Four diametrically opposed in vessels up to pilot scale. More applied in production vessels. Thickness typically 0.1 - 0.05 tank diameter.
Baffle height is dependent on the gas holding but generally accepted height is equivalent to the cylindrical height of the vessel i.e. includes headspace but excludes torispherical ends.
Small gap between vessel and baffle to stop biomass build up, enhance oxygen transfer and cleaning action. Gap us usually 0.1 of the baffle width, fixed to vessel such that they can be removed.
Baffles can be placed at an angle, i.e. not perpendicular to the fermenter wall, to enhance scouring if necessary. Some fermentations may perform "better" without baffles.
In some cases the baffles can also form part of the fermenter cooling element.