Reynolds number effects in a simple planetary mixer

• Published in: Chemical engineering science Vol. 59; no. 16; pp. 3371 - 3379
• Main Authors: Clifford, M.J, Cox, S.M, Finn, M.D
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.08.2004; Elsevier
• Subjects: Applied sciences; Chaotic advection; Chemical engineering; Exact sciences and technology; Fluid mechanics; Laminar flow; Mixing; Nonlinear dynamics; Stokes flow; Fluid mechanics; Nonlinear dynamics; Mixing; Laminar flow; Chaotic advection; Stokes flow; Numerical simulation; Computational fluid dynamics; Reynolds number; Mixing quality
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2004.03.043

Planetary mixers are widely used in a diverse range of industrial applications. This paper presents an experimental investigation of mixing in a planetary mixer, and a comparison with numerical simulations based on a simple mathematical model of the flow. The model allows an exact expression for the velocity field in the Stokes flow regime, apparently the first for a mixer with genuinely moving parts, which permits accurate numerical tracking of material interfaces. Experiments performed at low Reynolds number ( Re≪1) show good agreement with corresponding numerical simulations, but as the Reynolds number is increased, the agreement between experiments and Stokes-flow numerics worsens, in a manner that reflects improving experimental mixing quality. Specifically, we find that islands of poor mixing shrink as Re increases. Our results suggest that, while numerical simulations in the Stokes flow regime may be used as a ‘sieve’ to select good mixing protocols at small Re, experiments or computational fluid dynamics simulations are required properly to evaluate mixing protocols operated at finite Reynolds numbers.