Power consumption and flow field characteristics of a coaxial mixer with a double inner impeller

Liu, Baoqing; Zhang, Yikun; Chen, Mingqiang; Li, Peng; Jin, Zhi Min

doi:10.1016/j.cjche.2013.09.001

Cited by 19 publications

(11 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The values of parameters mentioned in the text are given in Table 4 according to Wu [50]. The power number was determined from the Np vs. R e chart [51]. During biogas production, the volume of effluent displaced in the extension chamber was stored as potential energy (P.E).…”

Section: Operationmentioning

confidence: 99%

Effect of Mixing Regimes on Cow Manure Digestion in Impeller Mixed, Unmixed and Chinese Dome Digesters

2019

View full text Add to dashboard Cite

This study examines the effect of mixing on the performance of anaerobic digestion of cow manure in Chinese dome digesters (CDDs) at ambient temperatures (27–32 °C) in comparison with impeller mixed digesters (STRs) and unmixed digesters (UMDs) at the laboratory scale. The CDD is a type of household digester used in rural and pre-urban areas of developing countries for cooking. They are mixed by hydraulic variation during gas production and gas use. Six digesters (two of each type) were operated at two different influent total solids (TS) concentration, at a hydraulic retention time (HRT) of 30 days for 319 days. The STRs were mixed at 55 rpm, 10 min/hour; the unmixed digesters were not mixed, and the Chinese dome digesters were mixed once a day releasing the stored biogas under pressure. The reactors exhibited different specific biogas production and treatment efficiencies at steady state conditions. The STR 1 exhibited the highest methane (CH4) production and treatment efficiency (volatile solid (VS) reduction), followed by STR 2. The CDDs performed better (10% more methane) than the UMDs, but less (approx. 8%) compared to STRs. The mixing regime via hydraulic variation in the CDD was limited despite a higher volumetric biogas rate and therefore requires optimization.

show abstract

Section: Operationmentioning

confidence: 99%

Effect of Mixing Regimes on Cow Manure Digestion in Impeller Mixed, Unmixed and Chinese Dome Digesters

2019

View full text Add to dashboard Cite

show abstract

“…Although single shaft impellers are commonly employed in industrial processes due to their easy operation and well-known design methods, they are usually designed to meet the requirements of specific applications [117]. These systems, however, are prone to failure in rheologically evolving processes, and alternative configurations such as coaxial mixers should be employed to overcome such challenges.…”

Section: Coaxial Mixersmentioning

confidence: 99%

Gas Dispersion in Non-Newtonian Fluids with Mechanically Agitated Systems: A Review

2022

View full text Add to dashboard Cite

Gas dispersion in non-Newtonian fluids is encountered in a broad range of chemical, biochemical, and food industries. Mechanically agitated vessels are commonly employed in these processes because they promote high degree of contact between the phases. However, mixing non-Newtonian fluids is a challenging task that requires comprehensive knowledge of the mixing flow to accurately design stirred vessels. Therefore, this review presents the developments accomplished by researchers in this field. The present work describes mixing and mass transfer variables, namely volumetric mass transfer coefficient, power consumption, gas holdup, bubble diameter, and cavern size. It presents empirical correlations for the mixing variables and discusses the effects of operating and design parameters on the mixing and mass transfer process. Furthermore, this paper demonstrates the advantages of employing computational fluid dynamics tools to shed light on the hydrodynamics of this complex flow. The literature review shows that knowledge gaps remain for gas dispersion in yield stress fluids and non-Newtonian fluids with viscoelastic effects. In addition, comprehensive studies accounting for the scale-up of these mixing processes still need to be accomplished. Hence, further investigation of the flow patterns under different process and design conditions are valuable to have an appropriate insight into this complex system.

show abstract

“…Aerated mixing systems are widely utilized in a variety of industrial applications, such as wastewater treatment, methane biodegradation, antibiotic and polysaccharide productions, syngas fermentation, and cell culture. − The energy consumption of such processes is one of the main factors that characterize the mixing efficiency since it is directly related to the cost of operation . Therefore, energy-efficient agitated systems have been designed aiming at reducing the power demand to reach equal or superior gas–liquid mixing. − For instance, several investigations have demonstrated that coaxial mixers can enhance the gas distribution efficiency in highly viscous liquids and non-Newtonian fluids. , Coaxial mixers combine the rotation of a high-speed central shaft and a low-speed close-clearance impeller, which results in a more uniform distribution of the shear rate . In fact, the uniform mixing characteristic favors the gas dispersion in pseudoplastic fluids by reducing stagnant zones in the stirred vessel, which is also advantageous for other industrial processes containing solid particles such as in polymerization, water treatment, and chemical reactions with catalysts. − In view of that, several researchers have provided insights into the power demand behavior of coaxial mixers.…”

Section: Introductionmentioning

confidence: 99%

Power Consumption Characterization of Energy-Efficient Aerated Coaxial Mixers Containing Yield-Stress Biopolymer Solutions

Barros

Ein‐Mozaffari

Lohi

2022

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

The operations of mixing systems utilized in a variety of industrial applications for dispersing gas in non-Newtonian fluids are complex. The main challenge is to maintain a homogeneous medium throughout the vessel. In fact, coaxial mixers have demonstrated an energy-efficient performance for systems containing rheologically complex fluids. However, the accurate characterization of the power demand for gas dispersion in yield-stress fluids using coaxial mixers remains unclear. Hence, the objective of the present work was to investigate the power characteristics of a coaxial mixing system comprising the xanthan gum solution, which is a shear-thinning fluid possessing yield stress. The power consumption of an Anchor-PBT mixing configuration was measured experimentally at different central and anchor impeller speeds, rotation modes, and aeration rates. The main effects of the operating variables and their interactions were quantified using a central composite design of experiments. Significant effects of the central impeller speed and the interaction between the anchor speed and the aeration rate were identified. Also, a generalized power curve for this mixing system was proposed based on a predefined equivalent impeller speed and impeller diameter expressions to develop the novel power number and Reynolds number. The findings of this work provide an asset in designing and scaling up of energy-efficient aerated coaxial mixers by rapidly estimating the power demand.

show abstract

Power consumption and flow field characteristics of a coaxial mixer with a double inner impeller

Cited by 19 publications

References 9 publications

Effect of Mixing Regimes on Cow Manure Digestion in Impeller Mixed, Unmixed and Chinese Dome Digesters

Effect of Mixing Regimes on Cow Manure Digestion in Impeller Mixed, Unmixed and Chinese Dome Digesters

Gas Dispersion in Non-Newtonian Fluids with Mechanically Agitated Systems: A Review

Power Consumption Characterization of Energy-Efficient Aerated Coaxial Mixers Containing Yield-Stress Biopolymer Solutions

Contact Info

Product

Resources

About