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1.
The flow of power-law liquids through tapered dies has been analyzed in an earlier paper.1 We now consider a taper which is additionally streamlined so as to make the transition from a broad and sluggish flow to a flow which is narrow and fast and as smooth as possible. This involves (1) the rational selection of an appropriate taper function within the relevant flow geometry and (2) the integration, between limits, of that function.  相似文献   

2.
王俊博  谢攀  刘志春  刘伟 《化工学报》2016,67(Z1):307-311
在流体对流换热分析的基础上得到局部?损率的表达式,以局部?损率为优化目标,满足能量与质量守恒条件,在流动功耗为定值条件下,根据拉格朗日泛函极值原理得到?损为极值时的控制方程组,发展了最小?损优化方法。将该方法应用到椭圆换热单管中,得到优化后的速度场与温度场。优化结果表明,优化流动结构为纵向旋流,具有较好的传热及流动性能,相比未优化椭圆管综合换热性能(Nu/Nus)/(f/fs)可达3.21,同时得到了纵向涡在流场中的分布情况,这对椭圆管内强化换热发展具有指导意义。  相似文献   

3.
While there are several computational studies on differential mobility analyzers (DMA), there is none for high flow DMA to classify nanoparticles less than 3?nm. A specific design of a high flow DMA, a half mini DMA, is investigated to predict its performance through numerical modeling in the incompressible flow regime. The governing equations for flow field, electric field and aerosol transport are solved using COMSOL 5.3. The transfer function of the half mini DMA is compared with that of a nano DMA (TSI 3085). The results show that both the height of the transfer function and resolution (R) of the half mini DMA are much better than those of nano DMA in sub-2?nm particle size range. Finally, the transfer function of half mini DMA is evaluated for different values of aerosol flow rate to the sheath flow rate (q/Q). Comparison of the simulated transfer function with existing models from Knutson–Whitby and Stolzenburg is also elucidated. It is found that the former model overestimates the resolution; whereas the latter is close to the simulation results for q/Q above 0.067. This work provides a useful method to study the flow regimes and transfer function of a high flow DMA.

Copyright © 2018 American Association for Aerosol Research  相似文献   


4.
几种有限元分析方法在机头流道分析中的应用研究   总被引:1,自引:0,他引:1       下载免费PDF全文
秦晓南  江波 《橡胶工业》2002,49(9):542-548
研究了 3种有限元分析方法———流函数法、侧壁因子修正法和全高三棱柱单元法在挤出机平板机头流道分析中的应用情况。结果表明 ,流函数法只适合分析流道高度不变化或变化极小的情况 ;侧壁因子修正法误差较小 ;全高三棱柱单元法比较精确 ,但分析方法复杂  相似文献   

5.
A model is proposed for cocurrent gas liquid flow through a packed bed. For a given packing, gas and liquid flow rates, we proposed that (i) liquid holdup is a function only of pressure gradient and liquid flow rate and (ii) pressure gradient is only a function of liquid holdup and gas flow rate. Equations are presented which permit the prediction of pressure gradient and liquid holdup for cocurrent upflow and cocurrent downflow in a packed bed. Predictions from the model are shown to be in reasonable agreement with the experimental observations of Turpin and Huntington.  相似文献   

6.
Patterns of a liquid film falling across a vertical array of horizontal tubes change from droplet mode at low flow rates to liquid sheet at high flow rates. Between these limits, liquid columns form as a further stable flow pattern. The transition from one flow mode to another occurs via unstable structures consisting simultaneously of droplets and columns or of merging columns. The boundaries of the flow modes can be obtained from relationships expressing the flow rate as a function of physical properties, that is, the Reynolds number as a function of the Kapitza number. Correlations for the pattern boundaries recommended in the literature are compared with each other and found to be in acceptable agreement for practical purposes.  相似文献   

7.
The aim of this paper is to present the evolution of plug flow developing in three densely packed granular materials in the model of a hopper made of Plexiglas. For this purpose, the digital particle image velocimetry (DPIV) technique is applied to analyse the flow field of the granular material. When discharge starts, a plug flow zone in the flowing material expands upward. This zone changes its width reaching the upper surface of the material. The plug flow evolution as a function of time is described using DPIV. This technique yields the velocity profiles of flowing granular materials, velocity magnitude contours, vector fields, velocity distributions on certain levels in the model and traces of the selected particles. The results obtained for the evolution of the vertical velocity, height and width of the plug flow zone as a function of time, measured at the symmetry axis of the model for the amarantus seed are compared to the results obtained by Waters and Drescher. Measurements of the stagnant boundary as a function of time are compared to the results available in the literature.  相似文献   

8.
Limin Shi 《Powder Technology》2011,212(1):253-257
Earlier work showed that a batch of microcrystalline cellulose (MCC, Avicel PH102) exhibited minimum acceptable flow properties required for successful high speed tableting. The aim of this work was to assess the suitability of using Avicel PH102 as a reference indicator of minimum powder flow by examining the reproducibility of flow properties of seven batches of Avicel PH102. Powder flow properties have been characterized in terms of flow function, flow factor, cohesion, bulk density, effective angle of internal friction, angle of linearized yield locus, and angle of internal friction at steady-state flow. Results show that the measured flow function is independent of operator. Batch-to-batch flow functions are not statistically different at 95% confidence level suggesting acceptable reproducibility. These results corroborate that Avicel PH102 may be used as a reference powder for predicting flow performance of a new formulation during high speed tableting.  相似文献   

9.
The hydrodynamics of an airlift-loop reactor (ALR) and a bubble column (BC) were studied in the same reactor unit. When the liquid circulation in the ALR was impeded gradually in order to obtain a BC mode of operation, there was a transition flow regime inbetween that of the ALR-type flow and the BC-type flow. In the BC the heterogeneous flow was represented by an instationary circulatory flow pattern and characterized by a liquid circulation velocity. The liquid flow in the ALR was represented by a drift-flux model. In the transition flow regime, hydrodynamic calculations based on the plug-flow behavior of an ALR appeared to be valid up to a certain defined value of the total gas-liquid flow rate. To distinguish between BC and ALR flow characteristics, a simple criterion is proposed, qualifying that the distinction between both flow patterns is determined by the superficial liquid velocity and the liquid circulation velocity. If the latter velocity exceeds the superficial liquid velocity a hydrodynamic transition will occur from a uniform ALR type of flow to a heterogeneous BC type of flow. The criterion coincides with an empirical power law function in which the liquid velocity is given as a function of the gas velocity. The values of the power-law coefficients depended on the characteristics of the two-phase flow. The change in value cohered with the onset of a change in the flow pattern.  相似文献   

10.
Pressure fluctuations and bed voidages are obtained in the dilute phase flow and dense phase flow regimes of vertical pneumatic conveying systems of fine particles. Statistical parameters of the pressure fluctuations are utilized to study the transition from the dilute phase flow to the dense phase flow. Out of the four types of fine particle used in the experiments, three types of fine particle exhibit a choking transition, which is characterized by a sharp change in the bed voidage. At the choking transition, sharp changes in the power spectral density function and standard deviation of the pressure fluctuations are also observed. The fourth type of fine particle does not exhibit any sharp changes in bed voidage, power spectral density function, or standard deviation of the pressure fluctuations over a wide range of air velocities used in the experiments. It is shown that the power spectral density function and the standard deviation of pressure fluctuations can be effectively used to accurately determine the choking transition. The experimentally determined choking velocities and bed voidages in the slugging dense phase flow are compared with available correlations.  相似文献   

11.
A novel noninvasive approach, based on flow-induced vibration, to the online flow regime identification for wet gas flow in a horizontal pipeline is proposed. Research into the flow-induced vibration response for the wet gas flow was conducted under the conditions of pipe diameter 50 mm, pressure from 0.25 MPa to 0.35 MPa, Lockhart-Martinelli parameter from 0.02 to 0.6, and gas Froude Number from 0.5 to 2.7. The flow-induced vibration signals were measured by a transducer installed on outside wall of pipe, and then the normalized energy features from different frequency bands in the vibration signals were extracted through 4-scale wavelet package transform. A “binary tree” multi-class support vector machine(MCSVM) classifier, with the normalized feature vector as inputs, and Gaussian radial basis function as kernel function, was developed to identify the three typical flow regimes in-cluding stratified wavy flow, annular mist flow, and slug flow for wet gas flow. The results show that the method can identify effec-tively flow regimes and its identification accuracy is about 93.3%. Comparing with the other classifiers, the MCSVM classifier has higher accuracy, especially under the case of small samples. The noninvasive measurement approach has great application prospect in online flow regime identification.  相似文献   

12.
Experiments with laser Doppler velocimetry show that, for flat bottom hydrocyclones, the axial velocity field is a function of the radius and a linear function of the axial co-ordinate, while the tangential velocity is a function of the radial co-ordinate only. Based on these results, a physical model is presented, where the flow field is divided in two zones. Zone I corresponds to the feed inlet, which occurs through a ring in the upper portion of the cylinder, the length of which depends on the length of the vortex finder tube. Zone II includes the rest of the cylinder. The axial symmetric solution of Reynolds equations for the isotropic turbulent flow leads to two sets of field equations, one for each zone in the hydrocyclone. In zone II, where experimental data were determined, simulation compares favourably with the flow pattern determined experimentally for water in a 100-mm flat bottom hydrocyclone.  相似文献   

13.
Liquid‐liquid two‐phase flows are encountered in several process industries, multiphase reactors and oil industries. In each of these applications, identification of flow patterns poses a challenging problem and many efforts are directed towards developing suitable devices for this purpose. In the present work, attempts have been made to use pressure gradient and transient pressure signals to study flow patterns during the simultaneous flow of two liquids through a horizontal pipe. It is observed that the slope of the pressure gradient curves as a function of fluid superficial velocities is a weak function of the flow pattern. However, the variation of the slope with the pattern transition is much more significant when the pressure gradient is normalized with respect to only kerosene flow through the pipe (ΔpTPpKO). Further attempts have been made to identify flow patterns from transient pressure signals and the statistical analysis of these random signals has been undertaken. The PDF analysis and the wavelet multiresolution technique have been adapted to explain the signals in detail. The flow regimes identified are smooth stratified, wavy stratified, plug flow, ‘three‐layer' flow, ‘oil dispersed in water and water' and ‘oil and water in oil' flow patterns. The signal characteristics are depicted for each flow pattern.  相似文献   

14.
A theoretical model is developed to predict the time‐dependent behaviors of “flow burst” and centrifugal capillary flow in Lab‐on‐a‐CD systems. Enabling the calculation of flow field, flow burst, and flow timing as a function of fluid properties and system specifications, the model is a useful design tool for understanding and controlling flow behaviors in Lab‐on‐a‐CD devices. More importantly, the model shows great promise in the development of a new method for digital chemical analysis.  相似文献   

15.
朱恂  辛明道 《化工学报》2004,55(7):1060-1065
微三角形截面通道是现代工程实际应用中常涉及到的流动通道.针对微三角形槽道利用正交函数法求解了滑移流区内带温度跳跃边界条件的能量方程,对不可压缩气体在微三角形槽道内充分发展层流滑移流动的换热特性进行了理论分析,获得了轴向定热通量加热、周向均匀壁面温度条件下微三角形槽道内的温度分布和换热特性的分析解.计算结果表明:正交函数法适用于微三角形槽道内滑移流动换热特性的分析计算;在滑移流区,微三角形槽道内的平均Nusselt数随Knudsen数的增加而减小,其随高宽比变化的分布曲线随Knudsen数的增加而平行下移,Nusselt数比随Knudsen数的变化关系基本不受高宽比的影响.  相似文献   

16.
Modifications were made to the Packed Bed Reactor Experiment (PBRE) and flown on the International Space Station as PBRE-2 to eliminate external pressure oscillations at higher liquid flow rates and the packing diameter was reduced to increase the pressure gradient for lower flows. It is found that gas hold-up is a function of bed history at low liquid and gas flow rates whereas higher gas hold-up and pressure gradients are observed for the test conditions following a liquid only pre-flow compared to the test conditions following a gas only pre-flow period. Over the range of flow rates tested, the capillary force is the dominant contributor to the pressure gradient, which is found to be linear with the superficial liquid velocity but is a much weaker function of the superficial gas velocity and varies inversely with the particle diameter.  相似文献   

17.
Due to increasing demand for alternative fuels and theneed to reduce dependence on fossil fuels, the growth of bioethanol production has been rising. One of the problems facing this industry is transportation of the coproduct dried distillers grains with solubles (DDGS) over long distances, because caking and agglomeration between particles can lead to bulk flow problems. In this study, DDGS was prepared by combining condensed distillers solubles (CDS) and distillers wet grains (DWG) and then oven drying to achieve 8% (db) moisture content. The effects of drying temperature (100, 200, and 300°C) and CDS (10, 15, and 20%wb ) level on the resulting flowability behavior of the DDGS particles were investigated. Statistical analyses indicated significant differences (α = 0.05, 95% confidence level) due to drying temperature and CDS main effects and significant interaction effects between CDS level and drying temperature for many of the flow parameters. Surface regression analysis of the ratio of total flow index/Jenike flow function as a function of CDS and drying temperature resulted in an R 2 value of 0.94. Partial least squares (PLS) regression yielded an R 2 of 0.90 for the Jenike flow function index as a function of all flow and physical properties using only two multivariate components. Understanding the effects of varying drying temperatures and CDS levels can help guide efforts to overcome DDGS flowability problems.  相似文献   

18.
转化过程气体换热器的副线调节性能:操作气量的影响   总被引:2,自引:2,他引:0  
丁华 《硫酸工业》1999,(6):15-19
以转化过程中采用的圆缺形折流板和双圆缺形管束排列的管壳式气体换热器,推导出操作气量负荷率,管壳程副线率与换热面积富裕系数之间的定量解析关系式,它们仅是换热器管壳各进出口温度的函数。副线调节的灵敏性以调节管程及温差大的流体走管程为最佳,操作气理负荷率所对应的换热器相对压降与副线调节方式及流体走法无关。  相似文献   

19.
New experimental data for air–water flow in a horizontal square cross‐section channel (H = 24.25 mm) is presented, including data on liquid hold‐up, gas and liquid velocities, and wave velocities and frequencies. For the majority of gas and liquid flow rates studied, the regime observed was pseudo‐slug. Using visualization studies it was possible to identify wavy‐stratified and pseudo‐slug flows. For the pseudo‐slug regime new correlations were obtained for liquid hold‐up, for gas and liquid velocities as a function of the ratio between gas and liquid mass flow rates, and for the frequency of roll‐waves as a function of gas and liquid mass flow rates.  相似文献   

20.
气体在任意截面形状微尺度槽道中的滑移流动   总被引:2,自引:2,他引:0       下载免费PDF全文
朱恂  辛明道  廖强 《化工学报》2003,54(7):902-906
利用正交函数法对气体在具有任意截面形状的微尺度槽道内的充分发展层流滑移流动特性进行了理论分析,获得了任意截面形状微槽道内的速度分布和流动阻力特性的分析解,并以矩形微槽为例分析了微槽截面上的速度分布和阻力特性.结果表明:随Kn数的增加,由于壁面处滑移流动的影响,气体流经微槽的流动阻力常数小于大尺度理论预测值;理论分析解的结果与实验结果吻合较好,表明在一定的Kn数范围内Navier-Stokes方程在考虑了速度滑移后可以描述微通道内的气体流动过程;正交函数法在微槽内滑移流动的分析中是可行的.  相似文献   

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