Ultra Low Temperature Microturbine for MAS System

Abstract We investigate the fluid dynamics of a microturbine system that is applied in a device for chemical and biological analysis -- a so-called Magic Angle Spinning (MAS) NMR probe. The present system is utilized in a wide temperature range from 45K to 293K. Pressurized air, nitrogen or helium are used to drive a Pelton type microturbine. This turbine is mounted on an MAS rotor with diameter between 0.7mm and 3.2mm. The rotor system is equipped with a pressurized gas bearing that is operated by the same gas species as the turbine. Computational fluid dynamics (CFD) simulations have been performed and compared with fluid dynamics measurements of the MAS system for different diameters, temperatures and spinning rates between 23kHz and 120kHz. To our knowledge this work is the first comprehensive CFD and experimental study of such a wide temperature range that has been carried out for microturbines with pressurized gas bearings. The results show good agreement between measurements and CFD simulations with appropriate (real) gas models: i.e. ideal gas model for air at room temperature, Peng-Robinson model for nitrogen at 105K and ideal gas model for helium at 45K.