Valuesof exergy loss for different heatingconditions are presented in Table 2. The specific exergy loss values varied between 2.25 and 4.42 (MJ/kgwater evp) for 316L St electrode, 2.39 and 4.04 (MJ/kg water evp) for Brelectrode, 2.
75 and 5.11 (MJ/kg water evp) for Al electrode, and significantlydecreased as the voltage gradient and salt content increased (p<0.05). The treatmenttime was longer under low salt content and voltage gradient levels henceentering exergy to the heating cell wasincreased. For this reason, exergy lossincreased with decreasing salt content and voltage gradient. From thermodynamic point of view, the exergy loss increased when the temperatureboundary of the heating system is higher than the ambient temperature (Darvishiet al.
, 2015; Corzo et al., 2008). Thus, prevention of heat transfer across theboundary of the system could reduce the exergyloss. It is not recommended using of the aluminum metal as electrode for ohmicconcentration/evaporation processes due to the higher exergy consumption and lower exergyefficiency as compared with the 316L St and Br electrodes at the same heatingconditions.Figure(5) shows that the IP increased with increasing of voltage gradient and saltcontent. In fact, the IP is the maximum useful exergywhich can be absorbed from the exergyloss and increased the exergy efficiencyof process by applying some changes in the initial system such as isolation of cellwall, selection of suitable electrode, and applied the energy out of cell by watervapor for preheating of fresh product.
The IP of control samples varied between2.37 – 3.64 (MJ/kg water evp) for Brelectrode, 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 contentvaried 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 Alelectrode at the same heating conditions.
Maximum improvement potential can beassessed and structural inefficiencies become apparent, which might triggerinterests in process innovations. ConclusionThe effectof salt content, electrode type and voltage gradient evaluted on exergy aspetsof ohmic tomto paste prdocution, and found as:- Exergy efficincy increased withincreasing salt content and voltage gradient.- Applied of Al electrode incresedthe exergy consumption than Br and 316L St electrodes.- There is no significant differencebetween exegy aspects of Br and 316L St electrodes.- Exergy loss significantly decreasedwith increasing voltage gradient and salt content (p<0.05).- The minimum improvement potentialwas obtained 1.86 MJ/kg water in 2% (w/w) and 11 V/cm for 316L St electrode.