吹气发泡法制备闭孔泡沫铝发泡过程的三维数值模拟

吹气发泡法制备闭孔泡沫铝的过程实质上是搅拌流场中复杂的两相流动过程,应用计算流体力学方法分析由倾斜轴倾斜叶片引起的发泡熔池内气液两相强旋湍流流动过程. 在双流体模型基础上引入多重参考系法描述搅拌两相流场,通过分析相间相互作用及湍流模型进行封闭. 解气泡数密度函数的输运方程来分析气泡聚合和破碎引起的气泡尺寸变化. 应用体积积分的方法,计算平均及局部气含率及气泡直径. 考察了桨叶转速及气体流率对气泡直径及其分布的影响. 结果显示,气含率随桨叶转速和气体流率增加而增大;气泡直径随气体流率增加而增大,随桨叶转速增大而减小.     

气固搅拌流化床中压力脉动特性

气固搅拌流化床反应器可用于黏结性聚合物颗粒的流态化过程,流化床中通气湍动与搅拌的相互作用关系仍不明确。通过压力脉动的统计分析、功率谱分析和小波分析,考察了搅拌桨型式和搅拌转速对流态化特性的影响规律。实验发现,搅拌转速和搅拌桨型式对床层压力影响较小,但对压力脉动影响显著。搅拌流化床中搅拌与通气湍动对流态化共同作用,双层锚式桨、框式桨等小桨叶面积的搅拌桨在较高转速条件下能强化流态化过程,与普通流化床相比具有更小的气泡尺寸和压力脉动,搅拌可抑制气泡聚并、破碎气泡,维持床层均匀流态化;而新型具有大桨叶面积的自清洁桨的搅拌作用强烈,在较高的转速下易形成桨叶前方的颗粒堆积和桨叶后方的气体短路等非正常流化现象,适宜于中等转速的操作条件。     

气固搅拌流化床中压力脉动特性

气固搅拌流化床反应器可用于黏结性聚合物颗粒的流态化过程,流化床中通气湍动与搅拌的相互作用关系仍不明确。通过压力脉动的统计分析、功率谱分析和小波分析,考察了搅拌桨型式和搅拌转速对流态化特性的影响规律。实验发现,搅拌转速和搅拌桨型式对床层压力影响较小,但对压力脉动影响显著。搅拌流化床中搅拌与通气湍动对流态化共同作用,双层锚式桨、框式桨等小桨叶面积的搅拌桨在较高转速条件下能强化流态化过程,与普通流化床相比具有更小的气泡尺寸和压力脉动,搅拌可抑制气泡聚并、破碎气泡,维持床层均匀流态化;而新型具有大桨叶面积的自清洁桨的搅拌作用强烈,在较高的转速下易形成桨叶前方的颗粒堆积和桨叶后方的气体短路等非正常流化现象,适宜于中等转速的操作条件。     

挡板进气多级搅拌槽内的气—液分散特性

研究了挡板进气多级搅拌槽内的气－液分散流型、临界分散转速、搅拌功率、气含率和气泡停留时间。试验证明，这种结构的搅拌槽，比标准通气式搅拌槽具有更优良的气－液分散特性，并回归得到了搅拌功率、气含率和气泡停留时间的关联式。     

挡板进气多级搅拌槽内的气－液分散特性

研究了挡板进气多级搅拌槽内的气－液分散流型、临界分散转速、搅拌功率、气含率和气泡停留时间。试验证明，这种结构的搅拌槽，比标准通气式搅拌槽具有更优良的气－液分散特性，并回归得到了搅拌功率、气含率和气泡停留时间的关联式。     

不同类型搅拌器的气—液分散和混合特性

在通气式搅拌槽内研制了直叶圆盘涡轮、直叶桨式涡轮、４５度折叶圆盘涡轮、４５度折叶桨工涡轮、凹弧叶圆盘涡轮、锥形涡轮和布鲁马金式搅拌器的临界分散转速、分散状态、搅拌功率、气含率、气泡停留时间、排量准数和输出效率，并获得了适用上述种类搅拌器的临界分散转速、搅拌功率、气含率和气泡停留时间关联式。     

剪切变稀体系同心双轴搅拌釜内的气液分散模拟

气液搅拌设备因其良好的适用性被广泛应用于过程工业中。为更好地比较不同工况下剪切变稀体系中的气液分散情况,通过实验研究整体气含率和相对功耗确定适宜的转动模式,进而模拟研究表观气速、体系黏度、搅拌转速对气含率和气泡尺寸的影响。结果表明,相同功率下内外双桨反向旋转模式在理想气液分散条件下,相较于单轴内桨和内外双桨同向旋转模式具有更高的气含率和更好的气体泵送能力;表观气速的增加有利于气泡的均匀分散,但气泡尺寸也会随之增大;有效黏度的增加使得搅拌桨的影响区域变小,不利于气泡的均匀分散,气泡尺寸也随之增大;搅拌转速的增加使得循环涡流的影响区域变大,高气含率区不断扩大。     

双层桨气液搅拌反应槽气液分散特性

采用搅拌功率与氧传质系数方法,对一双层桨搅拌反应槽的自吸分散和表面充气分散性能进行研究.比较了两种桨叶组合在两种分散方式下的气相分散临界转速、搅拌功率及两种桨叶组合自吸分散时的气含率和气液传质系数.结果表明,六叶圆盘直叶桨和六叶圆盘斜叶桨的组合在自吸分散时具有较优的分散性能.     

搅拌反应器内气液两相流的CFD研究进展

搅拌式气液反应器因其操作灵活、适用性强等优点,在过程工业中应用广泛.综述了采用计算流体力学CFD技术对搅拌反应器内气液两相流动行为的数值模拟研究.Euler-Euler双流体模型作为主要方法用于描述气液两相流动,在其基础上耦合相对简单的气泡数密度函数模型或复杂的群体平衡模型,可较为准确地预测搅拌反应器内气泡尺寸和局部气含率及其分布规律.CFD模拟结果可用以分析和评价不同搅拌桨叶、搅拌桨组合和气体分布器的气液分散性能,对气液反应器的结构优化和过程强化提供了有效手段.     

三种湍流模型下搅拌釜内气含率特性的模拟

采用计算流体力学（CFD）方法,应用Euler-Euler双流体模型,桨叶采用多重参考系法（MFR）,与考虑气泡聚并与破碎对气泡尺寸影响的群体平衡模型（PBM）相结合,比较了标准k-ε、Realizable k-ε和RNG k-ε3种湍流模型对双层涡轮搅拌釜内气-液两相液相流场、局部气含率及气泡尺寸分布的影响。结果表明：3种湍流模型预测的液相流场流型相似,总体气含率预测值相差不大,均与实验值吻合较好。对于局部气含率,标准k-ε和RNG k-ε模型在桨叶区的预测值偏大,在接近自由液面处三者预测值均偏低,Realizable k-ε模型预测结果与实验值符合最好;对于气泡尺寸,3种湍流模型预测结果均与实验值较吻合,在靠近自由液面处预测值均偏小,气泡尺寸分布与湍流长度分布相吻合。     

气固搅拌流化床压力脉动的小波分析

在内径188 mm、静床高400 mm的搅拌流化床中,采用Geldart D类颗粒为实验物料,通过小波分析研究了不同气速和搅拌桨转速下搅拌流化床的压力脉动行为.实验发现,搅拌桨的转动作用促使在普通流化床中不易散式流态化的D类颗粒形成了散式流态化.随着气速的增加,第1尺度的小波能量特征值在某一个气速范围内发生急剧变化,进而提出了将该气速范围的下限和上限分别定义为临界鼓泡速度和充分鼓泡速度的判据.随搅拌转速的增加,散式流态化的气速操作范围线性增加.在鼓泡流态化状态下,气速是流化床气泡行为的主导因素,搅拌桨转速的增加对气泡产生的频率无明显影响但可使气泡的直径变小.     

Gas–liquid mass transfer in rotating solid foam reactors

Three-phase reactor designs based on rotating solid foams for the application in the fine chemical industry are developed. The aim is to use solid foams both as a catalyst support and stirrer in order to mix the gas and liquid phases and create fine gas bubbles. Gas–liquid mass transfer data are presented for different solid foam stirrer configurations and compared to an optimized Rushton stirrer. Solid foam stirrers were developed in a blade and a block design. Both foam reactor designs work at stirring rates below 600 rpm. Using the foam blade design, gas bubbles are mainly created by the turbulence at the gas–liquid interface. Large bubbles are broken up by the foam blades. Using a foam block design, rotation leads to the structurization of the reactor volume into sections strongly differing in gas holdup, flow behavior and bubble size distribution. This results in a gas–liquid mass transfer, which is 50% higher than the Rushton stirrer used as comparison. The foam stirrer designs can be easily used in ordinary three-phase reactors and show a high potential for further optimization of the gas–liquid flow pattern and therefore for further increase of the rate of mass transfer.     

Experimental studies of ventilated cavities in a channel

Ventilated cavities are characterized by the cavity shape, size, inception mechanism, cavity pressure with drag reduction, re-entrant jet and bubble breakoff from the cavity tip. All these characteristics are dependent upon each other. The aim of the present work is to study these aspects in an integrated way. Ventilated cavity formation was studied in a transparent acrylic channel by sparging gas behind straight blades. Clinging, partial, full and large cavity shapes were observed. Cavity transitions are correlated with the Froude and aeration numbers. Other cavities such as slug, and emulsion cavity were also observed. Bubble breakoff from the cavities is found to be dependent on the cavity type. Typically, large bubbles breakoff from slug cavities while smaller bubble sizes are observed breaking off from emulsion cavities. Other cavity shapes show a mixed breakoff pattern of varying proportion of large and small bubbles. Change in drag force on the blade is found to be dependent on the cavity shape and size. The cavity pressure is correlated with the liquid velocity over the blade and the superficial gas velocity. Negative and positive cavity pressure is found to be associated with the presence and absence of re-entrant jet.     

垂直筛板流化床中FCC催化剂的流化性能

以FCC催化剂颗粒研究垂直筛板流化床内构件对气固两相流化性能的影响,考察了板孔气速、颗粒循环量和帽罩开孔比等筛板结构对流化床压降和提升量强度的影响. 结果表明,气固两相总体逆流流动条件下,帽罩内气速达4 m/s,气固高速并流喷射无气泡,两相接触好、返混小,属快速流态化. 由于没有气泡,床层压力波动小,在塔板上颗粒返混小. 垂直筛板压降随板孔气速、帽罩底隙高度增大而增大,随帽罩开孔比、板孔径增大而减小,颗粒提升量大,床层压降大. 提升量强度随板孔气速、帽罩底隙高度、颗粒循环量增加而增大,随帽罩高度与塔节高度比增大而减少,随帽罩筛孔孔径变化存在最大值. 当帽罩开孔比为1.2~2.5、板孔面积与帽罩截面积比为0.42、帽罩底隙高与板孔孔径比为0.36~0.64时帽罩流化性能较好.     

Bubble behavior in corrugated‐wall bubbling fluidized beds—Experiments and CFD simulations

A new concept to harness bubble dynamics in bubbling fluidization of Geldart D particles was proposed. Various geometrical declinations of a cold‐prototype corrugated‐wall bubbling fluidized bed were compared at different flow rates (U_g) to conventional flat‐wall fluidized bed using high‐speed digital image analysis. Hydrodynamic studies were carried out to appraise the effect of triangular‐shaped wall corrugation on incipient fluidization, bubble coalescence (size and frequency), bubble rise velocity, and pressure drop. Bubble size and rise velocity in corrugated‐wall beds were appreciably lower, at given U_g/U_mb, than in flat‐wall beds with equal flow cross‐sectional areas and initial bed heights. The decrease (increase) in size (frequency) of bubbles during their rise was sustained by their periodic breakups while protruding through the necks between corrugated plates. Euler‐Euler transient full three‐dimensional computational fluid dynamic simulations helped shape an understanding of the impact of corrugation geometry on lowering the minimum bubbling fluidization and improving gas distribution. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

新型径向叶片式旋转床压降分析及气相流场模拟

针对折流式旋转床压降高、能耗大的问题,提出了一种新型超重力旋转床设备--径向叶片式旋转床。首先,对该旋转床的压降进行了理论分析和建模,并利用水-空气体系进行了实验研究。通过改变气量、转速和液量探究了新型径向叶片式旋转床压降的变化规律,结果表明压降随气量、转速和液量的增加而增加,且随着气量和转速的增加,液量对压降的贡献逐渐减小。压降模型的预测值与实验数据的相对偏差基本在10%以内,表明模型可以较好地预测新型径向叶片式旋转床的压降。另外,通过计算流体力学（CFD）软件的模拟获得了旋转床内气相流场和压力分布的结果,发现转子内压降是总压降的主要部分;气体进入转子后会因叶片作用使得周向速度变大,并在转子外缘处达到最大值;气体的进口流速将会影响旋转床内的气相分布。利用实验数据对CFD模拟结果进行了验证,两者的相对偏差在10%左右。     

一种多翼离心风机流场模拟与性能分析

综合多叶片离心风机噪音低以及长短叶离心风机气流稳定的优点,设计了一种具有大小叶片交错组合结构的多翼离心风机.采用计算流体力学方法,分别模拟了前向式和后向式2种不同叶轮形式的风机流场.通过对比发现,在相同转速和流量下,后向式风机进出口压差比前向式叶轮风机小11.8％,但功率消耗降低了24.5％,综合效率较前向式高;后向式...     

Performance of the monolithic stirrer reactor: applicability in multi-phase processes

The novel monolithic stirrer reactor is a promising replacement for a conventional slurry reactor in multi-phase reactions. In this reactor monolithic structures are used as stirrer blades, creating a catalytic stirrer. The most important advantage of the monolithic stirrer reactor is the easy catalyst handling. The influences of different parameters on the performance of the monolithic stirrer reactor in the selective hydrogenation of 3-methyl-1-pentyn-3-ol were investigated. The decreasing catalyst layer thickness with increasing cell density proved to be beneficial for the performance of the monolithic stirrer reactor. An increasing stirrer speed caused an increase in the activity because of the higher flow through the monolith channels and the improved gas–liquid mass transfer. If the length of the monolithic stirrer blades was smaller than 0.03 m the performance of the monolithic stirrer was enhanced.     

Fluidization of Group B particles with a rotating distributor

A novel rotating distributor fluidized bed is presented. The distributor is a rotating perforated plate, with 1% open-area ratio. This work evaluates the performance of this new design, considering pressure drop, Δp, and quality of fluidization. Bed fluidization was easily achieved with the proposed device, improving the solid mixing and the quality of fluidization.In order to examine the effect of the rotational speed of the distributor plate on the hydrodynamic behavior of the bed, minimum fluidization velocity, U_mf, and pressure fluctuations were analyzed. Experiments were conducted in the bubbling free regime in a 0.19 m i.d. fluidized bed, operating with Group B particles according to Geldart's classification. The pressure drop across the bed and the standard deviation of pressure fluctuations, σ_p, were used to find the minimum fluidization velocity, U_mf. A decrease in U_mf is observed when the rotational speed increases and a rise in the measured pressure drop was also found. Frequency analysis of pressure fluctuations shows that fluidization can be controlled by the adjustable rotational speed, at several excess gas velocities.Measurements with several initial static bed heights were taken, in order to analyze the influence of the initial bed mass inventory, over the effect of the distributor rotation on the bed hydrodynamics.