Values
of exergy loss for different heating
conditions are presented in Table 2. The specific exergy loss values varied between 2.25 and 4.42 (MJ/kg
water evp) for 316L St electrode, 2.39 and 4.04 (MJ/kg water evp) for Br
electrode, 2.75 and 5.11 (MJ/kg water evp) for Al electrode, and significantly
decreased as the voltage gradient and salt content increased (p<0.05). The treatment time was longer under low salt content and voltage gradient levels hence entering exergy to the heating cell was increased. For this reason, exergy loss increased with decreasing salt content and voltage gradient. From thermodynamic point of view, the exergy loss increased when the temperature boundary of the heating system is higher than the ambient temperature (Darvishi et al., 2015; Corzo et al., 2008). Thus, prevention of heat transfer across the boundary of the system could reduce the exergy loss. It is not recommended using of the aluminum metal as electrode for ohmic concentration/evaporation processes due to the higher exergy consumption and lower exergy efficiency as compared with the 316L St and Br electrodes at the same heating conditions. Figure (5) shows that the IP increased with increasing of voltage gradient and salt content. In fact, the IP is the maximum useful exergy which can be absorbed from the exergy loss and increased the exergy efficiency of process by applying some changes in the initial system such as isolation of cell wall, selection of suitable electrode, and applied the energy out of cell by water vapor for preheating of fresh product. The IP of control samples varied between 2.37 – 3.64 (MJ/kg  water evp) for Br electrode, 2.89 – 3.70 (MJ/kg water evp) for 316L St electrode, and 2.94 – 4.68 (MJ/kg water evp) for Al electrode. While these values at 2% w/w salt content varied between 1.99 – 2.81 (MJ/kg water evp), 1.86 – 2.68 (MJ/kg water evp), and 2.39 – 3.98 (MJ/kg water evp) for Br, 316L St, and Al electrodes, respectively. Also, IP values of 316L St and Br electrodes are lower than that found for Al electrode at the same heating conditions. Maximum improvement potential can be assessed and structural inefficiencies become apparent, which might trigger interests in process innovations. Conclusion The effect of salt content, electrode type and voltage gradient evaluted on exergy aspets of ohmic tomto paste prdocution, and found as: -          Exergy efficincy increased with increasing salt content and voltage gradient. -          Applied of Al electrode incresed the exergy consumption than Br and 316L St electrodes. -          There is no significant difference between exegy aspects of Br and 316L St electrodes. -          Exergy loss significantly decreased with increasing voltage gradient and salt content (p<0.05). -          The minimum improvement potential was obtained 1.86 MJ/kg water in 2% (w/w) and 11 V/cm for 316L St electrode.

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