Pressure Drop Studies on Flow of Viscoelastic Fluid Through a Packed Bed

In the present study, pressure drop-flow rate behavior for the flow of viscoelastic fluid through porous media has been investigated. Aqueous solutions of polyacrylamide (PAM) and water in the concentration range of 0.02 to 0.1% wt/vol were used to elucidate the effect of fluid elasticity on bed pressure drop. Based on the observed data, the existing pore model was extended to predict the bed pressure drop for viscoelastic fluid flowing through a porous media. A statistical comparison between the existing models and the present model was made. The proposed correlation based on modified pore model predicts the data well to within a reasonable accuracy of ±10% with arithmetic relative error (%ARE) and mean relative quadratic error (MRQE) of 8.3% and 0.122, respectively.     

Behavior of Granular Material in Packed Bed Under Influence of Gas Injected Through a Nozzle

Cavity size hysteresis is an important phenomenon that affects the aerodynamics of any packed bed reactor significantly. Using the discrete element method approach, the mechanism of cavity size hysteresis in the presence of gas flow has been studied. The modeling results on cavity size have been compared with experiments and show a reasonable agreement. It is found that bed history, interparticle interaction forces, and gas drag all play an important role in the formation of cavities. The bed porosity in the decreasing gas velocity case was always found higher than the increasing gas velocity. The net gas drag at any location above the gas injection point in the bed decreases as the gas velocity is increased. It is also found that the change in interparticle interaction forces with gas flow rate is a major cause of the hysteresis phenomenon.     

不同填料旋转床功耗与气体压降特性对比研究

采用同心环波纹碟片填料和不锈钢波纹丝网两种填料，在气液逆流CO2吸收操作时，对旋转床的功耗及气体压降进行了对比实验分析。功耗特性对比结果表明，当液流量不变，旋转床转速低于38rad／s时，丝网填料旋转床吸收器消耗的功率大于碟片填料旋转床吸收器消耗的功率；转速高于38rad／s时则相反。气体压降特性对比结果表明，在液流量和旋转床转速不变的操作条件下，碟片填料旋转床的气体压降要大于丝网填料旋转床的气体压降约50Pa；在气流量和转速不变的操作条件下，当液流量较小时，丝网填料旋转床的气体压降大于碟片填料旋转床的气体压降；当液流量较大时则相反。在相同气流量和液流量下，碟片旋转床气体压降要大于丝网填料旋转床气体压降。研究结果为AIP系统旋转床吸收器的填料优选及全系统的优化设计提供了重要的依据。     

Modeling Performance of a Tangential Flow Cyclone: Effects of Secondary Outlet Geometry and Boundary Conditions

Numerical calculation of the performance of cyclones for gas-particle separation is becoming a popular tool for cyclone analysis and design. A traditionally accepted way to treat these problems is by solving the flow field and particle transport equations in the spatial domain (C1) limited by the inlet and overflow outlet cross-sections, where the flow is usually assumed fully developed, and the dust outlet cross-section. Formulation of the boundary conditions for the flow and particles’ transport at the dust outlet cross-section remains an open question. We address this problem numerically by comparing results of calculations performed by the above traditional approach, i.e., treating the problem in configuration C1, as well as in extended domains, namely those including a dust collecting bin (configuration C2) and a downcomer tubular outlet (configuration C3). Two boundary conditions at the downflow outlet were checked for each configuration, namely, a blocked outlet (zero velocity) and an open outlet (zero gas flow rate). Toward this goal, an efficient computational fluid dynamic (CFD) model of turbulent flow based on the Reynolds Stress turbulent closure scheme was developed, validated, and used to calculate velocity field and the pressure drop as well as particle cut size and separation efficiency in several Stairmand-type tangential flow cyclones. The results were tested and corroborated against the experimental data reported in the literature, including careful measurements performed by Gottschalk and Bohnet (1995 Gottschalk , O. , and M. Bohnet . 1995 . Two stage circuit for the separation of fine particles. PARTEC 95, Europ. Symposium on Separation of Particles from Gases, Nurnberg, March.  [Google Scholar], 1998 Gottschalk , O. , and M. Bohnet . 1998 . Calculation of grade efficiency and pressure drop of aerocyclones with suction of partial gas stream. PARTEC 98, European Symposium Separation of Particles from Gases, Nurnberg, March.  [Google Scholar]) for a 225 mm tangential flow cyclone, with downflow outlet connected to a tubular extension.

Particle separation in the traditional C1 cyclone configuration was shown to be most sensitive with respect to the choice of the boundary conditions at the downflow outlet, whereas with the dust outlet connected to a bin (C3 configuration) this condition has a much weaker effect on the fractional efficiency. Solutions for the C1 and C2 configurations, both combined with the blocked downflow outlet boundary condition yielded the cyclone's pressure drop in agreement with the Gottschalk and Bohnet's data. However, C2 configuration which contained a downcomer tubular extension was found preferable for correlating the measured fractional efficiency.