INVESTIGATIONS INTO PUMPING CHARACTERISTICS OF AXIAL FLOW IMPELLERS IN AN INTERNAL LOOP REACTOR FOR ANIMAL CELL CULTURE
Titel:
INVESTIGATIONS INTO PUMPING CHARACTERISTICS OF AXIAL FLOW IMPELLERS IN AN INTERNAL LOOP REACTOR FOR ANIMAL CELL CULTURE
Auteur:
Varecka, Roland M. Bliem, Rudolf F.
Verschenen in:
Chemical engineering communications
Paginering:
Jaargang 96 (1990) nr. 1 pagina's 81-96
Jaar:
1990
Inhoud:
This investigation was intended to aid in the selection of impeller design and operating conditions, which would exhibit minimum turbulence in an internal loop reactor for axial flow velocities up to 18 cm/s. For this purpose we measured power consumption, liquid flow velocity and mixing time with two marine propellers (pitch ratio tan alpha =1 and 0.57, respectively) and with flat-blade fan-type impellers (blade angles 10 to 90°). The present results showed that at flow velocities between 7 and 14 cm/s a reduction in the pitch ratio (tan alpha) of the marine propeller from 1 to 0.57 increased the mechanical flow efficiency. In addition, the fan-type impeller with a blade angle of 20° displayed flow characteristics comparable to the marine propellers; therefore, owing to its simple design, the fan-type impeller offers a practical substitute for the marine propellers. In cell culture, draft-tubes used in impeller-driven reactors (internal loop reactors) offer two important features: 1. They simplify the design and scale-up process over that of open-blade impellers (flow patterns are more uniform); 2. They provide a mechanical support for bubblte-free membrane oxygenators; Furthermore, on the assumption that loop reactors display lower bulk turbulence than open blade impellers for similar power consumption, this investigation was intended to aid in the selection of impeller design and operating conditions which would exhibit maximum pumping efficiency (with minimum mixing). For this purpose, using a pH tracer method, we determined mechanical flow efficiency and dimensionless mixing time, which served as parameters for pumping efficiency to establish the following specific design characteristics: 1. Bulk mixing decreases relative to bulk flow with increasing bulk flow (mixing therefore conforms to the flow-in-pipe model) for two marine propellers (pitch tan alpha = 1 and 0.57) and for fan-type impellers (variable pitch) up to a blade angle of 30°; 2. Liquid velocity increases directly proportional to impeller speed up to 17 cm/s for (above) propellers, as well as fan-type impellers with blade angles of less than 30°; 3. The mechanical efficiency of axial flow (liquid velocity/power input) increases by decreasing the impeller pitch of marine impellers from tan alpha = 1 to tan alpha = 0.57, in the range of 7-14 cm/s; 4. A fan-type impeller (variable pitch) with a pitch angle of 20° displayed flow velocity and mechanical efficiency values, which lay between those of the (above) two marine propellers. Fan-type impellers are considerably simpler in construction and are simpler to modify than marine propellers; for this reason this impeller type serves as a useful investigational tool. In addition we have found that at an impeller of 20° this type of impeller may be used to substitute marine propellers with a pitch ratio between 1 and 0.57. We also suggest that square pitch marine propellers are not the most suitable for reactors in which mechanical efficiency of axial flow is critical, such as those for “shear sensitive” animal and plant cells.
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