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Bioreactor Scale-Up Strategies
Published in S Rangabhashiyam, V Ponnusami, Pardeep Singh, Biotechnological Approaches in Waste Management, 2023
Aayush Kumar Choudhary, A. Ayush Kumar, Ojshwi Prakash, Godwin Glivin, N. Kalaiselvan, H. Hareesh Krishnan, M Premalatha, V. Mariappan, Joseph Sekhar
As explained by (Deshpande et al., 2019) the productivity of a bubble column reactor is dependent on gas-liquid mass transfer coefficient, kLa. Bubble column scale up is impacted by the values of kLa which can be explained as a function of design and operating conditions. The mass transfer coefficient, kLa has been characterized experimentally as a function of superficial gas velocity (Usg), using the power law relation: kLa=α*Usgβ
Ozone Processing
Published in Mohammed M. Farid, Mathematical Modeling of Food Processing, 2010
Kasiviswanathan Muthukumarappan, Colm P. O’Donnell, Patrick J. Cullen
Bubble columns are utilized as multiphase contactors and reactors in various food, chemical, petrochemical, biochemical and metallurgical industries [16]. Processes include oxidation, chlorination, alkylation, polymerization, hydrogenation, and various other chemical and biochemical processes such as fermentation and biological wastewater treatment [17,18]. A bubble column reactor is a cylindrical vessel with a gas diffuser to sparge a gas (ozone, oxygen, carbon dioxide, etc.) into either a liquid phase or liquid–solid dispersions (Figure 22.2). The design of a bubble column is limited by the gas-liquid mass transfer [19], which is controlled by the gas hold-up, specific interfacial area, and bubble size distribution [20]. Available literature shows that the design and modeling of ozone bubble columns are based on determination of overall mass transfer coefficient (KLa), gas hold up (∊G), and Sauter mean diameter (SMD, SD) defined as the diameter of a bubble that has the same volume/surface area which can be determined as follow: ds=Abπdv=(6Vbπ)3 where Ab and Vb are the surface area and volume of the bubble, respectively. ds and dv are usually measured directly using image analysis. Individual bubble diameter may be determined by Equation 22.5 assuming that the bubble is an ellipsoid (Figure 22.2). This three dimensional technique may be simplified by assuming that shortest length of the bubble, dx, and width of the bubble, dz, are of equal length, thus reducing this measurement to a two dimensional approach [20]: db=dxdydz3=dxdy23
Hydrodynamic studies in sectionalised external loop air lift reactors
Published in Indian Chemical Engineer, 2021
Shivanand M. Teli, Channamallikarjun Mathpati
The majority of the industrial processes involve gas–liquid contacting. The gas phase solute is transferred to the liquid phase and then gets reacted. The rate controlling step is frequently mass transfer at the gas–liquid interface. The conventional equipment used for gas–liquid contacting is a bubble column reactor. The bubble column reactors have disadvantages such as high-pressure drop and significant backmixing. These disadvantages are eliminated to significant extents in the case of modified systems such as air lift reactors. They are divided into two types, external loop air lift reactor (EL-ALR) and internal loop air lift reactor (IL-ALR) [1–3].
Effect of bubble plume on liquid phase flow structures using PIV
Published in Particulate Science and Technology, 2020
Sonia Besbes, Ibtissem Gorrab, Mahmoud ElHajem, Habib Ben Aissia, Jean Yves Champagne
In a bubble column reactor, gas is injected at the bottom of the column, through which the gas bubbles rise upwards. The resulting flow is characterized by a combination of intrinsically unstable complex flow processes with highly variable spatial and temporal scales (Majumder 2016). Flow structure in a bubble column is a result of a multitude of factors arising out of the motion of individual phases associated with pertinent viscous and turbulent effects. Turbulence of the liquid phase is important to the local distribution of the dispersed bubble by eddies of a wide range of length and time scales. The largest eddies are typically comparable in size to the characteristic length of the mean flow and depend on the column geometry and boundary conditions. The smaller scales depend on the bubble dynamics and are proportional to the bubble size. The smallest scales relate to the Kolmogorov scale (Kolmogorov 1941) and are generally smaller than the bubble size. It is responsible for the dissipation of turbulence kinetic energy. Depending on the required resolution, different approaches for modeling dispersed multiphase flows have been developed. Each approach is used to study specific hydrodynamic phenomena, prevailing at a scale (Yang et al. 2007; Ma et al. 2015). Furthermore, these different scales usually interact with each other in a non-linear manner to lead to a huge variety of phenomena that underlines the complexity of the bubble behaviors. For such a model validation, comprehensive experimental data are needed. Such data must provide locally resolved flow parameters since all effects in bubbly flows are strongly connected to each other. Moreover, the data should include the gas volume fraction, the liquid velocity, basic turbulence parameters, bubble size distribution (Deen and Hjertager 2002; Sathe, Joshi, and Evans 2013; Besagni and Inzoli 2016a, 2016b). In particular, the bubble size distribution is of importance because all closure models depend on the bubble size (Lau et al. 2013; Karn et al. 2015; Besagni, Brazzale et al. 2016).