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A new type of Lorentz force bearing design method is proposed based on the superposition magnetic field and composite magnetic steel to solve the problem of the high power consumption and non-uniformity of the working air gap in the existing Lorentz force magnetic bearing. Firstly, the electromagnetic torque model of the traditional Lorentz force magnetic bearing is established, and the corresponding relationship between the power consumption and control precision of the Lorentz force magnetic bearing and its magnetic field performance is revealed. On this basis, the concepts of the average magnetic field intensity and magnetic field uniformity are introduced. The new plan is designed to combine the axial magnetizing magnetic steel with radial block magnetizing magnetic steel creatively. To ensure the circumferential homogeneity of the work air gap, the main magnetic field is generated from the axial magnetizing magnetic steel. The magnetic field mainly accumulates in the work air gap with radial block magnetizing magnetic steel. Compared with the existing magnetic bearing, under the condition of the same size constraint, the magnetic field uniformity of a new magnetic Lorentz force bearing increases by 8.7%, and the magnetic field intensity increases by 51.8%, significantly higher circumferential field continuity. The research results can provide a new technical way to develop high precision magnetic levitation actuator. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the effect of surface roughness on gas flow in microchannels is highly desirable in microfluidic devices. Non-equilibrium molecular dynamics simulation is applied to investigate the effect of the surface roughness on slip flow of gaseous argon in submicron platinum channels. The geometries of the surface roughness are modeled by triangular, rectangular, sinusoidal and randomly triangular waves respectively. The results show that the boundary conditions of velocity slip, including slip, no-slip and negative slip, depend not only on the Knudsen number but also on the surface roughness. Induced by the roughness, the slip length of gas microflow over a rough surface is less than that predicted by the Maxwell model and shows a non-linear relationship with the Knudsen number. The friction coefficient increases not only with decreasing the Knudsen number but also with increasing the surface roughness. The impacts of the surface roughness and the gas rarefaction on the friction coefficient of gas microflow are strongly coupled. The roughness geometry also shows significant effects on the boundary conditions and the friction characteristics. The distortion of the streamlines and the enhancement of the penetrability near the rough surface are demonstrated to be responsible for the roughness effect. [Copyright &y& Elsevier]