intervieW
Question and ansWer
on ‘fluid mixing
and mixers’
ixing is at the heart of most
production systems and is
of vital importance in the
chemical process industry,
pharmaceutical industry,
food industry and other allied industries.
Mixing is critical because the quality
of the final product and its attributes
depend on the quality of the mix. Good
mixing is imperative for improved product
quality, providing high yields, lowering
operating costs and thereby enhancing
profitability.
m
Fluid mixing can be broadly classified
into the following application classes -
blending of miscible liquids, blending
of immiscible liquids, liquid gas mixing,
liquid solid mixing, fluid motion. Though
mixing of solids to some extent resemble
the mixing of low-viscosity liquids, there
are significant differences between the
two processes. The wide variety and ever
increasing complexity of mixing processes
encountered in industrial applications
requires careful selection, design and
scale up to ensure effective and efficient
mixing.
Fluid mixing technology has vastly
improved over the past decade. In
addition to the laboratory and pilot scale
trials, design engineers have access to
tools such as Computational Fluid Mixing
(CFM), Digital Particle Image Velocimetry
(DPIV), Laser Doppler Anemometry (LDA),
Laser Induced Fluorescence (LIF), for
better understanding of mixing systems.
As a result, equipment manufacturers
have been able to develop and improvise
impeller designs customized for end user
applications. Moreover, the improvements
and the technological advances in the
mechanical, electrical, and electronic
components, instrumentation and
process control, have accelerated the
development of mixing equipment that
maximize mixing performance at lower
power consumption.
40
PECM Issue 29
The success of mixing equipment
largely depends on a good working
relationship between the equipment
manufacturer and the end user. While
it is the responsibility of the equipment
manufacturer to build, install and
commission mixing equipment best
suited to end user’s applications, it is
equally important that the end user
should clearly define the process
materials, conditions and any special
requirements.
.A mixing equipment is no longer a
generic production tool, but a critical
and decisive business tool. This is
because profitability and competitive
advantage are dependent upon subtle
improvements in product quality through
gains in mixing performance and
efficiency.
1) H OW DO FLUID MIXERS DIFFER FROM
OTHER TYPES OF MIXERS / BLENDERS ?
Industrial applications involve mixing of
solids to solids (free flowing solids and
pasty materials), solids to liquids, solids
to gas (reactions), liquids to liquids, and
liquids to gas. Fluid mixing is generally
associated with liquid – liquid mixing and
liquid-gas mixing. Though mixing of solids
to some extent resembles the mixing of
low-viscosity liquids, there are significant
differences between the two processes.
These are as follows:
Fluid mixing depends on the creation of
flow currents, which transport unmixed
material to the mixing zone adjacent to
the impeller. In heavy pastes or masses
of particulate solids there are no such
currents are possible and mixing is
accomplished by other means.
Power required for mixing of dry solids
and viscous pastes is higher than that
consumed in blending of liquids.
In fluid mixing, a “well-mixed” product
usually means a truly homogenous
liquid phase. In mixing pastes and
powders the product often consists of
two or more easily identifiable phases,
each of which may contain individual
particles of considerable size. From a
“well-mixed” product of this kind, small
random samples will differ markedly in
composition.
As a result, there are several differences in
the design, construction and operation of
fluid mixing equipment as compared to
solid mixers. Fluid mixing equipment are
termed as liquid agitators. Solid mixing
equipment are commonly referred to as
mixers and blenders. While fluid mixing
technology has been extensively studied
and understood, solid mixing is more
complex. The understanding of solid
mixing, and the design of solid mixers
continues to be art rather than a science.
2) H OW HAS FLUID MIXING
TECHNOLOGY EVOLVED OVER THE
PAST DECADE ? H OW IS THE FLUID
MIXING TECHNOLOGY OF TODAY
MORE EFFECTIVE / EFFICIENT THAN
THE TECHNOLOGY OF PREVIOUS
GENERATIONS ?
The end user’s understanding of fluid
mixing technology has improved over
the past decade. The highly competitive
industrial environment requires that
mixing equipment manufacturers
constantly improve and provide
customized solutions which are
productive, efficient and economical.
Equipment manufactures, industry
are constantly in search of newer
technologies and are investing in product
research and development. The following
are some of the significant improvements
in the field of fluid mixing technology and
equipment.