XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 251
sorting application). Multimode applicators can support
wider tubes than single-mode applicators, which in turn
support higher throughputs than single-mode applicators
and can be optimized to achieve a higher degree of treat-
ment uniformity. With high power microwave supplies and
careful design of the microwave field pattern, sufficiently
high power density can be achieved to efficiently induce
fracture.
As a rule of thumb, the maximum particle size to enable
mass flow should be approximately five times smaller than
the flow path diameter (depending on other factors such as
particle shape, size distribution, etc), shown in Table 1 for
the single-mode applicator case. Thus, multimode applica-
tors may also support a coarser feed size and it is highly
desirable to determine the feed ore flow properties to maxi-
mise the particle top size of a given system.
The flow path diameter to achieve mass flow follows
the trends shown in Figure 2 for the different nominal par-
ticle size distributions illustrated. The large-scale system
described by Buttress et al. (2017) used a 200 mm tube,
and 915 MHz in other regions of the world) and 433 MHz.
When the microwave frequency is reduced from 2.45 GHz
to 433 MHz, the wavelength increases proportionally, and
larger waveguide are required to propagate the microwave
energy. Table 1 gives the relevant dimensions.
Single-mode applicators support a well-defined field
pattern inside a waveguide-sized applicator due to the super-
position of forward and reflected microwaves. Thus, larger
waveguides enable larger diameter single-mode applica-
tors to be used, which in turn support higher throughputs.
However, no microwave heating magnetrons currently exist
at 433 MHz and its development would require significant
resources.
When the size of the applicator exceeds the waveguide
dimensions, the applicator may support many different
field patterns (or modes) and is referred to as a multimode
applicator. The field pattern can be controlled by geom-
etry of the applicator, waveguide entry angles and by using
multiple microwave inputs to the same applicator (refer
to Batchelor et al. (2016a 2016b) for an example in the
Table 1. ISM frequency scaling parameters
ISM
Frequency
(MHz)
Approx.
Wavelength
(cm)
Waveguide
Code
(WR)
Approx.
Waveguide
Width
(mm)
Approx.
Waveguide
Height
(mm)
Approx.
Maximum
Particle Size
(mm)*
2,450 12 WR340 86 43 17
896 33 WR975 248 124 50
433 69 WR2300 584 292 117
*Maximum particle size to achieve mass flow for the single-mode applicator waveguide dimension case.
-16mm
-40mm
-60mm
-80mm
-100mm
-120mm
-140mm
-160mm
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
0 100 200 300 400 500 600 700 800 900
Flow Path Diameter (mm)
Ore 1
Ore 2
Figure 2. Flow path diameter requirements for gravity fed mass flow systems for two ore types
Maximum
Throug
hpu t
(t/h)
2.45GHz
si
le-mode
896MHz
si
le-mode
433MHz
single-mode
sorting application). Multimode applicators can support
wider tubes than single-mode applicators, which in turn
support higher throughputs than single-mode applicators
and can be optimized to achieve a higher degree of treat-
ment uniformity. With high power microwave supplies and
careful design of the microwave field pattern, sufficiently
high power density can be achieved to efficiently induce
fracture.
As a rule of thumb, the maximum particle size to enable
mass flow should be approximately five times smaller than
the flow path diameter (depending on other factors such as
particle shape, size distribution, etc), shown in Table 1 for
the single-mode applicator case. Thus, multimode applica-
tors may also support a coarser feed size and it is highly
desirable to determine the feed ore flow properties to maxi-
mise the particle top size of a given system.
The flow path diameter to achieve mass flow follows
the trends shown in Figure 2 for the different nominal par-
ticle size distributions illustrated. The large-scale system
described by Buttress et al. (2017) used a 200 mm tube,
and 915 MHz in other regions of the world) and 433 MHz.
When the microwave frequency is reduced from 2.45 GHz
to 433 MHz, the wavelength increases proportionally, and
larger waveguide are required to propagate the microwave
energy. Table 1 gives the relevant dimensions.
Single-mode applicators support a well-defined field
pattern inside a waveguide-sized applicator due to the super-
position of forward and reflected microwaves. Thus, larger
waveguides enable larger diameter single-mode applica-
tors to be used, which in turn support higher throughputs.
However, no microwave heating magnetrons currently exist
at 433 MHz and its development would require significant
resources.
When the size of the applicator exceeds the waveguide
dimensions, the applicator may support many different
field patterns (or modes) and is referred to as a multimode
applicator. The field pattern can be controlled by geom-
etry of the applicator, waveguide entry angles and by using
multiple microwave inputs to the same applicator (refer
to Batchelor et al. (2016a 2016b) for an example in the
Table 1. ISM frequency scaling parameters
ISM
Frequency
(MHz)
Approx.
Wavelength
(cm)
Waveguide
Code
(WR)
Approx.
Waveguide
Width
(mm)
Approx.
Waveguide
Height
(mm)
Approx.
Maximum
Particle Size
(mm)*
2,450 12 WR340 86 43 17
896 33 WR975 248 124 50
433 69 WR2300 584 292 117
*Maximum particle size to achieve mass flow for the single-mode applicator waveguide dimension case.
-16mm
-40mm
-60mm
-80mm
-100mm
-120mm
-140mm
-160mm
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
0 100 200 300 400 500 600 700 800 900
Flow Path Diameter (mm)
Ore 1
Ore 2
Figure 2. Flow path diameter requirements for gravity fed mass flow systems for two ore types
Maximum
Throug
hpu t
(t/h)
2.45GHz
si
le-mode
896MHz
si
le-mode
433MHz
single-mode