In this study, the performance of an ohmic concentrating system was analyzed based on the second law of thermodynamics. The influence of the salt content (0-2% w/w), the voltage gradient (5-11 V/cm) and the type of electrode (316L St, Al and Br) was evaluated on the exergy aspects. The results showed that increasing salt content and voltage gradient reduced specific exergy consumption and increased exergy efficiency (p0.05). Nowadays, there is a growing demand for more innovative 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 whereby the electrical resistance of the food itself generates heat as an electric current flows through it (Sakr and Liu, 2014). The advantages of the ohmic heating method are fast and uniform heating process, improved product quality, decreased energy consumption, and saved process costs (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 Shouldn't Be Banned"? Get an original essay The previous study also stated that ohmic heating could be a promising method in the fruit juice industry, especially in the evaporation/concentration process of fruit juices. The process of producing concentrated juice using conventional vacuum heating requires high energy and capital (Nargesi, 2011). Most thermal processes and heating equipment have low energy efficiency. Therefore, it is crucial for researchers and engineers to increase the thermal efficiency of heating systems using engineering analyses. Exergy analysis is a useful tool for evaluating the energy performance of an ohmic concentration system for tomato paste production. The use of exergy analysis can overcome the limitations of energy analysis which focuses only on the amount of energy, and thus becomes more meaningful. Determined exergy analysis of energy quality disintegration during energy transfer and conversion (Prommas et al., 2012). Furthermore, exergy is a more easily understood 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 possible useful work that a system can provide when undergoing 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 managing energy planning and decision making for sustainable development. Exergetic analysis of the ohmic heating system of liquid foods presents a new approach to the performance evaluation of ohmic systems, which could be used especially in the industrial implementation of these systems. Bozkurt and Icier (2010) performed exergy analysis of ohmic cooking of ground meat in an ohmic heater and reported that the energy and exergy efficiency values ​​for the ohmic cooking process with voltage gradients ranging from 20 to 40 V/ cm they werein the range of 0.69–0.91% and 63.2–89.2%, respectively. Darvishi et al. (2015) only studied the effect of voltage gradient on the thermodynamic aspects of ohmic concentration of tomato juice, and their results revealed that the values ​​of energy and exergy efficiencies increased with increasing voltage gradient. The choice of suitable electrode in ohmic heating systems is one of the important parameters to consider. Unwanted electrochemical reactions at the interface between the electrode and the solution and corrosion can affect the efficiency of the ohmic heating system and this can be avoided by selecting electrodes with a suitable material (Adetunji et al., 2016; Alvarez et al., 2012 ; Assiry, 2003; Zell et al., 2009). The heat generated and efficiency values ​​of the ohmic heating system depend on the conductive nature of the material to be worked and the intensity of the electric field. Many researchers adding salt to products have increased the electrical conductivity and improved the heating performance and quality of the final product (Icier and Ilicali, 2005; Assiry et al. 2003; Zell et al., 2009; Marra et al., 2009; Icier et al., 2006). Assiry et al. (2010) reported that the electrical conductivity increases with the increase of dissolved ions in the solution because the electric current is passed by the ions in the solution. Many researchers have evaluated 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 (exergetic analysis). On the other hand, studies such as Darvishi et al. (2015), Cokgezme et al. (2017) and Bozkurt and Icier (2010) only examined the effect of voltage gradient on exergetic aspects. In the literature review, no studies were found on the effect of electrode type and salt content on the energy performance of the ohmic concentration system. Therefore, the specific aim of this study was, as a first work, to investigate the effect of salt content, metal electrode type and voltage gradient on the energy performance of the ohmic concentrating system. Tomato fruits (Early Urbana111 Var.) were purchased from a local market, in Sanandaj, Kurdistan, Iran. After washing the tomato samples, the skin of the tomatoes is peeled using the hot-cold water method. Peeled tomatoes were processed in a simple mixer/juicer to produce fresh tomato juice. Tomato juice was filtered using a vacuum filter for seed separation. The juice samples were stored at 2±0.5 °C during the experiments to slow respiration and physiological and chemical changes. The average moisture content of the tomato samples was 9.53 ± 0.15 (on a dry basis), as determined by baking at 103 ± 1 °C for 24 h (Hosainpour et al., 2014). Fig. 1 shows the static ohmic heating system. The ohmic heating unit consisted of a cylindrical Teflon cell (inner diameter 50 mm; wall thickness 10 mm; length 150 mm), two removable electrodes (three types: 316L St, Al and Br) with a gap of 100 mm each other and 2 mm thick, a power analyzer (DW-6090, Lutron, Taiwan), two Teflon-coated type K thermocouples (connected to digital thermometers), a voltage regulation transformer (1 kW, 0–320 V, 50 Hz, MST – 3, Toyo, Japan) and a computer. Type of metal electrode (316L St, Br and AL) selected based on the studies of Torkian et al. (2017); Adetunji et al. (2016); Alvarez et al. (2012), Zell et al., (2011). The properties of the electrodes and the ohmic cellare presented in Table 1. Three holes with diameters of 1 mm and 10 mm were created on the surface of the cell respectively for the insertion of the thermocouples and the steam outlet on the cell. To prevent juice from leaking out of the cell due to rapid boiling of the juice (from a 10 mm hole), we used a pillar trap on the top surface of the ohmic cell (Torkian et al., 2015) as shown in Fig. 1 . Variation of the mass sample recorded by a digital scale (A&D GF 600, Japan) with precision of ±0.01 g placed under the ohmic cell as shown in Fig. 1. Approximately 100 g (± 0.5) of juice fresh tomato 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 (on a dry basis) using different voltages 50, 70, 90 and 110 V (as voltage gradient 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 ranged from 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 in tomato paste is 2% (w/w). Two salt concentration levels 1:100 g/g (salt/tomato ratio) and 2:100 g/g (as 1 and 2% w/w) were provided by salt (NaCl) and the results were compared without sample of salt as a control sample. Salt added to tomato samples during the process via mixer/juicer to be 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 this information to the computer with a data logger. Exergy analysis Based on the heating control volume (Fig. 2), the exergy balance for the ohmic system was expressed as follows (Darvishi et al., 2015): The exergy transfer rate due to evaporation in the control volume of heating was (Nanaki and Koroneos, 2017; Sarker et al., 2015): the specific exergy of the input or final product was calculated using Eq. (3) stated as follows (Prommas et al., 2010): The exergy efficiency was calculated using Eq. (4) stated as follows (Darvishi et al., 2015): The exergy loss is determined by Eq. (5): The specific exergy consumption was determined using the following equation: Furthermore, the following equation was applied to find the energy enhancement potential of the ohmic concentrating system (Icier et al., 2010; Cokgezme et al., 2017 ). Statistical method All data are expressed as mean and standard deviation values ​​from three replicate measurements for different heating conditions. ANOVA and Duncan tests were used to analyze the effect of salt content, voltage gradient and electrode type on selected properties at a significance level of 5% (p=0.05). Statistical evaluation was performed using SPSS V.18 software. Furthermore, Table Curve 3D, V4 software was used to plot the 3D view of the parameter relationship 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, the exergy consumption decreased significantly (p < 0.05) as the voltage gradient and the salt content. This is due to the drastic reduction in concentration time with an increase in voltage gradient and salt content. The.