环已烷／PDMS体系起泡脱挥中气泡场的激光全息研究

在介绍环已烷／ＰＫＭＳ体系中起泡脱挥气泡场的激光全息图记录与再现的基础上，对其全息图通过计算机进行了ＶＰＰＳＡ颗粒开头分析和数据处理。讨论了液体高度、操作真空度和环已烷初始浓度对数均气泡直径的影响。实验结果表明，数均气泡直径随液体高度增加而增加，随操作真空度和环已烷初始浓度的增加而稍增大，液体高度是其主要影响因素。同时，对测量误差的影响因素也进行了讨论。     

二甲苯鼓泡吸收及模型研究

针对工业中一些尾气中二甲苯的回收,用二甲苯液体对其进行吸收,利于环保。通过建立鼓泡模型,给出了在不同管径下,气泡形状因子,最大气泡直径,鼓泡频率,最大上升高度等的变化规律。研究表明：气泡的形状因子随喷嘴内径和雷诺数的增大而增大;最大气泡直径随喷嘴内径的增大几乎成线性增大;鼓泡频率随喷嘴内径的增大而明显减小;最大上升高度则随着喷嘴内径的增大而增大,但幅度较小。     

鼓泡塔反应器的两级气泡模型参数研究

为了研究鼓泡塔反应器两级气泡模型在高黏度下的适用性,采用动态气体逸出法,在内径为286 mm,总高为7 200 mm的鼓泡塔中考察了液体黏度(1.2×10-3—210.4×10-3Pa·s)和操作条件对塔内总气含率,大、小气泡相含率和大、小气泡上升速度等两级气泡模型参数的影响。结果表明:床层总气含率随表观气速的增加而增大,大气泡相含率受液体黏度的影响较小,受表观气速的影响较大;小气泡相含率随黏度的增加而迅速下降,在高气速时受表观气速的影响较小。大、小气泡上升速度均随液体黏度的增加而降低,但随表观气速的升高有着不同的变化关系:前者明显升高,后者略有降低。大气泡直径随着黏度增大而稍有增大,小气泡直径随着黏度增大急剧减小。     

流化床还原铁精矿粉动力学初算

采用鼓泡床模型对流化床还原铁(精)矿粉动力学进行了初步的研究、计算和讨论.结果表明,流化床内的气泡直径随密相床层高度的增加而增加,气泡-气泡晕交换系数(Kbc)b及气泡晕一密相交换系数(Kbc)b则随密相床层高度的增加而降低;(Kbc)b＞(Kce)b;小粒度颗粒的还原速度随密相床层高度的增加变化不大,大粒度颗粒还原到一定程度后还原速度会降低,而且明显慢于小粒度颗粒的还原速度.     

C12G1.50/正丁醇/环己烷/H2O W/O体系中的酶催化酯合成反应研究

研究了在十二烷基聚葡糖苷C12G150/正丁醇/环己烷/H2O体系形成的油包水(W/O)微乳液中,脂肪酶Novozym100T催化正己酸和正丁醇的酯合成反应及其影响因素。结果表明,反应初始速率V0随正己酸的初始浓度CHA0增大而增大;随正丁醇的初始浓度CROH0的增大而减小,后V0进入一"坪区"。这可能是形成酶-正丁醇络合物所致。C12G1.50、正丁醇的浓度及两者的总浓度对初始浓度的影响也进行了讨论。     

气泡聚并的实验研究

气泡聚并对气泡运动速度和形状有重要影响,本文通过实验探究气泡聚并过程以及不同因素对于聚并的影响。经过多次实验得出,在相同的实验条件下,氮气的聚并时间小于空气气泡的聚并时间。液体浓度增加,气泡聚并时间增大。气泡直径的增加,加大了液膜的体积,增加了液膜脱落时间。     

不同管口浸没方式下气泡生成行为特性

对三种管口浸没方式下气泡生成行为过程进行可视化实验和三维数值模拟。对比分析了管口浸没方式、管口直径、气体流量等因素对气泡生成形态、气泡脱离直径、气泡膨胀脱离时间以及气液流场速度的影响。实验与数值模拟取得较为一致的结果。研究发现,气泡生成过程可分为单气泡生成和双气泡生成聚并两种模式,两者之间存在明显的气泡脱离形态转折点;三种管口浸没方式下,气泡脱离直径均随着管径和气体流量的增大而增大;气泡膨胀脱离时间随管径的增大而增加,而随气体流量的增加先急剧下降然后趋于平缓;在底吹和侧吹方式下,气泡长短轴比C值分别在0.75和1.1附近波动,其最终脱离形式均接近于球形;而顶吹方式下,C值在1.5附近波动,气泡脱离形态为椭球形。     

PVA膜在低浓度正丁醇/水溶液中渗透汽化行为研究

在传统的正丁醇发酵过程中,通常正丁醇的浓度不仅很低,而且对发酵过程有一定的产物抑制,影响发酵过程的连续正常进行。因此考虑使用聚乙烯醇(PVA)膜在渗透蒸发的作用下浓缩低浓度正丁醇/水溶液,考察了正丁醇原料液浓度、实验温度、真空度等操作条件对膜渗透通量和分离因子的影响。结果表明,渗透通量和分离因子均随温度的增加而增加,在60℃时,分离因子达到最大值;渗透通量随正丁醇进料浓度的增加而降低,分离因子则呈先升高后减小的趋势,并出现最大值;渗透通量和分离因子均随真空度的增加而增加。     

双孔连续出流气直接接触泡聚并行为数值模拟

气泡作为气液流体行为和传递特性的最基本元素,其聚并的运动特性对于化工、石油等工业具有重要作用。本文基于VOF对双孔连续出流气泡直接接触式聚并行为进行数值研究,揭示了聚并演变机理,考察了孔间距、进气速度、液面高度对聚并行为的影响。结果表明:气泡初始纵横比随进气时间增加而减小,聚并时突然增大,气泡开始聚并时刻与进气速度负相关;气泡脱离时间与孔间距、进气速度均负相关,液面高度对入口气泡聚并行为影响不大。     

微孔塑料挤出成型的研究

以超临界CO2作为物理发泡剂,对低密度聚乙烯(LDPE)进行了微孔发泡的研究。介绍了微孔塑料成型过程中聚合物/气体均相体系的形成、气泡成核和气泡长大及定型这三个步骤。并分析了加工工艺因素(温度、压力)等对制品中泡孔尺寸和密度的影响:泡孔直径随挤出压力的增加而减小;泡孔密度随压力的增加而增加;泡孔直径随压力降速率的增大而减小;泡孔密度随压力降速率的增大而增加;而适当提高温度有利于减小泡孔直径、增加泡孔密度。     

近化学专业“液体物性测定”综合实验研究

通过物性测定综合实验,判定无色透明纯液体A和B。综合运用数字式真空计测定不同温度下纯液体A和B的饱和蒸气压,用图解法求得该液体在实验温度范围内平均摩尔汽化热与正常沸点;用最大泡压法测定液体A和B的表面张力;用阿贝折光仪测定A和B液体的摩尔折光率等参数。系列物化综合探索试验显示,液体A应是环已醇,而液体B应是环已烷。     

Single bubble formation in high pressure liquid—solid suspensions

Bubble formation from a single nozzle is investigated analytically and experimentally in nonaqueous liquid and liquid—solid suspensions at pressures up to 17.3 MPa. A mechanistic model is proposed to predict the initial bubble size in liquid—solid suspensions, by taking into account the various forces affecting the bubble growth including those induced by the presence of the particles, such as the suspension inertial force and the particle-bubble collision force. It is found that the initial bubble size in the suspensions is generally larger than that in the liquid mainly due to the inertia effect of the suspension. The initial bubble size increases with the solids holdup. The pressure has an insignificant effect on the initial bubble size in both the liquid and liquid—solid suspensions under the conditions of this study. The model can reasonably predict the initial bubble sizes obtained in this study and those reported in the literature.     

Single bubble ignition after shock wave impact

The ignition behavior of single bubbles during the first oscillation after a shock wave impact was investigated experimentally. The bubbles were created by injection of oxygen into liquid cyclohexane. High speed pressure and optical measurements were applied. The experiments were performed inside cyclohexane, at room temperature and at an initial pressure of 1 bar. It was found that an incident shock wave with a peak pressure of 85 bar ± 8.5 bar can ignite bubbles with equivalent initial diameters between 2.4 and 7.2 mm. Measurements related to the shock-induced bubble compression process, the jet formation inside the bubble, the ignition delay, the light illumination during the bubble explosion, as well as other aspects of the observed bubble behavior are presented. In addition to the experimental observations a theoretical analysis is presented. The set of equations for the theoretical estimation of the pressure and the temperature and of the gaseous mixture inside the bubble at the moment of the observed bubble ignitions is shown and explained.     

Numerical simulation of bubble growth in a limited amount of liquid

In this study, we examined the growth of a spherical bubble in a limited amount of liquid by using a finite‐element‐based numerical simulation method. The bubble growth was assumed to be controlled by both momentum and mass transfer. A truncated power‐law constitutive equation was used to describe the rheology of the melt. The gas inside the bubble followed the ideal gas law. The gas concentration at the bubble surface obeyed Henry's law. A computer code was programmed to solve the equations with the Galerkin method. A backward Euler scheme was used to discretize time. Grids were remeshed after each incremental time step to ensure the accuracy of the numerical results. The bubble growth process was simulated with the code. The numerical results, such as the instantaneous bubble size, gas pressure inside the bubble, and gas concentration profile in the liquid, were predicted. The influences of the liquid volume, initial gas pressure, temperature, and rheology of the melt on bubble growth were also studied. The results of the bubble growth simulation in this study were in satisfactory agreement with others' work. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Pressure fluctuations and bubble size in viscous three-phase circulation fluidized bed bioreactors

Characteristics of pressure fluctuations and bubble size were investigated in the riser of a three-phase circulation fluidized bed bioreactor with viscous liquid medium, whose diameter is 0.102 m (ID) and 3.5 m in height. Effects of gas (0.01–0.07 m/s) and liquid (0.17–0.23 m/s) velocities and liquid viscosity (0.96–38 mPa·s) on the bubble size in the riser were examined. The bubbling phenomena in the bioreactor with viscous liquid medium were interpreted effectively by measuring and analyzing the pressure fluctuations by adopting chaos theory. The bubble size increased with increasing gas velocity or liquid viscosity, but decreased with increasing liquid velocity. The bubbling phenomena became more complicated and bubble size distribution tended to broad, with increasing gas velocity or liquid viscosity. The bubble size was well correlated in terms of correlation dimension of pressure fluctuations as well as dimensionless groups within these experimental conditions.     

On the formation of Taylor bubbles in small tubes

The formation of Taylor bubbles and resulting bubble lengths were studied in a ID vertical tube for air-water and air-octane systems. In the co-flow tube/nozzle arrangement two nozzle sizes were used as gas inlets. Superficial velocities varied between 0.001- for the liquid and 0.002- for the gas. Three different mechanisms of initial bubble formation were observed. Of the three mechanisms, mechanism 3 is periodic (with period consisting of a bubble and a liquid slug), reproducible and can be simply modelled. After initial bubble formation further modifications may occur in the formed bubble size by coalescence or pairing. Bubble pairing is encouraged by smaller nozzles and liquid flow rates, while coalescence is observed only for cases where non-Taylor bubbles form initially.Two simple models have been proposed, the first predicts the size of the Taylor bubbles formed by mechanism 3 while the second attempts to predict the condition for bubble pairing to occur. Reasonable agreement with experimental results validates the predictions of the first model for a strong dependence of the volume of Taylor bubbles formed on the gas and liquid flow rates, a moderate dependence on nozzle diameter and a weak dependence (if at all) on the surface tension of the liquid used. Mismatch with the experimental results is caused (at least in part) by the experimental setup where there was no perfect axial alignment of the gas inlet. The experiments also suffered from problems at the outlet at low flow rates where smooth bubble disengagement could not be ensured for long Taylor bubbles. The second model for pairing predicts its occurrence for concentric tube/nozzle arrangements as a function of flow rates and channel diameters. The model over-predicted the range of liquid flow rates at which pairing was observed experimentally, but it captured the form of the boundary between different bubble volume modification mechanisms when represented on superficial velocity graphs.     

Hydrodynamics and mass transfer in bubble column: Influence of liquid phase surface tension

According to literature, few experiments are performed in organic solvents which are mostly used in commercial gas-liquid reactors. However, it is commonly accepted that data obtained in aqueous solution allow to predict the surface tension effects, and to model the behaviour of organic solvents. In this work, we examine the validity of this approximation.In this objective, the flows observed in two pure media having similar viscosity but different surface tension—respectively, water (reference) and cyclohexane (solvent)—are successively compared at two scales: in a bubble column and in bubble plumes.In bubble plumes, as expected, the mean bubble size is smaller in the medium having the smallest surface tension (cyclohexane), but for this medium the destabilisation of flow is observed to occur at smaller gas velocity, due to break-up and coalescence phenomena. In bubble column, these phenomena induce the bubbling transition regime at lower gas velocity, whatever the operating conditions for liquid phase: batch or continuous. Consequently, when the two media are used at similar gas superficial velocity, but in different hydrodynamic regimes, greater gas hold-up and smaller bubble diameter can be observed in water; the interfacial area is then not always higher in cyclohexane.This result differs from the behaviour observed in the literature for aqueous solutions. The analysis of bubble plumes in aqueous solutions of butanol shows that this difference is due to a fundamental difference in coalescent behaviour between pure solvents and aqueous mixtures: the surface tension effect is less important in pure liquid than in aqueous solutions, because of the specific behaviour of surfactants.It is then still difficult to predict a priori the bubbling regime or the flow characteristics for a given medium, and all the more to choose an appropriate liquid as a model for industrial solvents.     

Bubble and gas holdup characteristics in a bubble column of CMC solution

The local bubble behavior such as holdup, bubble frequency, bubble size and rising velocity in a bubble column of CMC solution was measured using the eleclroresislivity probe technique, and the effects of gas velocity and CMC concentration on the behavior were investigated. Also, the total gas holdup was measured from the liquid level in the column, and its relation with gas velocity and CMC concentration was studied. Two correlations of mean bubble size and total gas holdup with dimensionless groups, composed of gas velocity and physical properties of gas and liquid, were obtained from the experimental results.     

Shock induced condensation in a fuel-rich oxygen containing bubble in a flammable liquid

Shock induced dynamics and explosion of a single oxygen containing bubble in liquid cyclohexane is calculated. The possibility, in principle, of fuel vapor condensation during bubble compression is shown. This condensation takes place, if the gas inside the bubble has a relatively high initial temperature or a low initial pressure. As a result of fuel vapor condensation the bubbles, which have an initial gas composition above the upper flammability limit, can, nevertheless, explode.It is shown that the fuel vapor condensation in fuel-rich bubbles is possible during compression stages of oscillations and during a few milliseconds after the end of bubble dynamics. The rate of the condensation process is estimated. According to estimations, this process is fast enough to significantly change the chemical composition of the bubble and shift it into the flammable range even during the compression stage of the first bubble oscillation.Explosion limits of a single bubble as a function of initial temperatures and pressures are calculated. It is shown that condensation processes extend the explosion range.The influence of a chemically inert gas (argon), on the bubble ignition threshold and parameters of bubble explosion is analyzed. It is shown that argon addition in a bubble can reduce the ignition threshold and therefore increase the explosion hazard. On the other hand, such additions reduce explosion pressure and can be used for mitigation of explosions in bubbly liquids.     

A numerical study of mass transfer of ozone dissolution in bubble plumes with an Euler-Lagrange method

In this paper we study the mass transfer process of ozone dissolution in a bubble plume inside a rectangular water tank, as a model problem for a water purification system. The effect of bubble diameter and plume structure on mass transfer efficiency of ozone in bubble plumes is investigated numerically. In order to capture the detailed plume structure, the interaction between liquid and bubbles is treated by a two-way coupling Euler-Lagrange method. The motion of the continuous phase (a mixture of liquid and gas bubbles) is solved using a finite difference method in an Eulerian framework. The motion of the dispersed phase (bubbles) is tracked individually in a Lagrangian approach. The ozone transfer process from bubbles to liquid is computed by modelling the mass transfer rate of individual bubbles. Our numerical results show a nonlinear dependence of the ozone dissolution efficiency on the initial bubble size. The dissolution efficiency varies rapidly when the initial bubble size reaches certain value while the change of efficiency is much slower at other bubble sizes. Therefore, for a given tank size it is not necessary to generate bubbles much smaller than the optimal size. This result is of importance for engineering since it is difficult to generate small bubbles in practice. Our results also show that the instantaneous dissolution rate of ozone could be increased by increasing the initial volumetric fraction of ozone inside bubbles even up to 20% while maintaining the dissolution efficiency.