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Title: The effect of moisture on the mixing characteristics of powders : the nature and magnitude of interparticulate forces due to moisture bonding, and the effect of this bonding on powder flow characteristics and equilibrium mixture quatity are experimentally and theoretically examined
Author: Coelho, M. B. C.
ISNI:       0000 0001 3559 7335
Awarding Body: University of Bradford
Current Institution: University of Bradford
Date of Award: 1976
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Closely sized cuts of ballotini and sand were prepared and mixed in a Y-cone blender, adding varying amounts of water, in order that the effect of the moisture content on the equilibrium mixture quality might be studied. The moisture additions caused the mixtures to exhibit an increasingly cohesive behaviour, and marked improvement in the equilibrium mixture quality, which occurred at a well defined though difficult to predict value of the moisture content. Two forms of water retention were examined, (adsorbed layers and liquid bridges) and the value of the interparticulate force calculated, as a function of humidity, temperature. pressure, solid nature and surface roughness. Two datum values of the humidity were defined: a) A minimum humidity at which adsorbed layer interaction becomes important. b) A critical humidity at which liquid bridges first appear. These two datum values are related to the solid nature, surface roughness, temperature and pressure. Statistical analysis of the mixing process is made for a binary mixture taking aggregation into account, and formulae for the segregated and random variances are derived. These become a function of the aggregation pattern, and it is shown that as aggregation increases both the random and the segregated variances should decrease, statistically confirming the experimentally known fact that cohesive powders are not segregation prone. A simple pattern of aggregation is used to illustrate the above concepts and the validity of the statistical approach confirmed by a computer simulation of sampling from such a mixture, the results of which were in good agreement with the calculated values. Computer routines for the calculation of interparticulate forces and random and segregated standard deviations, and the simulation program are included.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available