三支管平行微通道内气液两相流相分配特性实验研究

微通道的集成和放大对于微型反应器及散热器的开发具有重要意义。文章以高纯度氮气和质量分数为0.03%的SDS水溶液分别作为气相和液相工质,通过一系列可视化实验,研究了入口流型为弹状流和环状流时,在拥有一个主管(水力直径为0.6mm)与3个平行侧支管(水力直径为0.4mm)的平行微通道内气液两相流的相分配特性。实验结果表明,侧支管的相分配特性与入口流型密切相关。当入口流型为弹状流时,气相富集于中间的侧支管。当入口流型为环状流时,第一个支管中始终走液相,气液两相在后面两个支管中的分配则相对均匀。     

热流密度对立式螺旋管内气液两相流摩擦阻力特性的影响

在气液两相流体模型的基础上,对立式螺旋管内气液两相流体进行了数值模拟,探究了热流密度对管内摩擦阻力的影响.研究表明：在低压低质量流速下,摩擦阻力降、分液相摩擦阻力系数ΦL都随着热流密度的增大而增大;传热系数随着热负荷的增大而显著增大,在热负荷一定的情况下,传热系数随干度的增大而减小;换热器的综合性能在不同的热流密度条件下相差不大.研究结论对立式螺旋管内气液两相流摩擦阻力问题的研究有一定的参考价值.     

商用空调分液器内气液两相流的数值模拟研究

采用CFD数值模拟方法,基于VOF两相流模型,建立了商用空调用分液器及其管组件内气液两相流动数学模型,分析了三种分液器管组及分液器放置角度对分液器内部制冷剂气液两相体积分数分布及分配性能。结果表明:加长混合室后的文丘里型分液器管组在垂直放置或者具有倾斜角度的情况下分流性能均优于原文丘里型管组;翼型叶片型分液器管组分流性能相对最优。     

多通道烘缸通道内蒸汽冷凝流动对传热特性的影响

为提高多通道烘缸的换热效率,优化其蒸汽利用率,本研究探究了蒸汽在多通道烘缸通道内的冷凝换热过程,并借助高速摄像机对蒸汽冷凝换热过程进行了可视化观测。在蒸汽质量流速(kg/(m~2·s))与冷却水质量流量(kg/h)两种不同工况下,分析了多通道烘缸通道内气液两相流型的变化情况,研究了通道内蒸汽冷凝换热系数及其沿通道壁面方向压降的变化规律,为多通道烘缸通道内蒸汽的流动与传热机理研究提供了依据。     

横向水流作用下气泡运动数值模拟

由于气液两相体系中气泡的诸多流体力学行为不仅影响两相流的速度分布,还可通过改变气液相界面等途径改变整个体系的传热传质效果,对气液接触设备性能具有重要影响。课题组利用数值模拟对恒定水速下管道中喷射的气体进行分析,追踪管道中气泡流的变化情况。气液两相流采用层流模型,并运用VOF对气液两相界面进行追踪,速度与压力的耦合求解采用PISO算法。计算结果表明:气体在管道中成类似泡状流,并受浮力作用逐步靠近上壁面形成连续的长气泡;水流速度和气泡到达上壁面距离进口处的距离近似呈线性关系;最大气泡粒径与进口水速负相关,与进口气速正相关。研究结果可为相关气泡运动特性的进一步研究提供参考。     

柴油机喷嘴内部空穴流动的三维瞬态数值模拟

建立了柴油机喷嘴内部空穴两相流动的三维气液两相流模型,并针对多孔垂直喷嘴进行了喷孔内部空穴两相瞬态流动的数值模拟;研究了喷嘴内部的瞬态速度场、压力场和湍动能的分布特点.通过计算可知,湍动能主要集中在喷孔上部空穴区,随着针阀升程的增大,喷孔入口的环状压降愈加明显,入口上拐角处形成的涡流区范围不断扩大.同时分析了不同针阀升程下空穴流动特性,获得了空穴产生、发展过程的规律,为进一步准确模拟和分析喷雾特性提供依据.模拟计算结果与已有的实验结果吻合较好.     

基于红外热像的气液两相分层流液膜厚度非介入测量

对于输送高压、易燃易爆、强腐蚀性介质的气液两相流管道,电导探针等传统的介入式液膜厚度测量方法不适用.针对这种情况,提出了通过红外热像测量气液两相分层流液膜厚度的新方法:在管道外壁敷设加热带,通过施加恒定热流密度来增加气液相温差,通过采集红外图像识别气液界面获得液膜高度.在建立VOF多相流模型模拟恒定热流密度条件下管截面上温度分布特征基础上,实验在气液两相流环道上进行,采用热像仪采集管壁红外图像,真实液膜厚度由介入式电容探针测量,在试验范围内红外方法液膜厚度测量最大误差8.2%.     

弯曲灌装管道内油制辣椒流场的模拟分析

为优化油辣椒灌装管道设计,以油辣椒固液多相流体为研究内容,以水平90°弯管模型为对象,计算适合该灌装管道模型的油制辣椒湍流临界速度,利用多相流Mixture模型分别对入口流速为5,7,9 m/s的油辣椒制品固液多相混合流体进行模拟,分析弯管内固液多相流的速度场和密度场分布情况,并与单一辣椒油流动性进行对比。结果表明:流速大于临界湍流速度时输送效果较为理想,当流速低于临界速度时,容易发生沉降现象;几何弯曲对多相流场影响较大,弯管段与出料口之间直管长度不宜过大。研究结果可为油辣椒制品灌装设备设计提供有利的理论依据。     

基于CFD的不同搅拌组合多相流流场研究

针对在设计发酵搅拌设备过程中往往依赖经验判断传质混合效果以及能耗等的现状,课题组利用CFD技术对设计的4种搅拌模型进行气液两相流非稳态数值模拟.模拟采用了多面体网格划分物理模型以及滑移网格模型法求解,探究了其速度场、气相体积分数和功率耗损情况.结果表明:相同工况下,不同搅拌组合的流场特性差异较大;上桨采用径向流桨的搅拌...     

固液两相流理论在采卤工程中的应用

如何防止固相物在管道中的沉积,以及保证不溶物就地沉积不被搬运,是采卤工程中非常关切的问题。本文介绍了固液两相流理论,尝试了临界流速计算在钙镁泥输送和水平井建槽流量控制方面的应用。并且指出采卤工程中的管道所输送的多数介质都可以看成固液两相流或者多相流,在管径参数设计时,应该充分考虑介质的流速要求。     

金属丝径大小对液膜流动影响的CFD研究

精馏过程气液两相流动分布特征对分离效率具有重要影响,为研究金属丝网波纹填料表面液膜流体动力学特性,建立基于VOF法的液膜在金属丝网表面上的气—液两相逆流CFD模型,并根据液膜流动特点考虑了表面张力动量源项和气液界面作用力动量源项。模拟结果与文献流动形式相符,表明文中提出的CFD液膜流动模型具有一定的可靠性。文中主要考察丝径大小对液膜流动的影响,模拟结果表明适当改变丝径的大小有助于改善液膜的稳定,对于提高丝网填料气液之间的传质效率有重要意义。     

超声波辅助泡沫分离回收溶液中牛血清白蛋白的性质研究

本文提出了一种超声波辅助泡沫分离富集水溶液中牛血清白蛋白的新方法。首先利用傅立叶红外光谱研究泡沫分离前后牛血清白蛋白分子结构的变化,利用高效分子排阻色谱测定超声波对牛血清白蛋白聚集效果的影响,随后,研究了装液高度、气体体积流量、分布器孔径对泡沫分离回收牛血清白蛋白效率的影响,并对回收的牛血清白蛋白的理化性质进行评价。结果表明,泡沫分离过程中牛血清白蛋白在气液界面上的吸附会诱导分子间二硫键的产生,超声波辅助泡沫分离能有效抑制牛血清白蛋白分子聚集。在温度25℃,pH6.0,牛血清白蛋白浓度0.20 g/L,气体分布器的孔径180 μm,液体高度300 mm,进料速率2 mL/min,气体体积流量150 mL/min,超声波功率600 W和超声波处理时间2 min的条件下,牛血清白蛋白的富集比和回收率分别达到6.3%和85.3%。超声波处理能够明显抑制泡沫分离过程中牛血清白蛋白分子聚集体的产生,进而提高消泡液的表面疏水性、泡沫性能和乳化性。     

Degradation of waste gas containing toluene in an airlift bioreactor

Suspension microorganisms in an internal-loop airlift bioreactor were utilized to treat waste gas containing toluene. The working volume of the reactor was 35 L, and the biomass concentration was 3 kg/m3. The gas pollutant flowed into the reactor from the bottom; it then transferred from the gas phase to the liquid phase and was degraded by the microorganisms suspended in the liquid phase. The microorganisms were able to degrade 50-90% of the inlet toluene when its concentration was from 0.5 to 10 g/m3, and the superficial gas velocity ranged from 0.15 to 1.23 cm/s. A comprehensive mathematical model was also developed to describe the overall degradation process of toluene in the internal-loop airlift bioreactor. The overall degradation process included gas flow, gas-liquid mass transfer, flow and dispersion of the liquid phase, and microbial kinetics. The hydrodynamic properties including the gas and liquid superficial velocities, the gas holdup, the volumetric mass transfer coefficients of toluene and oxygen, and the microbial kinetics were obtained for this model. The substrate inhibition theory was used to simulate the microorganism growth kinetics, and its kinetic constants were obtained experimentally. The penetration theory was used to predict the volumetric mass transfer coefficient. And the drift-flux theory was used to predict the hydrodynamic properties in each section (riser, gas-liquid separator, downcomer, and bottom) of the airlift bioreactor. The concentration distributions of toluene and oxygen in the airlift bioreactor and the removal efficiency of toluene predicted by the mathematical model agreed well with the experimental data.     

多通道烘缸通道内流体流动特性数值模拟研究

探讨了多通道烘缸内流体通过通道时的流动特性,建立了多通道烘缸通道的计算流体力学模型,并用计算流体力学软件FLUENT模拟通道内在不同气相折算速率及不同液相折算速率工况下,通道内气液两相分布及其沿通道壁面方向的压力降,得出了通道内流型的变化情况,为多通道烘缸的流动与传热机理研究提供了理论依据。     

溢流染色机圆喷嘴流场建模与涡流场仿真分析

针对喷嘴内部气液两相流流动特性对织物染色产生的影响,建立计算流体动力学数学模型,对喷嘴内部液相的流动特性及液相流动对气相产生的影响进行三维模拟仿真,并根据仿真结果分析喷嘴盖内气体动静态压力的变化及喷嘴内染液的速度场和压力场的分布.研究结果表明:液相的快速运动引起喷嘴盖内气相的动态脉动,喷嘴盖内压力为负值,喷孔处液相的速...     

Alkaline biofiltration of H2S odors

Hydrogen sulfide (H2S) is a very common odor nuisance which is best controlled by chemical or biological scrubbing. Under alkaline pH, the amount of H2S that can be solubilized in a scrubbing liquid increases significantly, and therefore, gas-liquid mass transfer limitations can be reduced. To date, biological scrubbing of H2S has been limited to neutral or acidic pH, despite the potential benefit of reduced mass transfer limitations at alkaline pH. In the present paper, an alkaliphilic sulfoxidizing bacterial consortium was deployed in a laboratory-scale biotrickling filter treating H2S at pH 10. The gas contact time ranged from 1 to 6 s, and H2S inlet concentrations, from 2.5 to 18 ppm(v). The results showed that under most conditions, H2S removal exceeded 98% and the degradation end-product was sulfate. At the highest H2S concentrations and shortest gas contacttimes, when the loading exceeded 30 g m(-3) h(-1), the H2S removal efficiency decreased significantly due to biological reaction limitation, and incompletely oxidized sulfides were measured in the trickling liquid. An analysis of the process demonstrated that operating the biotrickling filter at high pH results in an enhancement of the mass transfer by a factor of 1700-11 000. Overall, alkaline biotrickling filtration was shown to be very effective at low concentration of H2S and very short gas contact time. This is the first demonstration of a biotrickling filter for air pollution control operated at high pH.     

In situ removal of 2-chlorophenol from unsaturated soils by ozonation

A mathematical model considering mass transfer process at the gas-liquid interface in soil ozonation was developed and validated with laboratory column experiments. Experimental data, specifically, concentration profiles of the organic contaminant and the ozone breakthrough curves, were obtained. In this model, the mass flux of ozone transferred from the gas phase into the liquid phase was described by the two-film theory incorporated with an enhancement factor approach as to account for chemical reactions. With the enhancement factor, the ozone gas transport in the experimental column can be described by an advection-dispersion-reaction equation with pseudo-second-order kinetics in the liquid film. This greatly simplifies the governing equations of the system. Results show that parameters such as degradation yield factor, diffusion coefficients, thickness of liquid film, ozone gas concentration, and gas-liquid interfacial area play an important role on the soil ozonation process. Using the scaled model, important universal dimensionless variables were obtained. The Stanton number (St) is the most important parameter in controlling the performance of system. When St approaches zero, the process is reaction-controlled. Conversely, when St is large, it is convection-controlled. Only when the system is convection-controlled (i.e., large St values) can an increase of ozone flow rate enhance the removal of soil contaminants such as 2-chlorophenol.     

Foams generated from viscous non-Newtonian shear-thinning liquids in a continuous multi rotor-stator device

Whilst aeration is ubiquitous in the food industry, little work has been done on foams generated from viscous non-Newtonian liquids. We study the production of foams from viscous shear-thinning liquids containing a non-ionic food grade surfactant (PGE 55), Xanthan gum and caster sugar, using a continuous pilot-scale device having twelve rotor-stator pairs. The effects of process parameters (rotor speed, gas-liquid volumetric flowrate ratio (G/L)) and liquid composition (surfactant concentration, Xanthan gum concentration) on foam gas volume fraction and bubble size distribution are elucidated. X-ray micro-Computed Tomography is employed to characterise the 3D microstructure of the foams. Rotor speed and G/L ratio are the dominant factors in determining the gas volume fraction and bubble size distribution. The foams produced exhibit a rich fine texture with high static stability. For a given energy input in turbulent flow, a higher G/L ratio results in a higher gas fraction and a smaller bubble size.Industrial relevanceAeration is ubiquitous in the food industry and innovative ways to generate stable foams with fine texture from viscous non-Newtonian media are needed to satisfy the increasing demand for better quality, healthier and cheaper products. The use of continuous multi rotor-stator devices operating in turbulent flow and under atmospheric pressure achieves optimum aeration efficiency and prevents foam expansion. The use of an effective surfactant such as PGE 55 and a thickener such as Xanthan gum help provide the desired fine texture and stability for longer shelf-life. Operating at high gas-liquid ratios in turbulent flow achieves the production of finer more uniform foams with less energy input.     

科里奥利质量流量计在烟草自动加香系统中的应用

通过对科里奥利质量流量计工作原理的分析 ,探讨了质量流量计在自动加香控制系统应用中影响计量精度的因素 :介质密度、液体压力、液体温度、机械振动以及气 -液二相流。对于两种进口质量流量计的使用技术和工作性能进行了介绍 ,并将国产和进口同类型科里奥利质量流量计进行了对比测试。