共查询到17条相似文献,搜索用时 218 毫秒
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本文采用实验研究与数值模拟相结合的方法,研究了冰浆在水平直管内流动过程中冰晶粒径的分布及其演化规律。通过CFD-PBM耦合模型模拟研究冰浆在不同过冷度、流速、含冰率下冰晶粒径分布及其演化规律,并通过实验对数值模拟结果进行验证。结果表明:在含冰率为15%的冰浆管道入口处,冰晶粒径数量密度分布均近似高斯分布;随着冰浆流速和含冰率的增加,沿流动方向中心轴的冰晶平均粒径增大,截面冰晶粒径分布越不均匀;流速越小、含冰率越大,冰晶粒径的长度数量密度分布曲线的峰值升高,峰值所对应冰晶粒径的平均值减小。 相似文献
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冰浆是一种有效的空调蓄冷和输送冷量的介质,有着广阔的应用前景,而冰浆的流动特性和传热性能又是将冰浆介质应用于实际工程的最为重要的基础资料。在对冰浆流体的换热情况做出一些假设的前提下,利用等效比热描述冰晶粒子融化吸收潜热,建立了管内湍流冰浆的传热模型。运用有限差分的方法,对所得的离散方程进行了求解,从而得到了定热流状态下圆管内湍流冰浆流体的传热特性。计算数据表明,随着含冰率和流速的增大,对流换热系数增大,换热性能得到加强。 相似文献
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《制冷与空调(北京)》2016,(11)
冰浆在实际中的应用大多是先通过管道输送的方式到达需要冷却的地方进行热交换,研究输送过程中的流动换热特性对改善其实际应用效果具有重要意义。流动压降主要受到含冰率、冰粒直径、黏度、流速以及管径、管长和管道形状的影响。水平直管是最简单的管道形式之一,目前国内外学者研究方法主要是结合试验方法和数值模拟对已有的理论模型进行修正,尚未有统一的理论模型。本文采用数值模拟的方法,在双欧拉流体理论模型和相变换热基础上,定性分析流动过程中的压降受管径、含冰率、流速和管长的影响,并且在考虑冰晶和水两相相变的情况下,得到直管横截面上冰晶的分布情况。 相似文献
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冰浆流体流动与换热研究综述 总被引:4,自引:0,他引:4
介绍了冰浆流体的特点、应用以及固液两相流体等效比热的概念及其在冰浆流体中应用的困难;概述目前国内外冰浆流体的传热性能、流变模型和流态以及粘性和流动阻力的研究成果,指出由于固液两相密度的不同导致了在不同流速下冰水分层的现象;同时对冰浆流体的的研究进行了综述,最后提出了关于冰浆流体的进一步研究建议. 相似文献
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本文采用以颗粒相动力学为基础的Euler-Euler模型,利用FLUENT研究冰浆在水平直管、90°弯管和T型管中的流动压降特性(计算过程不考虑相变)。模拟结果显示,在管道入口处压降较明显,90°弯管拐弯后内侧压力小于外侧,T型管在分流直角拐角处出现压力最高点和最低点。冰浆流动实验发现,冰浆单位压降随流速和含冰率的增加而增大,且3种管型中直管压降最小,T型管压降最大。对比实验与模拟结果,单位压降随流速的变化趋势一致,且误差在20%以内,但在大流速时,模拟值大于实验值。 相似文献
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采用二维流体力学模型研究了多级直流弧放电装置中流速对处于局部热平衡状态下氢等离子体特性的影响.分析了氢等离子体中心轴线处电场和压强的分布情况;各粒子密度在通道中的分布状态;通道出口处等离子体温度以及电导率的分布情况.模拟结果表明,随着流速的增大,中心轴线处电场和压强均增大;通道中氢等离子体的各粒子密度变化很小;通道出口处等离子体温度以及电导率在出口处沿径向的分布影响不大. 相似文献
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Lingling Cai Zhiqiang Liu Sha Mi Chun Luo Kebo Ma Aixiang Xu Sheng Yang 《Advanced Powder Technology》2019,30(10):2299-2310
Elbow pipes are important components for ice slurry pipeline transport. However, the flow characteristics of ice slurry in elbow are far from fully being understood, especially the influence of ice particle kinetics on ice particle size distribution (PSD). This study is intended to provide a better understanding of the behavior of ice slurry flow in elbow pipe. A CFD-PBM coupled model is employed to investigate the flow characteristics of ice slurry in horizontal 90° elbow pipe. The quadrature method of moments is utilized to solve the population balance equations. Based on the revised model, the flow characteristics of ice slurry in the horizontal 90° elbow pipe are investigated. The simulation results show that in the range of calculations, the pressure drop of elbow pipe is increased with the increase of velocity and ice packing fraction (IPF). An adverse pressure gradient is formed due to the change in flow direction. The emergence of secondary flow is caused by the centrifugal force. It makes the ice particles gather on the outer wall of the elbow section. The ice diameter increases along the flow direction due to the aggregation. The evolution of particle size distribution (PSD) is not significant. However, aggregation and stratification cannot be ignored in the process of long distance transport of ice slurry. The results are of significance for guiding the safety design and operation of ice slurry transportation. 相似文献
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Experimental studies concerning the characterization of a dilute swirling gas-solid flow were carried out in a vertical pipe with a height of 12 m and an inner diameter of 80 mm. Polyethylene pellets, with mean diameter of 3.2 mm, were used as test particles. The initial swirl number varied from 0.0 to 0.94, the mean gas velocity varied from 9 to 25 m/s, and the solid-gas ratio varied from 0.2 to 0.7. In this study, the particle velocity and concentration profiles were measured by the photographic image technique for both nonswirling (axial) and swirling gas-solid flows. It was found that the particle velocity of the swirling flow is lower than that of the axial flow in the range of high gas velocity; however, high particle velocity in the former flow can be obtained in the range of low gas velocity. The particle velocity profiles, on the other hand, were found to be nearly uniform in both the swirling and axial flows. The particle concentration profiles in the swirling flow exhibited symmetric distributions with respect to the pipe axis, and a higher particle concentration appeared in the vicinity of the wall located in the acceleration region.
gas-solid two-phase flow particle concentration particle velocity pipeline swirling flow 相似文献
gas-solid two-phase flow particle concentration particle velocity pipeline swirling flow 相似文献
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《Advanced Powder Technology》2020,31(6):2285-2292
To reduce the power consumption of a horizontal-vertical pneumatic conveying system, an oscillator is mounted with a 45° oblique plane through the pipe axis in this study. This experimental study focuses on the effect of oscillatory flow using the oscillator on the horizontal-vertical pneumatic conveying system in terms of the overall pressure drop of the system, power consumption, local pressure drop, and particle velocity. Compared with conventional pneumatic conveying (axial-flow), the pressure drop and power consumption can be reduced using the oscillatory flow in a lower air velocity range. Meanwhile, the particle axial velocity of the oscillatory flow is higher than that of the axial-flow near the bottom of pipe. This outcome indicates that the accelerating effect of oscillatory flow is obvious near the bottom of the pipe, and the particle vertical velocity of the oscillatory flow is positive, whereas the particle vertical velocity of the axial-flow is almost negative. This result shows that the particles of the oscillatory flow are suspended sufficiently, but the particles of the axial-flow have a tendency of deposition. Furthermore, the fluctuation intensity of the particle velocity of the oscillatory flow is higher than that of the axial-flow, especially near the bottom of the pipe. 相似文献
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We investigated inhomogeneity in ice slurry, which can pose problems such as sudden increase in pressure drop and blockages in flow. Although in many previous studies fully dispersed ice slurry flow is assumed homogeneous, inhomogeneity appears as a variation in physical properties in the actual measurements. From experiments, it was found that the fluctuation in pressure drop is relatively small at the beginning, but becomes larger after long-term periods. Additionally, the ice particle size included in the ice slurry also affects this fluctuation. We supposed the fluctuation is caused by the variation in IPF, because it appears only in laminar flow. This implies ice slurry is not homogeneous after long flow periods. From the present study, the variation of IPF was estimated to be 2.6 wt% at maximum. Although the physical mechanism of the variation in IPF has not been clarified, we suggest that it is a consequence of the accumulation/adhesion of ice particles in the pipe. 相似文献
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Mathematical modeling of two phase flows, especially liquid–solid flows is very complex. Especially when a distribution of the solid phase in a carrier liquid is not homogenous but heterogeneous or even when a moving or stationary bed occurs. In this case, the rheological characteristics of suspension are changing and affect transport characteristics. Therefore, the slurry flow may present a Newtonian and non-Newtonian fluid as well, depending on the operation characteristics. In this paper the fully suspended ice-slurry flow in a horizontal pipe is analysed. The model allows us to avoid the definition on what kind of fluid ice-slurry is present. For the taken ice-particle diameter, the ice-concentration profiles depending on various average velocities and pipe diameters are shown. The viscosity of the ice-slurry is presented, depending on average concentration, velocity, pipe diameter and ice-particle size. The results of the analysis have shown that the ice slurrys can be treated as Newtonian-fluid at higher average velocities, and lower average concentrations as well. As the ice concentration increases and velocity decreases the viscosity depends not only on the ice concentration but also on the average velocity and the pipe diameter. The ice-slurry behaves then as a non-Newtonian fluid. The results show also the area where the safe operation of an ice-slurry-district-cooling system can be performed. 相似文献
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Hiroyuki Kumano Tetsuo HirataYosuke Hagiwara Fumito Tamura 《International Journal of Refrigeration》2012,35(1):122-129
The effect of storage on flow and heat transfer characteristics of ice slurry was investigated experimentally. After ice slurry had been stored in the storage tank, variations in ice particle size were measured using a microscope, and diameter distribution and average diameter determined. The ice packing factor, Reynolds number and storage time were varied as experimental parameters. The pressure drop and heat transfer coefficient were measured when the ice slurry flowed in the horizontal tube. For laminar flow, the ratios of pipe friction and heat transfer coefficient decreased with storage time. For more than 12 h storage time, the ice slurry could not flow in the tube. The adhesion between ice particles seemed to cause a blockage in the tube. On the other hand, for turbulent flow, the pipe friction and ice slurry heat transfer coefficients were similar to that of the ethanol solution, and the storage effect was insignificant. 相似文献
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V. LangloisW. Gautherin J. LaurentL. Royon L. FournaisonA. Delahaye X. Jia 《International Journal of Refrigeration》2011,34(8):1972-1979
The development of ice slurry for refrigeration systems and the enhancement of its efficiency depend on an accurate control of the ice concentration. We present here an ultrasonic method capable to measure precisely the particle concentration in ice slurry. To calibrate the ultrasonic measurement, we first determine the sound velocity and attenuation in two model suspensions (glass beads/polyethylene glycol and polyethylene beads/vaseline oil) for different particle volume fractions. The experimental results show a good agreement with the predictions of the two-component models in the long-wavelength limit. Additionally, the sound attenuation reveals a clear signature of the aggregate formation in the nearly iso-dense suspension. We next conduct the measurement of the sound velocity in the polypropylene glycol ice slurry where the ice concentration changes with temperature. The ice concentrations extracted from our sound velocity measurements are well consistent with the values determined from the binary phase diagram. 相似文献