2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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any interference of disordered void spaces inside sample.
At nearly end of drying period, heat and mass transfer do
not only occur at the surface of rubber sheet but also they
stimulate inside the rubber sheet. However, moisture
inside rubber sheet moves to surface slower than the
movement from the surface of rubber sheet to ambient
environment. Drying rate will be relative lowers
compared to the beginning of drying time. Additionally,
the moisture content of sample is decreased easily when
the thickness of rubber sheet decrease. A thickness of
rubber sheet is decrease the moisture inside rubber can
evaporate easier than the infrared hot air.
Consequently, at a higher drying air temperature, rate
of moisture removal became relatively faster than those of
a lower temperature. These drying curves are typical
equations for predicting drying kinetics of grain kernel
and food stuff, corresponding to the previous works [13].
C. Moisture diffusion coefficient of rubber
Experimental drying a thin layer of rubber was dried
in the drying rate decreased. The equation for the
effective diffusion coefficient of the rubber can be written
in the form equation exponential. An effective diffusion
coefficient (D) is a function of rubber with temperature
(T) and can express the effective diffusion coefficient in
the mathematical equation (12) for infrared drying:
(12)
R
2
=0.925
D. Effect of temperature
0.0
0.2
0.4
0.6
0.8
1.0
0
20
40
60
80 100
Moisture Ratio, MR
Drying time (h)
IR 4000W, 51.2
°
C, Min= 36.7 %d.b.,
H= 3.25 mm
IR 4000W, 64.1
°
C, Min= 38.7 %d.b.,
H= 3.34 mm
Fig. 8. Effect drying air temperature of rubber sheet at drying
temperatures of 51.2
q
C and 64.1
q
C (initial moisture contents of 36.7-
38.7% dry-basis, IR intensity of 4000 watt)
.
Further investigating, Fig. 8 performed the evolution of
moisture ratios among drying time at inlet air
temperatures of 51.2
q
C and 64.1
q
C. At the drying air
temperature of 64.1
q
C, the reduction of moisture was
faster than that of a low drying air temperature 51.2
q
C.
Moreover, the initial moisture content of the rubber had
low relatively effect on decreasing rate of moisture
content compared to drying temperature and thickness of
sheet rubber.
E. Quality analysis and specific energy consumption
(SEC) of rubber sheet
(a) (b) (c)
Fig. 9.
Visual characteristics of dried rubber sheet (a) IR heating 44.0°C
(b) IR heating 64.1°C and (c) open sun 12 hours 27.4 °C and
conventional drying 28.9°C.
Considering the visual characteristic of the drying at
inlet air temperatures of 27.4-64.1ºC as show in Table IV,
it reported that before starting the experiment, white
granules were dispersed uniform in its texture. After
drying at low inlet air temperatures of 27.4-51.2°C, the
dried rubber texture seemed to be bright and then became
uniform gel on its texture as revealed in Fig. 9(a) and (c).
On the other hand, when drying at high inlet air
temperature of 54.2-64.1ºC, dried rubber sheet texture
appeared to be darker and stickier than those obtained of
low inlet air temperature (Fig. 9(b)). Obviously seen in
high inlet drying air temperature, the visual observation
showed that mostly texture of the dried rubber contained a
small amount of bubble granule on sheet. As mentioned
earlier, these results were corresponding to chemical
quality test as shown in Table III. Also, the quality of
dried rubber sheet was determined by following with STR
5L standard methods because this sample was the grade in
marketing. Of these, all data imply that this research using
IR source as low drying temperature might be another
approaches to be applied for preparing a good quality
drying rubber sheet.
TABLE
III
C
HEMICAL QUALITY TESTING OF RUBBER SHEET WITH
STR 5L
STANDARDS
;
I
NFRARED RADIATION
Exp.
no
Drying temperature
(°C)
Chemical quality testing
Drying time (h)
%Dirt
%Ash
%VM
%N
2
P
o
%PRI
Colors
1
39.2
0.079
0.34
0.60
0.30
48.0
87.5
3.0
127
2
44.0
0.070
0.22
0.49
0.35
50.0
100.0
4.5
111
3
51.2
-
-
-
-
-
-
-
89
4
54.2
-
-
-
-
-
-
-
46
5
62.9
0.031
0.32
0.57
0.33
46.0
100.0
4.0
44
6
64.1
0.026
0.29
0.51
0.39
44.5
100.0
4.0
39
Note: Standard STR 5L block rubber must be limited as follows:
%
Dirt
d
0.04 %
,
%
ASH
d
0.40 %
,
%
VM
d
0.80 %
,
%
N
2
d
0.60
%,
%
P
O
!
35 %
,
%
PRI
!
60
%
, Color
d
6.0.
TABLE
IV
»¼
º
«¬
ª
u
RT
0.02618508
exp7-10 7
9.9999999
=D
