Power consumption in shaking flasks on rotary shaking machines: II. Nondimensional description of specific power consumption and flow regimes in unbaffled flasks at elevated liquid viscosity

Abstract

This article is the second part of a series presenting and modeling the hydrodynamics and specific power consumption in shaking flasks on rotary (orbital) shaking machines. In part I, a new method was introduced that enables the accurate determination of the specific power consumption in shaking flasks. The method was first applied to investigate unbaffled flasks with a nominal volume of < or =1 L at low viscosity. In part II, the results for the specific power consumption of unbaffled shaking flasks at elevated viscosities are investigated after varying shaking frequency, flask size, filling volume, and shaking diameter. The theory introduced in part I is extended to liquids of elevated viscosities using nondimensional equations. With these results, the specific power consumption in unbaffled shaking flasks can now be fully described. For the first time, the phenomenon of the liquid being "out of phase" is observed and described. This occurs at certain operating conditions and is characterized by an increasing amount of liquid not following the movement of the shaking table, thus reducing the specific power consumption. This, of course, has much relevance for practical work with microbial cultures. The phenomenon of being "out-of-phase" is described in the form of a newly defined nondimensional phase number (Ph) in analogy to a partially filled, rotating horizontal drum. The Ph can be used to determine reasonable operating conditions for shaking flask experiments when using viscous media, avoiding unfavorable "out-of-phase" operation.

The oxygen transfer rate as key parameter for the characterization of Hansenula polymorpha screening cultures

“…6b, lines) were a close match thus confirming the validity of the linear balance Eq. 3, 4, 5, 6,7,8,9,10,11,12,13 and the input values.…”

“…In these screening processes, shaking bioreactors have been widely used as they are inexpensive and large numbers of reactors can easily be handled in parallel [7]. Indeed, in the field of biotechnology, up to several hundred-thousand individual experiments per company are run every year in shaking bioreactors [8]. Nevertheless, the conditions in these cultures are not well understood.…”

A hydrodynamic description of the flow behavior in shaken flasks

“…Despite the importance of this initial step, only few investigations have attempted to understand the hydrodynamic foundations of orbital shakers. Büchs et al [6][7][8], were the first authors to identify the hydrodynamic condition that restricts the operating performance in such systems. They reported a range of operation conditions.…”

An experimental comparison of respiration measuring techniques in fermenters and shake flasks: exhaust gas analyzer vs. RAMOS device vs. respirometer

“…To design an industrial fermentation a large number of experiments, according to [3] in large companies up to several hundred thousand individual experiments per year, are necessary, to select a strain, to improve the medium and to characterize the productivity at different culture conditions. These screening tasks are normally performed in shake flasks or laboratory fermenters.…”

“…Shake flasks are inexpensive and can be operated simultaneously in large numbers. In large industrial companies, up to several hundred thousand individual experiments may be performed in shake flasks every year [3]. Nevertheless, most experiments are still conducted without any online monitoring hampering focused screening and complicating scale-up by neglecting the effect of oxygen supply and fermentation time on growth and product formation.…”