Effect of elevated temperature and silica sand particle size on minimum fluidization velocity in an atmospheric bubbling fluidized bed

The impact of temperature and particle size on minimumfluidizing velocity was studied and analyzed in a small pilot scale of bubbling fluidized bed reactor.This study was devoted to providing some data about fluidization to the literature under high temperature conditions.The experiments were carried out to evaluate the minimum fluidizing velocity over a vast range of temperature levels from 20℃ to 850℃ using silica sand with a particle size of 300-425μm,425-500μm,500-600μm,and 600-710μm.Furthermore,the variation in the minimumfluidized voidage was determined experimentally at the same conditions.The experimental data revealed that the Umf directly varied with particle size and inversely with temperature,whileεmf increases slightly with temperature based on the measurements of height at incipient fluidization.However,for all particle sizes used in this test,temperatures above 700℃ has a marginal effect on Umf.The results were compared with many empirical equations,and it was found that the experimental result is still in an acceptable range of empirical equations used.In which,our findings are not well predicted by the widely accepted correlations reported in the literature.Therefore,a new predicted equation has been developed that also accounts for the affecting of mean particle size in addition to other parameters.A good mean relative deviation of 5.473% between the experimental data and the predicted values was estimated from the correlation of the effective dimensionless group.Furthermore,the experimental work revealed that the minimum fluidizing velocity was not affected by the height of the bed even at high temperature.

Prediction of Minimum Spouting Velocity at Elevated Pressures and Temperatures

Minimum spouting velocity （Ums） is one of the most important flow characteristics for proper design and operation of spouted bed reactors. Many correlations for Ums have been published since spouted bed technology was initiated in 1955. In this paper, a new correlation is developed for Ums based on 767 published experimental data covering both high pressure and high temperature conditions. The calculated and the measured results of Ums are in better agreement than other published correlations.

Temperature influence on minimum fluidization velocity:Complexity,mechanism,and solutions

Fluidized-bed reactors are widely employed in various high-temperature industrial processes.Thus,it is crucial to understand the temperature effect on various fluidization phenomena,specifically the minimum fluidization velocity(U_(mf))that governs various aspects of fluidized bed behavior.In this study,we comprehensively analyze U_(mf) data from the literature to unravel the complexity and underlying mechanisms of temperature influence on this critical velocity.The research examines experimental data encompassing a wide range of temperatures,pressures,and solid particles.The analysis reveals that the influence of temperature on U_(mf) is fundamentally determined by the relative importance of hydrodynamic forces and interparticle forces within fluidized beds and is realized by three distinctive temperature-induced changes:gas properties,bed voidage,and physiochemical characteristics of particles.On this basis,an equation is derived to enable predictions of temperature influences on the minimum fluidization velocity under broad temperature conditions.

On the Existence of a Minimum Universal Speed of Physical Transmissions Associated with Matter Wave in Special Relativity

In this work, we show that it is possible to establish coordinate transformations between inertial reference frames in the theory of special relativity with a minimum universal speed of physical transmissions. The established coordinate transformations, referred to as modified Lorentz transformations because they have almost identical form to the Lorentz transformations, also comply with the requirement of invariance of the Minkowski line element. Particularly, the minimum universal speed can be associated with the phase speed of de Broglie matter wave. As application, we also discuss the possibility to formulate relativistic classical and quantum mechanics for the special relativity associated with the modified Lorentz transformations, which describes physical processes that represent an expansion or a collapsing of massive quantum particles.

点状热干扰源诱导的准各向同性高温超导股线失超特性

第二代高温超导带材因其较高的临界电流密度以及良好的机械特性,近年来在超导研究领域得到极大关注。由REBCO带材组成的高温超导导体在液氮温度下的零电阻特性使其在超导输电领域具有巨大的潜力。从安全角度看,高温超导导体的失超保护研究是其获得广泛应用的一个关键。该文建立了准各向同性超导股线的三维失超仿真模型,耦合了电场、磁场和温度场,模拟了不同运行电流以及不同点状热干扰能量下超导股线的失超行为,求解出股线的温度、电流密度以及磁场分布,得到了准各向同性高温超导股线的最小失超能(MQE)以及失超传播速度(QPV),对超导装置的失超保护具有重要意义。该文对准各向同性超导股线建立的三维失超模型,也可以应用到其他结构的高温超导导体的失超研究中。

网联环境下的交叉口信号配时与车辆轨迹联合优化方法

文中提出一种综合考虑交叉口信号配时和车辆轨迹的联合优化法.以车辆的原始轨迹为基础,以交叉口车辆通行时间最小化为信号控制优化目标,建立信号配时优化模型来计算最优的信号周期序列和相位时间,并根据相位时间划分车辆运动轨迹为到达交叉口停车线前的加速、匀速阶段,以及驶过交叉口停车线的加速、匀速阶段,在每个阶段获取最佳的车头时距和期望速度,优化车辆的原始轨迹.基于新的轨迹再次进行信号配时优化.以交通需求量、左转比率和信号周期时长作为考虑因素,进行SUMO仿真实验将所提出的联合优化法与实时信号控制方法进行比较.结果表明:联合优化法在不同的平衡交通需求量下能够提高交叉口通行能力30.5%;在随机交通需求量下能提高交叉口通行效率17.3%;而在不同的左转比率和信号周期时长情况下能提高通行效率66.6%和21.7%,验证了提出的联合优化方法提高线交叉口通行效率的有效性.

Performance analysis of a 2D numerical model in estimating minimum fluidization velocity for fluidized beds

The minimum fluidization velocity of a fluid-solid particle fluidized bed is the primary focus of this paper.The computationally economic Eulerian Granular model has been used to analyze fluidization for both gas-solid particle and liquid-solid particle fluidized beds.The conventional approach of finding minimum fluidization velocity(umf)is either with a pressure drop across the particle bed or the change in bed height.However,these parameters are often unstable and cannot be used to generalize the degree of fluidization accurately.In this paper,the dominant factor of unstable pressure drop estimation in the 2D Two-Fluid Model(TFM)and a key non-dimensional Euler number has been investigated in deter-mining minimum fluidization velocity for different quasi-2D fluidized beds for different bed sizes,par-ticle sizes,and particle numbers.Averaging assumptions and limitations of these numerical models are discussed in detail for four different fluidized bed cases.A comparative study of the drag model shows little to no influence in unstable pressure drop estimation near fluidization velocity,and all drag models perform similarly.It is observed that particle-particle collision is not the dominant reason for unstable pressure drop near minimum fluidization.Instead,wall effects on the particle bed including frictional losses and wall-particle collision play a key role in unstable pressure drop calculation for the quasi-2D fluidized beds.Pressure drop characteristics alone do not suffice to obtain minimum fluidization ve-locity with 2D TFM using existing models.Thus,a different approach has been proposed to investigate minimum fluidization involving the Euler number,which has shown promising performance in deter-mining minimum fluidization velocity and characterizing fluidization with 2D TFM.Results show con-sistency in Euler number characteristics for all different fluidized bed cases considered in this paper.This can revitalize computationally economic 2D Eulerian simulations,increase the range of possible appli-cations,and provide guidance to the future development of computationally efficient and more accurate numerical models,and empirical correlations for minimum fluidization velocity.

集输管道临界携液流速计算模型研究

为预防管道低洼处积液带来的生产安全问题,采用最小压降梯度模型和双流体模型确定临界携液流速,通过单因素实验模拟不同影响因素下的临界携液流速,并通过均匀实验设计获取因素间的交互作用强度,最终利用随机森林模型完成非线性数据回归和现场结果验证。研究结果表明,压力与临界携液流速呈幂函数关系,温度、管径与临界携液流速呈线性正相关,含水率、上倾角与临界携液流速呈对数关系;单因素中上倾角对临界携液流速的影响最大,其次为含水率和系统压力,二次项因素中系统压力和上倾角的交互作用最强;在20口气井集输管道的验证中,随机森林模型的符合率为90%,陈建磊模型、王旭模型的符合率分别为55%、65%,证明了随机森林模型可以用于临界携液流速的预测和判断。

辽宁地区最小一维速度模型研究

根据辽宁测震台网最近10年的观测资料,从中筛选出2851个地震事件的Pg、Sg走时数据,使用Velest程序,反演了辽宁地区P波和S波最小一维速度模型及台站校正值,并对震源位置进行了重新定位。结果显示走时数据方差和走时残差均方根分别下降70%和45%以上。台站校正的分布情况体现出辽宁地区地下介质的横向不均匀性。重定位后的震源位置更加集中,与震群和发震构造的对应关系更明显,平均震源深度为10.16 km。经过正负扰动测试和震源位置恢复性测试检验,证明此研究所得最小一维速度模型较为稳定并具备一定的可靠性。

基于速度概率分布的空投场空域容量理论模型研究

空投作为重要的资源补给手段,相对于传统陆水运输,可以高效安全地实现物资保障,其空域容量对空投计划的制定有着不可或缺的影响。目前对于空投场场景的空域容量理论研究较浅,首先研究分析空投场运行特点,结合空投场场景的运行、结构特征,提出了空投场空域容量定义;其次分析空投场运行中可能出现的航空器追赶情况,建立了空投场空域容量计算模型;最后,以某空投场为例,计算该结构下的空投场理论容量,通过蒙特卡洛仿真验证理论模型的可靠性。同时探究了航空器运行速度及小于最小安全间隔概率变化下空投场空域容量的变化规律。

无级变速拖拉机跃度最优化调速控制

针对无人驾驶拖拉机加减速导致的作业平稳性低和燃油经济性差等问题,该研究基于CVT(constantly variable transmission,无级变速传动)拖拉机,设计了一种基于贝尔曼最优性原理的最小跃度多项式局部速度规划算法。基于贝尔曼最优性原理和最优控制思想设计全局规划目标、局部规划目标及约束,提出基于最小跃度多项式的局部速度规划算法并开发速度跟随控制系统。田间试验表明,相对于无最优化调速技术的对照组,U型掉头的速度误差平均值和均方根分别降低42.31%和50.75%,加速度平均值与方差分别降低8.26%和16.36%,跃度平均值与方差分别降低7.65%和14.23%,发动机转速方差降低63.36%,发动机扭矩百分比方差降低60.26%,瞬时油耗方差降低71.25%,总油耗降低2.37%。直线行驶调速效果呈现相同趋势,与对照组相比,速度误差平均值和均方根分别降低9.45%和11.14%,加速度平均值与方差分别降低6.03%和13.68%。跃度平均值和均方根分别降低1.55%和3.59%。发动机转速方差降低31.78%,发动机扭矩百分比方差降低25.13%,瞬时油耗方差降低31.82%,总油耗降低2.48%。所提方法满足无级变速拖拉机无人驾驶速度平稳切换需要,并提高了燃油经济性。

2013年辽宁灯塔M5.1地震前小震序列震源机制一致性特征

从辽宁测震台网2012年1月1日至2022年7月10日的观测报告中筛选出36049条Pg震相走时数据,反演了辽宁地区最小一维P波速度模型。采用P波初动方法求解了2012年1月1日至2013年1月23日灯塔M 5.1地震发生前,震中附近M_(L)2.5~4.1地震震源机制解,并根据三角形图解分类方法进行了分类。计算了这些小震与灯塔M 5.1地震震源机制解的最小空间旋转角,通过分析其变化趋势,发现灯塔M 5.1地震前小震序列存在明显的震源机制一致性特征。

液-固流化床最小流态化速度的数值模拟与验证

为使用计算颗粒流体力学(CPFD)的数值模拟法代替实验法,建立单管的液-固两相流化床实验系统;实验测量5种颗粒的最小流化速度;应用CPFD方法对单管液-固流化床模型进行数值模拟,比较5种颗粒的最小流态化速度的实验值与模拟值,并进行误差分析,验证数值模拟方法的正确性。结果表明:5种实验颗粒的最小流态化速度实验值分别为0.0216、0.0367、0.0293、0.0555、0.0845 m/s;2种公式验算值与实验值的最大相对误差小于10%,平均相对误差小于5%,证明实验结果是可靠的;5种模拟颗粒的最小流态化速度模拟修正值分别为0.024、0.044、0.041、0.069、0.062 m/s;颗粒S_(1)、S_(2)、S_(4)、S_(5)的模拟修正值与颗粒E_(1)、E_(2)、E_(4)、E_(5)的实验值之间的最小流态化速度的误差分别为11.1%、19.9%、24.3%、26.6%,均为正向偏差且在工程允许范围内,证明CPFD数值模拟方法是可靠的;最小流态化速度随固体颗粒的密度和粒径的增大而增大。

Minimum spouting velocity of flat-base spouted fluid bed

Experiments were performed on spout characteristics of a cylindrical spout-fluidized bed （I.D. = 10 cm） with different static heights and two materials （A1203 and high density polyethylene）. Results of minimum spouting velocity obtained in this study were compared with reported correlations for both spouted and spout-fluidized beds. Considerable discrepancies were found between the values obtained using different model equations as well as with respect to experimental results. Based on the Mathur-Gishler correlation, a new correlation is proposed for calculating the minimum spouting velocity that introduces the ratio U/Umf. It was found that the minimum spouting velocity decreases with increasing fluidizing gas velocity （U/Umf）. The pressure drop at the point of minimum spouting velocity is also correlated using this dimensionless group and is presented in this work. This investigation demonstrates that the use of correlations reported in the literature that focus primarily on conical bottom spouted beds are not applicable to fiat-bottom spouted and spout-fluidized beds.

基于速度移动窗的最小熵法在GPR逆时偏移中的应用

速度是决定探地雷达(GPR)偏移成像分辨率的关键参数,基于图像最小熵与偏移相结合的方法通常将整体偏移剖面作为固定窗计算熵值曲线来估计介质速度,不但难以适用于介质非均匀分布情况,而且试速度过大或过小均会使双曲线绕射波的收敛位置溢出固定窗,降低估计精度。为此,本文利用试速度精确控制偏移剖面中的计算窗,提出了一种基于速度移动窗的最小熵法,并与逆时偏移相结合,估计最佳偏移速度。该方法通过试速度自动调整计算窗位置,可使双曲线绕射波收敛位置始终位于计算窗中心,从而获得稳定、准确的熵值曲线。将一条典型双曲线绕射波的固定窗和速度移动窗最小熵法的计算结果作对比,验证了速度移动窗的最小熵法的正确性和有效性。数值试验和实测数据测试表明:与固定窗最小熵法相比,速度移动窗的最小熵法可将双曲线绕射波收敛位置精确固定于计算窗中心,熵值曲线更稳定,计算量更小,偏移速度估计精度更高,逆时偏移成像效果更好。

Improved Minimum Detectable Velocity in Bistatic Space-Based Radar

Single orbit bistatic space-based radar （SBR） is composed of two radars in the same orbit. The characteristics of the clutter Doppler-angle spectrum of a single orbit bistatic SBR show that the slope of the mainbeam clutter spectrum is highly sensitive to the cone angles. Therefore, the minimum detectable velocity of the bistatic system is dependent on the cone angle. Then a new combined working mode of singleorbit bistatic SBR system was developed in which one radar will act as the transmitter and another as the receiver to improve detection performance for all angles. Simulation results by space-time adaptive processing verify the improved detection performance. The new design also reduces the average power of each radar system and the size and weight of the on-board solar array-battery system.

Effect of Pressure on Minimum Fluidization Velocity

在 0.5， 1.0， 1.5 和 2.0 MPa 的不同压力下面的石英沙和玻璃祷告的最小的使液化速度被调查。最小的使液化速度与增加压力减少。到最小的使液化速度的压力的影响比为更小的为更大的粒子是更强烈的。基于测试结果和 Ergun 方程，最小的使液化速度的一个经验方程被建议，计算结果比得上另外的研究人员鈥 ? 结果。

Modified correlation for minimum fluidization velocity of low-density particles in inverse liquid-solid fluidized beds

The minimum fluidization velocity(U_(mf))is a key parameter for the scale-up of inverse liquid-solid flu-idized beds.Theoretical predictions using common correlations were compared against experimental minimum fluidization velocity measurements of low density(28-638 kg/m^(3)),0.80-1.13 mm Styrofoam particles in a fluidized bed with a height of 4.5 m and 0.2 m diameter.The average absolute relative deviation for the predicted minimum fluidization velocity for particles below 300 kg/m^(3) was above 40%using the studied common correlations.A modified Wen and Yu correlation was thus proposed based on novel and past measurements with low-density and small-diameter particles,expanding the range for predicting U_(mf).The new correlation predicted U_(mf) with deviations below 15%for ST028,ST122 and ST300.This modified correlation also improved U_(mf) predictions for comparable particles from a previous study,demonstrating its validity for a larger range of low-density particles.

Effect of Gaussian size distribution width on minimum fluidization velocity in tapered gas–solid fluidized beds

This paper investigated the effect of Gaussian distribution width,average particle diameter,particle loading,and the tapered angle on minimum fluidization velocity(U_(mf))by conducting extensive experiments in tapered fluidized beds.Three powders with Gaussian size distribution and different distribution widths were used in the experiments.An increase in U_(mf)with increasing the average particle diameter,particle loading,and the tapered angle was observed.There was also a nonmonotonic behavior of Umf as the Gaussian distribution width increased.An empirical correlation including dimensionless groups for predicting Umf in tapered beds was developed in which the effect of distribution width was considered.The proposed correlation predictions were in good agreement with the experimental data,with a maximum deviation of 16.5%and average and standard deviations of,respectively,6.4%and 7.4%.The proposed correlation was also compared with three earlier models,and their accuracy was discussed.

生物质与煤混合颗粒流化特性的实验研究

在 D1 1 5 mm× 1 0 0 0 mm有机玻璃制成的圆柱型流化床中 ,对玉米秆、稻秆、煤及其混合物的流化特性进行了实验研究 .实验结果表明 ,单一生物质颗粒不能形成良好的流化状态 ,而加入一定量煤构成生物质和煤二组分混合颗粒可以实现稳定流化 .当生物质和煤混合颗粒中生物质的质量分率小于 5 0 %时 ,可以达到很好的流化状态 ,生物质和煤二组分混合颗粒的最小流化速度随生物质质量分率的增加而减小 .