Liquid viscosity is a vital metric in microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS). The application of conventional viscosity measurements in micro/nano scale is complex and not economically viable. Self-propelled catalytic microrockets, capable of converting energy into movement and forces, have shown considerable promise for diverse practical applications in MEMS/NEMS. In this work, a novel micromotor-based viscometer is developed. The relation between the velocity of microrocket and the viscosity of solution is experimentally studied and theoretically modelled. A linear relationship between both variables is observed, with a decrease in the velocity of microrocket as the viscosity of solution increases. The microrocket based viscometer can be used to measure the viscosity within the range of 1.5-6.361 cP, 1.5-6.575 cP, and 1.5-7.486 cP in 5%, 7.5% and 10% H2O2 solutions, respectively. Compared with traditional viscometers, the newly developed microrocket-based viscometer represent a cost-effective, and ultracompact sized alternative that can be used for viscosity measurement in MEMS and NEMS.
Rotor stability and rotation accuracy, which are highly dependent on the dynamic coefficients of supporting hybrid bearings, are two important issues of high-speed water-lubricated spindles. To improve the spindles' performance, the dynamic coefficients of high-speed water-lubricated hybrid bearings were experimentally identified by the noncontact harmonic excitation method and the additional unbalance excitation method, respectively. Comparisons between experimental results and theoretical predictions were made. The experimental technique and the identification model were validated to be effective. Besides, the influence of supply pressure and rotating speed on dynamic coefficients was also presented. As for different operating conditions, valuable guides were provided to investigate the dynamic performance of high-speed and ultra-high-speed spindles.
To improve the performance of a heavy-loaded and high-speed hydrodynamic bearing, partial texture is designed on the journal surface. A three-dimensional thermo-hydrodynamic analysis model is developed based on the computational fluid dynamics method. Thermal conduction of bearing bush and journal, heat convection on the air-bearing surface, viscosity–temperature effect, and cavitation effect are taken into account. Performance of textured and un-textured high-speed journal bearing under different eccentricity ratios and different external loads is compared. The results indicated that partial texture on journal surface can play a positive role for large eccentricity ratio conditions in this study, and the textured bearing has a higher load carrying capacity, a lower maximum oil pressure, and a lower oil temperature rise than the un-textured bearing based on an optimal design of texture.
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