full2011_inter.pdf - page 140

2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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air temperature of dry air, water vapor and wet rubber
(°C), Wmix and Wf is the humidity ratio of dry air before
and after drying (kg of H2O/kg of dry air) and hfg is the
specific evaporated enthalpy (kJ/kg)
Calculation of moisture content after drying
The procedure for calculating moisture content
after drying of each thin section is to calculate an
empirical thin layer drying equation developed by Page
(Page, 1949) is used. It can be written as the following
equation:ൌ ൬ ‹ െ ‡“
‹ െ ‡“ ൰ ൌ ‡š’ሺെš–› ሻ (6)
š ൌ െͲǤͲͲͲͲͳʹ ʹ ൅ ͲǤͲͲͲͳͷͲ͹ ൅ ͳǤͲͲͲͲͶͳͳͲͻ (7)
› ൌ ͲǤͲͲͲͶͻ͸͹Ͷ ʹ ൅ ͲǤͳͲͳ͸ͳͶͶ͹ ൅ ͳͷǤʹͻͳͳͶͷ (8)
where, MR is the moisture ratio, Min and Mf is the initial
and final moisture content (% dry-basis), respective, Meq
is the equilibrium moisture content (% dry-basis) and T is
the drying temperature (K)
Performance model
The performance of dryer is defined as specific
energy consumption (SEC) and average drying rate (DR).
There can be written as the following equation:ൌ ሺʹǤ͸ ൅ ሻȀሺ ‹ െ ˆሻ’ (9)
ൌ ™ Ȁ (10)
where, the value of 2.6 is the energy conversion factor,
Min and M f is the initial and final moisture content (%
dry-basis), respective, mp is the dry mass of product (kg
of dry rubber), mw is the mass of water evaporated from
rubber (kg of water) and DT is the drying time (min).
E. Rubber drying system modeling (RDSM)
The mathematical model of rubber drying system
program was written by Visual Basic Version 6 software.
The simulation flow chart is show in Fig. 2. For running
the program, a number of know data are needed as input.
The input parameters were composed of initial moisture
content, rubber temperature, and inlet ambient air
temperature, specific air flow rate, and relative humidity,
depth bed of skim block rubber, the desired drying time
and the time interval.
Fig. 4.Simulation flow chart of fixed-bed drying.
III. RESULTS AND DISCUSSION
A. Equilibrium moisture content (EMC)
The four widely recommended models which were
investigated for skim rubber was shown in Table I and
Fig. 3 and Fig. 4. The constant values that were estimated
for each of the models, and the indices for estimating the
errors associated with the models, which are the
coefficient of fit (R2) and RMSE, are shown in Tables I at
temperature of 40-60qC. The modified Oswin model has
good relation to the experimental values, corresponding
to its higher R2 and lowest RMSE value compared to the
others. The R2 and RMSE value of modified Oswin
model 0.977 and 0.0011 (Table I), respectively.
Fig.3. Relationship between equilibrium moisture content with
difference model of Skim rubber at temperatures of 45q C and relative
humidity of 10-90%.
0
1
2
3
4
0 50 100
Equilibrium moisture content
(%dry-basis)
Relative Humidity (%)
Experimental
Modified Oswin
Modified Hendersonl
Modified Halsey
Iglesias and Chirife