Evaluating the impact of simulated microgravity of a Random Positioning Machine on the stability of emulsions applying scaling analysis via dimensionless numbers

Schmidt, Svenja; Adebowale, Modupe N.; Rebrov, Evgeny; Fisk, Ian; Yang, Ni; Saarela, Maria; Hessel, Volker

Abstract

Random Positioning Machines (RPM) are commonly used to simulate microgravity for plant growth and cell culturing experiments, but not properly in multi-phase flow studies, e.g., emulsions. The implications of fluid motion induced by RPM movement patterns have only been studied for one-phase system using computational fluid dynamics (CFD). This study investigates the impact of fluid motion of 5 different RPM motion modes (0 g, 0.4 g, Clinostat of different frame rates) on dispersed droplets (d32 = 0.1-70 μm) applying scaling analysis. These computations are based on well-established fluid-dynamic laws and correlations, thereby giving microgravity researchers easier tool to evaluate potential deficiencies in their study design compared to CFD. We found that the Clinostat modes (80 deg/sec; 100 deg/sec; 120 deg/sec) induce a transitional flow regime in the continuous phase, and considerate shear rates acting on the dispersed droplets. Under certain conditions, the shear rates might even impact the average particle size, representing a major corruption in study design, which must not be mistaken as an effect of simulated microgravity. On the other hand, the 0 g and 0.4 g motion modes lead to a laminar flow in the continuous phase, low shear forces, Stokes flow surrounding the dispersed droplets, little relative droplet movement, as well as neglectable forced convection and gravitational force, thus resembling a state similar to true microgravity (0 g motion mode) and partial gravity (0.4 g motion mode).

Citation

Schmidt, S., Adebowale, M. N., Rebrov, E., Fisk, I., Yang, N., Saarela, M., & Hessel, V. (2025). Evaluating the impact of simulated microgravity of a Random Positioning Machine on the stability of emulsions applying scaling analysis via dimensionless numbers

• Working Paper Type: Working Paper
• Online Publication Date: Apr 25, 2025
• Publication Date: Apr 25, 2025
• Deposit Date: Jun 3, 2025
• Publicly Available Date: Jun 3, 2025
• DOI: https://doi.org/10.26434/chemrxiv-2025-327tp
• Public URL: https://nottingham-repository.worktribe.com/output/49893253
• Publisher URL: https://chemrxiv.org/engage/chemrxiv/article-details/680a07eae561f77ed49c453a
• Additional Information: This content is a preprint and has not undergone peer review at the time of posting.