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air over the timber surface. The air À ow rate and direction is controlled by fans and
the temperature and relative humidity of the air can be adjusted to suit the species and
sizes of timber being dried. It is thus possible to make full use of the increase in drying
rate which can be achieved by raising the temperature to the maximum value which
a particular timber species can tolerate without excessive degrade. Contrary to the
results presented [9] microwave heating improved the strength in comparison to the
strength obtained in conventional hot air drying. It is also noted that the infrared dry-
ing can reduce the strength of the spruce woods signi¿ cantly. It should be noted that
by applying natural convection the highest strength can be obtained with the highest
drying duration. This can take weeks, months, or even years [9]. The discussion sug-
gests further investigation for future work on different specimens.
Diameter
mm
21.00
UTS
MPa
49.60
Maximum
%
14.02
Stress MPa
50
45
40
35
30
25
20
15
10
5
0
0
2
4
6
8
10
12
14
16
18
20
Strain %
FIGURE 14
Stress-strain for microwave dried wood.
Diameter
mm
21.00
UTS
MPa
44.52
Maximum
%
10.50
Stress MPa
50
45
40
35
30
25
20
15
10
5
0
0
1.25
2.50
3.75
5.00
6.25
7.50
8.75
10.00
11.25
12.50
Strain %
FIGURE 15
Stress-strain for infrared dried wood.
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