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Gas hold-up analysis in an unsteady stirred vessel by means of infinite series

Frankiewicz Sebastian S., Woziwodzki Szymon

Polish Journal of Chemical Technology

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2023

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Vol. 25, nr 2

30--35

EN

The use of a liquid level sensor made it possible to measure changes in gas hold-up over time in a stirred tank during unsteady mixing. These results were subjected to Fourier time series analysis and a model of gas hold-up changes in time was proposed. It allowed one to determine the model value of gas hold-up, which can be useful for characterizing gas hold-up during unsteady mixing and as a comparison to gas hold-up during steady mixing. The characteristic frequency was also determined, which corresponds to about twice the oscillation frequency. Model gas hold-up values for coalescing and non-coalescing systems were compared. Moreover, the change of the gas hold-up at constant maximum stirrer rotation frequency and variable gas flow rate for different oscillation frequencies was investigated.

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Axial thrust in a vessel with unsteady rotating axial impeller

Woziwodzki Szymon

Chemical and Process Engineering : New Frontiers

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2023

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Vol. 44, nr 2

art. no. e11

EN

Unsteady motion of the impeller is one of the several methods to improve mixing in unbaffled vessel. It is very important in pharmaceutical industry, crystallization processes or some chemical reaction with catalyst where baffles are not recommended. The literature data shows that unsteady mixing cause generation of axial flow for radial impellers (Rushton turbine). The purpose of this study was to investigate axial force for axial impellers like A315, HE-3 and SC-3. Moreover, the momentum number, flow number and pumping efficiency were analysed. Results shows that axial force for unsteady mixing is higher in comparison to steady-state mixing. Also, the comparison of axial force between impellers shows that blades influence momentum number and flow number. Impellers with larger blade surface generate stronger axial force. The obtained results reveal that unsteady mixing with axial impellers could be apply for solid-liquid mixing as suitable alternative to steady-state mixing.

3

Mieszanie układów ciecz-gaz w mieszalniku mieszadłem A310 wykonującym ruch nieustalony

Woziwodzki S., Broniarz-Press L., Radecki R.

Inżynieria i Aparatura Chemiczna

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2015

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Nr 6

364--365

PL

Badano mieszanie układu ciecz-gaz w mieszalniku bez przegród zaopatrzonym w mieszadło A310 wykonujące ruch nieustalony. Analizowano zapotrzebowanie na moc mieszania, stopień zatrzymania gazu oraz objętościowy współczynnik wnikania masy. Uzyskane wyniki wskazują, że zastosowanie mieszania nieustalonego powoduje intensyfikację wymiany masy. Wartości współczynnika kLa dla mieszania nieustalonego są od 1,33 do 1,85 razy większe. Uzyskane wyniki pokazują również większy stopień zatrzymania gazu w porównaniu do mieszania standardowego, a także większe zapotrzebowanie na moc mieszania.

EN

Gas-liquid mixing in a vessel equipped with the unsteadily rotating A310 impeller was investigated. The power requirements, gas hold-up and the volumetric mass transfer coefficient were examined. The results indicate that the use of unsteady mixing intensifies mass transfer process. The values of kLa for unsteady mixing were from 1.33 to 1.85 times greater than for the standard mixing. The results also indicate a higher degree of gas hold-up and greater power requirements in comparison to the standard mixing.