In this study, the performance of an ohmic concentration system was analyzed based on the second law of thermodynamics. The influence of salt content (0-2% w/w), voltage gradient (5-11 V/cm) and electrode type (316L St, Al and Br) was evaluated on the aspects exergetics. The results showed that increasing the salt content and voltage gradient decreased the specific exergy consumption and increased the exergy efficiency (p0.05). Today, there is increasing demand for the latest technologies in the field of thermal food processing with low energy consumption, high energy efficiency and preservation of food quality. Ohmic heating is one of the alternatives and latest technologies in thermal food processing, in which the electrical resistance of the food itself generates heat when electric current passes through it (Sakr and Liu, 2014) . The advantages of ohmic heating method are rapid and uniform heating process, improvement of product quality, decrease of energy consumption and reduction of process cost (Sakr and Liu, 2014; Farahnaky et al., 2012; Moreno et al., 2012). ).Say no to plagiarism. Get a tailor-made essay on “Why violent video games should not be banned”?Get an original essay The previous study also indicated that ohmic heating could be a promising method in the fruit juice industry, especially in the process of evaporation/concentration of fruit juices. . The process of producing concentrated juice by conventional vacuum heating requires a lot of energy and capital (Nargesi, 2011). Most thermal processes and heating equipment have low energy efficiency. It is therefore essential for researchers and engineers to increase the thermal efficiency of heating systems using engineering analyses. Exergy analysis is a useful tool to evaluate the energy performance of an ohmic concentration system for the production of tomato paste. The use of exergy analysis can overcome the limitations of energy analysis which focuses only on the quantity of energy, and thus becomes more meaningful. Exergy analysis determined the decay of energy quality during energy transfer and conversion (Prommas et al., 2012). Furthermore, exergy is an easier-to-understand thermodynamic property than entropy for representing irreversibilities in complex systems (Nanaki and Koroneos, 2017; Hammond and Winnett, 2009). From the second law of thermodynamics, exergy can help identify irreversibilities associated with energy flow and its conversion. Energy is defined as the maximum useful work that a system can provide when it undergoes a reversible process from the initial state to the state of its environment, the dead state (Akbulut and Durmu, 2010; Prommas et al., 2012). The exergy method is a particularly useful tool in the management of energy planning and decision-making in favor of sustainable development. Exergy analysis of the ohmic heating system for liquid foods presents a new approach to the performance evaluation of ohmic systems, which could be particularly used in the industrial implementation of these systems. Bozkurt and Icier (2010) performed the exergy analysis of ohmic cooking of ground beef in an ohmic heater and reported that the energy and exergy efficiency values ​​for theohmic baking process at voltage gradients between 20 and 40 V/cm were in the range of 0.69–0.91% and 63.2–89.2%, respectively. Darvishi et al. (2015) studied only the effect of voltage gradient on the thermodynamic aspects of ohmic concentration of tomato juice and their results revealed that the energy and exergy efficiency values ​​increased with increasing voltage gradient. Choosing the appropriate electrode in ohmic heating systems is one of the important parameters to consider. Undesirable electrochemical reactions at the interface between the electrode and the solution, as well as corrosion, can affect the efficiency of the ohmic heating system, which can be avoided by selecting electrodes with appropriate material (Adetunji et al., 2016; Alvarez et al., 2012; The heat and efficiency values ​​generated by the ohmic heating system depend on the conductive nature of the material to be processed and the intensity of the electric field. Many researchers, by adding salt to products, have increased the electrical conductivity and improved the heating performance and the quality of the final product (Icier and Ilicali, 2005; Assiry et al. 2003; Zell et al., 2009; Marra et al. al., 2009; Icier et al., 2006). Assiry et al. (2010) reported that the electrical conductivity increased with increasing dissolved ions in the solution, because the electric current passed through the ions in the solution. Many researchers have studied the effect of electrode type and salt content on electrode corrosion, heating rate, electrical conductivity, and final product quality. But ohmic heating systems have not been studied from the point of view of the second law of thermodynamics (exergy analysis). In contrast, studies such as Darvishi et al. (2015), Cokgezme et al. (2017) and Bozkurt and Icier (2010) only examined the effect of voltage gradient on exergy aspects. In the literature review, no study can be found on the effect of electrode type and salt content on the energy performance of the ohmic concentration system. Thus, the specific objective of this study was to investigate the effect of salt content, metal electrode type and voltage gradient on the energy performance of the ohmic concentration system. The tomatoes (Early Urbana111 Var.) were purchased from a local market, in Sanandaj, Kurdistan, Iran. After washing the tomato samples, the skin of the tomatoes was peeled using a hot-cold water method. Peeled tomatoes were processed in a regular blender/juicer to produce freshly squeezed tomato juice. Tomato juice was filtered using a vacuum filter for seed separation. The juice samples were kept at 2 ± 0.5 °C during the experiments to slow down respiration as well as physiological and chemical changes. The average moisture content of the tomato samples was 9.53 ± 0.15 (dry basis), determined by the oven at 103 ± 1 °C for 24 h (Hosainpour et al., 2014). Figure 1 shows the static ohmic heating system. The ohmic heating unit consisted of a cylindrical Teflon cell (internal diameter 50 mm; wall thickness 10 mm; length 150 mm), two removable electrodes (three types: 316L St, Al and Br) with a gap 100 mm apart and 2 mm thick, a power analyzer (DW-6090, Lutron, Taiwan), two Teflon-coated K-type thermocouples (connected to digital thermometers), a voltage regulation transformer (1 kW, 0–320 V, 50 Hz, MST – 3, Toyo, Japan) and a computer. Metal electrode type (316L St, Br and AL) selected based on studies by Torkian et al. (2017);Adetunji et al. (2016); Alvarez et al. (2012), Zell et al., (2011). The properties of the electrodes and the ohmic cell are shown in Table 1. Three holes with a diameter of 1 mm and 10 mm were created on the surface of the cell for the insertion of the thermocouples and the exit of steam onto the cell, respectively. To prevent juice from flowing out of the cell due to rapid boiling of the juice (from a 10 mm hole), we used a column trap on the top surface of the ohmic cell (Torkian et al ., 2015), as shown in Fig. 1. Variation of sample mass recorded by a digital balance (A&D GF 600, Japan) with an accuracy of ±0.01 g which is placed under the ohmic cell as shown in Fig. 1. About 100 g (± 0.5) of fresh tomato juice at 20° Initial temperature C was poured through the column trap into the ohmic cell (the cell is completely filled). The heating process was carried out until the final moisture content reached 2.43% ± 0.02 (dry basis) using different voltages of 50, 70, 90 and 110 V (as voltage gradient of 5, 7, 9 and 11 V/cm) at a frequency of 50 Hz. (Torkian et al., 2017; Hosainpour et al., 2014). The salt content of tomato paste samples varied within the range of 0.6 to 2.5% (w/w) for various production companies (Sobowale et al., 2012). According to the Food and Drug Administration, the maximum salt content of tomato paste is 2% (w/w). Two salt concentration levels 1: 100 g/g (salt/tomato ratio) and 2: 100 g/g (at 1 and 2% w/w) were provided by the salt (NaCl) and the results were compared without salt sample as a control sample. Salt added to the tomato samples during the process by blender/juicer so that it is evenly distributed throughout the tomato juice. After each test, the electrodes were rinsed using a brush and distilled water. Voltage, current, mass and temperature data were measured during heating and transmitted to the computer using a data logger. Exergy analysis According to the heating control volume (Fig. 2), the exergy balance of the ohmic system was expressed as follows (Darvishi et al., 2015): The exergy transfer rate due to evaporation in the volume heating control was (Nanaki and Koroneos, 2017; Sarker et al., 2015): The specific exergy of the input or final product was calculated using Eq. (3) stated the following (Prommas et al., 2010): Exergy efficiency was calculated using Eq. (4) stated the following (Darvishi et al., 2015): The exergy loss is determined by Eq. (5): The specific exergy consumption was determined using the following equation: Additionally, the following equation was applied to find the energy enhancement potential of the ohmic concentration system (Icier et al ., 2010; Statistical method All data are expressed as mean values ​​and standard deviation from three repeated measurements for different heating conditions. ANOVA and Duncan tests were used to analyze the effect of salt content, voltage gradient and electrode type on the selected properties at the 5% significance level (p = 0.05). The statistical evaluation was carried out using SPSS V.18 software. Additionally, Table Curve 3D, V4 software was used to plot a 3D view of the relationship between parameters and extract the regression equations. Results and discussion The 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. That.