2 results
Now showing1 - 2 of 2
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Gas-Liquid Flow, Oxygen Mass Transfer, and Mixing Characterization of a Transparent Single-Use Bioreactor Model (Biostat STR® 200)(Sartorius, 2025); ; ; ; In recent years, the biopharmaceutical industry has had to become more flexible and increase upstream yields, driving the uptake of process intensification strategies such as perfusion. This requires production equipment to support high cell density cell cultures requesting an oxygen uptake rate of 20 mmol O2 L-1 h-1 and above. Testing equipment capabilities typically involves characterization approaches such as determining oxygen mass transfer, energy input, and mixing performance. A broad measurement database and an appropriate mass transfer model CFD can be applied to better predict culture impact. However, cell activity sometimes deviates from expectations, and empirical validation of the used model is often lacking. In this research, a transparent version of the Biostat STR® 200, made of acrylic glass, was erected at the Institute of Multiphase Flows at Hamburg University of Technology to gain deeper insights into the two-phase flow pattern. The gas distribution and mixing behavior were investigated using high-resolution pictures and videos. In these assessments, two different stirrer combinations have been investigated for varied aeration rates and stirrer frequencies. With regards to oxygen mass transfer rate, the acrylic reactor replica behaves similarly to the industrial single-use bioreactor system, with deviations lying within the predefined ranges determined by the Sartorius Biostat STR product characterization approach. The volumetric mass transfer coefficient kLa is also comparable for both reactors. Consequently, it can be assumed that the visual recordings from the transparent model reflect dynamics from industrialized single-use cultivation chambers. Furthermore, high-resolution imaging of the acrylic replica of the Biostat STR® 200 enabled the systematic characterization of the mixing and mass transfer performance, helping us to understand the influence of stirrer speeds and gassing rates in combination with different sparger and impeller types as well as their interaction.Publicationtype: Learning Object73 301 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of mixing and shear stress on Chlorella vulgaris, Scenedesmus obliquus, and Chlamydomonas reinhardtii(Springer, 2012-08-04); ; ; ; Photosynthetic activity (PA) and growth of different microalgae species (Chlorella vulgaris, Scenedesmus obliquus, and Chlamydomonas reinhardtii) depends in addition to other factors on mixing (tip speed) and shear stress (friction velocity) and was studied in a stirring tank (microcosm). In order to detect cause-effect relationships for an increase in photosynthetic activity, experiments were conducted under different pH values (6. 0-8. 5) and CO2 concentrations (0. 038 and 4 % (v/v)). The PA was determined as the effective quantum yield by pulse amplitude modulation during a stepwise increase of the tip speed from 0 to 589 cm s-1 (friction velocity: 0-6. 05 cm s-1) in short-term experiments. The increase caused a distinctive pattern of PA of each species. Compared to 0 cm s-1, C. vulgaris and S. obliquus showed a 4. 0 and 4. 8 % higher PA at the optimum tip speed of 126 cm s-1 (friction velocity of 2. 09 cm s-1) and a 48 and 71 % higher growth, respectively. At 203 cm s-1, the PA dropped to the value of the unstirred control, while at 589 cm s-1, the PA decreased of up to 7 and 8 %. In contrast, C. reinhardtii showed 7 % stronger growth at 126 cm s-1, while the PA decreased about 15 % at an increase of tip speed to 589 cm s-1. For all investigated microalgae, the pattern of PA and higher growth was not only explained by the main contributing factors like light supply, nutrient supply, and overcoming diffusion gradients. The results indicate that hydrodynamic forces have a stimulating effect on the physiological processes within the cells.Publicationtype: Journal Article53