All of the data are expressed as
mean and standard deviation values from three replicate measurements for
different heating conditions. The ANOVA and Duncan test were used to analyses the effect of salt content, voltage
gradient and electrode type on selected properties at the 5% significance level
(p?0.05). The statistical evaluation was performed by using software SPSS V.18.
Also, the software Table Curve 3D, V4 was used to plotting 3D view of the
relationship of parameters and extraction of regression equations.
specific exergy required for the ohmic concentration of tomato juice is shown in
Fig. 3. For all electrodes, exergy
consumption decreased significantly (p<0.05) as the voltage gradient and salt content increased. This was because of the dramatic reduction in the concentration time with an increase in voltage gradient and salt content. The electrolytic content increases with the salt concentration which increases the electrical conductivity. Therefore the heat generating rate increased inside the sample (Duguay et al., 2016; Icier and Ilicali, 2005; Sarkis et al., 2013; Darvishi et al., 2015). However, exergy consumption of Al electrode is higher than the 316L St and Br electrodes under different concentration processes (p<0.05). The results also showed that there was no significant difference between the exergy consumption of 316L St and Br electrodes (p>0.05) at the same heating condition. The minimum specific
exergy consumption of 316L St and Br
electrodes was obtained 2.73 (MJ/kg water evp) and 2.85 (MJ/kg water evp),
respectively, at high voltage gradient (11 V/cm).
Fig. 4 demonstrated
that the exergy efficiency increased with
increasing of voltage gradient and salt content (p<0.05). This consequence indicates that heating and water evaporation rates within the sample were quicker with higher salt content and voltage gradient. Because the passing current through the sample was higher and this increased the heat generation rate in the sample and consequently exergy efficiency increased significantly (p<0.05). As can see in Fig. 4, the exergy efficiency of 316L St (10.12-17.63%) and Br (9.84-16.73%) electrodes is higher than the exergy efficiency of Al electrode (8.41-15.17%). A similar trend has been observed by Bozkurt and Icier (2010) in the ohmic cooking process of beef, and Darvishi et al. (2015) in the ohmic concentration of tomato juice. They reported that the lower processing time and higher homogeneous heating reduced the exergy losses or equivalently entropy generation, which meant the increase in the exergetic efficiency of the system. In order to estimate the mean amount of exergy efficiency at the desired level of the variables, variation of exergy efficiency was correlated as follows: