Computational snapshot approach

Concluding, it is essential to represent complex, real-life flow situations by computationally tractable models that retain adequate details. As an example, a computational snapshot approach that simulates the flow in stirred reactors or other vessels for any arbitrary impeller has been developed [5]. This approach lets the engineer simulate the detailed fluid dynamics around the impeller blades with much less computations that would otherwise be required. Improvements in CFD technique are likely to encourage further work along these lines. 

In order to assess the computational snapshot approach in more detail, predicted normalized mean velocity components and normalized turbulent kinetic energy were directly compared with the available data of Schafer et al. (1997). In the case of... 

Results described so far suggest that the snapshot approach can be used to make a priori predictions of the complex flow generated in stirred vessels for impellers of any shape. A number of industrial stirred tank reactors make use of two or more impellers mounted on the same shaft. When more than one impeller is used, the flow complexity is greatly increased, especially when there is interaction between the flow generated by the two impellers. The extent of interaction depends on relative distances between the two impellers (and clearance from the vessel bottom). In order to examine whether the computational snapshot approach can be used to simulate... 

The computational snapshot approach was used to simulate flow generated in these three impeller configurations (for more details, see Deshpande and Ranade, 2001). The predicted velocity vectors in the r-z plane located midway between the two baffles for parallel, merging and diverging flow configurations are shown in... 

Many of the situations encountered by reactor engineers involve (refer to Table 10.1) contact with more than one phase in a stirred tank. It is, therefore, essential to examine whether CFD models can simulate complex multiphase flows in stirred tanks. Here the case of gas-liquid flows in a stirred tank is considered. Similar methodology can be applied to simulate other two-phase or multiphase flows in stirred vessels. The computational snapshot approach discussed previously has been extended to simulate gas-liquid flows (see Ranade et al., 2001c for more details). A two-fluid model was used to simulate gas-liquid flow in a stirred vessel the model equations and boundary conditions are listed below. 

In general, it may be concluded that the computational snapshot approach or other equivalent, state of the art CFD models can capture the key features of flow in stirred tank reactors and can be used to make either quantitative (for single-phase or pseudo-homogeneous applications) or semi-quantitative (for complex, multiphase applications) predictions. Possible applications to reactor engineering are discussed below. 

Deshpande, V.R. and Ranade, V.V. (2001), Simulation of flow generated by dual Rushton turbines using computational snapshot approach, submitted for publication, Chem. Eng. Commun. 

Ranade VV, Krishnan YTH (2002) CFD predictions of flow near impeller blades in baffled stirred vessels Assessment of computational snapshot approach. Chem Eng Comm 198 895-922... 

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