Friction Factor Distribution at the Side Wall of a Turbulent Agitated Vessel with Baffles Using a MAXBLEND Impeller

Significance 

The main aim of mixing in most industrial processes, especially those in agitated tanks, is to control the dispersion state by homogenizing the material concentration and fluid temperature. Most agitated tank reactors have simple geometrical configurations comprising a tank and a mechanical impeller. Nevertheless, the design of these tanks and determination of favorable operating conditions is relatively complicated, considering the differences in the properties of fluids and complex transport phenomena. Therefore, a thorough understanding of the transport phenomena in agitated vessels, such as heat, momentum and mass transfer, is imperative. This is important in designing appropriate processes using tank reactors and estimating other critical parameters like heat transfer coefficient, mixing time and power consumption.

Most chemical reactions require high controllability of thermal properties to improve the rate of reaction to efficiently and safely remove heat from processes. Helical coils are commonly used to control thermal heat transfer in agitated tanks. In addition, heat transfer at the tank wall has also drawn significant research attention owing to its benefits in simplifying the tank geometry for efficient operation and cleaning. To this end, several researchers have studied the heat transfer coefficients of the tank’s sidewall in different flow regimes. Although mass transfer coefficients at the sidewall of the agitating tank are predominantly dependent on the impeller configurations, recent studies show that it is also influenced by the friction factor. Unfortunately, the friction factor distribution in agitated vessels with large impellers is not fully explored. This is of great significance due to the benefits of large impellers, including superior performance in different processes.

To fill this research gap, Dr. Yusuke Ochi, Professor Yoshiyuki Komoda and led by Professor Naoto Ohmura from Kobe University in collaboration with Dr. Katsuhide Takenaka from Sumitomo Heavy Industries Process Equipment Company, studied the local distribution of the friction factor on the sidewall in a turbulent agitated vessel equipped with MAXBLEND impeller using computational fluid dynamics simulation. The numerical procedure was validated by calculating the fluid flow in the vessel and the resulting velocity near the wall. The work is published in the journal, Industrial and Engineering Chemistry Research.

The research team reported a larger friction factor value at the sidewall in a range characterized by strong discharge flow and a smaller friction factor value in the upper part of tank wall. A drastic increase in the friction factor, especially near the baffles, was observed when the baffle clearance was added. Consequently, the friction factor in the baffled vessel exhibited large-scale fluctuations when the baffle cleared was installed. These results suggested the possible improvement of heat/mass transfer as the sidewall of the turbulent agitated vessel. In addition, the impeller induced a circulation flow that was, however, deformed upon adding the baffle clearance, resulting in a more complex flow pattern.

In a nutshell, a numerical investigation of the effects of the clearance between the sidewall and baffles on the friction factor of a turbulent agitated vessel with a large impeller was reported. The velocity distribution of the paddle impeller obtained numerically agreed well with the theoretical and experimental values, indicating the reliability and accuracy of the numerical procedure. In a statement to Advances in Engineering, Professor Naoto Ohmura explained that the study provides valuable insights that would enhance heat and mass transfer and the overall performance of agitated vessels with larger impellers used in various industrial processes.

About the author

Yusuke Ochi received his Ph.D. in Chemical Engineering from Kobe University in 2022, defending a thesis on the mixing process in agitated vessels.

His research interests are mixing technology and process intensification based on transport phenomena.

He is currently working at AGC Yokohama Technical Center (AGC Inc.).

About the author

Katsuhide Takenaka is a technical manager in Sumitomo Heavy Industries Process Equipment Co., Ltd.

He received the Ph.D in Engineering from Yamagata University in 1999.

Major roles of his group in the company are to optimize and to design the reactor with agitator for polymerization.

Therefore his recent interest is to investigate the cause of fouling, the particle agglomeration and handling of non-Newtonian fluid.

About the author

Yoshiyuki Komoda was born in Osaka Prefecture, Japan, in 1974. He graduated from the Department of Chemical Engineering, Osaka University, in 1995 and received his Ph.D. degree in 2001 from Osaka University. After working at a Pharmaceutical company for three years, he joined the Department of Chemical Science and Engineering at Kobe University as an Assistant Professor in 2004 and became an Associate Professor in 2010. In addition, he was a cross-appointment research fellow at the Advanced Institute of Science and Technology (AIST), Japan, to conduct collaborative research on the secondary battery manufacturing process. One of his research interests is the development of unique and novel fluid mixing processes utilizing unsteady impeller motion. He also devotes himself to studying the manufacturing process of particulate film, covering from the dispersion of particles into fluids, the channel flow in coating apparatuses, and the internal structure analysis in the coating layer with the evaporation of fluids. These findings are essential for manufacturing high-performance batterie.

About the author

Naoto Ohmura is a professor in the Department of Chemical Science and Engineering at Kobe University since 2007. He is also an Executive Vice President in Kobe University from 2021. He received the Ph. D. in Engineering from Kobe University in 1997.

His main research interest is elucidation and modeling of complex phenomena in chemical processes with the aid of transport science dealing with fluid flow, heat and mass transfer. His recent interest also goes to process intensification and development of novel chemical processes utilizing vortex dynamics, oscillatory flows and ultrasound.

Reference

Ochi, Y., Takenaka, K., Komoda, Y., & Ohmura, N. (2022). Friction Factor Distribution at the Side Wall of a Turbulent Agitated Vessel with Baffles Using a MAXBLEND ImpellerIndustrial & Engineering Chemistry Research, 61(3), 1514-1522.

Go To Industrial & Engineering Chemistry Research

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