Agriculture Reference
In-Depth Information
Table 1. Analysis of variance (ANOVA) of the responses for
convective dried sugar beet pulp
R
e
zidu
a
l
Model
Response
R
2
SS
DF
MS
SS
DF
MS
F
p-value
UT 1/k
1
0.5150
3
0.1717
51.939
6
8.657
50.429
0.00421
0.896
UT 1/k
2
0.0320
3
0.0107
141.889
6
23.648
2213.932
0.00002
0.918
CT 1/k
1
0.9131
3
0.3044
47.034
6
7.839
25.755
0.01124
0.807
CT 1/k
2
0.3391
3
0.1130
1264.502
6
210.750
1864.452
0.00002
0.967
UT - untreated (plain dried sugar beet pulp); CT - chemically treated sugar beet pulp
R
ESULTS AND
D
ISSCUSION
Convective Dried Sugar Beet Pulp
Empirical models that are commonly used for mathematical representation of the process
of rehydration, Peleg and Weibull equation, proved to be adequate to fit the kinetic data of
convective dried sugar beet pulp, both untreated and treated. The coefficient of determination
(R
2
) was within the limits of 0.987 to 0.999 for Peleg equations while the Weibull equation
within the limits of 0.984 to 0.999. The predicted equilibrium moisture content values were
comparable for both models. As both given empirical equations satisfactory represent the
experimental results for further analyzing Peleg equation is selected, because for its
application it is necessary to determine only two parameters k
1
and k
2
are, while for the
Weibull equation necessary to determine three parameters α, β and equilibrium moisture
content (Me). Another reason for choosing this equation is the fact that in addition to the
equilibrium moisture content which can be obtained from both equations, Peleg equation
provides an opportunity to estimate the initial speed of rehydration.
The ANOVA results are reported in Table 1. for responses of kinetic parameters in the
case of convective dried samples. High values of R
2
, obtained for all responses indicate good
fit of experimental data to Eq. (5). All polynomial models tested for the selected responses
were significant at 95% confidence level (p-value; 0.05, Table 1). Second-order polynomial is
fitted well the experimental results for both the rehydration initial rate as well as the
equilibrium moisture content of untreated and treated sugar beet pulp subjected to convective
drying.
Finding polynomial dependence of these values it is possible to estimate the impact of
these two temperatures on the initial rate and the equilibrium values of the mass transfer, i.e.,
sugar beet pulp rehydration. Table 2. shows the values of the coefficients of the polynomial
regression. The significance of individual factors and their square influence but also their
mutual interaction was measured by the t-values (Djuric et al. 2004). The larger the
magnitude of the t-value the more significant is the corresponding coefficient.
The greatest linear effect on the initial speed of rehydration for untreated sugar beet pulp
has rehydration temperature, while its quadratic influence is even more significant when
compared with the linear. However, the most important factor in the quadratic polynomial is
