Читать книгу Agitator Design for Gas-Liquid Fermenters and Bioreactors - Gregory T. Benz - Страница 49

Although this could be lumped in under geometric ratios, it affects things in different and important ways, so I decided to mention it separately. Essentially, it represents total baffle width (calculated normal to the tank wall) divided by tank diameter:

(3.11)

Power draw and vortex formation depend on baffle number. At a baffle number of zero, the tank is called unbaffled and power draw is at a minimum. Under such a condition, in turbulent flow, there is a lot of swirl, with mostly tangential motion rather than axial or radial. Gas dispersion is essentially impossible to do under such a condition. As baffle number increases, power draw increases to a maximum and then falls off. In the USA, “standard” baffling is 4 baffles at 90° to the tank wall, each one being 1/12 of the tank diameter, resulting in a baffle number of 0.33. In Europe, it is more common to use a baffle width of 1/10 of the tank diameter, giving a baffle number of 0.4. The power draw is pretty constant over this range and is basically at the maximum. D/T and impeller type also interact with baffle number.