The deviation of flow characteristics from the predictions of the conventional theory for microtubes was attrib- uted to the change of fluid viscosity resulted from the interactions between the molecules on solid wall...The deviation of flow characteristics from the predictions of the conventional theory for microtubes was attrib- uted to the change of fluid viscosity resulted from the interactions between the molecules on solid wall and in fluid. The degree of this departure is dependent on the microtubes materials. A concept of equivalent thickness with which conventional theory can be used to predict the flow in microtubes without modifying the fluid viscosity was put forward. The values of equivalent thickness for fused silica and stainless steel materials were determined as 1.8 μm and 1.5 μm, respectively, by repeated numeri- cal simulation.展开更多
Entrance region may have important effect on gases flow characteristics in micro-channels. It's concluded in the available papers that the entrance effect causes significant difference. An experimental system of s...Entrance region may have important effect on gases flow characteristics in micro-channels. It's concluded in the available papers that the entrance effect causes significant difference. An experimental system of single-phase gas flow characteristics in microchannels was set up. Flow characteristics of nitrogen in PEEK polymer micro-tube (hydraulic diameter is 553btm) was studied experimentally. According to the data of nitrogen flow in the micro-tube with the length ranging from 0. 1m to1.524m, it is shown that the friction constant becomes higher when the tube becomes shorter. By using pipe cutting methods, it's confirmed that entrance effect is one of the key factors that cause friction constant higher than conventional theory. It's found that friction constant of fully developed flow is lower than the value predicted by conventional theory in turbulent region. The result indicates that the flow transition occurs at Reynolds number ranging from 1600-2000. The phenomenon of obvious early transition is not found.展开更多
Co0.6Cu0.16Ni0.24Fe2O4/multi-walled carbon nanotube nanocomposites (CCNF/MWCNTs) were synthesized by solution filling method.The phase structure,thermal stability,morphology and electrical-magnetic properties of the s...Co0.6Cu0.16Ni0.24Fe2O4/multi-walled carbon nanotube nanocomposites (CCNF/MWCNTs) were synthesized by solution filling method.The phase structure,thermal stability,morphology and electrical-magnetic properties of the samples were characterized by means of modern testing technology.The effect of iron concentration,filling time,sintering temperature on their electrical and magnetic performance was discussed.The results indicated that conductivity was related to the content of MWCNTs,while the magnetism correlated with the volume fraction of the filled CCNF in the composites.When the optimal condition satisfied the filling time of 18 h,ferric concentration of 0.25 mol L-1 and sintering temperature of 350°C,the prepared composite had the best magnetic loss performance,and its minimum reflection loss reached-22.47 dB on 9.76 GHz,the available bandwidth was beyond 2.0 GHz.Hence,the obtained composite can be used as advancing absorption and shielding material due to its favorable microwave absorbing property.展开更多
基金Project (No. 20299030) supported by the National Natural ScienceFoundation of China
文摘The deviation of flow characteristics from the predictions of the conventional theory for microtubes was attrib- uted to the change of fluid viscosity resulted from the interactions between the molecules on solid wall and in fluid. The degree of this departure is dependent on the microtubes materials. A concept of equivalent thickness with which conventional theory can be used to predict the flow in microtubes without modifying the fluid viscosity was put forward. The values of equivalent thickness for fused silica and stainless steel materials were determined as 1.8 μm and 1.5 μm, respectively, by repeated numeri- cal simulation.
基金supported by the National Natural Science Foundation of China (No. 50776006)"863" plan (No. 2006AA05Z228)Technological Innova tion Fund of Excellent Doctoral Candidate of Beijing Jiaotong University (No. 48013)
文摘Entrance region may have important effect on gases flow characteristics in micro-channels. It's concluded in the available papers that the entrance effect causes significant difference. An experimental system of single-phase gas flow characteristics in microchannels was set up. Flow characteristics of nitrogen in PEEK polymer micro-tube (hydraulic diameter is 553btm) was studied experimentally. According to the data of nitrogen flow in the micro-tube with the length ranging from 0. 1m to1.524m, it is shown that the friction constant becomes higher when the tube becomes shorter. By using pipe cutting methods, it's confirmed that entrance effect is one of the key factors that cause friction constant higher than conventional theory. It's found that friction constant of fully developed flow is lower than the value predicted by conventional theory in turbulent region. The result indicates that the flow transition occurs at Reynolds number ranging from 1600-2000. The phenomenon of obvious early transition is not found.
基金supported by the National Natural Science Foundation of China (Grant No. 21071125)the Science and Technology Key Project of Zhejiang Province (Grant No. 2010C11053)the subproject of Science-Technology Innovation Team in Zhejiang Province (Grant No.2011R09006-06)
文摘Co0.6Cu0.16Ni0.24Fe2O4/multi-walled carbon nanotube nanocomposites (CCNF/MWCNTs) were synthesized by solution filling method.The phase structure,thermal stability,morphology and electrical-magnetic properties of the samples were characterized by means of modern testing technology.The effect of iron concentration,filling time,sintering temperature on their electrical and magnetic performance was discussed.The results indicated that conductivity was related to the content of MWCNTs,while the magnetism correlated with the volume fraction of the filled CCNF in the composites.When the optimal condition satisfied the filling time of 18 h,ferric concentration of 0.25 mol L-1 and sintering temperature of 350°C,the prepared composite had the best magnetic loss performance,and its minimum reflection loss reached-22.47 dB on 9.76 GHz,the available bandwidth was beyond 2.0 GHz.Hence,the obtained composite can be used as advancing absorption and shielding material due to its favorable microwave absorbing property.
