Abstract: The effect of rapid mixing on floc formation, breakage and re-formation using aluminium sulfate ('alum'), polyaluminium chloride and a cationic polyelectrolyte were investigated using a continuous optical monitoring technique. For the aluminium-based coagulants it was found that, with shorter times of rapid mix, larger flocs were formed, but only limited re-growth occurred in all cases, indicating a significant irreversibility of the floc break-up process. For cationic polyelectrolytes, the re-growth of flocs occurred to a much greater extent and with longer rapid mix times floc breakage was almost fully reversible. Residual turbidity values before floc breakage and after re-formation were consistent with the dynamic monitoring results. (C) 2004 Society of Chemical Industry.

Abstract: Rockfill stress-strain behavior is strongly controlled by the breakage of rock particles. Particle breakage is shown to depend on stress level and the ambient relative humidity. A technique to perform tests on rockfill samples under relative humidity control has been developed. It has been applied to testing large diameter samples of a crushed quartzitic shale under oedometric conditions. Relative humidity is imposed by means of a double stage approach: moist air in thermodynamic equilibrium with a given saturated salt solution is first circulated through the sample. Circulation of moist air is interrupted and the specimen is allowed to reach equilibrium. A technique to extend the feasible suction range of the technique down to 2.5 MPa is described. Details of the evolution of collapse and swelling/shrinkage strains, as changes in Relative Humidity are imposed, are reported in the paper. Experimental findings are consistent with an underlying mechanism of particle breakage explained by the phenomenon of subcritical crack propagation.

Abstract: A drop weight tester was designed for the purpose of analyzing single particle impact breakage characteristics of different materials. Test results were evaluated through the breakage distributions of different size fractions at various impact energy levels. Breakage parameter t10 (Narayanan, 1986) is used to represent the degree of size reduction which is assumed to be represantative of the breakage product size distribution obtained from drop-weight tests. Relation between specific comminution energy level and breakage index number (t10) was established on the size fractional base so that the variation in impact breakage characteristics of different materials can be evaluated. It can be concluded that, drop-weight test method is a useful and practical way of evaluating the impact strengths of various materials on the size fractional base and results of which can be used in the mathematical modelling of autogenous and ball milling.

Abstract: The particle size distribution (psd) produced by breakage of wheat in the Perten Single Kernel Characterisation System (SKCS) was measured using sonic sifting, for a range of wheat varieties, kernel sizes and moisture contents. At moisture contents of 16% wb, the psd produced by the SKCS was very evenly spread over the range 106–3350 μm, with the average particle size much greater than would result from roller milling. Hard wheats gave slightly smaller average particle sizes in the broken material (this was unexpected and contrasts with First Break roller milling, for which hard wheats give larger output particles than soft wheats), but the variation in psd among different wheat varieties was surprisingly small. This indicates that the SKCS exerts a very positive breakage action on wheat grains, giving similar degrees of breakage to kernels of different hardness. The reported hardness index therefore depends primarily on the crushing force profile or energy to grind, and is not confounded by differences in the extent of breakage achieved. Kernel size similarly gave little difference in the output psd. The effect of increasing the moisture content from 9 to 17% wb was to increase the average output particle size greatly; moist kernels do not break so readily in the SKCS.

Abstract: A new low-amplitude filtering technique has been developed for the identification of fiber breakage in fiber reinforced plastics from acoustic emission data. In this approach, the acoustic emission hits associated with fiber breakage are separated from the hits associated with other failure mechanisms by filtering out the low amplitude hits from the measured data. The lowest remaining amplitude upon the cumulative plot of the remaining hits vs. load coinciding with the cumulative signal strength vs. load plot is taken as the borderline between fiber breakage hits and non-fiber breakage hits. Experiments were conducted on unidirectional-fiber specimens and complex-fiber specimens to examine the efficacy of the proposed technique. Evaluation of the experimental results by visual inspection and extensive scanning electron microscope studies verifies the low-amplitude filtering technique as a reliable tool for identifying fiber breakage in fiber reinforced plastics.

Abstract: A method is presented for developing multiple particle breakage distribution functions that include the shape factor, as well as the particle size. The technique is to first develop a joint probability distribution that accounts for the size and shape factor of each child particle. This is then reduced by successive integration to the marginal probability used in the breakage equation. This technique guarantees mass conservation and exchangeability of child particles while allowing the user to choose the number of child particles formed per breakage. It also allows the user to choose the functional form for the size distribution of particles as well as independently choosing the functional form for the shape factor distribution of particles. To solve the breakage equation, a discretization method is used that conserves particle mass during breakage and correctly predicts changes in the total number of particles. Simulation results show that the shape distribution functions may yield distinguishable shape factor profiles after crushing. Comparison with experimental data indicates that these theoretical functions can be used to model real systems. © 2004 American Institute of Chemical Engineers AIChE J, 50: 937–952, 2004

Abstract: Monosodium L-glutamate crystals, which are of fragile needle, were obtained by batch crystallization with a natural cooling mode from aqueous solution. The effect of seeding on the product size was examined over a wide range of seed-loadings. The seed-loading ratio C s , defined as the mass ratio of the added seeds to the theoretical yield per batch, had basically the same effect on the product crystal size as observed previously in cooling crystallization of mechanically strong granular crystals such as potassium alum. At high seed-loading ratios as C s ≥ C b *, where C s * is a critical value of C s , seed crystals grew with practically no secondary nucleation. Crystal breakage due to mechanical impacts brought by an agitator occurred only slightly for the small products. For the large crystals the breakage was significant. The breakage also depended on the type of stirrers used; the anchor stirrer induced less breakage than the turbine stirrer. The transient supersaturation was measured on-line by an electro-conductivity method.