ARR - Annual Report
As described in the contract proposal the first phase of work was to:
- I prepare and characterise a model dispersion
- develop or evaluate a suitable low stress viscometer
and progress in these in reported in section 2 and 3 of this report. The model dispersion was chosen to consist of well characterised particles in which the degree of flocculation/deflocculation could be controlled by suspension in a fluid whose viscosity could be modified thus altering the shear stresses present for a given strain rate. For reasons previosuly discussed it was decided to use a mono-disperse polystyrene latex as the model dispersion and this report describes how sufficient quantities for rheological experiments were synthesised, worked up and characterised. Work is still proceeding on the characterisation of these latices, particularly to measure their zeta potentials as a function of salt concentration and to determine the effect on this of high sucrose and gylcerol concentrations, these substances being chosen to alter the viscosity of the suspending fluid.
A requirement of the programme of work to be done under this contract is the ability to measure shear stress/strain properties at low strain rates and in oscillation at small amplitudes. To this end the University has purchased a Deer Rheometer and this report gives a preliminary assessment of this instrument. Section 4 of this report is an account of preliminary experiments to study 2 the effect on the viscosity of a calcium carbonate/water/Dispex system of increasing the viscosity of the suspending liquid. The results of this work are discussed in relations to a published suspension flow equation and to a theoretical model of the balance of interparticle and hydrodynamic forces on suspension stability.
Abstract
Pressure drop-velocity measurements for flow of water slurries comprised of various concentrations of narrow size fractions of fine glass beads in l.0", 1.5", 2.0" and 2.5" diameter straight pipes, and in an array of 1.0" and 2.0" pipe bends, fittings and valves were taken. Using these data friction loss coefficients, and equivalent lengths (in numbers of pipe diameters) were calculated for the various fittings. The experimental facility used in getting these data, the actual data and the preliminary analysis of the results are presented in this report.
Experience in powder handling industry have shown that some powders exhibit flow problems when transported through pipes and hoppers, and also the tendency of particles to adhere to conveyor belts and machinery. These problems have been thought to be the cause of electrostatic charge build up on the powder particles. In some cases it has been observed that two almost identical powders will behave differently, one may cause flow and other problems whilst the second may be quite acceptable.
The aim of this short study was to measure a few electrical properties of some powders which caused problems and to compare them with those similar powders which did not give rise to any problems. The properties studied were:
- (i) Tribocharging characteristics of the powders.
- (ii) Resistivity as a function of pressure.
- (iii) Dielectric constant and spectroscopic analysis.
The tribocharging behaviour of the powders was studied by passing small quantities through different tubes, for example, copper, aluminium, perspex etc, and measuring the charge generated as a function of powder velocity and tube length. The magnitude and polarity of charge acquired by the powder determines the nature and severity of the problem.
The resistivity and dielectric constant both play a role in determining the build up of charge and rate of discharge. The higher the resistivity of a powder the longer it takes for the charge to leak away from it. The greater the dielectric constant the higher the charge it would acquire. Both these parameters were measured and compared for different powders. Spectroscopic analysis such as infra-red spectra of the powders were also compared.
Removal of liquid from filter cakes can be accomplished by mechanical or hydraulic methods after cake formation is The local porosity in porous beds (Tiller and Cooper, 1962) is a complete. This paper deals with the latter procedure.
Function of Hydraulic Pressure Distribution
Function of hydraulic pressure distribution and cake compressibility. Calculation of average porosity requires an integration of local values as determined by liquid flow patterns. As most compressions of filter cakes are irreversible, the local porosity is a function of the maximum effective pressure (frictional pressure loss) reached during cyclical operations.
Reversal of Flow
Reversal of flow through a cake develops radically changed pressure distributions which can be utilized to reduce local porosities. Analytical expressions are presented for reduction of average porosity brought about by reversing flow of liquid in plate-and-frame and recessed plate filter presses.
A general discussion of deliquoring operations
A general discussion of deliquoring operations is given as an introduction to a more complete analysis made at the University of Houston of three different types of hydraulic deliquoring. Objectives and deliquoring methods are listed. A short discussion of solid-liquid separation provides a general background in relation to the topic under consideration.
Cake structure
Cake structure as affected by particle size and shape is discussed. The simplest method of reducing average porosity consists of increasing applied filtration pressure. Unfortunately, for compressible difficult-to-dewater materials, increasing pressure neither decreases liquid content nor increases flow rate after a usually relative low pressure is reached.
Hydraulic deliquoring methods
For such materials the hydraulic deliquoring methods discussed in the attached thesis hold considerable promise. The three methods are:
- Reverse flow
- Right-angled or three-dimensional flow
- High viscosity deliquoring
Mechanical expression, deep cone thickening, dispersion, and centrifugal drainage are briefly treated.
An art review on the measurement of various agglomerate strengths in Japan, as the request of IFPRI, has been already reported on 20th April, 1982. The present paper deals with the experimental results of some agglomerate strengths for polymeric materials such as polypropylene of polyethylene particles. These agglomerates of polymeric particles were produced by hot fluidized beds at The City College of The City University of New York.
As indicated in the preliminary IFPRI report (Gabriel Tardos, Dominick Mazzone and Robert Pfeffer: Agglomeration of Particle Systems in Fluidized Beds - Phase 31, Tardos, G. et al. made a detailed investigation into the minimum sintering fluidization velocity necessary to keep a bed of sticky or agglomerated particles in the fluidized state. In this connection, three samples of agglomerated polymeric particles were sent from New York to Tokyo in order to obtain agglomerate strength data at several temperatures between 80 and 170°C.
Unfortunately, the usual strength testing procedure regarding a cylindrical agglomerate with the diameter/length ratio about half does not apply to three samples of agglomerated polymeric particles because of irregular shape. An advantage of agglomerate strength measurements in this work, for this reason, is that the presumed tensile strengths of the agglomerates can be calculated from experimental results of interparticle forces at temperatures ranging from 80 to 170°C. In addition to this measurement, a new method for measuring the breakage strengths of three samples in streams of hot air was introduced into this work.
The aim of the following study is the evaluation of the feasibility of electrostatic classification in the size range below approx. 1 um. The study has been subdivided into the following chapters: