THE GROWTH OF CAVERNS FORMED AROUND ROTATING IMPELLERS DURING THE MIXING OF A YIELD STRESS FLUID

The growth of caverns, formed around rotating impellers in a yield stress fluid during mixing in a stirred vessel, has been studied by observing impeller speeds at which fluid motion was first observed at the vessel's wall and base, and at the free liquid surface. The effect of impeller geometry has been studied with a disk turbine (DT), a two bladed paddle (2BP), a pitched blade turbine (PBT) and a marine propeller (MP).

The presence of four baffles (10%) was found to increase the impeller speed at which the cavern reaches the vessel wall by 9% on average over that observed without baffles. After the cavern has reached the vessel walls, impeller type had a small effect upon the vertical expansion of the cavern with increasing impeller speed. Radial flow impellers (DT and 2BP), on average, performed better than an axial flow impeller (MP), with a mixed flow impeller (PBT) in between. Baffles significantly reduce the rate of this vertical expansion of the cavern. Clearance of the impeller from the vessel base had little effect upon the growth of the cavern above the impeller.     

旋转填充床内液—液法制备碳酸锶纳米粉体

在旋转填充床中采用液液相法合成了平均粒径为（３０～４０）ｎｍ、粒度分布窄的碳酸锶纳米粉体。探讨了转速及干燥过程对颗粒平均粒径、无因次方差的影响,并对颗粒进行了ＴＥＭ、ＸＲＤ表征。该法过程简单,生产率高,易于工业化。     

YIELD STRESS DETERMINATION OF ASPHALT EMULSIONS

The yield stress of asphalt emulsions was investigated as a potential quality control parameter. Viscometric data were determined using concentric cylinder, parallel plate, and cone and plate geometries. The use of a novel slotted-plate technique was investigated to determine the yield stress of asphalt emulsions in a direct way, that is to say, without extrapolation. The Saybolt viscosity was determined following the AASHTO T 72-97 standard procedure. It was found that the slotted-plate technique produced reproducible and consistent results, which were far superior to those obtained by rotational rheometer techniques. The yield stress of the emulsions appears to be a more accurate measure of the performance specification for asphalt emulsions than the Saybolt data.     

YIELD STRESS DETERMINATION OF ASPHALT EMULSIONS

The yield stress of asphalt emulsions was investigated as a potential quality control parameter. Viscometric data were determined using concentric cylinder, parallel plate, and cone and plate geometries. The use of a novel slotted-plate technique was investigated to determine the yield stress of asphalt emulsions in a direct way, that is to say, without extrapolation. The Saybolt viscosity was determined following the AASHTO T 72-97 standard procedure. It was found that the slotted-plate technique produced reproducible and consistent results, which were far superior to those obtained by rotational rheometer techniques. The yield stress of the emulsions appears to be a more accurate measure of the performance specification for asphalt emulsions than the Saybolt data.     

ON THE MOMENT COEFFICIENT CALCULATION OF A ROTATING DISK IN A TURBULENT FLUID FLOW

Mixing in co-rotating sinusoidal cavity flows is studied with period, T, and phase shift, a, as parameters. Notice that the main obstacle to uniform mixing is the existence of stable :ower periodic orbits, mixing windows, where uniform mixing takes place, are found in the T— a space u:iing bifurcation analysis. The main advantage of this method is a great saving of the computation time.     

FLOW OF VISCOPLASTIC FLUIDS ON AN INCLINED PLANE: EVALUATION OF YIELD STRESS

Within the general category of so called generalized Newtonian fluids, there exists a class of materials which do not deform until the applied shear stress exceeds a critical value called yield stress. Conversely, such a material behaves like a solid as long as the shear stress is less than the yield stress. This class of materials is called viscoplastic fluids. The question whether the true yield stress exists or not is indeed far from settled (1), but the notion of a yield stress has proved to be quite useful in practice in describing the steady shear rheological behaviour of a range of materials especially of particulate suspensions. Consequently, yield stress appears as a parameter in all constitutive relations (which purport to describe the steady shear behaviour of viscoplastic materials), and its evaluation is important before an engineering flow problem can be solved. Conversely, there are some simple hydrodynamic situations which allow the value of the yield stress to be extracted from macroscopic quantities such as flow rate-pressure drop data. In this paper, we examine this possibility using gravity driven flow of a viscoplastic material on an inclined plane.     

FLOW OF A NON-NEWTONIAN FLUID WITH HEAT TRANSFER ABOVE A ROTATING DISK CONSIDERING THE ION SLIP

The steady flow and heat transfer of a conducting non-Newtonian fluid due to the rotation of an infinite nonconducting disk in the presence of an axial uniform steady magnetic field are studied considering the ion slip. The governing nonlinear equations are solved numerically using finite differences, and the solution shows that the ion slip and the non-Newtonian fluid characteristics give some interesting results.     

FLOW OF A NON-NEWTONIAN FLUID WITH HEAT TRANSFER ABOVE A ROTATING DISK CONSIDERING THE ION SLIP

The steady flow and heat transfer of a conducting non-Newtonian fluid due to the rotation of an infinite nonconducting disk in the presence of an axial uniform steady magnetic field are studied considering the ion slip. The governing nonlinear equations are solved numerically using finite differences, and the solution shows that the ion slip and the non-Newtonian fluid characteristics give some interesting results.     

EFFECTS OF HALL CURRENT ON UNSTEADY FLOW OF A SECOND GRADE FLUID IN A ROTATING SYSTEM

Rotating flow of a second grade conducting fluid on an infinite oscillating plate is investigated when the fluid is permeated by a transverse magnetic field and the Hall effects are taken into account. It is once again found that an asymptotic solution exists in the presence of both suction and blowing at the plate. For fixed magnetic field parameter the boundary layer thickness increases with the increase in Hall parameter. The present analysis is more general than any previous investigations.     

EFFECTS OF HALL CURRENT ON UNSTEADY FLOW OF A SECOND GRADE FLUID IN A ROTATING SYSTEM

Rotating flow of a second grade conducting fluid on an infinite oscillating plate is investigated when the fluid is permeated by a transverse magnetic field and the Hall effects are taken into account. It is once again found that an asymptotic solution exists in the presence of both suction and blowing at the plate. For fixed magnetic field parameter the boundary layer thickness increases with the increase in Hall parameter. The present analysis is more general than any previous investigations.     

TECHNICAL NOTE: THE EFFECT OF SLIP ON THE FLOW IN A ROTATING CHANNEL

Slip flow occurs in a wide variety of practical chemical engineering processes. This work models, for the first time, the interaction of surface slip and system rotation normal to the flow direction. It is found that the flow fields are affected considerably. For Poiseuille flow, slip increases the longitudinal flow rate at low rotation, but decreases it at high rotation. For Couette flow, slip decreases the longitudinal drag. The solutions are also exact solutions of the Navier-Stokes equations.     

MEASUREMENT OF THE DIFFUSIVITY OF 1-NAPHTHOL IN WATER WITH A ROTATING DISC

The solubility and diffusivity of 1-naphthol in water are reported at several temperatures.     

复合材料层合板孔边应力场的有限元计算

纤维增强复合材料具有较高的比强度、比刚度和比模量,在航空航天领域得到越来越广泛的应用.层合板是当前复合材料在工程结构中应用的主要形式.对于含孔的层合板结构,由于材料的各向异性以及孔的影响,其应力分布比较复杂,采用数值解是较好的选择.本文基于层合板的可设计性特点,综合考虑铺层角度、铺层顺序等对层合结构的影响,设计出了一种二十四层对称层合板.以有限元方法为基础,借助ANSYS分析工具,对该层合板含孔结构的孔边应力重点分析,得出了不同铺层角度铺层中应力分布的云图和孔边应力分布曲线.本文结论对复合材料层合板优化设计和带孔层合结构的应力计算具有较好的参考价值.     

DRAG AND TORQUE ON A SLOWLY TRANSLATING DISK IN A ROTATING FLUID; EFFECTS OF A PLANE WALL, ANOTHER DISK OR A SIDE WALL

A previously presented analytical method for determining the Stokes drag on a disk sedimenting in the presence of fixed boundaries (Davis, 1990) is adapted to the case of a disk translating broadside in a rotating fluid, possibly with relative rotation. By carefully simplifying the potentially lengthy algebra, concise formulations are again developed for the cases of two disks translating together with opposite relative rotations, a disk translating towards a rigid plane that rotates with the fluid and a disk translating within a similarly rotating concentric circular container. Flows that are asymmetric allow the possibility of adjusting the relative rotation so that the disk is torque free. Values of the Taylor number, based on the disk radius, up to 50 are considered.     

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.     

SOLIDS DISTRIBUTION IN STIRRED SLURRY REACTORS: INFLUENCE OF SOME MIXER CONFIGURATIONS AND LIMITS TO THE APPLICABILITY OF A SIMPLE MODEL FOR PREDICTIONS

The features of solids concentration distribution were investigated in baffled and unbaffled tanks of high aspect ratio, stirred with multiple radial, mixed-flow or axial impellers. In the baffled tanks the average profiles can be predicted with the sedimentation-dispersion model regardless of impeller type - in spite of slight systematic departures from the average trend at the impeller plane and/or midway between the impellers. This is hardly possible for the unbaffled tanks due to lack of physical foundation of this simple model. When the unbaffled tank is stirred with hydrofoil impellers, an inverted profile is even obtained. The mentioned departures and this last anomalous behaviour are qualitatively discussed with reference to particle-turbulence interaction.     

SOLIDS DISTRIBUTION IN STIRRED SLURRY REACTORS: INFLUENCE OF SOME MIXER CONFIGURATIONS AND LIMITS TO THE APPLICABILITY OF A SIMPLE MODEL FOR PREDICTIONS

The features of solids concentration distribution were investigated in baffled and unbaffled tanks of high aspect ratio, stirred with multiple radial, mixed-flow or axial impellers. In the baffled tanks the average profiles can be predicted with the sedimentation-dispersion model regardless of impeller type - in spite of slight systematic departures from the average trend at the impeller plane and/or midway between the impellers. This is hardly possible for the unbaffled tanks due to lack of physical foundation of this simple model. When the unbaffled tank is stirred with hydrofoil impellers, an inverted profile is even obtained. The mentioned departures and this last anomalous behaviour are qualitatively discussed with reference to particle-turbulence interaction.     

EFFECTS OF TURBULENT SHEAR STRESS ON THE GROWTH OF SUSPENDED PLANT CELLS IN A BUBBLE COLUMN REACTOR

In this paper,effects of increasing the height of column,bubble size and gas flow rate onthe growth of suspended Catharanthus roseus plant cells in a 1.5 litre bubble column were studied.Statistical characteristics of turbulence such as auto-correlation function,and auto-power spectral den-sity function of the nuctuating liquid velocity were measured in a bubble column employing pseudo-cell-granulated agar.Calculations of turbulent shear stress were carried out.From these studies it is sug-gested that in plant cell suspension culture sparged with large bubbles.turbulent shear stress is prob-ably one of the most important reasons for the inhibited cell growth and cell damage.Larger bubblesor higher gas flow rates lead to the increase in shear stress and are more detrimental to plant cells.     

挖补角度对复合材料修补片固化过程温度和热应力的影响

利用有限元方法,数值模拟了不同挖补角度的树脂基复合材料修补片热固化过程中的温度场和热应力场,并分析了挖补角度对修补片的温度、固化度和热应力的影响。仿真计算结果表明:挖补角度越小,修补片中心点处的温度峰值越大,固化速率越快,热应力越大;挖补角度越小,修补片非中心点处的固化速率越快,热应力越小,且挖补角度对非中心点处的热应力影响较大。综合分析后可知,在一定挖补角度范围内,合理选择挖补角度,可控制修补材料内部热应力,并获得较好的复合材料修补质量。研究结果为实际修理提供了良好的数值依据。