Hydrodynamic and mass transfer characteristics of power-law fluids in bubbling reactors

doi:10.11949/j.issn.0438-1157.20171253

Abstract

Abstract:

Multiphase flow and mass transfer of non-Newtonian fluid are widely encountered in wastewater treatment equipment. Study of gas-liquid mass transfer in non-Newtonian fluid is essential to achieve optimal design and energy-efficient operation of these equipment. Tap water and carboxyl methyl cellulose (CMC) aqueous solution with different mass fraction were selected to study hydrodynamic and mass transfer characteristics of Newtonian and non-Newtonian fluids in bubbling reactors. The influences of gas superficial velocity and liquid rheological behavior on bubble size distribution, overall gas holdup and volumetric oxygen transfer coefficient were investigated in detail. The results show that characteristic parameters of mass transfer are significantly affected by rheological behavior of liquid phase. In CMC aqueous solutions, bubble equivalent diameters were larger and bubble diameter distributions were broader than those in tap water. Overall gas holdup was increased with superficial gas velocity in both tap water and CMC aqueous solutions, whereas volumetric oxygen transfer coefficient of CMC aqueous solution was smaller than that of tap water. Under the same gas superficial velocity, volumetric oxygen transfer coefficient was decreased when CMC mass fraction in aqueous solution was increased. Based on experimental results, a modified formula of volumetric oxygen transfer coefficient and a dimensionless correlation of oxygen transfer in power-law non-Newtonian fluid were proposed to calculate gas-liquid mass transfer parameters of non-Newtonian fluids in wastewater treatment equipment.

Key words: non-Newtonian fluid, mass transfer, bubble size distribution, overall gas holdup, volumetric oxygen transfer coefficient

摘要：

很多废水处理装置涉及非牛顿型流体中的多相流动和传质问题，研究其中的气液传质过程有助于实现装置的优化设计和高效节能运行。以鼓泡反应器内清水和不同质量分数的羧甲基纤维素钠（CMC）水溶液为实验对象，分别研究气相表观气速和液相流变特性对气泡尺寸分布、全局气含率和体积氧传质系数的影响。实验结果表明，液相的流变特性对其传质特性参数均有较大影响。与清水相比，CMC水溶液中气泡平均直径和分布范围更大；清水和CMC水溶液的全局气含率均随表观气速的增加而增大；CMC水溶液的体积氧传质系数随CMC水溶液质量分数的增加而减小。基于实验研究，得出修正的体积氧传质系数公式和适用于幂律型非牛顿流体流动体系氧传递过程的无量纲关联式，可很好地实现非牛顿流体流动的废水处理装置中气液传质参数的计算。

关键词: 非牛顿流体, 传质, 气泡尺寸分布, 气含率, 体积氧传质系数

CLC Number:

TQ021.4

DONG Xin, XU Xiaofei, LIU Fengxia, ZENG Qian, WANG Xiaojuan, WEI Wei, LIU Zhijun. Hydrodynamic and mass transfer characteristics of power-law fluids in bubbling reactors[J]. CIESC Journal, 2018, 69(6): 2446-2454.

董鑫, 许晓飞, 刘凤霞, 曾倩, 王晓娟, 魏炜, 刘志军. 鼓泡反应器中幂律型流体流动与传质特性[J]. 化工学报, 2018, 69(6): 2446-2454.

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