带内置水平管的大颗粒振动流化床流体力学研究

以大颗粒MAP（磷酸-铵）为试验物料对带内置水平管的大颗粒振动流化床流体力学进行了试验研究,结果表明,振动的引入对床层临界压降有明显的降低作用;同样床层条件下振动频率越大床层临界压降越低,振幅的改变对床层压降影响不大;低气速下振动使床层孔隙率降低而导致压降高于普通流化床;在带内置水平管的大颗粒振动流化床中,振动对大粒径颗粒的影响小于小粒径颗粒;由试验拟合出经验公式,与试验数据吻合良好。     

内置水平管的振动流化床中混合物的临界流化速度

在内置水平管的矩形振动流化床内研究了玉米粒和塑料珠混合物(Geldart D颗粒)中的流体力学性质。考察了颗粒质量分数、振动频率、振幅和内置水平管对混合颗粒的临界流化速度的影响。实验表明,振动的加入降低了混合物的临界流化速度。根据振动流化床的动力学特性,分析床层中颗粒受力情况,建立了混合颗粒物在振动流化床中临界流化速度的两类数学模型。通过实验数据建立两种模型的关联式所得的计算值和实验值误差控制在10%以内,吻合较好。     

振动流化床内污泥颗粒与内置水平管的局部传热特性研究

研究了污泥颗粒在振动流化床中与浸没水平管的传热规律,考察了流化气速、振动频率和振幅对局部传热系数的影响,实验结果表明,局部传热系数因水平管圆周位置而异,局部传热系数随着气速、振动频率和振幅的增加呈先增长后降低的趋势。水平管的迎风面的局部传热系数要远远小于背风面。研究结果能为污泥在内置水平管的振动流化床的干燥设计提供理论依据。     

单组分颗粒振动流化床的流体力学研究（1）——起始流化时床层压降

国内外振动流化床流体力学的研究由于实验条件的限制，其结果尚存在着分歧，在此情况下，本文在内径为１４８ｍｍ的振动流化床下，研究Ｇｅｌｄａｒ‘ｓＡ，Ｂ，Ｃ类物料起始流化时的床层压降，分别研究了颗粒物性与振动特性对床压降的影响，并且根据上述因素的影响，关联了起始流化时床层压降的计算式，并与画外学者的关联式进行了比较。     

内置水平管振动流化床停留时间分布模型

采用理论分析和实验研究相结合的方法研究了内置水平管的振动流化床停留时间分布密度。在带内置水平管的二维振动流化床内,以米粒为实验物料进行停留时间分布的实验研究,考察了振动强度、气速、进料流率对流化床内停留时间分布的影响。实验表明,降低振动强度、入口气速和提高进料流率可使停留时间分布相对集中。对实验用流化床内颗粒流动样式的分析,建立了停留时间分布密度函数模型,并将模型预测与实验结果进行了对比,误差在20%以内。     

振动流化床中流体力学的研究

建立了振动流化床冷模试验装置，以陶瓷球、柠檬酸、尼龙１０１０等为试料，研究了一定振幅和较低开孔率下振动频率、床层高度、气速等参数对振动流化床床层压力降的影响，得出了振动对床层最小流化压力降降低的程度。     

大颗粒振动流化床颗粒临界流化速度研究

建立了带内置水平管的振动流化床,并以颗粒状磷酸一铵为实验物料对带内置水平管的大颗粒振动流化床颗粒临界流化速度进行了实验研究。结果表明,振动的引入对颗粒临界流化速度有着明显的降低作用;同样床层条件下振动频率和振幅越大,床层临界流化速度越低;振动对小粒径颗粒的影响稍强于大粒径颗粒;由实验数据拟合出用于预测该类流化床临界流化速度的经验公式,公式与实验数据吻合良好。     

振动流化床中双组分颗粒流化特性的研究

本文研究了内径为１４８ｍｍ振动圆柱床中等密度和不等密度的双组分颗粒流化特性,考察了不同振动强度对双组分颗粒的床层空隙率、最小流化速度及相图的影响,给出了床层空隙率和最小流化速度的计算式,此计算值与实验值基本相符,且对振动流化床的实际操作和工程设计起到一定的指导作用。     

振动流化床中颗粒的混合与分离研究

在矩形有机玻璃的振动流化床中,对小米和钛精矿双组分体系进行颗粒的混合与分离研究。实验表明,在低气速、小振动频率的情况下,颗粒的分离效果好。另外,在床中增设内构件也能促进颗粒混合物的分离。     

振动流化床中大颗粒与水平管局部传热特性

在二维振动流化床中,以平均粒径1.83 mm的玻璃珠为物料,研究了大颗粒与水平管间局部传热规律;考察了气速、振动频率等因素对局部传热系数的影响,同时与小米和小玻璃珠实验结果进行对比。结果表明:大颗粒与小颗粒局部传热系数有很大差异;对于大颗粒,低速下局部传热系数随振动频率的增大先增加后减小,高速下局部传热系数随着振动频率的增加而降低;一定振动频率下,气速小时局部传热系数在60°左右达到最大,气速逐渐增加后,其最大值向90°转移。通过实验数据得到了计算大颗粒与水平管局部传热系数的关联式,计算值与实验值吻合较好,误差在±20%范围内。结果可为带浸没水平管的振动流化床设计和研究提供参考。     

An analysis of pressure drop fluctuation in a circulating fluidized bed

The characteristics of pressure drop fluctuation in a 5.0 cm I.D.×250cm high circulating fluidized bed with fine polymer particles of PE and PVC were investigated. The measurements of time series of the pressure drop were carried out along the three different axial locations. To determine the effects of coarse particles and relative humidity of air on the flow behavior of polymer powders-air suspension in the riser, we employed deterministic chaos analysis of the Hurst exponent, correlation dimension and phase space trajectories as well as classical methods such as standard deviation, probability density function of pressure drop fluctuation. From a statistical and chaos analysis of pressure fluctuations, the upper dilute region was found to be much more homogenous flow compared to that in the bottom dense region at the same operating conditions. It was also found that the addition of coarse particles and higher humidity of air reduced the pressure fluctuations, thus enhancing flow stability in the riser. The analysis of pressure fluctuations by statistical and chaos theory gave qualitative and the quantitative information of flow behavior in the circulating fluidized bed.     

内置加热管的振动流化床中污泥干燥传热特性

采用内置加热管的振动流化床对污泥进行了干燥实验,考察了流化气速、进气温度、振动频率和内加热功率对污泥干燥传热特性的影响,分析了体积传热系数的变化规律。结果表明,适度提高流化气速、进气温度、振动频率和内加热功率,有利于提高体积传热系数,降低污泥湿含量。根据实验数据拟合出了体积传热系数的经验公式,可将误差控制在30%以内。结论为污泥干燥的设计和操作提供实验依据。     

Modeling of the pressure drop and flow field in a rotating fluidized bed

Rotating fluidized beds (RFB) have found applications as dust filters, dryers, particle coaters, and granulators, and recently as catalytic reactors for the clean up of diesel exhaust. However, successful design and operation of an RFB requires an in-depth understanding of the fundamentals of the fluid dynamics involved. In this study, mechanistic models have been developed to account for the pressure drop relationship with respect to rotating speed, flow rate, properties of the granular particles, and fluidization conditions in the RFB. The models show that the total pressure drop across the bed is quadratically dependent on the rotating speed as well as the flow rate. These quadratic relationships have also been validated experimentally. The pressure drop relationship has further been validated through a full flow field numerical simulation of flow through a rotating bed with a slotted cylindrical distributor but without granular particles in the bed. Using our analytical model together with experimental results from three different types of distributors, a slotted cylinder with a thin metal screen, a perforated cylinder with a thin metal screen, and a sintered metal cylinder, three semi-empirical quadratic equations are obtained to predict the pressure drop across these distributors. A comparison of the distributor pressure drop with that across the fluidized bed (granules only) shows that the pressure drop across the distributor is appreciable and cannot be neglected in RFB applications. The higher the rotating speed, the more significant the pressure drop across the distributor.     

带浸没管的惰性粒子振动流化床传热特性

采用带浸没加热管的惰性粒子振动流化床对膏状物料干燥进行了实验研究。考察了加料速率、进气温度、进气速度、加热管功率、振动强度等参数对床温和体积传热系数的影响,得出了计算体积传热系数的关联式。结果表明,在流化床中增设振动和浸没加热管装置,能大大强化传热传质,体积传热系数随加料量、振动强度、加热管功率、进风速度的增加而增大,随进气温度的增加而减小。其结果对惰性粒子流化床干燥器的设计和改进具有重要的指导意义。     

内热式惰性粒子流化床中膏状物料干燥模型

通过对惰性粒子流化床中膏状物料干燥机理的分析,得到了干燥时间及单位面积床层水分汽化量的数学计算式,可对干燥器的性能进行预测。采用带浸没加热管的惰性粒子流化床对膏状钛白物料进行干燥中试研究,采用气流式喷嘴将膏状物料分散成200～400μm的小液滴喷洒在惰性粒子表面进行干燥,探索了适宜的干燥条件,测定和确定了最佳的干燥工艺参数、操作参数和设备参数。结果表明:该干燥工艺能强化床内传热传质,促进高黏性膏糊状物料很好地分散,床层温度分布均匀,干燥器的操作弹性大,热量消耗低,干燥强度高,传热系数可达300W·m-2·K-1以上。     

Particle-scale simulation of fluidized bed with immersed tubes

In order to simulate gas-solids flows with complex geometry, the boundary element method was incorporated into the implementation of a combined model of computational fluid dynamics and discrete element method. The resulting method was employed to simulate hydrodynamics in a fluidized bed with immersed tubes. The transient simulation results showed particle and bubble dynamics. The bubble coalescence and break-up behavior when passing the immersed tubes was successfully predicted. The gassolid flow pattern in the fluidized bed is changed greatly because of the immersed tubes. As particles and gas are come in contact with the immersed tubes, the gas bubbles will be deformed. The collisions between particles and tubes will make the tubes surrounded by air pockets most of the time and this is unfavorable for the heat transfer between particles and tubes. __________ Translated from Chemical Engineering, 2007, 35(11): 21–24 [译自:化学工程]