CONTRIBUTION OF FLUID MECHANICS TO FERMENTATION TECHNOLOGY

Fluid mechanics is accepted as the integral part of study in civil engineering. It is also an important component in the study of physics. The study of fluid mechanics, especially fluid dynamics will try to explain the behavior and properties of fluid in motion. While fluid mechanics is important in the design of civil structures such as dams and bridges, it is of similar importance too in the field of fermentation technology, especially in trying to understand the behavior of the fermentation broth in the fermentors. Knowing the fluid mechanics in fermentors not only allow us to design better fermentors but will also improve the efficiency of the fermentation process.
In fluid mechanics it is important for us to appreciate that water or liquid could show two different behaviours under different conditions applied. We could treat the behavior of water as particle as in Langarian theorem or as a moving packets or bodies of flowing water in restricted volume in accordance with Eularian concept. Both approaches have their strength and weaknesses.
How does fluid mechanics has to do with fermentors?
A simple observation will tell you that all fermentors are equipped with some stirring mechanism of some sort. It could be in the form of stirrers with impellers or it could even be in the form of simple gyrating movements or waves in the case of the disposable reactors or fermentors.
The objectives of these stirrings or mixings is to bring about uniform composition throughout the fermentor and to improve its various mass transfer processes. Poor mixings and mass transfers will always result in sub optimum fermentation process.
There are many attempts to improve the optimum fermentation process by improving the efficiency of it kLa. But the solution is not as simple as increasing the oxygen flow or input. Attempts to increase the oxygen flow will lead to negative secondary problems such as shearing of cells and increase in foaming!
The type of fluid dynamics generated within a fermentor could be very complex. It might not only involved primary, secondary and even turbulent flow within the fermentor. This situation is further compounded by the size and geometry of the fermentors involved and by the presence of barriers such as the baffles and other structures. In certain situation the interaction of these liquid flows within the fermentor could lead to cancellation or even strengthening of the flow pattern and shear forces.
As we have said earlier in the mixing of the fermentation broth there are also very complex mixing of various sold, gas and liquid phases which respond differently to the mixing process and will affect the efficiency of the fermentation process
So how do we try to solve the problem of fluid mechanics that occur in the fermentor? The most likely answer will be the use of computational fluid dynamics in helping design and even locate the areas that need further attention

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