Volume SH 9: Part
1 State-of-the-Art Review
Part 1
considers the mixing of bulk solids (i.e., powders)
into liquids. These solids may be in an agglomerated
form, in which case the mixer will normally be required
both to deagglomerate and to distribute the solids throughout
the liquid phase. Alternatively, the solids may consist
of primary particles which should not be broken down
further during the mixing operation.
The part
opens by considering the various processes involved
when solids are contacted and incorporated with a liquid.
This involves wetting and the removal of air initially
on the particle surfaces, as mixing proceeds. Details
of the agglomeration process are discussed to illustrate
that a critical shear strength must usually be exceeded
at some position in a mixer in order that all agglomerates
are properly broken down.
The effects
of different types of non-Newtonian property of the
initial or developing mix on the efficiency of mixer
action are reviewed. Estimation of mixer power consumption
in different mixer types is covered. In particular,
the consequences for the efficacy of the mixing operation
are reviewed when a "cavern" is formed during
the agitation of a shear-thinning mix (either with or
without a pronounced yield stress). Viscoelastic properties
are also considered.
A comprehensive
survey of all commercially-available mixers suitable
for powder-liquid mixing has been undertaken and is
included. The many different generic mixer types available
have been classified into several sub-categories (Types
A to F); most of these types have been further classified
into sub-categories. The mixers have been grouped according
to the typical viscosity range they are capable of covering,
the shear rates developed, and the speed of rotation
of the mixing element(s). Both batch and continuous
mixers are considered. The commercially-available mixers
considered have been summarised, using manufacturers'
literature, in Appendix A.
A full
discussion is included on the approaches to mixer selection.
Finally, alternative methods of scaling up a mixing
operation are reviewed.
Volume SH 9: Part
2 Design Guide
Part 2
is intended to provide a simple tool for the designer
to use in the design and selection of powder-liquid
mixers. The part is split into two main sections: the
first half covering material, operational and systems
considerations and the second half providing selection
and design procedures.
Sections
2 to 4 cover the influence of: the solid and liquid
raw material components properties; the finished product
on mixer selection with particular reference to the
end use, and mixture quality in particular; systems
considerations; the actual design and selection procedure
consists of Sections 5 to 7. Section 5 provides a summary
classification of the mixer types available.
Section
6 gives the procedures for mixer selection from consideration
of several important parameters: by viscosity, particle
size, scale of mixing, shear rate and energy, and de-agglomeration
and de-aeration capability. Section 7 gives suggested
mixer sizing procedures. The experimental work required
is outlined. Small-scale testwork and the treatment
of results, including size and power requirement scale-up
and limits of applicability are discussed. Finally full
scale testing and discussions with the suppliers are
mentioned.
