Civil Engineering Reference
In-Depth Information
4.31 cm
10 cm
10 cm
1.02 cm
5 cm
8.63 cm
5 cm
0
2.28 cm
0
30°C4560
75
90
105 120 135
45°C 50
55
60
(a)
65
70
75
80
(b)
10 cm
5 cm
0.4 cm
0
1 cm
30°C 0
65
80
95
110
125
(c)
Figure 3.18
Temperature distribution across the heated zone of a saturated concrete
after (a) 5 seconds of microwave heating at 2.45-GHz frequency; (b) 2 sec-
onds of microwave heating at 10.6-GHz frequency; and (c) 1 second of
microwave heating at 18-GHz frequency (incident power = 1.1 MW/m2).
Table 3.2
Dimensions of standard waveguides
Microwave frequency (GHz)
Designation
Width (mm)
Height (mm)
2.45
WR340
86.36
43.18
10.6
WR90
22.86
10.16
18
WR42
10.66
4.31
Figures 3.19 to 3.21 show that, regardless of the microwave frequency
and concrete water content, the temperature in the concrete decays expo-
nentially with distance from the exposed surface. Again, it is also obvi-
ous that at a constant microwave power, there is an inverse relationship
between the penetration depth of microwaves with the water content and
the microwave frequency. As a result, an increase in either the water con-
tent of concrete or the microwave frequency results in faster decay in the
microwave power within the concrete specimen.
Figure 3.22 shows the temperature distribution across the microwave
incident surface of the concrete. The temperature distribution across the
concrete surface is a function of the microwave mode excited by the micro-
wave generator and the waveguide used to deliver the power. The modes
of transmission in the waveguides are basically the multiple solutions of
Maxwell's equations governing the behaviour of the electromagnetic waves
Search WWH ::
Custom Search