Agriculture Reference
In-Depth Information
where: M
0
- moisture content at time t=0 (g/g), M
t
- moisture content at time t (g/g), k
1
and k
2
- the parameters of the model (k
1
is the Peleg rate constant and k
2
is is the Peleg capacity
constant) and t - time, min. In equation (1) “±” becomes “+” if the process is absorption or
adsorption and “-” if the process is drying or desorption.
This kinetic model offers the advantage that by calculating the inverse of the two
constants (k
1
and k
2
) it is possible to obtain the initial rate of mass transfer parameters and the
mass transfer parameters values at the equilibrium:
t
d
k
k
t
dM
1
1
2
lim
(2)
dt
dt
k
t
0
1
t
o
t
1
lim
M
M
lim
(3)
t
k
k
t
k
1
2
2
t
Weibull equation takes the form:
β
M
M
t
t
0
1
exp
(4)
M
M
α
e
0
where: M
t
- moisture content at time t, (g/g), M
e
- equilibrium moisture content (g/g), α and β
- parameters of Weibull equation (α is the scale parameter (s) and β is the dimensionless
shape parameter. The scale parameter α is a kinetic coefficient.), t - time, (min).
The disadvantage of this equation is that next to the parameters which have no particular
physical meaning and the equilibrium moisture content is a variable that has to be determined,
so that in this case is determined by three parameters.
Response surface methodology (RSM) is useful model for studying the effect of several
factors influencing the responses by varying them simultaneously and carrying out limited
number of experiments (Morgan, 1991). For the description of the responses Y (inverse
values of k
1
and k
2
for convective and microwave drying) a second-degree polynomial model
was fitted to data:
2
Y
b
X
b
X
b
X
X
(5)
i
i
ii
ii
ij
i
j
where b
i
- represents the linear, b
ii
- the quadratic and b
ij
- the interaction effect of the factors,
X
1
- convective drying temperature (or in case of microwave drying microwaves power) and
X
2
- rehydration temperature.
Statistical analysis was performed using Statistica software (Statsoft, 1995). Plotting
responses as a function of two factors drew response surface plots. Plots were generated with
the same software.
