2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 160 -
Mathematical modelling and drying
characteristics of GABA rice
S. Wanthong
1
, S. Tirawanichakul
2
and Y. Tirawanichakul
3
1
Discipline of Excellent of Chemical Engineering, Faculty of Engineering,
Prince of Songkla University, Songkhla 90110 (Thailand)
2
Energy Research Technology Center and Department of Chemical Engineering, Faculty of Engineering,
Prince of Songkla University, Songkhla 90110 (Thailand)
3
Energy Research Technology Center, Department of Physics, Faculty of Science,
Prince of Songkla University, Songkhla 90110 (Thailand)
Corresponding author e-mail:
Abstract
The objective of this study is to determine
experimentally some thermo-physical properties of
GABA rice. Thermo-physical properties in terms of
equilibrium moisture content (EMC), apparent
density (
U
), void fraction (
H
), specific heat capacity (c
p
)
and moisture diffusion coefficient (D) were studied.
These parameters are useful and necessary for drying
analysis at moisture contents ranging from 16 to
50%dry-basis. For determining the EMC equation,
the five models chosen to fit the experimental data;
the modified Oswin model gave the best results for the
desorption isotherms of for GABA Sungyod rice,
providing the highest R
2
(0.9800) and the lowest
RMSE (0.0611). For determination of other thermo-
physical parameters, the result showed that the
apparent density, the void fraction and the specific
heat capacity of GABA Sungyod rice were linearly
dependent on moisture content. For drying thin layers
model of GABA Sungyod rice, the results concluded
that the simulated values using the Page’s model and
Midlili’s model had a good agreement with the
experimental values for air impingement drying and
infrared drying, respectively. In addition, the effective
diffusion coefficient determined by the model is
dependent on the drying temperature. The effective
diffusion coefficient value when using air
impingement drying was slightly higher than infrared
drying.
Index Terms
- GABA Rice, Impingement dryer,
Mathematical modelling, Thermo-physical properties
I. N
OMENCLATURE
n
Number of pairs of data
x
i
Independent variable
y
i
Dependent variable
X
ei
Experimental moisture content (dry-basis)
X
pi
Predicted moisture content (dry-basis)
N
Number of experimental points
U
Apparent density of parboiled grain (kg/m
3
)
m
Mass of the grain (kg)
V
b
Volume of volumetric vessel (m
3
)
H
Percentage of void fraction (%)
V
oil
Oil volume (m
3
)
V
b
Volume of volumetric vessel (m
3
)
c
p
Specific heat capacity (kJ/kg
q
C)
c
c
Specific heat capacity of calorimeter
(kJ/kg
q
C)
c
w
Specific heat capacity water (kJ/kg
q
C)
m
c
Mass of calorimeter (kg)
m
w
Mass of water (kg)
m
p
Mass of paddy (kg)
T
eq
Equilibrium temperature (
q
C)
T
ci
Initial temperature of calorimeter (
q
C)
T
wi
Initial temperature of water (
q
C)
T
pi
Initial temperature of paddy (
q
C)
M
eq
Equilibrium moisture content in decimal
RH
Relative humility in decimal
T
Absolute temperature, K
R
Universal gas constant (8.314 kJ/kmol-K)
MR
Moisture ratio
M
in
Initial moisture content of the GABA rice
(decimal dry-basis)
M
t
Moisture content at time t (dry-basis)
a, b, c Empirical constants in the drying models
t
Drying time (s)
R
2
Correlation coefficient
RMSE Root mean square error
D
eff
Effective diffusion coefficient (m
2
/s)
D
0
Pre-exponential Arrhenius factor (m
2
/s)
E
a
Activation energy (kJ/ mol)
L
Grain length (m)
r
o
Radius of the grain (m)
O
n
Root of the Bessel function of the n
th
kind of
zero order (
O
1
=2.4048,
O
2
=5.5201,
O
3
= 8.6537)
II. I
NTRODUCTION
Rice parboiling process involves soaking paddy in
cold water (or hot water) and then in steaming at variable
pressures, followed by drying and finally, milling. It is a
good source of dietary fibers, essential amino acids,
proteins, carbohydrates, vitamins and other [1], especially
on brown rice and
J
- amino butyric acid (GABA) rice
because they are highly nutritious; however, texture of
brown rice has been more slightly hard, low stickiness
and crumbly texture compared to GABA brown rice. It is
realized that GABA plays an important role in the central
nervous system as a neurotransmitter. GABA is a well-
known blood pressure lowering compound (lower
