Numerical investigation on the flow and heat transfer for a millimeter-scale rotor-stator system with ultrahigh rotational speed

Abstract

Micro turbine engine (MTE) is a promising device for the future energy application. However, the literature to date is limited in the research on the millimeter-scale rotor-stator system with the ultrahigh rotational speed in MTE. This work investigates the flow and heat transfer for a rotor-stator system with the radius of 4 mm and the rotational speed from 0.2 × 106 to 1.0 × 106 rpm. The mechanisms of centrifugal force and centrifugal buoyancy force are analyzed at the rotational Reynolds number within 0.2 × 105 and 1.0 × 105 and the rotor excess temperature of 25 and 275 K. The effect of geometric configuration including the spacing and opening is also discussed. The results demonstrate that the difference between the millimeter-scale and conventional rotor-stator system lies in not the flow structure, but the heat transfer, which is due to the viscous dissipation induced by the ultrahigh rotational speed. With the increasing rotational Reynolds number, the larger centrifugal force enhances the radial flow and raises the heat transfer. Meanwhile, the increasing viscous dissipation results in the heat transfer deterioration at high radius, especially at low rotor excess temperature. The large centrifugal buoyancy force induced by the high rotor excess temperature reduces the heat transfer by suppressing the radial flow, though it weakens the viscous dissipation. The spacing and opening determine the flow structure, the increase of which enhance the average heat transfer especially at low gap ratios. These findings can provide the reference for the design of millimeter-scale rotor-stator system in MTE.