2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 168 -
under different drying strategies was comparative
determined.
III.
M
ATERIAL AND
M
ETHOD
A. Materials
The fresh natural rubber sheets were provided from
Cooperative rubber station (CRS) at Hat Yai, Songkhla
province and Biochemistry research laboratory (BRL),
Faculty of Science Prince of Songkla University. The
dimension of sample rubber sheet of CRS and BRL was
about of 40
u
90 cm
2
and 70
u
50 cm
2
, respectively
correlated to their weight of 0.8-1.5 kg and 1.4-2.0 kg.
The moisture content of samples was determined
following by ASAE, 1982 method [3].
B. Equilibrium moisture content (EMC)
At the present, equilibrium moisture content (EMC) of
unsmoked rubber sheet was determined by the
gravimetric-static method [11]. Six selected saturated salt
solutions for taking equilibrium stage as follows: KNO
3
,
NaCl, Mg (NO
3
)
2
•6H
2
O, MgCl
2
•6H
2
O, (NH
4
)
2
SO
4
and
LiCl. All of the saturated salt solutions provide relative
humidity surrounding of 10-90% among surrounding
temperatures of 40-60
q
C. Thus, small pieces of rubber
sheet samples were kept in airtight vial with each
saturated salt solution. The sample vials were tempered
in incubator with a constant temperature of 40, 50, 55
and 60
q
C. After a few weeks, the samples were in
equilibrium state with surrounding. The samples were
weighed at 5 days interval until three successive reading
were each less than 0.5% of the previous one Then the
moisture content of rubber sheet samples was determined
by following of ASAE 1982 method [3]. The average
EMC value of sample was showed by means of
triplication. Finally, the experimental data were fitting
curved by four conventional EMC models which were
shown in Table I.
TABLE
I
E
QUILIBRIUM MOISTURE CONTENT MODEL
Model
Eqn.
Modified Halsey [5]
(1)
Modified Oswin [9]
(2)
Modified Henderson [9]
(3)
Modified Smith [10]
(4)
where M
eq
is the
equilibrium moisture content (% dry-basis), T is the
absolute temperature (K), RH is the relative humidity, A, B, C, D and E
are the constant value
.
C. Drying methodology
Fig. 1 illustrated the green house dryer. The
dimension of drying room was about 1
u
1.2
u
1.5 m
3
. All
sides of dryer were made of black plastic sheet for acting
as solar collector whilst the translucent plastic sheet was
used for making roof. At the bottom and top of dryer
there were two inlet and two outlet air tubes for heating
and exhausting air, respectively.
Fig. 1. Schematic diagram of green house drying system.
Fig. 2. Schematic diagram of hot air drying system.
Fig. 3. Schematic diagram of infrared drying system.
Fig. 2 showed the small scale drying unit with 20 rubber sheet samples
capacity. The drying temperature was measured by K-typed
thermocouple connected to a data logger with an accuracy of +1
q
C and
was recorded every half an hour.
E
D
RH 1
RH
)2CT BT A(
eqM
»¼
º
«¬
ª
1/C
B)
A(T
RH))
ln(1
eqM
»
¼
º
«
¬
ª
RH)]
ln(1 2CT BT[A eqM
1/D
A-
eqM
RH ln) CT (BT
2
»
¼
º
«
¬
ª
