Intrusive probes in riser applications

Many of the probes used to understand hydrodynamics in circulating fluidized bed risers intrude into the environment they are measuring, although assumptions are typically asserted that the intrusive probes do not affect the data collected. This could be a poor assumption in some cases and conditions. We found that intrusive fiber‐optic probe measurements consistently mis‐predicted the solids concentration compared to the nonintrusive pressure drop measurements outside the fully developed flow region of a riser containing fluid catalytic cracking catalyst or glass bead particles. The discrepancy was sensitive to superficial gas velocity, solid circulation rate, probe position, and flow direction. Barracuda VR? computational fluid dynamics simulations confirmed this, and indicated that particle momentum was lost at the leading edge of the probe and particles were spilling over to the probe tip. Accordingly, new probe designs were proposed to mitigate the intrusiveness of a fiber‐optic probe for more accurate characterization. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5361–5374, 2017     

内循环微型流化床流动特性

针对开发适用于化学气相沉积反应动力学研究的微型流化床反应分析仪的应用需求,研究了外径为30 mm的内循环微型流化床中气固流动特性,具体考察了中心射流管伸入高度、内导流管直径和颗粒装载量对实现固体物料内循环的最小操作气速和导流管与环隙区间窜气的影响。结果表明,随着射流管伸入高度的增大,实现颗粒内循环流动的最小操作气速变大;存在最优的导流管直径（20 mm）,使得实现颗粒环流的最小操作气速较小;增大颗粒装载量有利于降低颗粒内循环的最小操作气速。通过检测示踪气体在环隙区内的质谱信号,发现在所考察的参数范围内,反应器底部不存在导流管区向环隙区的窜气;在反应器上部,由于颗粒对气体的夹带,环隙区上部总能检测到示踪气体,且窜气特性随操作气速的增大而增强。研究结果可为设计适用于化学气相沉积反应的内循环微型流化床反应器提供参考。     

泵技术进展与发展趋势

泵作为一种典型的水力机械,在国民经济中扮演着重要的角色,其技术进展一直受到多个行业的关注。在各种应用需求的驱动以及材料、力学、信息和计算机等相关学科的带动下,泵理论和技术研究已取得巨大进展。人们对泵内流机理和运行特性的认识更为深入,数字化设计和信息化运维已得到广泛应用,泵产品已逐步具有生态友好和智能化特征。本文以2000年以来泵领域所取得的进展为重点,围绕旋涡泵、离心泵、混流泵、轴流泵和贯流泵等叶片式泵,从产品应用需求出发,针对泵的水动力学、设计技术、振动噪声、节能与运维技术等四个部分对技术进展进行综述,并对泵的发展趋势进行总结和展望。     

岩石渗透试验瞬态法的水动力学分析

压力脉冲瞬态法是一种专门进行岩石渗透率测试的新方法。对多孔介质渗流的水动力学分析表明,在岩石渗透试验的瞬态法中,水流动量方程可以不考虑流速的变化率。对于致密岩石,出现高速非Darcy流的特征不显著,在一般条件下Darcy定律仍然有效。给出压力脉冲瞬态法的物理模型和数学模型,采用等梯度假设简化连续性方程,针对上下游压力容器的不同控制条件,推导各种情况下压力测试曲线的解译公式。这些解译公式为分析不同控制方式下的试验过程和计算岩石渗透率提供了方便。实例表明,基于等梯度假设的解译公式对压力脉冲瞬态法所产生的渗透率测试曲线基本适用。     

流体力学教学中的传统教学与网络多媒体教学

通过论述传统教学模式与多媒体网络教学模式的利弊 ,提出了在流体力学教学活动中既要弘扬传统教学的优点 ,又要融入现代多媒体网络教学 ,两者有机地结合起来 ,高效率、高质量地培养出优秀人才。     

SSPH basis functions for meshless methods, and comparison of solutions with strong and weak formulations

We propose a new and simple technique called the Symmetric Smoothed Particle Hydrodynamics (SSPH) method to construct basis functions for meshless methods that use only locations of particles. These basis functions are found to be similar to those in the Finite Element Method (FEM) except that the basis for the derivatives of a function need not be obtained by differentiating those for the function. Of course, the basis for the derivatives of a function can be obtained by differentiating the basis for the function as in the FEM and meshless methods. These basis functions are used to numerically solve two plane stress/strain elasto-static problems by using either the collocation method or a weak formulation of the problem defined over a subregion of the region occupied by the body; the latter is usually called the Meshless Local Petrov–Galerkin (MLPG) method. For the two boundary-value problems studied, it is found that the weak formulation in which the basis for the first order derivatives of the trial solution are derived directly in the SSPH method (i.e., not obtained by differentiating the basis function for the trial solution) gives the least value of the L²-error norm in the displacements while the collocation method employing the strong formulation of the boundary-value problem has the largest value of the L²-error norm. The numerical solution using the weak formulation requires more CPU time than the solution with the strong formulation of the problem. We have also computed the L²-error norm of displacements by varying the number of particles, the number of Gauss points used to numerically evaluate domain integrals appearing in the weak formulation of the problem, the radius of the compact support of the kernel function used to generate the SSPH basis, the order of complete monomials employed for constructing the SSPH basis, and boundary conditions used at a point on a corner of the rectangular problem domain. It is recommended that for solving two-dimensional elasto-static problems, the MLPG formulation in which derivatives of the trial solution are found without differentiating the SSPH basis function be adopted.     

气液固三相循环流态化

<正>由于三相流化床反应器在石油化工、湿法冶金、环境工程和煤的液化等工业领域得到越来越广泛的应用,近年来对传统的三相流化床进行了大量的基础研究并取得了很大进展。以往的研究大部分是针对低液速(u_l相似文献   

三重环流生物流化床的流体力学与传质特性

从气相含率,液体循环速度和体积氧传质系数方面研究自行设计新型结构的三重环流生物流化床的流体力学与传质特性。流化床反应器的有效体积２３Ｌ,实验条件是以空气为气相,水为液相,树脂为固相,固含率分别为０％,３％,６％和９％。实验结果表明,气相含率是影响反应器流体力学和传质特性的主要因素,气相含率增大可降低液体循环速度,增大体积氧传质系数。     

固体颗粒对强化传递性质的多相气升式反应器流体力学影响

研究了加入机械搅拌和静态混合器后对多相气升式反应器流体力学性能的促进作用,重点考察固体颗粒的直径、固含率（固体质量分数,下同）对液体循环速度、气含率（气体体积分数,下同）等的影响。实验证明,对液体循环速度来说,在多相流中并非通气量、搅拌转速越大越好。对气含率而言,多相气升式反应器不但存在临界颗粒直径和临界固含率,还存在一个临界表观气速,在此气速以下,才能产生气含率随固含率增加而增加的现象。最后对气含率、固含率及能量耗散速率作了关联。     

Effect of liquid volume in the gas‐separator on the hydrodynamics of airlift reactors

Gas hold‐up and liquid circulation velocity measurements were made using a 167 dm³ external loop airlift reactor. The gas‐separator was of the open channel configuration. The reactor height was 2.5 m with riser and downcomer diameters of 0.19 m and 0.14 m respectively. The systems investigated were Newtonian air–water and air–glycerol with the superficial air velocity varying between 0.02 and 0.12 m s⁻¹. The ratio of the liquid volume in the gas‐separator to the liquid volume in the reactor (volume‐ratio) was varied from 0.0% to 37%, to find its minimum critical value for optimum operation of the airlift reactor. For the air–water system, discernible effects of the volume‐ratio on riser and, downcomer gas hold‐ups and liquid circulation velocity were observed at volume ratios ≤7%. Beyond this value, the volume‐ratio had no effect. For a viscous and foaming air–glycerol system the critical volume‐ratio was increased to 19%. New and simple correlations for predicting gas hold‐up in the riser, gas hold‐up in the downcomer, and liquid circulation velocity were developed with reasonable accuracy. © 1999 Society of Chemical Industry