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从实验和理论上对撞击流浓缩器(ISC)进行了研究。实验主要研究了空气进口温度、空气进口流量、液滴加速管的长度对ISC容积蒸发系数的影响。研究结果表明:ISC的容积蒸发系数随空气进口流量的增加、空气进口温度的升高而增大;并证明,宜使用较短的加速管。在理论分析的基础上建立了ISC浓缩溶液的理论模型,借助基于该模型的数值计算,模拟了ISC内液滴的蒸发过程,通过与实验值的比较证明了模型的正确性。 相似文献
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对喷嘴间距与喷嘴直径比为0.5~100范围内两喷嘴对置撞击流径向射流的湍流脉动特征、速度分布和扩展率等进行了实验研究和数值模拟。研究结果表明,撞击流径向射流明显较自由射流湍动强烈;从驻点开始径向射流速度逐渐增大到最大值后开始衰减,射流呈现自相似性;随着喷嘴间距增大,撞击流径向射流的扩展率呈现增大的趋势,大约为自由圆射流的1.5~3倍。采用CFD软件对撞击流径向射流的速度分布特征进行了数值模拟,与实验结果相比,两方程湍流模型预报的撞击流径向射流的扩展率明显偏小,雷诺应力模型的预报精度有较大改进。 相似文献
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采用大涡模拟对35≤Re≤145000、4≤L/h≤40范围内的平面撞击流偏斜振荡特性进行了研究。通过对平面撞击流模拟与实验结果的比较验证了数值模拟的可靠性,重点考察了不同流体介质、边界受限程度及喷嘴出口高宽比等因素对平面撞击流偏斜振荡特性的影响,并对平面撞击流发生偏斜振荡的量纲1参数范围进行划分。研究结果表明,不同流体介质对平面撞击流量纲1偏斜振荡周期几乎没有影响,量纲1偏斜振荡周期随着边界受限程度的增大而增大,随着喷嘴出口高宽比的增大而减小。 相似文献
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将直接模拟Monte Carlo(DSMC)方法应用于颗粒数目庞大的大规模气固两相撞击流的数值模拟研究,旨在解决基于拉格朗日法模型难以模拟含大量颗粒碰撞的多相流问题,建立了气固两相撞击流的数理模型。应用所建立模型计算分析了撞击流中的气相流动、颗粒运动、颗粒及颗粒碰撞位置分布;并对模型中考虑颗粒碰撞和不考虑颗粒碰撞时,计算获得的颗粒运动行为、停留时间以及对气相的影响等结果进行了对比分析。结果表明:经发展,DSMC方法能够有效地应用于大规模气固两相撞击流的数值研究;颗粒运动区域可分为颗粒碰撞区、颗粒射流区和颗粒发散区;颗粒碰撞主要发生在颗粒碰撞区内,使得颗粒在该区域富集,且明显缩短颗粒在撞击区的停留时间;在所研究的较小固气比条件下,颗粒的存在对气相流动的影响不显著。 相似文献
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提出一种集撞击流、超高压和微通道三者优势的新方法,超高压提供动力,颗粒在微通道中保持能量集中,受剪切力的作用得到初步粉碎细化,从微通道喷出的两股高速流体相互撞击,颗粒被进一步粉碎、分散。根据新方法设计了超高压微通道撞击流发生器,从模拟、理论和实验3个方面对结果进行了研究,成功制备了微纳米颗粒。 相似文献
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利用实验与数值模拟方法对动态阶跃型撞击流反应器流场特性进行研究,分析不同入口速度条件下流体流动规律、湍流特性以及能量水平。结果表明,动态阶跃型入口条件下,撞击面在两喷嘴之间周期性移动,流动参数也会发生周期性变化。随着入口平均速率的增大,驻点速度逐渐增大;随着两喷嘴入口速率差的增加,撞击面移动速度加快,撞击区流体湍流强度逐渐增加;随着入口平均速率与入口速率差的增大,XOZ平面在一个周期内的平均湍动能逐渐减小。对比动态撞击流反应器与稳态撞击流反应器内流场特性,探究动态入口条件对撞击流反应器流场特性的影响。结果表明,动态阶跃撞击流反应器湍流黏度、湍流强度和湍动能等参数均明显高于稳态撞击流反应器,撞击轴线上的湍动能梯度分布大于稳态撞击流反应器。动态入口条件下撞击流反应器流体湍动更剧烈,能量水平更高,有利于增加流场内流体扰动与促进混合。 相似文献
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Some results of our fundamental research on drying processes are summed up in this article. It consists of three parts: (1) Multistage fluidized bed drying, including particle flowing characteristics, heat and mass transfer between particles and drying medium, drying characteristics of drying materials; (2) Impinging stream drying, the flowing and drying characteristics of a vertical impinging stream dryer, one-stage and multistage semi-circular impinging stream dryer and combined vertical and semi-circular impinging stream dryer are discussed; (3) The effects of rapid transient heat and mass transfer on drying processes, such as time and space scales for nonFourier or nonFickian and influence of extreme heat and mass transfer are also discussed. 相似文献
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This paper illustrates the use of numerical simulation models for evaluating the performance of a moving bed dryer. A finite-volume method is employed in developing a steady state, two-dimensional numerical model for a double-deck conveyor dryer. Using this numerical model, variations in the product moisture content and temperature along the length and across the height of the product beds are predicted. Similarly, the resulting variations in the temperature and relative humidity of the drying air are predicted in the entire two-dimensional domain of a dryer. Effect of air-to-product mass flow ratio and product residence lime on the average moisture content of the outgoing product are also evaluated for three different drying air temperatures. 相似文献
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《Drying Technology》2013,31(1-2):145-164
Abstract Some results of our fundamental research on drying processes are summed up in this article. It consists of three parts: (1) Multistage fluidized bed drying, including particle flowing characteristics, heat and mass transfer between particles and drying medium, drying characteristics of drying materials; (2) Impinging stream drying, the flowing and drying characteristics of a vertical impinging stream dryer, one-stage and multistage semi-circular impinging stream dryer and combined vertical and semi-circular impinging stream dryer are discussed; (3) The effects of rapid transient heat and mass transfer on drying processes, such as time and space scales for nonFourier or nonFickian and influence of extreme heat and mass transfer are also discussed. 相似文献
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AbstractThis article presents the results of numerical simulation and experimental study of a multi-pin electrohydrodynamic (EHD) dryer. Combined effect of EHD flow and the external air cross-flow on drying performance was investigated with 3-D numerical model, which accounts for electric field, electric charge transport, external air cross-flow and material-gas moisture transport. Effect of cross-flow air stream on drying was positive in the range of low velocities, changing to negative at high velocities due to counteracting with EHD flow. Numerical simulation predicted previously unknown effect of EHD flow on the cross-flow air stream, which was quantified as an increase of airway resistance. This prediction was fully validated by experiments. Both numerical simulation and experiment proved that for given intensity of EHD flow there is an optimum value of the cross-flow, resulting in maximum drying performance. The numerical model can be applied to determine the optimal operating parameters for multi-pin EHD dryer. 相似文献
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ABSTRACT This paper illustrates the use of numerical simulation models for evaluating the performance of a moving bed dryer. A finite-volume method is employed in developing a steady state, two-dimensional numerical model for a double-deck conveyor dryer. Using this numerical model, variations in the product moisture content and temperature along the length and across the height of the product beds are predicted. Similarly, the resulting variations in the temperature and relative humidity of the drying air are predicted in the entire two-dimensional domain of a dryer. Effect of air-to-product mass flow ratio and product residence lime on the average moisture content of the outgoing product are also evaluated for three different drying air temperatures. 相似文献
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Patiwat Khomwachirakul Sakamon Devahastin Somchart Soponronnarit 《Drying Technology》2016,34(4):403-419
Impinging stream dryer (ISD) is an alternative for drying high-moisture particulate materials. Due to the complex multiphase transport phenomena that take place within an ISD, use of a reliable computational model instead of a tedious experimental route to aid the design of the dryer is desirable. In the present study, computational fluid dynamics were used in combination with the discrete element method (CFD-DEM) to predict, for the first time, the multiphase transport phenomena within a coaxial ISD; results from a model that does not consider particle-particle interactions (CFD) were also obtained and compared with those from the CFD-DEM model. In all cases, high-moisture particles having negligible internal transport resistance were assumed. Both models were used to simulate the gas-particle motion behavior, particle mean moisture content, particle mean residence time, and particle residence time distribution. The simulated results from both models were compared with the experimental data whenever possible. The results showed that the CFD-DEM model could be utilized to predict the particle motion behavior and led to more physically realistic results than the CFD model. The CFD-DEM model also gave predictions that were in better agreement with the experimental mean particle residence time and moisture content data. 相似文献
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Wojciech Sobieski 《Drying Technology》2013,31(12):1331-1343
This article discusses the key aspects of developing a simulation model of a spouted bed grain dryer for an analysis of fluid dynamics. The following aspects have been analyzed: selection of computational space, type of geometry and computational grid, configuration of the mathematical model (based on the Eulerian multiphase model) through the selection of “closures,” turbulence modeling, the simulation model's sensitivity to changes in phase and flow parameters, as well as the configuration of numerical parameters. The presented study makes reference to an earlier experiment carried out by the author, and it sums up the author's previous work in the modeling of a spouted bed grain dryer. This article presents a synthetic overview of the problems that are frequently encountered in the process of developing simulation models of a spouted bed grain dryer and proposes several solutions. 相似文献
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