Title: Fluid flow dynamics in MAS systems
Authors : Wilhelm, Dirk
Purea, Armin
Engelke, Frank
Published in : Journal of Magnetic Resonance
Volume(Issue) : 257
Pages : 51
Pages to: 63
Publisher / Ed. Institution : Academic Press
Issue Date: 2015
License (according to publishing contract) : Licence according to publishing contract
Type of review: Peer review (Publication)
Language : English
Subjects : MAS flow system; MAS turbine; Magic angle spinning; Computational fluid dynamic
Subject (DDC) : 620: Engineering
Abstract: The turbine system and the radial bearing of a high performance magic angle spinning (MAS) probe with 1.3 mm-rotor diameter has been analyzed for spinning rates up to 67 kHz. We focused mainly on the fluid flow properties of the MAS system. Therefore, computational fluid dynamics (CFD) simulations and fluid measurements of the turbine and the radial bearings have been performed. CFD simulation and measurement results of the 1.3 mm-MAS rotor system show relatively low efficiency (about 25%) compared to standard turbo machines outside the realm of MAS. However, in particular, MAS turbines are mainly optimized for speed and stability instead of efficiency. We have compared MAS systems for rotor diameter of 1.3–7 mm converted to dimensionless values with classical turbomachinery systems showing that the operation parameters (rotor diameter, inlet mass flow, spinning rate) are in the favorable range. This dimensionless analysis also supports radial turbines for low speed MAS probes and diagonal turbines for high speed MAS probes. Consequently, a change from Pelton type MAS turbines to diagonal turbines might be worth considering for high speed applications. CFD simulations of the radial bearings have been compared with basic theoretical values proposing considerably smaller frictional loss values. The discrepancies might be due to the simple linear flow profile employed for the theoretical model. Frictional losses generated inside the radial bearings result in undesired heat-up of the rotor. The rotor surface temperature distribution computed by CFD simulations show a large temperature gradient over the rotor.
Departement: School of Engineering
Organisational Unit: Institute of Applied Mathematics and Physics (IAMP)
Publication type: Article in scientific Journal
DOI : 10.1016/j.jmr.2015.05.006
ISSN: 1096-0856
1090-7807
URI: https://digitalcollection.zhaw.ch/handle/11475/10588
Appears in Collections:Publikationen School of Engineering

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