Over the last century the fluid mixing process in stirred vessels has become one of the most common operations in the chemical, petrochemical, pharmaceutical and food industries. Despite its wide use, the process is often poorly understood and empirically handled. Numerous efforts. both experimental and theoretic, have been undertaken to understand mixing inside stirred vessels. Because of its complexities in terms of flow regimes and multiphase operations, the process design and optimisation is not well defined and often evolved by empirical scale-up from laboratory results (at around 1dm³ scale) to plant-scale manuiacturing involving vessels up to 100m³ in size. Over the last two decades with the development of more powerful computers the theoretical study of the fluid mixing has become more tractable and attractive for use in engineering practice. This has led to the emergence of software packages based on detailed mathematical models. This work is an attempt to develop a mathematical model based on a simplified networks-of-zones concept, capable of providing detailed predictions in 3-D of the gas-liquid mixing and reaction behaviour in a triple impeller industrial bioreactor. Two major improvements of the previous gas-liquid model (Hristov et al, 2001) have been achieved: i. The effect of baffles, which was previously ignored, has been introduced to the model for the Rushton turbine (RT), using a simple pattern for the turbulent flow around them (Rahimi, 2000). ii. A 3-D networks-of-zones model has been developed to describe the performance of a novel geometry Narcissus (NS) impeller. The treatment in this case was simply adapted from the earlier version based upon the Rushton turbine, by a geometric stretching of the zone volumes. This accommodates the complex up-down liquid flow pattern by a simple adjustment of the zone volumes matrix, whilst the underlying mass and component balances on every zone stay unchanged.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:498668 |
| Date | January 2004 |
| Creators | Hristov, Hristo Vesselinov |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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