The growing demand for bio-pharmaceuticals necessitates improved methods for the characterization of stirred tank reactors (STRs) and their mixing heterogeneities. Traditional Eulerian measurement approaches fall short, culminating in the use of Lagrangian Sensor Particles (LSPs) to map large-scale STRs and track the lifelines of microorganisms such as Chinese Hamster Ovary cells. This study investigates the hydrodynamic characteristics of LSPs, specifically examining the effects that the size and position of the Center of Mass (CoM) have on their flow-following capabilities. Two Lagrangian Particle (LP) designs are evaluated, one with the CoM and a Geometric Center aligned, and another with a shifted CoM. The experimental study is conducted in a rectangular vessel filled with deionized water featuring a stationary circular flow. Off-center LPs exhibit higher velocities, an increased number of floor contacts, and moreover, a less homogeneous particle probability of presence within the vessel compared to LPs with CoM and Geometric Center aligned. Lattice Boltzmann Large Eddy Simulations provide complementary undisturbed fluid velocity data for the calculation of the Stokes number $St$. Building upon these findings, differences in the Stokes number $St$ between the two LP variants of $\Delta St$ = 0.01 (25 mm LP) and $\Delta St$ = 0.13 (40 mm LP) are calculated, highlighting the difference in flow behavior. Furthermore, this study offers a more representative calculation of particle response time approach, as the traditional Stokes number definition does not account for non-homogeneous particles, resulting in an alternative Stokes number ($\Delta {St}_{\mathrm{alt}}$ = 0.84 (25 mm LP) and $\Delta {St}_{\mathrm{alt}}$ = 2.72 (40 mm LP)). This study contributes to the improved characterization of STRs through the use of Lagrangian Sensor Particles. Results highlight the implications the internal mass distribution has on LSP design, offering crucial considerations for researchers in the field.

Spatial oxygen limitation is a major source of physiological stress and metabolic, scale‐dependent heterogeneity in aerobic bioprocesses. In gas‐liquid stirred tank reactors, oxygen availability is governed by hydrodynamics and mass transfer and is therefore inherently non‐uniform. Despite its importance, experimentally accessing spatial information on oxygen local supply remains challenging, as most established techniques rely on point‐wise sensing or intrusive tracer‐based methods. This work presents an optical method for visualizing local oxygen limitation based on the reversible redox chemistry of methylene blue in alkaline glucose solutions. After driving the reactor into a uniformly reduced, colorless state, the spatial reoxidation of the indicator during oxygen aeration is recorded and evaluated pixel‐wise. The resulting two‐dimensional fields of colorization time provide a spatially continuous indicator of local oxygen supply governed by hydrodynamic transport and gas‐liquid mass transfer. Systematic experiments were conducted to assess the influence of glucose and sodium hydroxide concentration on the stability and reproducibility of the redox system, enabling the selection of a robust reaction medium. The method was then applied to a laboratory‐scale stirred tank operated at different impeller speeds. The resulting colorization fields reveal characteristic spatial structures associated with oxygen‐limiting regions, including insufficiently supplied zones under weak agitation, progressive homogenization with increasing turbulence, and residual transport limitations near reactor walls at high agitation rates. The presented approach requires no local tracer injection and operates under normal aeration conditions, providing qualitative yet physically meaningful insight into oxygen‐supply and mixing related heterogeneities. It therefore offers a simple and cost‐effective tool for identifying limiting operating points, supporting future scale‐transfer studies, and complementing CFD‐based analyses of oxygen transport in stirred tank bioreactors.