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1.
流动结构的不均匀性是气固两相流反应器的主要弊端之一。采用变截面反应器,使沿流向速度不断变化,从而达到流场均匀的目的,实验结果表明,变截面反应器内流场均匀性得到很大改善,颗粒浓度趋于均匀。  相似文献   

2.
气—固并流上行系统的环/核内循环流动结构模型   总被引:2,自引:0,他引:2  
提出了一个概念台理,预测性能好的两通道模型,描述垂直向上气固流动系统的环/核内循环流动结构。基于气固相互作用最少及质量,动量守恒原理,确定了气固两相流动状态,计算结果(如预测核心区半径,核心区及环形区内空隙率,气体速度,颗粒速度及其轴向分布等)合理,且与实验结果有良好的一致性。该模型还可以用于预测在两通道内的曳力系数,气,固返混以及两区间质量交换速度率等,对反应器设计具有一定参考价值。  相似文献   

3.
提出了一个概念合理、预测性能好的两通道模型,描述垂直向上气固流动系统的环/核内循环流动结构。基于气固相互作用最少及质量、动量守恒原理,确定了气固两相流动状态、计算结果(如预测核心区半径、核心区及环形区内空隙率、气体速度、颗粒速度及其轴向分布等)合理,且与实验结果有良好的一致性。该模型还可以用于预测在两通道内的曳力系数,气、固返混以及两区间质量交换速率等,对反应器设计具有一定参考价值。  相似文献   

4.
刘景源 《化工学报》1995,46(1):95-99
研究了垂直气固上行流动系统的状态与空隙率的关系,指出当气固两相动能相等时,系统处于最稳定状态。此时颗粒集聚具有最大空隙率ε_(max)·根据上述原理推导出ε_(max)的表达式。将计算结果与Matsen等的结果进行了比较,表明本法合理,计算简单,物理意义明确。  相似文献   

5.
垂直气固并流上行/下行系统安全发展段的混沌研究   总被引:1,自引:1,他引:1  
程易  魏飞 《化工学报》1998,49(2):185-185
针对垂直气固并流上行/下行系统的完全发展段、使用光纤密度探头测得反映系统局部密度涨落信息的时间序列,利用确定性混沌理论进行分析,获得表片系统自由度的关联维烽和反映系统信息挂失速率的Kolmogorov熵,并对上行和下行系统做比较研究。研究发现反映局部瞬态行为特征的Dml和Kml在上行和下行系统中一定的操作条件下具有大致相同的数值,且混沌参数与局部固含率表现为对应关系。  相似文献   

6.
朱永康 《炭黑译丛》2002,(1):5-10,F003
现已清楚地确认,弹性体的补强与粒状填料聚集体和渗透阈之上形成的填料网络的分形性质密切相关,除此而外,通过控制聚合物-填料相偶联及填料聚集体之间的相互作用,填料的表面性质对补强也起着关键的作用。表面性质包括:(Ⅰ)长度规模小(低于原生粒子直径)的表面粗糙度;(Ⅱ)与原生粒子微观结构有关的部位能分布以及考虑聚合物基质的吸附部位的比反应性。最近,通过对炉法炭黑的平衡气体吸附,论述了表面粗糙度对所有炭黑的分形都相似,与它们的比表面积和BDP值无关,这可以通过一个通用的表面分维(Ds≈2.6)来表征,这些结果支持了以前的发现:所有的炉法炭黑品种每单位表面吸附的聚合物链量(数)相同,因此,不妨假定在炭黑表面上吸附时,化学性质相似的聚合物链类似地减小了其构造熵,由于这些强有力的实验证据,没有现由像理论预期所断言的那样,将其归因于表面粗糙度的特殊作用,在解释加工的影响和填充弹性体的机械性能时,更多地归功于表面性质的能量贡献。  相似文献   

7.
8.
蔡霞  陈振艺  牟守勇 《轮胎工业》2015,35(4):195-199
试验研究光面轮胎不均匀性对噪声的影响.噪声与动平衡力偶的曲线对比直接表明动平衡力偶是影响光面轮胎噪声的一个重要因素;通过数据处理得到光面轮胎不均匀性参数对噪声影响的多元线性方程,可表征各参数对噪声的影响程度.  相似文献   

9.
针对PVC等颗粒的干燥过程要求,设计并建立了多级旋流干燥系统.对其操作方式、流体力学特性进行了较为系统的研究.实验对气固逆流和气固并流两种操作方式分别进行了探讨.在多级旋流干燥器中成功地实现了气固逆流接触.并对旋流板结构、开孔率和操作气速对床层压降及床层平均密度的影响进行了研究,给出了气固逆流及并流操作时的操作性能曲线和操作窗口.  相似文献   

10.
软质粘土的不均匀性及其均化措施   总被引:1,自引:0,他引:1  
本文通过对陶瓷生产的关键原料-软质粘土进行化学成分分析和矿和分析,详细地阐述了软质粘土存在着极大的不均匀性以及软质粘土在陶瓷生产中的重要作用,提出一些均化措施,以满足陶瓷生产对软质粘土稳定供料的要求,对陶瓷生产具有一定的指导意义。  相似文献   

11.
压力循环流化床流体动力特性研究   总被引:1,自引:0,他引:1  
运用多尺度能量最小(EMMS)整体动力学模型,从理论上研究了循环流化床内流体动力学特性随床压的变化规律,为压力循环流化床设备的设计与运行提供指导。  相似文献   

12.
    
The axial and radial distributions of solid and gas holdups were investigated in an air‐water‐glass bead circulating fluidized bed (GLSCFB) using a new ultrasonic technique, with a new method based on signal fluctuations. The cross‐sectional averaged gas and solid holdups measured at two axial positions appear to be similar at all studied operating conditions. The radial non‐uniformity decreases with increasing liquid velocity but does not change with an increasing solid circulating rate. The radial distribution of gas holdup was more uniform for 1.3 mm beads than for 433 µm glass beads.  相似文献   

13.
We have investigated the axial distribution of the liquid phase in a three-phase fluidized bed in which the particles were glass beads of two different diameters, 710-850 μm and 2 mm. Two methods were used to reduce the axial heterogeneity and homogenize the bed: the use of packing elements and the addition of a small quantity of a high molecular weight polymer. The use of packing elements was shown to be very efficient in controlling phases distribution in the bed. The packing consisted of 1 mm thick steel horizontal plates punched and stretched to obtain parallelogram-shaped openings. The addition of a high molecular weight polyisobutylene (BASF Oppanol B246, Mu, =6.15 Lo6) on the phase distribution was also studied. Low polymer concentrations up to 397 ppm (based on the liquid phase) were investigated. The addition of the polymer reduced bubble coalescence and allowed for a better distribution of the phases.  相似文献   

14.
A simulation model based on the concepts developed previously (Tien el. al. 1977, Wang el. al. 1977) for the deposition of particles from suspensions flowing past single spherical and cylindrical collectors is presented. The model is capable of providing detailed information about the formation and growth of particle deposits at the surface of the collector. Reasonably good agreement with experimental data was observed.  相似文献   

15.
    
Our recently presented multi‐scale computational fluid dynamics (CFD) approach has proven to be able to capture the choking phenomena in a circulating fluidized bed (CFB). However, how to transfer this capability to assist industrial operation remains to be explored. To this end, this paper presents further simulation results over the intrinsic flow regime diagram and the operating diagram for gas–solid risers, showing the variation of flow regimes with gas velocity and solids flux as well as riser height. It is confirmed that the choking in CFB risers, characterized by the saturation carrying capacity and the coexistence of both dense and dilute flows, holds clear‐cut definition in hydrodynamics. In physics, both the choking, non‐choking transitions, and the critical point in‐between are intrinsic nature of gas–solid riser flows; they initiate as functions of gas velocity and solids flux. In engineering operation, however, their appearances vary with the riser height used. As a result, the intrinsic flow regime diagram can be defined by the combination of gas velocity and solids flux, although it is hard to obtain in practice owing to the limitation of riser height. The operating diagram of a CFB should be, accordingly, height‐dependent in practice, demanding the riser height as a parameter besides commonly believed gas velocity and solids flux.  相似文献   

16.
    
Fluidization regimes were studied in liquid‐solid and gas‐Liquid‐solid fluidized beds. The liquid velocities at which regime transitions occur in liquid‐solid and gas‐liquid‐solid systems were obtained for monosize and multicomponent systems. Minimum fluidization, complete fluidization and complete mixing velocities of particles were obtained from pressure drop measurements, a collision technique or a conductivity method. The collision technique provided accurate complete fluidization and complete mixing velocities by measuring directly the particle motion. The conductivity technique, which is easier to implement, gave similar but less accurate results.  相似文献   

17.
    
A new flow regime map, resulting from more fundamental studies on the hydrodynamics and new flow regimes, is proposed in response to more practical reclassifications of the existing regimes with the development of upward gas-solids fluidization systems. The previously reported flow regime maps and flow structures of some widely used fluidized beds are carefully examined. To better reflect the industrial applications, the fast fluidization regime is reclassified as high-density and low-density circulating fluidization regimes. A consolidated flow regime map is then proposed where the flow regimes of upward fluidization expand to include new types of fluidized beds such as circulating turbulent fluidized bed and high-density circulating fluidized bed. The proposed flow regime map consists of six flow regimes: bubbling, turbulent, circulating turbulent, high-density circulating and low-density circulating fluidization, and pneumatic transport. The transitions between the regimes are discussed with new correlations proposed for fluid catalytic cracking type particles. Analysis on the dominating phase in the different types of fluidized beds reveals the dynamic changeover from solids phase continuous in conventional low-velocity batch/“fixed” fluidization operations to gas phase continuous in high-velocity continuous/“moving” fluidization operations and provides more insights to the transitions between the flow regimes for industrial design and practice.  相似文献   

18.
19.
    
Experiments were conducted in a turbulent bed contactor (TBC) with and without downcomer operating in Type I and Type II modes to obtain the flow regime maps. The variables include flow rate of the gas and liquid phases, size and density of the particles, bed height, free open area of the supporting grid, and diameter and weir height of the downcomer. Static, partially fluidized, completely fluidized, flooding and annular regimes are identified depending on geometric and operating conditions. The effect of these variables on flow maps is discussed and correlations are proposed for delineating the flow regimes.  相似文献   

20.
    
The regime transition velocity from bubbling to turbulent fluidization was investigated in a 0.267 m diameter fluidized bed with FCC particles. Different transition velocities and processes are found from the measurements of differential pressure fluctuations and local solids concentration. The measurements of differential pressure fluctuations shows a relatively quicker global regime transition, while the local regime transition obtained from the local solids concentration presents a more gradual process marked by two transition velocities. These transition velocities increase with initial static bed height. For the same initial static bed height, increasing the spacing between two pressure taps leads to lower pressure fluctuations and the appearance of two transition velocities.  相似文献   

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