微小通道内液体扰流微孔逸出气泡串的迁移行为

对微小矩形通道内,液体扰流下微孔孔口逸出气泡串的迁移行为进行了可视化实验。基于图像处理方法,分别研究了液体流量和通道倾斜角度对气泡串尺寸、运动速度以及运动轨迹的影响。发现了不同工况下通道内的微气泡堆积现象,并对其进行了分析。结果表明：增大液体流量或者通道倾角,使得形成的气泡尺寸减小,气泡运动轨迹与通道壁面夹角减小,气泡运动速度增大。液体流量与通道倾角影响了通道内微气泡堆积的位置及数量。     

人字槽小孔节流动静压气体轴承承载特性研究

为提高动静压气体轴承的承载特性,以人字槽小孔节流动静压气体轴承为研究对象,运用流体力学理论对气体轴承的气膜流场特性和承载特性进行分析,研究不同转速时人字槽小孔节流动静压气体轴承承载力的变化规律,分析不同偏心率下人字槽槽数及几何参数对轴承承载特性的影响。结果表明:随转速的增加,人字槽产生的动压效应不断增强,轴承承载力不断提高;偏心率的增大可以提高轴承的承载力;同一偏心率下轴承的承载力随人字槽槽数的增多逐渐增大,当人字槽槽数小于10时,承载力增加较快,当人字槽槽数大于10时,承载力增加缓慢;随人字槽槽深比和槽宽比的增大承载力先升高后降低,在槽深比为2.4、槽宽比为0.55时承载力达到最高值。     

Observation Evaluation of Nozzle Clogging in a Micro-orifice Impactor Used for Atmospheric Aerosol Sampling

A micro-orifice impactor uses micro-orifice nozzles to extend the cut sizes of the lower stages to as small as 0.18 μm in diameter without resorting to low pressures or creating excessive pressure drops across the impactor stages. In this work, the phenomenon of nozzle clogging caused by particle deposition was investigated experimentally for a commercial micro-orifice uniform deposit impactor (MOUDI, MSP model 100). Using an optical microscope, we observed that the micro-orifice nozzles of the lower three stages were partially clogged due to particle deposition during the atmospheric aerosol sampling. To examine the effect of nozzle clogging on the performance of the impactor, the pressure drop and the particle collection efficiency were evaluated for the lower three stages. The pressure drops across the clogged nozzles were higher than the nominal values given by the manufacturer. The particle collection efficiency of each stage was evaluated by using an electrical method for fine particles with diameters in the range of 0.1-0.6 μm. Monodisperse liquid dioctyl sebacate (DOS) particles were used as test aerosols. A Faraday cage was employed to measure the low-level current of the charged particles upstream and downstream of each stage. The collection efficiency curves shifted to correspondence to smaller orifice sizes, and the 50% cutoff sizes were much smaller than those given by the manufacturer for the three stages with nozzles less than 400 μm in diameter.