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Home → Products → FFS → FFS for lab fermentors
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FerroLabs, Inc. manufactures FFS for lab fermentors of 0,01…0,02 m3 (Fig.1-3) that have been thoroughly tested for sterility, hermeticity, virus/cell neutrality, and recommended for biological industry. FFS configuration is autonomous and is made of (see Fig.1): casing 1, shaft 5 mounted on two shaft bearings 4, polar add-ons in the shape of a sleeve 2 with two or more circular grooves on the outer surface which hold permanent magnets 3 [1].
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Magnetic field enhancers 6 are located on the shaft 5 or on the inner surface of the sleeve 2. The gap between the sleeve and the shaft is filled with ferrofluid 7 that creates ring locks on each magnetic field enhancer 2. The static gaps between the casing 1 and sleeve 2 are hermetized with a spacer 8. If the shaft is made of non-magnetic-conductor, then the magnetic-conductive cylindrical skirt with magnetic field enhancers on its outer surface is placed on the shaft 5 under the sleeve 2. In the other FFS configuration, that includes non-magnetic-conductive shaft (Fig.2), a hollow cylinder 11 holding a sleeve 2 is fixed on bearings 4 and hermetically jointed to the shaft by the spacer 12. The cylinder embraces the magnetic-conductive cylindrical skirt 9 hermetially sealed in the casing 1 coaxial to the sleeve 2 [1].
The FFS operates as follows. The main magnetic fluxes from the permanent magnets 3 fixed in each circular groove on the outer surface of the sleeve 2 are divided into two components: working fluxes (F1, F2, F3) that flow through the working gap between the sleeve 2 and the shaft 5, and parasitic fluxes (F10, F20, F30) flowing through the sleeve itself under the circular groove.
Fig.3. FFS for lab fermentors
The working fluxes ensure the magnetic field value required for keeping ferrofluid in the working gap. Under the action of working magnetic fluxes, ferrofluid 7 creates circular ferrofluid-based locks over each magnetic field concentrator 6 that endure pressure drops. Meanwhile, the critical pressure drop (a maximum that a MFS can bear) is proportional to the number of concentrators and the magnetic field strength. Parasitic fluxes do not help holding the current pressure drop, so they should be kept as small as possible. For that purpose the sleeve thickness under the circular groove is selected the smallest, so that the sleeve can be magnetically saturated at that spot. Thus, the parasitic flux will be 10-15% of the working flux value which does not impose a significant negative effect on the critical pressure drop. Embodying polar add-ons as a sleeve allows a better uniformity on the edge of the working gap between the inner surface of the sleeve and the magnetic field enhancers. With this done, the base sleeve area by which it is jointed to the casing grows larger. This leads to the increase of the critical pressure drop in the proposed configuration by 20-30% in comparison to a typical one with the same dimensions. Moreover, for the proposed configuration, only one spacer is necessary to hermetically seal the static gap between the sleeve and the casing which makes the seal as a whole more reliable.
In the other FFS configuration with non-magnetic-conductive shaft (see Fig. 2), even greater uniformity on the working gap edge is ensured because there is no cantilevered mounting of the sleeve 2 relevant to the bearings 4 and because it is possible to technologically exclude the error of coupling the casing 1 with magnetic-conductive cylindrical skirt 9 that is caused by finishing the mounting surface of the casing 1 and magnetic field enhancers 6 after assembling the ’casing-cylindrical skirt’ system. Meanwhile the critical pressure drop for this FFS configuration is 30-40% higher than that of a typical one, given the same dimensions. Greater uniformity of the working gap and critical pressure drop allows greater stability of working characteristics of the MFS in time, and, consequently, their reliability and durability. According to the comments of the companies that have used lab fermentors with MFS, MFS failures usually occur because of ball bearings’ wear out. Time to failure for FFS is 10 years.
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