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长微直管道内多流态并存的流动特性研究不仅有理论意义,而且在太空飞行器的控制系统中有着重要的应用价值.采用实验研究和理论模型近似分析相结合的方法研究了长微直管道内的气体流动特性.实验中,以空气为工作介质,进口压力分别设定为130,250,320kPa,出口压力变化范围为9—100?kPa.沿程分布有五个测压点,进出口设有温度传感器,测量出口流量的同时可以得到沿程压力分布.近似理论模型采用二维平板近似模型.研究发现,在保持进口压力不变、不断降低出口压力的条件下,当进出口压比低于5.3左右时,质量流量随压比增加
关键词:
长微直管道
亚堵塞
表面积与体积比
多流态并存
临界压比 相似文献
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为研究小口径喷嘴冲击射流的噪声特性,测定了3mm口径的轴对称收缩喷嘴在各种压比情况下产生的亚音速和超音速射流冲击坚固大平板产生的噪声。发现噪声在空间呈近似四瓣分布,当喷嘴与平板距离减小时,噪声指向壁射流下游的瓣到增强,反之,噪声指向喷嘴上游的瓣得到增强。噪声随喷嘴距平板距离的增加呈增强的趋势,在距平板一定距离内有锯齿现象。噪声随喷嘴压比的增加而增强,相应于各种工况,存在一不同的压比值,此压比之前,噪声随压比的增大而迅速提高,但有起伏现象,在此压比之后,噪声平缓地随压比的增大而增强。 相似文献
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Experiments have been conducted to investigate nitrogen gas flow characteristics through four trapezoidal silicon microchannels with different hydraulic diameters. The volume flow rate and pressure ratio are measured in the experiments. It is found that the friction coefficient is no longer a constant, which is different from the conventional theory. The characteristics are first explained by the theoretical analysis. A simplified rectangular model (rectangular straight channel model) is then proposed. The experimental results are compared with the theoretical predictions based on the simplified rectangular model and the two-dimensional flow between the parallel-plate model which was usually used. The difference between the experimental data and the theoretical predictions is found in the high-pressure ratio cases. The influence of the gas compressibility effect based on the Boltzmann gas kinetic analysis method is studied to interpret the discrepancy. We discuss two important factors affecting the application extent of different prediction models. 相似文献
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微纳结构超疏水表面的湍流减阻机理研究 总被引:2,自引:0,他引:2
超疏水表面的优异性质使其在现代生活和工业生产中具有十分广泛的潜在应用价值. 本文采用了碳纳米管缠绕技术和聚氟硅氧烷疏水化处理方法制备了具有二级微纳米结构的超疏水表面. 测量了由该超疏水表面构建的槽道中的流动压降,将其与普通表面构建的槽道内的流动压降进行比较,发现在层流情况下,流动阻力减小最多达到了22.8%. 在湍流的情况下,超疏水表面的减阻比例约为53.3%,减阻效果比层流更加明显.利用PIV (particle image velocimetry) 技术测量了具有超疏水表面的槽道内的速度场,通过超疏水表面速度滑移和湍动脉动场信息,分析了湍流减阻效果比层流更加明显的物理机制. 相似文献
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使用大涡模拟方法对冲击面为平面的超声速中等欠膨胀冲击射流进行了数值模拟.利用三阶迎风和四阶对称紧致格式对无量纲化轴对称可压缩滤波N-S方程进行空间离散,时间上推进采用的是三阶精度的TVD型Rugge-Kutta法. 通过与经典的冲击射流实验比较,证实了程序的可靠性. 数值模拟得到了流场中不同尺度的涡结构和激波结构,观察到了上行声波和反射波以及流场中不同位置的声源,分析了冲击区剪切层附近区域的压强和涡旋转强度变化的频率、冲击平板上的压强变化频率以及射流剪切层中不同位置的涡合并出现的频率,发现冲击区剪切层附近区域的压强和涡强度变化以及射流剪切层中的涡合并现象和离散频率的冲击单音有重要关联. 相似文献
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A numerical scheme is developed to simulate electro-osmotic flow and mass transport in a microchannel which includes a 180° turn. The model has been used to predict the behaviour of electro-osmotically driven flows. The detailed structure of the flow field in a microchannel in combination with species mass diffusion can explain the concentration dispersion introduced by a 180° turn. The results of our simulations agree both qualitatively and quantitatively with experimental observation. It is demonstrated that an improved electro-osmotic force model could simulate the electrokinetically driven flow well without making detailed calculations of the electric charge density distribution within the electrical double layer. Additionally, because this model applies forces to the liquid as opposed to imposing local velocities, it should also be appropriate for use where pressure gradients exist in the flow field. 相似文献
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Controllable preparation of vertically standing graphene sheets and their wettability and supercapacitive properties 下载免费PDF全文
Vertically standing graphene(VSG) sheets have been fabricated by using plasma enhanced chemical vapor deposition(PECVD) method.The lateral size of VSG nanosheets could be well controlled by varying the substrate temperature.The higher temperature usually gives rise to a smaller sheet size.The wettability of VSG films was tuned between hydrophobicity and hydrophilicity by means of oxygen and hydrogen plasma treatment.The supercapacitor electrode made of VSG sheets exhibited an ideal double-layer-capacitor feature and the specific capacitance reached a value up to 9.62 F·m~(-2). 相似文献
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超音速冲击射流离散频率噪声的屏蔽抑制方法 总被引:1,自引:0,他引:1
根据导致超音速冲击射流离散频率噪声的反馈机理,提出了一种能够有效地破坏反馈环的形成,从而抑制超音速冲击射流离散频率噪声的喷嘴屏蔽方法。这种方法是通过阻隔反馈波使其不能到达喷嘴唇口从而破坏反馈环、同时屏蔽罩不与射流接触来实现降噪的目的的。本文介绍了这种方法的基本思想并提出了屏蔽罩的设计要点。实验结果表明,对于合适的屏蔽罩的参数,降噪效果达5分贝以上。应用LDV方法对超声速射流轴线速度进行了测量和比较,发现应用屏蔽降噪方法以后射流轴线速度显著增加,核心区长度增加50%左右。分析表明这种降噪方法对射流冲击障碍物的推力和除尘除水效率的提高有帮助。 相似文献