共查询到18条相似文献,搜索用时 609 毫秒
1.
2.
尽管文丘里管式微气泡发生器的注气口位置会对气泡在文丘里流道内的碎化特征产生直接影响,但迄今缺乏针对性的深入研究。通过可视化实验方法,对比分析了注气口分别位于喉管处(结构1型)和进水管处(结构2型)时的气液流型、气泡破碎特征以及成泡特性。实验表明,气、液相流量对结构1型微气泡发生器内的气液流型影响显著,初始成泡区域随液相流量增加,环状流或泡状流向弹状流转变,而随气相流量增加则由泡状流或弹状流向环状流转变;结构2型微气泡发生器则在此过程中始终为泡状流,其对操作工况的适应范围大于结构1型。在相同工况下,结构1型微气泡发生器的成泡Sauter平均粒径小于结构2型,但随着液相Reynolds数的增大,二者间的成泡平均粒径差值随之减小。分析原因是由于弹状流流型下,延伸至扩张段区域的弹型泡的表面积更大,能量转化率更高,气泡界面失稳碎化的程度更显著。随着液相Reynolds数的增大,初始成泡体积减小,湍流破碎机理作用占据主导,掩盖了由于界面失稳引起的气泡破碎。结构1型微气泡发生器的成泡能耗高于结构2型,并且随液相Reynolds数的增大,两者之间的差值随之增大。综合来看,结构2型微气泡发生器能够在低能耗下实现高效成泡,面向工程应用将更具优势。 相似文献
3.
4.
采用高速摄像系统研究了对称分支形并行微通道内气液两相流及弹状气泡均匀性规律。实验中分别采用含0.3% SDS的甘油-水溶液与氮气作为液相和气相。观察到弹状流和泡状流两种流型,作出了由两相操作条件构成的流型图及流型转变线。结果表明,气泡非均匀性主要由两微通道内流体之间的相互作用、下游通道中流体动力学的反馈作用以及通道制造误差造成。随液相黏度增大,气泡均匀性变好;在高液相流量以及低气相压力下操作,气泡尺寸分布更易达到均匀。基于压力降守恒原理和微通道内气液两相流阻力模型,构建了两通道中气泡尺寸的预测模型。 相似文献
5.
在工业生产过程中,气泡在液相中的上升行为及气液界面的传质行为极为常见。本文针对不同条件下气泡上升过程的实验研究方法以及数值计算方法进行了总结。从实验与数值计算的角度,综述了单气泡上升过程的影响因素、多气泡上升过程聚并与破裂的现象和机理以及工业装置中气液两相流型和气泡特性,并对传质模型进行了归纳,主要关注了气侧-界面传质模型的研究现状。综述结果表明:当前对于单气泡上升行为的研究较为充分,而对于多气泡的行为机理的研究尚需深入。此外,受到研究手段的限制,进行气侧-界面传质模型研究具有一定挑战性。针对当前的相关研究进展和存在的问题,对今后气泡上升行为和传质行为的研究提出以下建议,即开展气泡聚并与破裂可控性研究,强化对气侧-界面传质过程的研究,包括泡内流体行为可视化研究和相关传质模型的建立。 相似文献
6.
7.
利用高速摄像机对矩形微通道中不同黏度体系下气泡的形状及界面演变进行实验研究。实验观察到子弹状、棒槌状、平尾状和尖尾状四种气泡形状,其中液弹的挤压力控制气泡尾部由凸形变平形或凹形,而受限空间效应和液相黏性剪切导致气泡形状为贴近壁面的尖尾状。基于两相Ca数和气液流率比绘制了气泡形状分布图并建立形状转变模型。平尾状和尖尾状气泡均是由棒槌状气泡演变而来,转变距离分别随气泡上游液弹压力和液相黏性剪切力的增加而减小,并且均与气/液流率比呈幂律关系,幂律指数小于零。尖尾状气泡破裂发生在尖端且存在临界条件,根据Ca数和气液流率比提出了破裂条件的良好预测模型。本工作对于矩形微通道内气泡的流动与破裂调控具有重要的指导意义。 相似文献
8.
9.
《化工进展》2017,(Z1)
介绍了国内外微化工发展背景及发展现状,微通道内气液两相流流动气泡特性和传质特性。微通道中(横向及竖向微通道)气液两相流流型划分主要有泡状流、弹状流、环状流、搅拌流等。气泡形成过程中流体挤压力对气泡表面进行破坏致使分离,表面张力则在整个过程中维持着气泡形状及长度。着重介绍了微通道内气泡形成过程及经验长度计算,比较了不同研究者提出的经验公式中气液相表观速度比和气泡长度的关系,得出气泡长度均随气液相表观速度比的增加而增加,但依据研究者实验条件不同增加趋势也不尽相同。传质方面,研究基本集中在气液相比表面积较大的泡状流、环状流上,而气液表观速度、当量直径、压强等都会影响传质系数。微通道气液两相流虽然在传热、传质方面有很大的应用前景,但仍存在研究手段单一、理论数据不完善等问题,指出在未来的研究中研究者们要扩大领域范围,为传质传热的实际应用提供更可靠的理论依据。 相似文献
10.
11.
The interaction of bubbles is the key to understand gas–liquid bubbling flow. Two-dimensional axis-symmetry computational fluid dynamics simulations on the interactive bubbles were performed with VOF method,which was validated by experimental work. It is testified that several different bubble interactive behaviors could be acquired under different conditions. Firstly, for large bubbles(d: 4, 6, 8, 10 mm), the trailing bubble rising velocity and aspect ratio have negative correlations with liquid viscosity and surface tension. The influences of viscosity and surface tension on leading bubble are negligible. Secondly, for smaller bubbles(d: 1, 2 mm), the results are complicated. The two bubbles tend to move together due to the attractive force by the wake and the potential repulsive force. Especially for high viscous or high surface tension liquid, the bubble pairs undergo several times acceleration and deceleration. In addition, bubble deformation plays an important role during bubble interaction which cannot be neglected. 相似文献
12.
喷嘴释放单气泡的声发射特性 总被引:1,自引:1,他引:0
利用声发射技术在单气泡发生实验装置中研究了气液两相流中单气泡的动力学特性,使用自行开发的采集处理程序进行气泡声信号的参数提取,采用统计分析、小波变换和快速傅里叶变换对声信号进行时域和频域范围的分析。分析结果表明,声发射技术可以检测到管内气泡的声信号,具有较高的信噪比,且声信号随着喷嘴尺寸的增大而增大,随着液相表面张力的减小而减小。比较不同喷嘴直径下气泡的频率谱,发现喷嘴释放气泡发出的声信号频率为150~200 kHz,且随着喷嘴直径的增大,峰值频率相应增大,提出了声信号峰值频率与气泡尺寸之间的关联式。同时得到了气泡上升过程中的连续形态变化,分析了气泡产生声音的机理。研究表明,声发射技术是一种灵敏度高、测量手段方便的方法,可用于气液两相流气泡运动特性的检测。 相似文献
13.
14.
CONVECTIVE HEAT TRANSFER CHARACTERISTICS OF GAS IMPINGEMENT ON SMALL HEATED DEVICE IN LIQUID COOLANT BATH 下载免费PDF全文
Heat transfer characteristics of a small heated device have been investigated in a liquid bath with gas jetimpingement as function of gas flow rate,coolant temperature,liquid phsicochemical properties,heat flux,heat source size,ambient pressure and the distance between jet and heated wall.The experimental results show that the agitation of liquid caused by gas jet bubbles increases greatly therate of heat transfer,and the evaporation of coolant near the wall,which was due to the concentration differencebetween gas-liquid interface and bulk gas phase,gives additional enhancement of heat transfer.The rate ofevaporation related to the bubble growth was mathematically formulated.By using the simultaneous heat and mass transfer model,the convective heat transfer coefficient and masstransfer coefficient can be deduced from the experimental results.In addition,the local heat transfer coefficient and the distribution of evaporation heat flux on the smallheated surface are investigated mathematically and experimentally. 相似文献
15.
The size of initial bubbles is an important factor to the developed bubble size distribution in a gas-liquid contactor. A liquid cross-flow over a sparger can produce smaller bubbles, and hereby enhance the performance of contactor. A one stage model by balancing the forces acting on a growing bubble was developed to describe the formation of the bubble from an orifice exposed to liquid cross-flow. The prediction with this model agrees with the experimental data available in the literatures, and show that orifice size strongly affects the bubble size. It is showed that the shear-lift force, inertia force, surface tension force and buoyancy force are major forces, and a simplified mathematical model was developed, and the detachment bubble diameter can be predicted with accuracy of ±21%. 相似文献
16.
R. Sh. Abiev 《Theoretical Foundations of Chemical Engineering》2011,45(2):156-163
In addition to the previously constructed model of the hydrodynamics of a gas-liquid slug flow, a mathematical model is developed that describes pressure losses taking into account the rearrangement of a velocity profile in liquid slugs and energy losses on the formation and renewal of interfacial area during the motion of bubbles. The contribution of different forms of pressure losses in capillaries is analyzed. It is shown that in microchannels tangential stresses on the surface of a bubble substantially affect the total pressure losses. It is found that the length of bubbles does not affect the rate of surface formation and respective pressure losses if bubbles have the same velocity. The results of modeling are in satisfactory agreement with experimental data of other researchers. 相似文献
17.
通过对不同操作压力和不同液体性质气液鼓泡床的模拟值与实验数据进行对比,从而验证CFD-PBM耦合模型的通用性。结果表明,CFD-PBM耦合模型在加入了气泡破碎修正因子后,可以很好地预测压力对鼓泡床流体力学行为的影响趋势,当压力升高时,气含率显著升高。不同液体黏度和表面张力条件下CFD-PBM耦合模型的模拟结果与实验结果均吻合较好。随液体黏度增大,气泡破碎速率减小,气泡尺寸分布变宽,曳力显著下降,气含率随之降低。随表面张力减小,气泡破碎速率增大,气泡变小,气含率升高。CFD-PBM耦合模型具有很好的通用性,原因在于考虑了压力、液体黏度和表面张力对气泡聚并、破碎和气液相间作用力的影响。 相似文献
18.
《分离科学与技术》2012,47(4):537-552
Abstract A continuous bubble fractionation system consisting of a vertical Plexiglas tube provided with a source of air bubbles, means of continuous liquid feed, overflow, and bottom effluent has been operated to study the performance of the system. The study primarily involves an examination of the effects of variables such as gas rate, liquid rate, solute concentration, and column size on the effectiveness of the system for separating an organic solute from a dilute aqueous solution. The experimental results indicate that the effects of gas and liquid rate on the performance have generally followed the results expected from an equilibrium adsorption of a surfactant on the gas-liquid interface described by Gibbs' equation and material balances. An increase in gas rate increased the effectiveness of the system by providing more adsorption surface. The adverse transfer of the solute by the eddy diffusion caused by rising bubbles was found to be the factor limiting the effectiveness of the system. 相似文献