Investigation of turbulent fluid flows in stirred tanks using a non-intrusive particle tracking technique

Microbial lifelines in bioprocesses: From concept to application

Bioprocesses are scaled up for the production of large product quantities. With larger fermenter volumes, mixing becomes increasingly inefficient and environmental gradients get more prominent than in smaller scales. Environmental gradients have an impact on the microorganism's metabolism, which makes the prediction of large-scale performance difficult and can lead to scale-up failure. A promising approach for improved understanding and estimation of dynamics of microbial populations in large-scale bioprocesses is the analysis of microbial lifelines. The lifeline of a microbe in a bioprocess is the experience of environmental gradients from a cell's perspective, which can be described as a time series of position, environment and intracellular condition. Currently, lifelines are predominantly determined using models with computational fluid dynamics, but new technical developments in flow-following sensor particles and microfluidic single-cell cultivation open the door to a more interdisciplinary concept. We critically review the current concepts and challenges in lifeline determination and application of lifeline analysis, as well as strategies for the integration of these techniques into bioprocess development. Lifelines can contribute to a successful scale-up by guiding scale-down experiments and identifying strain engineering targets or bioreactor optimisations.

Mixing Characteristic and High-Throughput Synthesis of Cadmium Sulfide Nanoparticles with Cubic Hexagonal Phase Junctions in a Chaotic Millireactor

A four-stage oscillating feedback millireactor with splitters (S-OFM) was designed to improve the mixing performance based on chaotic advection. Three-dimensional CFD simulations were used to investigate its flow characteristics and mixing performance, and the generation mechanisms of secondary flows were examined. The results show that the mixing index (MI_cup) increased with the increase in the Reynolds number (Re), and MI_cup could reach 99.8% at Re = 663. Poincaré mapping and Kolmogorov entropy were adopted to characterize the chaotic advection intensity, which indicates that there is a intensity increase with the increase in Re. In addition, the results of Villermaux-Dushman experiments demonstrate that S-OFM performs excellently, and the mixing time could reach 1.04 ms at Re = 2764. Finally, S-OFM was successfully used to synthesize CdS nanoparticles with cubic hexagonal phase junctions. At a flow rate of 180 mL/min, the average particle size was 10.5 nm and the particle size distribution was narrow (with a coefficient of variation of 0.14).

Methods of preparation of microparticles for radioactive particle tracking experiments

Radioactive particle tracking (RPT) technique is a relatively newer technique for the characterization of flow of process materials (liquids, solids) in laboratory- and pilot-scale industrial systems. The technique uses a single particle labelled with a suitable radioisotope having similar physical properties to that of the bulk of the process material. The preparation of a representative radioactive microparticle is a challenging task in the implementation of the technique. There are no standard methods available for the preparation of radioactive microparticles. This paper discusses some of the methods of preparation of radioactive microparticles for RPT studies. A few examples of RPT applications using the prepared microparticles are also discussed.