Model-Informed Microwave Processing of Materials
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MODEL-INFORMED MICROWAVE PROCESSING OF MATERIALS W.A.
Geoffrey Voss and H.K. Kua
Electrical Edmonton,
Engineering Alberta,
Department,
University
of
Alberta,
Canada T6G 2G7
ABSTRACT This paper reviews the expanding application of microwaves for processing solid materials, both natural and synthetic. The Canadian interest ranges from food processing to forest products, ceramic drying and curing to the preprocessing of rare minerals and ores, with the zeolite family of particularindustrial interest. In all cases, across the world, the number of process variables is large and the known physical data are limited. Yet the engineer requires to know only in general, involve rate and limit a few specific properties which, functions. The problem posed here, which has to be considered as a part of the unification of the subject of electromagnetic heating, concerns the careful use of atomistic modelling to achieve a model-informed empiricism As an example, it is shown in this paper that the for process development. majority of solids have the same piecewise linear approximate temperature model for absorbing and reflecting power: more than twenty variables affecting the dielectric properties can then be reduced to five or six which Correctly interpreted, this approach (due, in its need to be measured. to M.F. Ashby, 1987) may help solve many broad philosophic format, electromagnetic engineering problems, including those associated with breakdown and thermal-runaway.
Sutton
[1],
in
an
1989
important
processing of ceramic materials,
review
of
the
microwave
lists the following four major
apply in fact, these, characteristics; microwave microwave power applications if a fifth one is added: of
microwave
energy
all
volumetric
1.
Direct coupling heating.
2.
Microwaves are polarized can be controlled.
3.
Differential microwave coupling to phases, constituents leads to selective heating.
4.
Dielectric losses (and heating) accelerate rapidly (for a critical solids) with increasing temperatures above
and coherent;
creates
to
field distributions additives
and
value. 5.
Microwave heating is is, in general, temperature.
selective and, for drying and curing, below a critical self-regulating
of these characteristics apply to rf heating Many but not all more than 85% of the industrial which still represents There are two major application dielectric equipment market. differences between rf and microwave: (a)
best Rf has a lower capital cost but is drying/curing materials of a regular shape.
Mat. Res. Soc. Symp. Proc. Vol. 189. @1991 Materials Research Society
suited
to
(b)
Microwave is not product-shape limited distributions are far easier to control. design (fitting) is almost unlimited, from sections to the very small ones.
and field Applicator very large
In the list above, (2) and (3) are predominantly microwaveonly (0.4 - 60 GHz) characteristics. However, every process evaluation must consider the entire electroheat range: from dc infra-red and U.V. System development is now rapidly accel
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