【作者】 臧晓红；

【导师】 王军； 刘延来；

【作者基本信息】 大连理工大学 ， 化学工程， 2005， 硕士

【摘要】 在气升式内环流反应器(ILAR)的实验装置中,分别添加不同的表面活性物质于牛顿流体(去离子水)和非牛顿流体(羧甲基纤维素钠水溶液,CMC)中,研究了气-液体系的流体力学特性和传质性能,并在理论上对实验结果进行了分析。 向空气-水体系中添加微量醇类物质(乙醇、叔丁醇、季戊四醇)可以显著强化ILAR中的气-液传质性能,其原因是添加微量醇类物质会改变气-液两相的界面状态,从而抑制了气泡间的聚并行为。但是,这种抑制气泡聚并的作用只存在于一定的醇浓度范围内,超过某一极限浓度时,氧的液相体积传质系数会有所降低。关于气含率的研究结果表明,当表观气速提高时,含醇体系和去离子水体系的气含率都增加;在相同的表观气速下,添加醇体系的气含率明显高于去离子水体系。此外,添加电解质氯化钙也会提高氧的液相体积传质系数,本文从离子强度的角度对其抑制气泡聚并,强化气-液传质的机理进行了分析。 非牛顿流体CMC水溶液的实验结果表明:与牛顿流体相比,非牛顿流体中气-液传质性能降低,并且随着黏度的增加而明显降低,这是由于黏度的增加会使Taylor泡的尾流更趋于稳定,降低了液相扰动,从而有利于气泡间发生聚并现象。向非牛顿流体中添加醇类物质也会影响气-液传质性能,其影响作用和聚合物的含量有关:对于聚合物含量低的非牛顿流体,添加微量醇可以强化气-液传质;聚合物含量高的非牛顿流体,微量醇的加入反而不利于气-液间传质过程。无论聚合物含量高低的非牛顿流体,添加电解质均会使液相体积传质系数k_Lα值有显著的提高。另外,随着黏度的增加,非牛顿流体在ILAR上升管中的气含率变化不大,而在下降管中气含率有所提高。更多还原

【Abstract】 In the present work, hydrodynamic and mass transfer characteristics of gas-liquid system containing Newtonian fluid (water) or non-Newtonian fluid (aqueous solution of sodium carboxymethylcellulose, CMC) as the liquid phase respectively in an Internal Loop Airlift Reactor (ILAR) are investigated experimentally in the presence of small amounts of surface active components as additives. Thereafter, the experimental results are interpreted based on theoretical considerations.The experimental results of air-water system in ILAR show that the addition of alcohols (ethanol, tertiary butanol, pentaerythritol) into water results in a significant increase in the oxygen transfer coefficient, which is mainly due to the change of gas-liquid interfacial properties and subsequent inhibition of bubble coalescence process. However, the intensification of gas-liquid mass transfer occurs in a certain concentration range. Beyond a limiting concentration value, the liquid phase volumetric mass transfer coefficient of oxygen decreases slightly. Gas holdups in both the water and aqueous solutions of alcohols increase significantly with the increase in gas superficial velocity, however, the latter is much higher at the same gas superficial velocity. In addition, an increase in the measured liquid phase volumetric mass transfer coefficient is also found when minute quantities of electrolyte are present in the water, which can be analyzed on the basis of ionic strength.The experimental results with respect to aqueous solutions of CMC reveal that gas-liquid mass transfer performance is inferior to that of Newtonian fluid. Meanwhile, an increase in the viscosity of non-Newtonian fluid will cause a further decrease in the oxygen transfer rate, showing that in such case bubbles are possibly more easier to coalescence because the increasing viscosity tends to stabilize the wake flow behind Taylor bubble and consequently reduces the turbulence level there. Also, the addition of alcohol into the non-Newtonian fluid has some certain influence on the gas-liquid mass transfer behavior in such system. However, this influence varies with the concentrations of CMC polymer in the aqueous solutions. That is, the addition of minute quantities of alcohol will increase mass transfer rate at low CMC concentrations while at high CMC concentrations the contrary trend is observed. As there are small amounts of electrolyte in the CMC solutions, the measured liquid phase volumetric mass transfer coefficients are always higher than those of CMC solutions of different concentrationswithout such electrolyte. When the viscosity of the non-Newtonian fluid increases, the gas holdup in the riser is found to change slightly while that in the downcomer increases.更多还原