补充风对水平管高压密相气力输送影响的模拟研究

针对水平管高压密相气力输送数理模型的缺陷与不足,引入Savage径向分布函数修正的颗粒动理学理论、基于Berzi摩擦压应力模型构建的摩擦应力模型以及修正的三段式曳力模型,在欧拉-欧拉方法的基础上建立了一个能同时兼顾水平管高压密相气力输送中稀相流、过渡流以及密相流输送特性的三维非稳态数理模型。并采用该数理模型考察了补充风对水平管高压密相气力输送的影响,模拟结果精准地预测了水平管压降及其随补充风的变化规律,而且其预测的水平管固相体积浓度分布与ECT图也是相吻合的,从而验证了数理模型的可靠性。模拟结果表明：随着补充风的增加,气固两相速度和湍动能以及颗粒拟温度增大,固相体积浓度减小。     

基于Aspen Plus的煤粉高压气力输送压降研究

为研究煤粉高压气力输送的管道压降,对Aspen plus中气力输送模型的原理及应用进行了详细介绍,首先用Aspen Plus对纯气相压降进行了模拟计算,回归出气相摩擦因子,气相压降模拟值与实测值误差在10%以内,然后在气相压降计算准确的基础上,对DN10 mm、DN15 mm及DN25 mm三种不同管径的气固两相流压降进行模拟计算,回归出颗粒摩擦系数,气/固两相压降的模拟值与实测值误差在30%以内,最后对输送压力(g)为7 MPa的超高压气/固两相流压降进行了预测分析。     

表观气速对密相气力输送流型影响的模拟研究

针对目前密相气力输送数值模拟关于流型演变方面所存在的问题,提出了一种基于颗粒所在局部空间的固相浓度及颗粒群运动特征来描述颗粒间相互作用的数学模型。该模型能够对气力输送,甚至是颗粒发生大量堆积情况下的密相输送进行数值模拟,使得长期以来缺乏有效模型对密相输送流型进行数值模拟研究的问题得到一定解决。利用该模型,对水平管中煤粉高压密相气力输送的颗粒流动过程进行了数值模拟,获得了输送过程中管道内所发生的气固两相之间的分离、沉积现象,展现了沙丘流及栓塞流等流型的演变特征,模拟结果与实验观察到的现象吻合较好,从而进一步验证了新数学模型的有效性。此外,通过对不同表观气速下固相流态分布的定量分析,揭示了输送流型变化的一些内在规律。     

竖直上升管中密相气力输送压降特性

研究了内径20 mm的竖直上升不锈钢管道中粉煤密相气力输送单位管长压降随输送参数的变化规律,并得到了Zenz相图。结果表明,在实验操作范围内管道压降主要由固相自身静压降和固相摩擦压降组成,气相产生的压降不超过总压降的1%;固相体积分数是影响压降变化的主要因素,并讨论了粉煤流速以及固相体积分数对固相静压降和摩擦压降的影响规律;考察了粉煤流速和固相体积分数对固相摩擦系数的影响,对实验数据拟合得到了固相摩擦系数的关系式,计算结果与实验值吻合较好。     

文丘里管收缩段高固气比气固两相流压降模型

为建立高固气比(10 kg/kg相似文献   

亚格子湍动能模型及循环流化床气固湍流特性分析

以气相大涡-颗粒相二阶矩双流体模型为框架,基于单相流亚格子湍动能推导方法,考虑固相影响推导气相亚格子湍动能方程,建立了适用于气固两相流动的气相亚格子湍动能模型;同时考虑气相亚格子湍动能与颗粒相速度脉动二阶矩之间的脉动能量传递,补充了气固相间脉动能量作用模型。模拟了循环流化床内气固两相湍流流动过程,模拟结果与实验数据吻合较好,并较未考虑湍流模型的模拟结果更接近实验值。比较了不同亚格子湍流模型对颗粒运动的影响,与Smagorinsky亚格子涡黏模型相比,亚格子湍动能模型能够更好地模拟两相流的湍流特性。分析了气体表观速度对湍流作用的影响。研究表明,随着气体表观速度的增加,气相亚格子湍动能和亚格子能量耗散逐渐增加,径向分布的非均匀性增强。     

旋流燃烧室内气体-颗粒两相湍流流动的数值模拟

综合应用代数Reynolds应力模型和流体相脉动速度大小和方向均具有随机性的颗粒相随机轨道模型,对旋流燃烧室内有直流射流与旋转射流相互作用的气-固两相湍流流动进行了数值模拟.得到的气相轴向与切向速度和轴向脉动速度均方根值分布以及颗粒相轴向总质量流通量和轴向与切向速度分布与实验基本相符合,并比对气相湍流采用k-ε模型的相应计算结果有较明显的改进.     

直接模拟蒙特卡罗方法研究循环流化床内颗粒聚团的流动

采用直接模拟蒙特卡罗方法(DSMC)模拟颗粒间的碰撞,用Lagrangian方法计算颗粒的运动.采用考虑颗粒脉动流动对气相湍流流动影响的大涡模拟(LES)研究气相湍流.数值模拟垂直管道内气固两相上升流动,对管内气相速度和颗粒相速度、浓度,以及聚团流动进行分析,得到气固两相上升流中颗粒流动的有关信息.     

考虑颗粒间碰撞的稠密气/固流动二阶矩两相湍流模型

将统一二阶矩两相湍流模型和颗粒动力学理论结合,推导并封闭了稠密两相流考虑颗粒间碰撞的统一二阶矩两相湍流模型.该模型用颗粒动力学理论模拟颗粒之间的碰撞,用各向异性的统一二阶矩模型考虑气相和颗粒相的湍流脉动,并用输运方程描述气固两相湍流之间的相互作用.最后用该模型对狭窄槽道内的气粒两相流动进行了模拟,模拟所得的颗粒水平方向和垂直方向的雷诺应力和实验结果吻合良好.结果表明,考虑颗粒间碰撞之后,颗粒水平方向雷诺应力的预报得到了明显改进.     

用于四氯化钛生产的复合式气力输送反应器的一维模拟—I. 数学模型

复合式气力输送反应器是一种将提升管和多颗粒气力输送床串联使用的新型反应器,其中多颗粒气力输送床是由循环床叠加在密相湍床上形成的,适合于所需单程反应时间较长且需颗粒间、气固间作用力较大-防粘结、提高传质效率等的气固反应体系. 本工作用一维流化床反应器模型研究了用于四氯化钛生产的复合式气力输送反应器的反应性质,其中气体成分在泡相和乳相间的扩散速率通过气泡聚并模型进行计算并用粒子数平衡模型(Population balance)模拟颗粒沿轴向的粒径分布变化. 该模型可以同时获得反应温度、床内颗粒组成、气体成分、颗粒扬析量、反应效率等对生产非常重要的指标参数.     

Three‐Dimensional Numerical Simulation of Dense Pneumatic Conveying of Pulverized Coal in a Vertical Pipe at High Pressure

A two‐fluid model based on the kinetic theory of granular flow was used to study three‐dimensional steady state flow behavior of dense phase pneumatic conveying of pulverized coal in a vertical pipe, where the average solid concentration ranges from 11 % to 30 %, and the transport pressure ranges from 2.6 Mpa to 3.3 Mpa. Since the solid concentration is rather high, a k–?–k_p–?_p model which considers the turbulence interaction between the gas and particle phase, was incorporated into the two‐fluid model. The simulation results including profiles of gas and particle phase axial velocity, profiles of solid concentration, profiles of the turbulence intensity of the particle phase, as well as the value of the pressure gradient were reported. Then, the influences of solid concentration and transport pressure on the flow behaviors were discussed. The experiment was also carried out to validate the accuracy of the simulation results which showed that the predictions of pressure gradient were in good agreement with the experimental data. Simulation results indicate that the location of maximal solid concentration deviates from the pipe center and the deviation becomes more obvious with the solid concentration increasing, which is analogous to the phenomenon in the liquid/solid flow. Besides, pressure gradient declines as the transport pressure decreases, which is validated by experiment described in the paper. Moreover, the analysis indicates that it is necessary to consider the turbulence of particles for the simulation of dense phase pneumatic conveying at high pressure.     

Numerical simulation on dense phase pneumatic conveying of pulverized coal in horizontal pipe at high pressure

A kinetic–frictional model, which treats the kinetic and frictional stresses in an additive manner, was incorporated into the two fluid model based on the kinetic theory of granular flow to simulate three dimensional flow behaviors of dense phase pneumatic conveying of pulverized coal in horizontal pipe. The kinetic stress was modeled by the kinetic theory of granular flow, while the friction stress is from the combination of the normal frictional stress model proposed by Johnson and Jackson [1987. Frictional–collisional constitutive relations for granular materials, with application to plane shearing. Journal of Fluid Mechanics 176, 67–93] and the modeled frictional shear viscosity model proposed by Syamlal et al. [1993. MFIX documentation and theory guide, DOE/METC94/1004, NTIS/DE94000087. Electronically available from http://www.mfix.org], which was modified to fit experimental data. For the solid concentration and gas phase Reynolds number was high, the gas phase and particle phase were all treated as turbulent flow. The experiment was carried out to validate the prediction results by three kinds of measurement methods. The predicted pressure gradients were in good agreement with experimental data. The predicted solid concentration distribution at cross section agreed well with electrical capacitance tomography (ECT) image, and the effects of superficial velocity on solid concentration distribution were discussed. The formation and motion process of slug flow was demonstrated, which is similar to the visualization photographs by high speed video camera.     

Resistance Properties of a Bend in Dense‐Phase Pneumatic Conveying of Pulverized Coal under High Pressure

Experiments of high‐pressure dense‐phase pneumatic conveying of pulverized coal with different mean particle sizes using nitrogen were carried out in an experimental test facility with a conveying pressure of up to 4 MPa. The effects of three representative operating parameters (solids‐to‐gas mass flow ratio, conveying pressure, mean particle size) on the total pressure drop were examined. The pressure drops across the horizontal and vertical bends were analyzed by experimental and analytical calculation. The results show that the pressure drop due to gas friction is of much less significance, while the pressure drop due to the solids friction component of the total pressure drop dominates. There exists a relationship between the pressure drop due to solids kinetic energy loss and mass flux of solids.     

Coupled DEM‐CFD Simulation of Pneumatically Conveyed Granular Media

A DEM‐CFD coupling for the simulation of gas‐solid flows was successfully implemented and simulations were performed for the application to industrial‐scale pneumatic conveying. Therefore, all particle collisions and phase interactions were considered and porosity determination was optimized. The aim of this work is to show the applicability of the presented simulation model to the different regimes of pneumatic conveying systems. As a first test case a dense vertical pneumatic conveying system was chosen and an individual plug was investigated in detail. Variations of the conveying air velocity were also considered. As a second test case dilute conveying in a horizontal‐to‐vertical pipe bend was simulated. The occurrence of roping and the reduction of particle velocity is of high interest for the design of specific pneumatic systems. It is shown that both regimes can be captured reasonably well and the results are rich in details.     

Study of the pressure drop of dense phase gas-solid flow through nozzle

Pressure drops are measured on different nozzles of various pipe sizes in dense phase pulverized coal pneumatic conveying. From the experimental results, we conclude that the effect of the gas phase nozzle pressure drop is negligible when comparing with the solid phase pressure drop in the experimental range. The main influence factors contributing to the nozzle pressure drop are gas and solid mass flow rate, solids loading ratio, and the diameters of the nozzle inlet and outlet. A new model was developed to predict the nozzle pressure drop in dense phase pneumatic conveying of pulverized coal based on the Barth's pneumatic conveying theory. The pressure drop predictions from the model are in good agreement with the experimental values. The model quantified the important influence factors of the nozzle pressure drop.     

HHT analysis of electrostatic fluctuation signals in dense-phase pneumatic conveying of pulverized coal at high pressure

Particle charging generated by particle-wall, particle–particle and particle–gas contacts in pneumatic transport pipelines contain rich information on gas–solid flow hydrodynamics. In this paper, experiments were performed in a dense phase pneumatic conveying system, and electrostatic fluctuation signals were detected by a ring-shape electrostatic sensor that is based on electrostatic induction theory. Power spectrum analysis and Hilbert–Huang transform (HHT) were applied to the electrostatic fluctuations, namely outputs of the electrostatic sensor, to extract and characterize the intrinsic features of dense-phase gas–solid flow. Results show that the dominant peak of the power spectrum of the electrostatic fluctuations moves toward higher frequency with the increasing gas superficial velocity. The Hilbert–Huang transform reveals the non-linear and non-stationary intrinsic nature of the electrostatic fluctuations. By using the non-linear and non-stationary signal processing method (HHT), non-linear inter-modulation characteristics in the dense phase gas–solid flow were analyzed, and the relations between the energy distribution transmissions in intrinsic mode functions (IMFs) with different orders and the flow characterization of the dense phase gas–solid flow, was investigated as well, which can represent the behavior, stability and regime transitions of the gas–solid flow in the dense-phase pneumatic conveying system at high pressure.     

离散单元法数值研究水平管中密相栓流气力输送

在对密相栓流气力输送过程中气固两相运动的特点和气固两相流的数值模拟方法进行分析的基础上,将广泛应用于岩土力学中的离散单元法引入以模拟多个颗粒之间长时间的相互作用,同时考虑颗粒与流体间的相互作用(双向耦合),建立了密相栓流气力输送过程中两相流的数学模型.对多个栓的密相栓流气力输送过程进行数值模拟,结果再现了栓的滑落、形成和运动过程,与实验观察到的现象基本一致,预示离散单元法在密相气固两相流数值模拟研究中具有广阔的应用前景,为密相栓流气力输送的进一步研究提供了基础.     

Signal modelling and algorithms for parameter estimation in pneumatic conveying

Capacitive measurement principles offer a non-invasive approach to determine particle velocity as well as particle concentration in pneumatic conveying. In order to assess the quality of a reconstruction method, it is mandatory to know the prevailing velocity and concentration profiles. For particulate bulk solids transportation, accurate reference systems are either not available or very expensive. Based on measurement data, a signal model of the particle flow is developed for dilute phase and dense phase conveying. These models are used to demonstrate the applicability of proposed algorithms for parameter determination — a cross-correlation technique for dilute phase and a two-step approach using the Fourier transform for dense phase.