## 3 Results and Analysis
### Infrared Thermal Image Analysis  
In this study, the surface temperature of specimens was photographed using an infrared thermal camera (FLIR T630 sc, Wilsonville, OR, USA) to check the heat distribution and temperature transfer pattern of PM and ECM specimens. The initial temperature of specimens is about 20 \({}^{\circ}\)C, and the surface temperature of specimens is marked on the infrared thermal images together with the initial temperature. Figure 8 shows infrared thermal images according to the parameters of each specimen taken at an applied voltage of 30 V and an electrode spacing of 120 mm. As seen in Figure 8a, the surface temperature of the PM specimen was measured to be 20.3 \({}^{\circ}\)C. As it was similar to the ambient room temperature, it was impossible to distinguish a clear difference in heating performance depending on the applied voltage. As shown in Figure 8b-d, the surface temperature of ECM specimens mixed with SF slightly increased to 20.4-21.5 \({}^{\circ}\)C, and the amount of heat generated was very insignificant, so the infrared thermal images were not clear. Because of this, heat could not be diffused throughout the specimen. In Figure 8e-i, however, the surface temperature of ECM specimens mixed with CF was measured at 30.1-65.9 \({}^{\circ}\)C, indicating that the temperature increases as the heat is diffused widely to the surroundings. It was confirmed through the infrared thermal images that the heating performance improved as the CF content increased.  
On the other hand, Figure 9 shows infrared thermal images according to the parameters of each specimen taken at an applied voltage of 30 V and an electrode spacing of 40 mm. As shown in Figure 9a-d, the surface temperature of the PM specimen and the ECM specimens mixed with SF was slightly improved to 20.3-21.8 \({}^{\circ}\)C, and the amount of heat generated was very insignificant, so the infrared thermal image was not clear. As evidenced in Figure 9e-g, however, the surface temperature of the ECM specimens mixed with CF was measured to be 77.0-88.1 \({}^{\circ}\)C, which was a significant improvement, and it was, thus, confirmed  
Figure 8: Surface temperature distribution in the ECM captured by an infrared thermal camera at 30 V and 120 mm: (**a**) PM, (**b**) ECM-SF25, (**c**) ECM-SF75, (**d**) ECM-SF125, (**e**) ECM-CF25, (**f**) ECM-CF50, (**g**) ECM-CF75, (**h**) ECM-CF100, (**i**) ECM-CF125.  
that the heat was distributed throughout and transferred to the specimen subsequently. In particular, from Figure 9h,i, it was confirmed that the heating performance improved greatly as the CF content increased. The highest surface temperature was 145.1 \({}^{\circ}\)C, which occurred in the ECM-CF125 specimen with 1.25% of mixed CF with an applied voltage of 30 V and an electrode spacing of 40 mm. The surface temperature of the specimen improved as the CF content increased, and the infrared thermal images became sharper and clearer. From the infrared thermal images, it was made clear that the heating performance was significantly improved. The analysis of the infrared thermal images revealed that the generated heat occurred mainly between the electrodes connected to the power supply, and the narrower the electrode spacing, the more advantageous it was in securing the heating performance. Such a result is believed to be due to heat diffusion and temperature transfer between the electrodes, the shortest distance, because current has a property of flowing across the shortest distance. Our results are in accordance with previous research results [39].