水声吸声材料与吸声结构研究进展

低频探测技术的发展对水下航行器的隐身性能提出了新的挑战。为了提高水下航行器的生存能力，通常会在其表面敷设水声吸声材料以吸收声纳发出的探测声波。本文综述了水声吸声材料及吸声结构的研究进展，介绍了基体材料改性、不同吸声结构对吸声性能的影响以及声学超材料在水声吸声领域中的应用，并总结了吸声材料和吸声结构中存在的问题与不足。

Effect of tube diameter on performances of Lurgi type reactor for methanol synthesis

Based on the two dimensional heterogeneous mathematical model of a fixed bed reactor, it was investigated that how the reaction tube diameter influenced the performance of Lurgi type reactor for methanol synthesis, loaded with domestic C302 Copper based catalyst. For equal volume of loaded catalyst, with the increase of reaction tube diameter, the hot point temperature and the radial temperature difference of catalytic bed rise, the location of the hot point moves towards the reactor outlet, the production per day of a reactor has a dropping trend, but the number of reaction tube needed reduces rapidly. Because of the limit of catalyst active temperature, the reaction tube diameter has an upper limit, and to the C302 catalyst the upper size is about 60 mm.