Flow patterns in granulating systems

Particle flow patterns were investigated for wet granulation and dry powder mixing in ploughshare mixers using Positron Emission Particle Tracking (PEPT). In a 4-l mixer, calcium carbonate with mean size 45 μm was granulated using a 50 wt.% solution of glycerol and water as binding fluid, and particle movement was followed using a 600-μm calcium hydroxy-phosphate tracer particle. In a 20-l mixer, dry powder flow was studied using a 600-μm resin bead tracer particle to simulate the bulk polypropylene powder with mean size 600 μm. Important differences were seen between particle flow patterns for wet and dry systems. Particle speed relative to blade speed was lower in the wet system than in the dry system, with the ratios of average particle speed to blade tip speed for all experiments in the range 0.01–0.25. In the axial plane, the same particle motion was observed around each blade; this provides a significant advance for modelling flow in ploughshare mixers. For the future, a detailed understanding of the local velocity, acceleration and density variations around a plough blade will reveal the effects of flow patterns in granulating systems on the resultant distribution of granular product attributes such as size, density and strength.     

Flow regime, hydrodynamics, floc size distribution and sludge properties in activated sludge bubble column, air-lift and aerated stirred reactors

This paper presents a comparative study how reactor configuration, sludge loading and air flowrate affect flow regimes, hydrodynamics, floc size distribution and sludge solids-liquid separation properties. Three reactor configurations were studied in bench scale activated sludge bubble column reactor (BCR), air-lift reactor (ALR) and aerated stirred reactor (ASR). The ASR demonstrated the highest capacity of gas holdup and resistance, and homogeneity in flow regimes and shearing forces, resulting in producing large numbers of small and compact flocs. The fluid dynamics in the ALR created regularly directed recirculation forces to enhance the gas holdup and sludge flocculation. The BCR distributed a high turbulent flow regime and non-homogeneity in gas holdup and mixing, and generated large numbers of larger and looser flocs. The sludge size distributions, compressibility and settleability were significantly influenced by the reactor configurations associated with the flow regimes and hydrodynamics.     

Flow and Flow Decay of Refractory Castables

Installation of refractory castables depend not only on flow,but also on how soon the flow is lost because of setting.The loss of flow(flow decay)has always been one of the main problems of refractory castable manufacturers,a problem that has not been too well described in literature.The flow decay has been studied for a castable system based on alumina,pointing out some general trends.The flow decay was found very temperature sensitive,being strongly accelerated by temperature increases.To compensate for excessive flow loss,a retarder like citric acid may be used.Thus flow decay was measured as a function of citric acid(retarder) addition at 35℃.     

Velocity measurements and flow field characteristic analyses in a turbo air classifier

Turbo air classifier is one of the most widely used powder classification equipment. The rotor cage as a rotary component can create a forced centrifugal field, so it is a key part for turbo air classifier. In order to investigate the effect of structural variations of the rotor cage on flow field characteristics, three dimensional velocity measurements of the annular region in a turbo air classifier equipped with two different rotor cage bottom plates (A and B type) are performed by laser Doppler velocimeter (LDV). It is found that the different bottom plates have different axial and tangential velocity distributions in the annular region. However, the structural variations of the rotor cage have hardly any effect on the radial velocity. Based on the classification principle, the relation between the classification performance and the flow field characteristics is investigated in great detail.The results of the flow field measurements were tested by the classification experiments carried out with cement raw meal and ground calcium carbonate. The results demonstrate that B type bottom plate can realize the production of narrow particle size distributions, so it is more favorable for classification than A type bottom plate. Classification experiment results are in good agreement with the results of the flow field measurements.     

Consolidation and flow of cohesive bulk solids

The strength and the flow properties of bulk solids can be determined by performing shear tests. A shear test always consists of two parts, consolidation and measurement of strength. The measured strength depends on the way and degree of consolidation. During consolidation a stress history is impressed on the bulk solid sample which only vanishes after steady state flow. Since the consolidation is normally done nonhydrostatically, the strength will depend on the direction of stress application (anisotropy). Thus, the strength of a bulk solid sample strongly depends on its stress history and it can show anisotropic behaviour. These effects have to be considered when comparing available shear testers.     

循环流化床中流动结构的动态变化

采用激光相位多普勒粒子分析仪（ＰＤＰＡ）测量了二维循环流化床中局部颗粒运动行为及流动结构．通过将ＰＤＰＡ采集的数据进行动态图形化处理，研究了稀、密相的结构以及颗粒聚团的形成和分解．研究结果表明：在循环流化床中不仅存在稀、密两相的不均匀流动结构，而且密相和稀相自身内部也存在不均匀性；颗粒聚团的形成和分解是一个动态过程，颗粒间不同速度造成颗粒相互碰撞，密相能够分解形成稀相，稀相能够合并成为密相．在流动过程中稀相、密相及介于稀、密相间的乳相以动态的形式存在和分解，形成复杂的动态流动结构．     

气固下行流化床反应器Ⅱ气固两相的流动规律

气固下行流化床反应器气固两相流动过程是比较复杂的，沿轴向气固两相运动可分为第一加速、第二加速和恒速３个运动段，沿径向局部气体速度、颗粒速度和颗粒浓度都具有不同程度的不均匀性。而这种不均匀性是由气固两相顺重力场湍动运动所决定的。和循环床提升管相比，下行管反应器气固两相沿径向分布的不均匀性得到有效地改善，气固可以实现超短接触操作，因而是一种新型高效气固超短接触反应器     

—Review Paper—Current State-Of-The-Art Measurements Of Ozone In The Gas Phase And In Solution

This paper is a critical review and summary of the analytical procedures currently used by operating water utilities to control ozone treatment processes, considering disinfection as well as the many oxidative applications of ozone in water treatment applications. The role of common interferences in the various methods is described.

In operating U S., Canadian, European, and Japanese water treatment plants currently employing ozone as a primary disinfectant, ozone nearly always is followed by the addition of small quantities of chlorine, chlorine dioxide, or chloramine to provide the residual in the distribution system and to act as a secondary disinfectant. Clearly, the analytical procedures used must distinguish between the various species. This review critically presents these various factors and their implication with respect to “true values” of ozone determined under widely varying conditions.     

梯形纵肋管束换热器传热及流阻特性研究

本文对纵肋管束换热器的传热、阻力特性进行了试验研究，得出传热特性和阻力特性关系式，并着重分析梯形纵肋管束换热器的特性。进一步探讨了管束节距、肋片高度对传热及流阻的影响情况。与相同结构的光管管束比较，换热增加１０％－３５％，而流阻最高增加４８％，最低情况下，低于光管。文中指出具有梯形纵肋的管束呈现出一种特殊的传热及流阻规律，它不但可获得较低的流动阻力，而且传热得以进一步强化。     

Effect of the geometry and pattern of the flow channel on the performance of polymer electrolyte membrane fuel cell

This research focuses on the effect of the geometry and patterns of the gas flow channel on the PEM fuel cell performance. Simulation was conducted and the results were verified by experiments. Three-dimensional, single phase, compressible and isothermal models of 5 cm² electrodes, anode and cathode, were developed and studied by utilizing a commercial Computational Fluid Dynamics (CFD) software, FLUENT 4.5. Two types of gas flow channel were investigated: conventional and interdigitated. The results showed that the flow channel pattern does not have a significant effect on the anode cell performance, whereas it has a strong effect/influence on the cathode cell performance. The interdigitated design provides a higher limiting current density and cell performance than the conventional design on the cathode side. Moreover, the cell performance does not depend on the inlet and outlet channel widths. On the contrary, for the interdigitated design, it was influenced by the shoulder width. Finally, experiments were conducted to validate the simulation results.