ARR - Annual Report
Preamble
The work reported here falls into three distinct areas. Part A provides a review of attrition and an appraisal of existing test methods. Part B presents the results of work on the behaviour of alumina particles in the annular attrition cell and in single particle crushing experiments and associated tests. Part C is concerned with developing insight into attrition kinetics by initial tests in the annular shear cell. The immediate goal was a clarification of the effect of molecular weight on the attrition of high density poly- ethylene.
This report describes work done at the Cambridge University Department of Chemical Engineering during the first year of an IFPRI contract. Most of the year’s work was spent on two aspects of the project, a literature survey and the development of a computer program to predict the rate of deaeration of a powder in a baker. The report on the former has been completed and is attached with this report. The results of the computer analysis have been written up in the form of a “final report” which it is hoped to distribute to IFPRI members by the end of next month.
In the present report we confine ourselves to details of the other aspects of the work during the year. This report therefore consists of the following sections:
- Introduction
- Experimental measurement of stress-strain curves.
- A report of some small flowrate measurements to investigate the effects of interstitial pressure gradient on flowrate.
- Future work.
- The current technical and fiscal status of the project.
SYNOPSIS
During this first year a preparation procedure for stable model suspensions was established. Preliminary rheological data suggest the presence of a deformable stabiliser layer. There seems to exist an analogy between oscillatory and steady state data.
The yielding of weakly flocculated suspensions starts at low strains (10 -2 - 1O'3) both in steady state and oscillatory flow. In the former it occurs before the stress overshoot is reached. Time effects suggest a kinetic contribution in yielding. The structural breakdown proceeds according to different patterns in different materials thus complicating the modelling.
Data reduction schemes for dielectric probing of structure have been suggested on the basis of data for carbon black suspensions. The application of transient dielectric data in studying thixotropic time scaler is demonstrated.
"THD makes no warranty or representation with respect to the application of any result or technique described in this report, and THD shall not be responsible in any way for any claims or liabilities arising out of the application by any party or any result or technique described herein. Any application, authorized or unauthorized by THD or TFPRI, shall' be made at the users own risk."
This disclaimer is in accordance with the standard policy of the T-H. Delft.
Summary
This is the fourth phase of a research program to study the agglomeration of particles in fluidized bed systems. The report contains an updated review of the literature on high temperature agglomerating fluidized beds as well as equilibrium shapes of liquid bridges between particles. It also includes a comparison between predicted and measured minimum gas velocities necessary to keep a bed of sintered granules in the fluidized state.
The use of a dilatometer to measure the minimum sintering temperature of potentially agglomerating particles is described together with measurements to determine agglomerate strength. Different materials such as glass, polymers, coal and inorganic salts were used during the experiments.
The correlation between the sintering temperature and other thermodynamic properties of these materials, as observed from a differential scanning calorimeter test, was determined experimentally. A new original theory concerning the strengthening of a liquid bridge between two particles due to relative motion (viscous dissipation) is proposed. Future theoretical and experimental work on the project including a means to verify the above theory are also outlined.
Abstract
This 1984 IFPRI Annual Report, covering the period from September 1, 1983 to April 15, 1985, presents the results of studies involving the characterization, the rheology and the flow in straight pipe as well as pipeline transitions of concentrated aqueous laterite suspensions. The report consists of two parts. The first part presents the results of comprehensive bench-scale tests whose aim was to probe the limits of the properties of laterite suspensions, and to explore some of the means to control them. Experimental data on sedimentation rates, zeta potential, 'in-situ' particle aggregate size, and yield stress for concentrated laterite suspensions were taken and have been correlated with suspension pH. The second part of the report presents the results of large scale pipeline flow experiments involving concentrated laterite suspensions. The experimental work in this part consisted of property characterization and rheology measurements for various concentrations of laterite suspensions, and also tests on laminar and turbulent flow of these suspensions through straight pipe and through pipeline bends, fittings and flow control and flow metering devices. The results of the experiments have been analyzed, and are presented as correlations of zeta potential, yield stress and stress-rate of strain dependence as functions of suspended solids concentration, as friction factor - generalized Reynolds number correlations for straight pipe flow, and as correlations of friction loss with generalized Reynolds number for flow through bends, fittings and valves.
Introduction
Sorting is synonymous to the separation of two- or multicomponent mixtures into its individual components. The newly produced materials being the better and the more valuable, the less they are contaminated with components i. e. materials of the other kind. The report mainly covers the dry sorting of two component mixtures by means Of a combination of two classification methods i. e. sieving and air classification. A method which has been developed at Clausthal.
The method can be used for coarse materials only, that is for particulate mixtures coarser than approximately one millimeter. Sorting in this size range becomes more and more important however, since it may be used for the recycling of waste or secondary products. The process described may, on the other hand, also be used for the dry softing of minerals such as coal or ore where water is scarce or not available in sufficient quantities, and also in countries with average temperatures below freezing point, and it may replace wet methods as used up until now in mineral Processing. The combined sorting process sorts mixtures into individual components with high throughputs, reasonable costs of investment and low specific costs.
Abstract
Many problems concerning the behaviour of particulate solids in a vessel remain unsolved. One of them is the phenomenon of wall pressure increase arising from vibrations or impacts on the wall of the vessel. An example is the insulation of low temperature tanks whore perlite powder is packed in the central annular space of double walled tanks holding liquefied gas. Tank wall expansion or contraction, caused by temperature changes whenever liquefied gas is added or removed, packs the perlite powder more densely and to quantify the wall pressure increase and to elucidate the mechanism of the phenomenon, so, that this can be taken into account in the design of storage tanks and vessels.
In the present study the wall pressure increases due to slight impacts on the front wall of a rectangular vessel containing particulate solids have been calculated by using a Janssen type equation which has been modified by introducing an angle between the direction of the major principal stress and the horizontal axis. This was then checked against experimentally obtained data.
The results indicate that the increase in wall pressure is probably due to the change in the angle of the principal stress in the powder bed and that this, in turn, comes from the change of the arrangement of the particles.