阶梯动压滑动轴承油膜流态可视化试验研究

阶梯动压滑动轴承深腔和浅腔油膜厚度相差较大,油膜流态会随之发生变化。采用可视化试验方案,利用气泡示踪法研究阶梯动压滑动轴承在深、浅腔及边界处的油膜流态变化规律,考察主轴转速、最小半径间隙对油膜流态的影响。结果表明:阶梯轴承的台阶突变处易导致油膜涡旋,出现紊流、层流混合现象;随着转速增加,深腔处油膜紊流现象加剧,随半径间隙增大,浅腔处容易产生紊流现象。试验数据与理论判据计算结果趋势一致。     

减轻碳酸饮料二次灌装起泡的方法

通过对碳酸饮料的生产性试验的研究,分析了中小型碳酸饮料设备二次灌装起泡的原因,给出了减轻起泡的几种方法。     

CO2气体进入聚合物熔体中的形态变化过程

在聚合物发泡中,CO2气体的浓度分散和扩散速率与初始气泡形态有关。用可视化方法,对挤出条件下CO2气体注入静、动态流场以及气体在高压和低压注入时的气泡形态和破碎问题的研究。研究表明气体小流量时,静态熔体中球形气泡形成、直径长大定型、长度不断伸长的3个阶段与动态熔体中的初始球形膨胀,头部变尖、中间涨大,尾部颈缩及断裂3个阶段有所不同;新型螺杆对气泡破碎和分离作用比收敛流道更有效。高压下,符合实际生产的气体大流量以射流注入螺槽,形成气熔混合的蜂窝状泡沫,促进了气泡的破裂和分散,加强了气体浓度分散和扩散,有助于聚合物/CO2均相溶液的形成。     

Effect of amylose/amylopectin ratio and extent of processing on the physical properties of expanded maize starches

Low-density expanded starchy products are often desirable, particularly in the snack food industry. Levels of shear and amylose are often deemed crucial factors for expansion. In this study, maize starches containing low (waxy), normal and high levels of amylose were compared after processing. Low shear processing used a popping head (similar to a rice-cake machine), while high shear (~450 kJ kg⁻¹) samples (pellets and directly expanded) were created using twin-screw thermomechanical extrusion. Native starches and ground extruded materials (<106 µm) were popped using the same conditions (230 °C, 4 s, water content 12% wwb). All samples tested created fused aerated cakes, which had little or no remaining crystallinity, except for the directly popped waxy sample, which retained ~17% of its original crystallinity. Water absorbances and solubilities were influenced greatly by the starch source and marginally by the amount of processing. On processing, waxy samples showed increased solubility while those with normal amylose content had greater absorption. The densities of all the popped samples were similar despite marked differences in shear regime history and the major variations in the amylose and amylopectin ratios. These results challenge the expected relationships between shear and different starches’ potential to expand.     

原位气泡拉伸法制备增韧聚丙烯

将5～30份的纳米碳酸钙(nano-CaCO<,3>)添加至无规共聚聚丙烯(PP-R)树脂中,采用原位气泡拉伸法(ISBS法)将树脂基体中的nano-CaCO<,3>分散,制备出PP-R/nano-CaCO<,3>复合材料.对复合材料进行扫描电子显微镜观察,发现ISBS法可以将nano-CaCO<,3>均匀地分散到PP-R中;通过力学性能测试表明:当nano-CaCO<,3>添加量为20份时,ISBS法制备的复合材料的缺口冲击强度与机械分散法相比提高20.4%.研究结果表明:与传统的机械分散法相比,ISBS法可以将nano-CaCO<,3>更均匀地分散到PP-R中,使nano-CaCO<,3>在PP-R中达到纳米级尺度的分散,进而得到高韧性的聚丙烯复合材料.     

Link between bubbling and segregation patterns in gas‐fluidized beds with continuous size distributions

Experiments involving a bubbling, gas‐fluidized bed with Gaussian and lognormal particle‐size distributions (PSDs) of Geldart Group B particles have been carried out, with a focus on bubble measurements. Previous work in the same systems indicated the degree of axial species segregation varies non‐monotonically with respect to the width of lognormal distributions. Given the widely accepted view of bubbles as “mixing agents,” the initial expectation was that bubble characteristics would be similarly non‐monotonic. Surprisingly, results show that measured bubble parameters (frequency, velocity, and chord length) increase monotonically with increasing width for all PSDs investigated. Closer inspection reveals a bubble‐less bottom region for the segregated systems, despite the bed being fully fluidized. More specifically, results indicate that, the larger the bubble‐less layer is, the more segregated the system becomes. The direct comparison between bubbling and segregation patterns performed provides a more complete physical picture of the link between the two phenomena. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Behaviour of a large bubble flowing through a sudden constriction between a cylindrical pipe and a rectangular cross section channel

The behaviour of a single large bubble flowing through a sudden constriction between a cylindrical pipe and a channel of rectangular cross section is studied experimentally. Two types of constrictions are considered: an abrupt one and a smooth one. Image analysis displays the deformation of the large bubble generated in the upstream vertical pipe and flowing through each kind of constriction. Image processing allows an estimate to be made of the velocity of Dumitrescu bubbles upstream of the constriction and the velocity of a 2D cap bubble flowing downstream of the constriction in a rectangular-cross-section channel. When the large bubble flows through a constriction, its behaviour can be considered in two steps: a first step corresponding to the disengagement of the large bubble and a second step corresponding to its transient behaviour after detachment. In terms of disengagement, an abrupt constriction induces systematic break-up of the large bubble whereas, with a smooth constriction, the large bubble undergoes strong deformations but does not break up. After detachment, large bubbles relax in a similar way and their velocities tend towards the terminal velocity of the 2D cap bubble.     

鼓泡塔中离子液体-空气两相流的CFD-PBM耦合模拟

针对咪唑类离子液体介质,采用Euler-Euler双流体模型与群平衡模型（PBM）耦合的方法,引入由实验结果拟合获得的适用于该介质的气液相间曳力系数模型,对内径0.203 m、高2 m的鼓泡塔中离子液体-空气两相流进行计算流体力学模拟,研究了不同表观气速下塔内气液两相速度场分布、气含率和气泡尺寸分布等流体动力学性质。与现有的相间曳力系数模型Schiller-Naumann模型模拟结果对比,采用本文模型得到的气含率与实验值吻合更好,气泡尺寸分布与实验结果一致。     

多级鼓泡塔中液相返混系数与交换速度的研究

采用示踪方法对高2 000 mm,内径282 mm多级筛板鼓泡塔内液相返混系数进行测量研究,并通过扩散-返混模型以及RTD曲线给出鼓泡塔内筛板上下二侧液体交换速度,同时考查了表观气速、开孔率等因素对轴向扩散系数与液体交换速度的影响.根据实验得出鼓泡塔内轴向返混系数以及液体交换速度与表观气速、开孔率有很大关系,均随表观气...     

纤维毡波折前后初始气泡点变化规律

纤维毡波折变形后孔径发生变化,引起初始气泡点变化.用过滤器渗透性试验仪测定了不同孔径纤维毡波折前后初始气泡点的变化情况.结果表明,纤维毡单重越大,纤维丝径越细,波折后初始气泡点变化越大;相同孔径的纤维毡,在细面形成波峰时比在细面形成波谷时初始气泡点变化大;纤维毡厚度越小,初始气泡点变化越大.