀-气泡石复合曝气器提高了氧总传质系数、氧传质速率，但降低了氧传质效率和曝气效率。本文还利用CFD模拟流场分布，解释了旋转流场的产生及其提高曝气充氧能力的原因。     

Distribution of the free and oil‐trapped air bubbles in simulated broths containing fungal biomass

The location of air bubbles (i.e. inside oil drops or free in the aqueous phase) was studied by image analysis as a function of the oil and biomass concentrations in a 2 L stirred tank using a simulated fermentation medium (aqueoussalt solution, castor oil, air and fungal biomass) agitated by a Rushton turbine. The solid (fungal) phase plays an important role in defining the location of bubbles, as the percentage (in bubble volume) of bubbles trapped in oil increases threefold when biomass is added to the medium. The bubbles located inside oil drops were found to occupy 60% of the total bubble volume and to be 40% smaller than those which were non‐oil associated. This phenomenon has important implications for oxygen mass transfer in multiphase fermentations.     

浓海水鼓泡过程中的气泡行为

鼓泡操作可强化浓海水蒸发过程,其气泡的大小及运动行为对浓海水蒸发过程有显著影响。实验通过搭建两种不同尺寸的鼓泡池,针对单鼓泡口、双鼓泡口及鼓泡阵列,在不同气量、鼓泡口深度与鼓泡口间距条件下,考察大气泡群与小气泡群在不同运动过程的行为。结果表明,在气体流量更低的情况下,液面上的小气泡群比大气泡群具有更高的表面覆盖度,更易于增加液相扰动,并能迸射出更多的小液滴,提出小气泡更适合于鼓泡浓缩晒盐过程。通过单因素实验优化后,小气泡群的覆盖率可以达到90%,蒸发速率可比传统滩晒过程增加1～1.5倍。优化后操作参数为：单鼓泡口气流量为0.4 L·min^-1、鼓泡口深度为8 cm、鼓泡口间距为12 cm。     

Effect of bubble contamination on rise velocity and mass transfer

An apparatus where individual bubbles are kept stationary in a downward liquid flow was adapted to simultaneously (i) follow mass transfer to/from a single bubble as it inevitably gets contaminated; (ii) follow its shape; and (iii) periodically measure its terminal velocity. This apparatus allows bubbles to be monitored for much longer periods of time than does the monitoring of rising bubbles. Thus, the effect of trace contaminants on bubbles of low solubility gases, like air, may be studied.Experiments were done with air bubbles of 1-5 mm initial equivalent diameter in a water stream. The partial pressure of air in the liquid could be manipulated, allowing bubbles to be either dissolving or kept at an approximately constant diameter.Both drag coefficient and gas-liquid mass transfer results were interpreted in terms of bubble contamination kinetics using a simplified stagnant cap model. Drag coefficient was calculated from stagnant cap size using an adaptation of Sadhal and Johnson's model (J. Fluid Mech. 126 (1983) 237).Gas-liquid mass transfer modelling assumed two mass transfer coefficients, one for the clean front of the bubble, the other for the stagnant cap. Adjusted values of these coefficients are consistent with theoretical predictions from Higbie's and Frössling's equations, respectively.