【作者】 李西营；

【导师】 于志家；

【作者基本信息】 大连理工大学 ， 化学工程， 2005， 硕士

【摘要】 本文采用电化学的方法研究了垂直上升管内弹状流的特性参数。研究了牛顿流体(水)空气体系中形成弹状流的壁面传质系数及在管路不同位置处液弹长度分布,此外还着重研究了非牛顿流体(缩甲基纤维素钠—CMC的水溶液)和空气体系在不同管径管路中形成弹状流的气液弹长度分布。 弹状流内传质系数表明:通入少许气体形成弹状流后平均传质系数较同样液速下单相流的传质系数显著增加。同样的表观气速下,传质系数随着液体流速的增加而增加,但较小液速下,传质系数波动较大,随着液速的不断增加,传质系数波动范围逐渐减小,同时增加液速对传质增强的贡献越来越小。原因是液速较小增加液速能有效的增加尾迹区的长度,该阶段的传质系数增加较为显著。但当液速超过一定值时,继续增加液速已不能再增加尾迹区的长度,相应的传质系数的变化不大。增加气体表观速度对传质系数的增加收效甚微。Campos实验证明增加气速仅能增加气弹长度,但尾迹区长度和气弹周围液膜内的剪切速率并没有发生太大变化,因此变化气速对壁面传质系数的影响不大。 实验得到管路25D,55D,以及100D处液弹长度分布均可以用对数正态分布函数来描述。随着测试位置的上移,液弹平均长度及液弹长度的标准偏差均增加,说明在测试段内气弹之间不断发生聚并,也即弹状流经历了逐渐的发展阶段。液弹长度分布对气液表观速度的变化并不敏感。 研究了CMC溶液—空气体系的弹状流在不同浓度、管径、表观气液速下的气液弹长度分布。结果表明:不同浓度CMC溶液下的气液弹长度分布均可以用正态分布描述。气弹长度随溶液浓度(黏度)的增加而增加,液弹长度随浓度(黏度)增加而减小。但0.3wt%的CMC溶液较为特殊。通过计算不同浓度下气弹尾迹区长度及雷诺数给变化作出相应的解释。气液速变化对液弹长度分布的影响是相似的,高浓度CMC(0.8wt%)溶液中的液弹长度和方差随气液速的增加而减小,低浓度CMC(0.3wt%)溶液中气液弹长度和方差随气液速的变化不规则。无论在高浓度还是低浓度CMC溶液中,气弹长度均随气速的增加而增加,随液速的增加而减小。管径对气弹长度分布的影响尤为显著,但液弹长度分布对管径变化影响并不敏感。并从雷诺数的变化,尾迹区的长度以及发展段长度对气弹长度分布变化进行了解释。更多还原

【Abstract】 By electrochemical method, characteristic parameters are investigated within the range of slug flow in vertical pipe. Emphases are placed on the study of the length distribution of elongated bubble and liquid slug with different diameter pipes in which slug flow can form when gas phase is introduced into CMC solutions whose concentrations are adjusted. Moreover, mass transfer coefficient (M.T.C.) together with the length distribution at different locations of the pipe, can be obtained in vertical pipe where slug flow is expected in the medium composed of gas and water.The introduction of small amount of gas can account for the greater enhancement with respect to single phase flow. While keeping gas superficial velocity constant, M.T.C increases as liquid superficial velocity. It is noticeable that the increase and the fluctuation of M.T.C experience two different phases. The first phase is characterized with the amplitude of the increase and fluctuation of M.T.C being at high level, but the amplitude of the increase and fluctuation becomes inapparent for the second phase. These phenomena can be explained clearly if the length of wake region is taken into account. The increase of gas or liquid superficial velocity has little contribution to the enhancement of M.T.C. According to the study of Compos, despite of the increase of Taylor bubble with the increase of gas superficial velocity, the value of M.T.C does not increase due to the fact that the length of wake region, along with the shear rate in the film around the bubble, does not change distinctively.The length distribution of liquid slug liquid slug can be depicted by log-normal distribution at three locations of the pipe such as 25D, 55D, 100D. As the measurement locations move upward, the gradual increase of the average length along with standard deviation shows that the coalescence between two consecutive bubbles occurs within the whole scope of measurement, so slug flow is under the condition of development.The length distributions of Taylor bubble and liquid slug are investigated in the system of CMC solution and gas with the changes of solution concentration, pipe diameters and gas or liquid superficial velocity. The length distributions of Taylor bubble and liquid slug are in accordance with normal distribution at the variety of concentration. With the exception of the concentration of 0.3wt%, the length of Taylor bubble increases as the solution concentration, and the length of liquid slug decreases as the solution concentration increases. The length ofelongated bubble decreases as liquid velocity increases, but the length of slug is immune to the change of liquid velocity. The effect of gas velocity on slug length distribution is more distinctive at high concentration of solution than at low. The length of Taylor bubble is always increases with increase of gas superficial velocity. The length distribution of Taylor bubble is susceptible to pipe diameter, but the length distribution of slug is not. The changes of Taylor bubble length can be explained according to the alterations of Re. and the length of wake region and development section.更多还原