Study on Internal Flow Characteristics of Non-Newtonian Fluids in Mechanical Stirred Tank

doi:10.3901/JME.2021.20.244

Abstract

Abstract: Most of the fluids, involved in mechanical agitation widely applied in the industry, are non-Newtonian ones and have different rheological properties from Newtonian fluids (elastic effect, shear thinning and shear thickening), so there is an urgent need to study the internal flow characteristics of non-Newtonian fluids in a mechnical stirred tank. Based on the results of Lin-A315 particle image velocimetry (PIV) experiment results, steady and unsteady numerical simulations are carried out with non-Newtonian fluid in the stirred tank. The distribution of flow field, turbulent kinetic energy at the axial section, the flow velocity profile at the radial transversely line, the necessary mixing time and the corresponding energy consumption are investigated and compared with experiments for xanthan gum solution with different mass fractions at different speeds. The results show that the internal flow characteristics revealed by numerical simulation agrees quite well with experiment for non-Newtonian fluid in the stirred tank. Increasing the stirring speed, the range and size of the main circulation flow are enlarged, and the distribution range of vortex and turbulent kinetic energy in the tank is increased as well. Compared with 100 r/min, higher stirring speeds 300 r/min and 500 r/min lead to the maximum axial velocity increased by 3.6 times and 5.9 times, and the necesary mixing time shortened by 0.46 times and 0.36 times. As the concentration of xanthan gum rising, the main circulation range of the flow field shrunk, the velocity gradient increased, the circulating velocity in the bottom zone is reduced, so the necessary mixing time is more sensitive to the the stirring speed than the concentration of non-Newtonian fluid. But increasing the stirring speed for non-Newtonian fluid will lead to higher energy consumption. Therefore, medium speed shall be preferred for low concentration non-Newtonian fluid and high speed be preferred in case of high concentration for better mixing performance and energy saving.

Key words: stirred tank, non-Newtonian fluid, PIV, numerical simulation, flow field characteristics

CLC Number:

TQ027

FANG Yujian, ZHANG Min, SUN Xianpeng, ZHANG Jinfeng, QU Yefei. Study on Internal Flow Characteristics of Non-Newtonian Fluids in Mechanical Stirred Tank[J]. Journal of Mechanical Engineering, 2021, 57(20): 244-253.

References

[1] BUFFO A,VANNI M,MARCHISIO D L. Multidimensional population balance model for the simulation of turbulent gas-liquid systems in stirred tank reactors[J]. Chemical Engineering Science,2012,70(10):31-44.
[2] 王凯,虞军. 搅拌设备[M]. 北京:化学工业出版社,2003. WANG Kai,YU Jun. Stirring equipment[M]. Beijing:Chemical Industry Press,2003.
[3] EIN-MOZAFFARI F,UPRETI S R. Using ultrasonic Doppler velocimetry and CFD modeling to investigate the mixing of non-Newtonian fluids possessing yield stress[J]. Chemical Engineering Research & Design,2009,87:515-523.
[4] 栾德玉,张盛峰,郑深晓,等. 基于流固耦合的错位桨搅拌假塑性流体动力学特性[J]. 化工学报,2017,68(6):2328-2335. LUAN Deyu,ZHANG Shengfeng,ZHENG Shenxiao,et al. Dynamic characteristics of impeller of perturbed six-bent-bladed turbine in pseudoplastic fluid based on fluid-structure interaction[J]. CIESC Journal,2017,68(6):2328-2335.
[5] 韩丹,李龙,程云山,等. 现代搅拌技术的研究进展[J]. 食品与机械,2004,20(4):31-34. HAN Dan,LI Long,CHENG Yunshan,et al. Research development of modern stirring technology[J]. Food and Machinery,2004,20(4):31-34.
[6] BAKKER B,VAN DEN AKKER H E A. Single-phase flow in stirred reactors[J]. Chemical Engineering Research & Design,1994,72(4):583-593.
[7] MURTHY B N,JOSHI J B. Assessment of standard k-ε、RSM and LES turbulence models in a baffled stirred vessel agitated by various impeller designs[J]. Chemical Engineering Science,2008,63(22):5468-5495.
[8] 洪厚胜,张庆文,万红贵,等. 搅拌生物反应器混合特性的数值模拟与试验研究[J]. 过程工程学报,2005,5(2):131-134. HONG Housheng,ZHANG Qingwen,WAN Honggui,et al. Numerical simulation and experimental study on mixing characteristics of stirred bioreactor[J]. The Chinese Journal of Process Engineering,2005,5(2):131-134.
[9] ZAMIRI Ali,CHUNG Jin. Numerical evaluation of turbulent flow structures in a stirred tank with a Rushton turbine based on scale-adaptive simulation[J]. Computers & Fluids,2018,170(18):236-248.
[10] MERONEY R N,COLORADO P E. CFD simulation of mechanical draft tube mixing in anaerobic digester tanks[J]. Water Research,2009,43(4):1040-1050.
[11] AMEUR H. Agitation of yield stress fluids in different vessel shapes[J]. Engineering Science & Technology an International Journal,2016,19(1):189-196.
[12] 徐玉明,迟卫,莫立新. PIV测试技术及其应用[J]. 舰船科学技术,2007,29(3):101-105. XU Yuming,CHI Wei,MO Lixin. PIV test technology and its application[J]. Ship Science and Technology,2007,29(3):101-105.
[13] SHARP K V,ADRIAN R J. PIV study of small-scale flow structure around a Rushton turbine[J]. AIChE,2001,47(4):766-778.
[14] KHAN F R,RIELLY C D,BROWN D A R. Angle-resolved stereo-PIV measurements close to a down-pumping pitched-blade turbine[J]. Chemical Engineering Science,2006,61(9):2799-2806.
[15] CHUNG K H K,BARIGOU M,SIMMONS M J H. Reconstruction of 3-D flow field inside miniature stirred vessels using a 2-D PIV technique[J]. Chemical Engineering Research & Design,2007,85(5):560-567.
[16] SONG K W,KIM Y S,CHANG G S. Rheology of concentrated xanthan gum solutions:Steady shear flow behavior[J]. Fibers & Polymers,2006,7(2):129-138.
[17] JUNKER B H,STANIK M,BARNA C,et al. Influence of impeller type on mass transfer in fermentation vessels[J]. Bioprocess Engineering,1998,19(6):403-413.
[18] SHIH T H,LIOU W W,SHABBIR A,et al. A new kappa-epsilon eddy viscosity model for high Reynolds number turbulent flows[J]. Computers and Fluids,1995,24(3):227-238.
[19] KIM S E,CHOUDHURY D,PATEL B. Computations of complex turbulent flows using the commercial code fluent[J]. Modeling Complex Turbulent Flows,1999:259-276.
[20] 李鹏飞,徐敏义,王飞飞. 精通CFD工程仿真与案例实战[M]. 北京:人民邮电出版社,2011. LI Pengfei,XU Minyi,WANG Feifei. Proficient in CFD engineering simulation and case practice[M]. Beijing:People's Posts and Telecommunications Press,2011.