三维流化床内生物质及石英砂混合颗粒的流动特性

选择锯花、花生壳、稻壳、蔗渣为实验对象,将不同质量的生物质与石英砂混合作为床料,加入三维流化床试验台内混合流动,测量床内的压差脉动信号,床高1000mm,截面尺寸为120mm×32mm。实验结果表明当生物质质量分数小于等于2%时,生物质的种类及质量分数对最小流化速度的影响可以忽略不计。利用快速傅里叶变换变换分析压差脉动信号,研究双组分流动特征。结果表明,添加稻壳时压力脉动在低气速下主频位于10~15Hz区间内,并随着气速的增加向20~25Hz的高频区移动;蔗渣、花生壳及锯花等片状生物质在较低气速下主频消失,较高气速下主频存在于10~15Hz区间内。     

气固流化床压力脉动信号的Hilbert-Huang变换与流型识别

采用Hilbert-Huang变换(HHT),提取出气固流化床压力脉动信号的各阶内禀模态函数(IMFs),进一步证明了压力脉动信号是由复杂的不同波间和波内频率调制成分所组成,具有气固两相运动相互调制的非线性特征。分析各阶内禀模态函数的能量分布及其转换,发现不同频段IMF的能量与流型状态之间有着很好的对应关系,能够从整体上反映流化床的流化状态,从而提出了应用IMF中频段能量进行流化床流型识别的新方法。该方法只需一个压力脉动信号,算法简单、实用,没有需要主观决定的参数,具有较好的工业应用前景。HHT分析比现有的分析方法更能深入地揭示流化床内的非线性流体动力学特征。     

流化床内生物质石英砂双组分混合流动混沌递归分析

采用递归分析方法对流化床内的压力脉动信号进行分析,研究了不同工况下石英砂与柱形生物质颗粒混合双组分颗粒的流动特性。柱形生物质颗粒尺寸为10 mm×10 mm(直径×长),石英砂粒径为0.8 mm。在鼓泡床阶段,随着生物质含量的增加,系统的周期性呈现先减弱再增强的变化趋势;该阶段确定性与层流率均表现为随气速的增加而增大,其值在生物质含量低时会明显减小,系统熵则随着气速的增大而减小。在腾涌阶段,生物质添加前后系统信号的递归图呈现相似的纹理特征,确定性与层流率变化较小,此时熵随着气速的增加而减小,与单组分流动呈现相反的趋势。     

流化床内生物质石英砂双组分混合流动混沌递归分析

采用递归分析方法对流化床内的压力脉动信号进行分析,研究了不同工况下石英砂与柱形生物质颗粒混合双组分颗粒的流动特性。柱形生物质颗粒尺寸为10 mm×10 mm（直径×长）,石英砂粒径为0.8 mm。在鼓泡床阶段,随着生物质含量的增加,系统的周期性呈现先减弱再增强的变化趋势;该阶段确定性与层流率均表现为随气速的增加而增大,其值在生物质含量低时会明显减小,系统熵则随着气速的增大而减小。在腾涌阶段,生物质添加前后系统信号的递归图呈现相似的纹理特征,确定性与层流率变化较小,此时熵随着气速的增加而减小,与单组分流动呈现相反的趋势。     

气固流化床压力脉动信号的Hilbert-Huang谱分析

首次将Hilbert-Huang变换（HHT）应用于气固流化床压力脉动信号的分析,提取并研究了压力脉动信号中隐含的表征复杂的粒子运动与气泡运动相互调制的非线性特征,以及压力脉动信号高、低阶内禀模态函数（IMF）之间的能量转换与流化床的流化状态相对应的新信息,在此基础上提出了采用压力脉动IMF分量的能量转移现象进行颗粒结块故障判别的新方法.结果表明,应用Hilbert-Huang谱对压力脉动信号分析的新方法能比现有的分析方法提供更多的有用信息,有助于更深入地揭示床内非线性流体动力学特征.     

气固流化床压力脉动信号的Hiibert-Huang谱分析

首次将Hilbert-Huang变换(HHT)应用于气固流化床压力脉动信号的分析，提取并研究了压力脉动信号中隐含的表征复杂的粒子运动与气泡运动相互调制的非线性特征，以及压力脉动信号高、低阶内禀模态函数(IMF)之间的能量转换与流化床的流化状态相对应的新信息，在此基础上提出了采用压力脉动IMF分量的能量转移现象进行颗粒结块故障判别的新方法．结果表明，应用Hilbert-Huang谱对压力脉动信号分析的新方法能比现有的分析方法提供更多的有用信息，有助于更深入地揭示床内非线性流体动力学特征．     

大颗粒鼓泡流化床压力脉动信号的小波分析

利用小波分析对试验所测得的大颗粒流化床的压力脉动信号进行小波包的完全分解,并对各个频段的信号的方差进行统计分析。结果表明,分解前后信号的能量是守恒的,脉动能随着流化数的增加逐渐集中在低频段;气泡经过测点的频率在0~12.5H z的范围内,且气泡的运动变化是影响测点压力数据波动的主要因素;通过分析流化床压力信号中的低频成分,可以判断床层物料的流化状态。     

喷动流化床流动特性数值模拟

为了捕捉喷动流化床中微观层次上的颗粒运动信息,建立了基于CFD的二维非稳态喷动流化床欧拉-欧拉两相流模型。分析了不同流化气速对喷动流化床气固流动特性的影响,即不同工况下的炉内压力降、颗粒浓度、床内空隙率分布、气体速度分布和固体颗粒速度分布。数值模拟研究结果表明:随流化气速的增大,压降和炉内平均空隙率逐渐增大,密相床层高度逐渐增加,沿着轴向方向的气体流量增大,喷动气的射流深度逐渐增加,同时射流半径也逐渐增加。     

二元颗粒在气固流化床中的轴向分布特性

通过大型冷模实验测量了二元混合颗粒在流化床内沿轴向的压力分布，考察了混合颗粒截面平均浓度沿轴向的变化特点。通过分析床层压差分布的转折点，确定了密相区与稀相区的相交界面高度，根据实验结果给出了经验关联式。通过压力信号标准差分析了流化床内混合颗粒流化性能与表观气速和颗粒混合比例的关系。实验结果表明，平均颗粒浓度沿流化床轴向呈下降趋势，且在密相区中随表观气速增加而减小，在稀相区中随表观气速增大而增大。二元颗粒中大颗粒比例x_l为0.685时，密相区总平均颗粒浓度存在最大值。密相区与稀相区相交界面高度随表观气速增大而提高。当0.225≤x_l≤0.479和0.561≤u_g≤1.122 m/s时，流化床内二元颗粒的流化性能和混合程度达到最佳。     

旋流筛板式气固挡板流化床内压力脉动特性

在表观气速Ug=0.04~1.14 m/s时,采用旋流筛板构型的挡板式内构件,通过对比分析旋流筛板式气固挡板流化床与自由床内流动现象、压差脉动标准偏差和压力脉动标准偏差等参数,确定了旋流筛板式气固挡板流化床能有效破碎气泡的流动与操作条件。结果表明,构件下方区域颗粒随表观气速增加而不断转移至构件上方床层,造成构件下方区域密相床层高度持续降低,该区域出现3种流动状态并直接决定构件是否能破碎气泡。当Ug<0.44 m/s时,构件下方区域密相床层料位较高,形成下部为密相床层、上部为密相与大气泡交替通过构件的鼓泡床,此时构件具有抑制气泡生长并破碎气泡的作用,全床压差脉动及压力脉动标准偏差低于相同条件下的自由床;当0.44≤Ug<0.66 m/s时,密相床层料位较低,形成下部为密相床层、上部为单一稀相的湍动床,此时构件不再直接抑制气泡生长或破碎气泡,但构件下方密相床层的存在能降低构件下方及构件上方一定高度内床层的压力脉动强度;当Ug≥0.66 m/s后,密相床层完全消失,形成气体为连续相的稀相流化状态,构件不能破碎气泡、降低床层压力和压差脉动强度。     

气液两相流差压测量波动信号的符号序列统计分析

将符号时间序列分析方法应用到两相流测量波动信号分析,并讨论了关键参数对符号统计量影响问题。在此基础上,利用垂直上升管中采集到的80组气液两相流差压动态波动信号,提取了时间不可逆转性Tfb及χ2fb统计量。当气相表观速度小于002 m·s-1时,随着气相表观速度增加,泡状流随机可变的运动特征逐渐加剧,其动力学特性变得相对复杂;当气相表观速度大于002 m·s-1时,在流型从泡状流向段塞流转变过程中,随着气相表观速度增大,流型演化的动力学特性逐渐变得相对简单;在流型从段塞流向混状流转变过程中,随着气相表观速度增加,混状流的动力学特性逐渐变得愈加复杂。研究结果表明,时间不可逆转性Tfb及χ2fb统计量两个符号是表征气液两相流流型的敏感特征量,考察这两个统计量随两相流流动参数变化规律有助于更好地理解两相流流型动力学特性。     

Effect of cohesive powders on pressure fluctuation characteristics of a binary gas-solid fluidized bed

The effect of cohesive particles on the pressure fluctuations was experimentally investigated in a binary gas-solid fluidized bed. The pressure fluctuation signals were measured by differential pressure sensors under conditions of various weight percentages of cohesive particles. The cohesive particles increased the fixed bed pressure drop per unit height and decreased the minimum fluidization velocity. The Wen & Yu equation well predicts the minimum fluidization velocity of the binary system. The addition of cohesive particles slightly decreased the bubble size in bubbling flow regime when the cohesive particles and the coarse particles mixed well, while the bubble size greatly decreased when the cohesive particles agglomerated on the bed surface. The time series of pressure fluctuations was analyzed by using the methods of time domain, frequency domain and wavelet transformation. The normalized standard deviation of pressure fluctuations decreased with increasing weight percentages of cohesive particles. A wide bandwidth frequency of 0 to 1Hz got narrower with a single peak around 0.6Hz with an increase in proportion of the cohesive particles. The meso-energy and micro-energy of pressure fluctuations were decreasing with increasing cohesive particles proportions, which indicated that adding cohesive particles could reduce the energy dissipation of bubble and particle fluctuations.     

垂直管气液两相环状流的界面扰动波速度

在气液两相环状流中,界面波是两相间质量、动量和能量转移的重要载体,对其特性参数（波速、波频和波幅）的研究具有重要意义。首先根据气液两相流界面波分类,对其特征进行了定性描述。针对现有的界面剪切力推导了界面扰动波速度预测模型,考虑了气核中夹带液滴引起的密度增量及气核与液膜表面相对速度的影响,得到了改进的垂直管环状流扰动波速预测模型。针对工业现场工况压力较高现状,设计了基于近红外吸收衰减技术和互相关原理的界面波波速测量传感器,在五种压力（0.2～0.9 MPa） 154个界面波波动速度条件下进行了实验。结果表明,改进后模型预测效果良好,相对误差在±10%左右,在不同系统压力条件下具有一定外推性。     

射流撞击过程中的高频压力脉动特性

引　言利用两束射流相互撞击或单射流撞击靶在微细颗粒制备、多相流快速微观混合及团聚颗粒单分散过程中具有特殊优点。用作预混合器或反应器 ,能够强化微细颗粒的成核与生长环境在微观尺度上的均匀性 ,尤其对于快速反应体系 ,可实现液液或液固多相流快速微观混合 ,有效控制反应过程和产物指标 .Ｍａｈａｊａｎ等[1] 利用两束撞击流实现流体的快速微观混合以合成超细微粉 ,并用萘酚与重氮苯磺酸两步反应表征两束撞击流体数十毫秒的微观混合时间 ,关联微观混合时间与射流速度的关系 ,通过控制射流的微观混合时间控制合成超细微粉的粒度分布 .…     

Hydrodynamics of three-phase fluidized bed systems examined by statistical, fractal, chaos and wavelet analysis methods

Hydrodynamic studies were conducted in gas-liquid-solid systems (0.1 m ID, 2 m high) of 3.0 mm glass beads and of 2.1 mm polypropylene low-density particles, with particles densities of 2471 and 1290 kg/m³, respectively. Simultaneous measurement of differential pressure and bubble conductivity probe signals sampled at 500 Hz for 60 s enabled the investigation of the change in flow structure in relation to the flow regime transitions. Superficial gas velocities ranged between 0.010 and 0.052 m/s for polypropylene particles, and extended to 0.12 m/s for glass beads, while the superficial liquid velocities covered the ranges of 0.0007-0.045 m/s for polypropylene particles, and ranged up to 0.056 m/s for glass beads.Spectral analysis of the pressure fluctuations revealed a transition from dispersed to coalesced bubbling flow with decreasing liquid velocity for a given superficial gas velocity. The use of a conductivity probe facilitated characterization of the local flow structure in terms of bubble movement. The measurements were extensively analyzed using fractals and chaos, power spectra frequency analysis and wavelet decomposition in addition to the standard statistical analyses. The coefficient of variation of the bubble probe signals was found to be the most effective in deducing the transition velocity between coalesced and dispersed bubbling flow regimes, while wavelet energy confirmed the similarity in the distribution between two axial positions once operated in the dispersed flow regime. Comparison of the flow structure between glass beads and polypropylene particles showed that both the minimum liquid fluidization velocity and the transition velocity between the bubble flow regimes were much higher for the glass beads than for the lighter polypropylene particles. Furthermore, the standard deviations of the decomposed bubble probe signals through wavelet transformation successfully highlighted the difference between the two systems of particles.     

Characteristics of slug flow in a fluidized bed of polyethylene particles

The slug flow behavior of polyethylene particles was examined in a fluidized bed of 7 cm ID and 50 cm in height. The employed polymer particles were high density polyethylene (HDPE) with the average particle size of 603 μm. The slugging flow of polyethylene particles was analyzed from the measured pressure drop signals by classical statistical methods such as absolute average deviation, probability density function, power spectrum, auto-cor-relation, and cross-correlation. The results show that in spite of high dielectric constant of polymer particles, the slugging phenomena such as incipient slugging velocity, slugging frequency and slugging rise velocity were very similar to the Geldart B type non-polymeric particles. It was observed that slug frequencies decreased with gas velocity and the limiting slug frequency was observed for the gas velocities in this study.     

Hydrodynamic characteristics of magnetically stabilized fluidized admixture beds of iron and copper particles

Hydrodynamic characteristics of fluidized beds of pure iron (1416 μm), copper (934 μ) and their admixture (25, 50 and 75 mass %) particles when exposed to a uniform magnetic field collinear with the gas flow are investigated. Bed pressure-drop data taken as a function of increasing and decreasing gas velocities (up to about 8 m/s) for different values of magnetic-field intensity over a wide range (0 to 17 272 A/m) are employed to determine the superficial minimum bubbling and fluidization gas velocities at ambient temperature and pressure. The minimum bubbling velocity is found to increase with an increase in the value of the magnetic-field intensity, as well as with the mass fraction of magnetizable particles in the bed. These data are correlated with an empirical relation, as well as with a semi-theoretical expression. The bed voidage data are also generated and analyzed, as also the bed quality fluidization in terms of interparticle magnetic forces. These hydrodynamic properties of magnetically stabilized fluidized-bed reactors are useful in their design and operation for a variety of chemical and biochemical applications.     

气液两相流差压波动信号的Hilbert-Huang变换特性

将Hilbert-Huang（HHT）变换应用于中小管径水平管气液两相流差压波动信号的分析.利用经验模态分解（EMD）方法把信号分解成多个内模函数(IMF),再对各内模函数进行Hilbert变换,得到信号的Hilbert谱,并提取各内模函数的信号能量特征.在此基础上比较了不同管径下信号分析的结果,分析了不同频段的能量分布与流型变迁的关系,并讨论了小波变换和HHT两种信号处理方法各自的特点.实验结果表明,HHT可以用于非线性非平稳信号的分析,提取的能量特征值反映了水平管气液两相流的流动状态和流型的变迁,该方法为水平管气液两相流差压波动信号的研究提供了借鉴.