Papers by Author: Shao Lin Zhang

Abstract: For high speed hybrid journal bearing with deep/shallow pockets, film thickness and film Reynolds number vary considerably in different position. Laminar flow and turbulent flow exist simultaneously in the bearing film. This paper establishes the laminar and turbulent mixed film control equations and the pressure boundary conditions together with the restrictor flow equation for a deep/shallow pockets journal hybrid bearing compensated by interior restrictor. The static characteristics such as attitude angle, load carrying capacity, friction power loss and flow volume rate are given by solving the equations with Finite Element Method. By comparing the laminar, turbulent and mixed flow results, it can be seen that the coefficients are proximity under journal speed 5000 rpm (only part of deep pockets is turbulent flow). But the characteristics coefficients of three flow models contrast evidently under journal speed 50000 rpm (deep and shallow pockets are turbulent flow, part of bearing land is laminar flow). Laminar and turbulence mixed flow lubrication theory is more accurate to high speed hybrid bearing with deep/shallow pockets.

Abstract: A novel and simple approach has been developed for a large-scale synthesis of ZnO nanorods using ultrasound radiation. Double-pod-like ZnO nanorods were directly grown from the starting precursors of zinc nitrate hydrate [Zn(NO3)26H2O] and hexamethylene tetramine (HMT) in deionized water without any templates or seeds. The obtained double-pod-like product had a diameter ranging from 80 to 150 nm and length ranging from 1 to 5 um. Scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM) revealed that these products are of high purity, hexagonal and of single-crystalline structure. The ZnO nanorods synthesized were utilized for gas sensing application. Alumina plate consists of Pt interdigitated electrode was used as sensor substrate. The as-prepared products were transferred to the surface of substrate by screen printing method to fabricate the gas sensor. The sensing properties of the sensor were investigated toward methyl mercaptan (CH3SH). The sensor shows good and fast response towards methyl mercaptan at a fixed operating temperature. The high sensitivity may be ascribed to the high surface area and aspect ration of the double-pod-like nanomaterial.

Abstract: The paper presents the effect of acid treatment on the structure of single-walled carbon nanotube (SWNT) bundles and on the characteristics of SWNT-based gas sensors. The commercial SWNT powder was treated with a mixture of concentrated H2SO4:HNO3 (3:1 in volume) before used to fabricate sensors for ammonia (NH3) detection at room temperature. The Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) images indicated that the acid treatment not only removed most of catalytic particles from the SWNT bundles, but also caused SWNT bundles to be fragile. The fracture of the SWNT facilitated for gas molecules to adsorb in the SWNT sites, leading to an enhancement in sensitivity of the sensors. Upon exposing to 50 ppm NH3 in 450 sccm of nitrogen flowing rate at room temperature, the resistance of the 2-h-stirred sensors increased to 38% compared to 22% of the 1-h-stirred sensor. The recovery of the SWNT sensor was also accelerated owing to the treatment. These findings opened a new direction to improve the characteristics of SWNT-based gas sensors.