Recently, high heat density has become a problem in electronic devices. Therefore, high heat-transfer efficiency is required in copper heat exchangers. Improvement ofwettability is reported to improve the heat-transfe...Recently, high heat density has become a problem in electronic devices. Therefore, high heat-transfer efficiency is required in copper heat exchangers. Improvement ofwettability is reported to improve the heat-transfer efficiency. In previous studies, copper oxide layer improves the wettability. In this study, we focus on a copper oxide layer produced under warm conditions （from 200 to 300 ℃）, which are suitable oxidation conditions for improving wettability. Experimental results showed that the surface of the specimens was covered by the oxidation layer and took on a black color. Furthermore, the wettability was improved by the warm copper oxide layer. While, the surface roughness was approximately constant to each warm oxidized specimen. Whereat, the warm oxide layer was observed by SEM （sanning electron microscope）. The results from SEM observations showed that the warm copper oxide layer consisted of stacks and combinations of nanoscopic warm oxidation particles. Thus, the warm oxidation layer has nanoscopic surface asperities. It is seemed that these nanoscopic asperities improved the wettability.展开更多
Rotor systems supported by angular contact ball bearings are complicated due to nonlinear Hertzian contact force. In this paper, nonlinear bearing forces of ball bearing under five-dimensional loads are given, and 5-D...Rotor systems supported by angular contact ball bearings are complicated due to nonlinear Hertzian contact force. In this paper, nonlinear bearing forces of ball bearing under five-dimensional loads are given, and 5-DOF dynamic equations of a rigid rotor ball bearing system are established. Continuation-shooting algorithm for periodic solutions of the nonlinear non-autonomous dynamic system and Floquet multipliers of the system are used. Furthermore, the bifurcation and stability of the periodic motion of the system in different parametric domains are also studied. Results show that the bifurcation and stability of period-1 motion vary with structural parameters and operating parameters of the rigid rotor ball bearing system. Avoidance of unbalanced force and bending moment, appropriate initial contact angle, axial load and damping factor help enhance the unstable rotating speed of period-1 motion.展开更多
文摘Recently, high heat density has become a problem in electronic devices. Therefore, high heat-transfer efficiency is required in copper heat exchangers. Improvement ofwettability is reported to improve the heat-transfer efficiency. In previous studies, copper oxide layer improves the wettability. In this study, we focus on a copper oxide layer produced under warm conditions （from 200 to 300 ℃）, which are suitable oxidation conditions for improving wettability. Experimental results showed that the surface of the specimens was covered by the oxidation layer and took on a black color. Furthermore, the wettability was improved by the warm copper oxide layer. While, the surface roughness was approximately constant to each warm oxidized specimen. Whereat, the warm oxide layer was observed by SEM （sanning electron microscope）. The results from SEM observations showed that the warm copper oxide layer consisted of stacks and combinations of nanoscopic warm oxidation particles. Thus, the warm oxidation layer has nanoscopic surface asperities. It is seemed that these nanoscopic asperities improved the wettability.
基金Supported by National Natural Science Foundation of China (No.50905061)the Fundamental Research Funds for Central Universities
文摘Rotor systems supported by angular contact ball bearings are complicated due to nonlinear Hertzian contact force. In this paper, nonlinear bearing forces of ball bearing under five-dimensional loads are given, and 5-DOF dynamic equations of a rigid rotor ball bearing system are established. Continuation-shooting algorithm for periodic solutions of the nonlinear non-autonomous dynamic system and Floquet multipliers of the system are used. Furthermore, the bifurcation and stability of the periodic motion of the system in different parametric domains are also studied. Results show that the bifurcation and stability of period-1 motion vary with structural parameters and operating parameters of the rigid rotor ball bearing system. Avoidance of unbalanced force and bending moment, appropriate initial contact angle, axial load and damping factor help enhance the unstable rotating speed of period-1 motion.
