## 4 Results and Discussion
### Influence of Scraper Rotating Speed  
The rotation of the scraper makes turbulence and vortexes possible to easily generate nuclei for phase change and it is closely related to the amount of heat transfer and IPF since it determines the time for ice to grow on the inner tube wall. As mentioned above, studies on the heat transfer according to the number of revolutions have been carried out for various scraper types, but the device using the double tube evaporator in this study using seawater requires experimental study. Through this experiment, the effects of IPF and cooling capacity on the scraper rotational speed were determined. Figure 11 shows the influence of the temperature of the ice slurry with seawater changing the scraper rotating speeds with respect to the seawater flow rate under nominal conditions. Figure 12 is a graph showing IPF calculated from the initial salinity of seawater and the temperature of the ice slurry with seawater. As the number of scraper rotations increases, the temperature of the ice slurry with seawater decreases slightly and the IPF increases. In the case of seawater flow rate of 0.75 LPM, the IPF increases by 13% to 15%, while the seawater flow rate of 1.25 LPM increases by 4.5% to 5.0%. Figure 10: Cooling capacity with respect to evaporating temperature. Figure 13 shows the cooling capacity in the evaporator as the number of revolutions of the scraper increases. As the flow rate of seawater flowing into the evaporator increases, the cooling capacity increases. As the number of revolutions of the scraper increases, the cooling capacity increases. Also, while the flow rate of the seawater flowing into the evaporator is 0.75 LPM, the cooling capacity varies from 1.143 kW to 2.227 kW, while the flow rate is 1.316 kW to 1.350 kW at 1.25 LPM, which is about twice as much. It was confirmed that as the flow rate decreases, the cooling capacity increment range becomes larger as with the scraper rotation speed. In [PERSON] et al. [14], with penetration theory, the heat transfer phenomenon in the scraper type heat exchanger is mainly influenced by the transient state conductivity newly formed in the tube wall by the scraper rotation, and increased heat transfer due to increased fluid film formation. As the same result of this experiment, as the rotating speed increases, the rotation Reynold's number also increases, thus turbulence is promoted and the fluid film formation is increased and the ice nucleus crystal is increased. Consequently, the heat transfer coefficient is increased, the thickness of the ice layer formed on the inner wall of the tube is thinned, and the conduction heat resistance is decreased, and therefore, the heat transfer is improved. The ice generator used in this experimental system shows an increase tendency in the cooling capacity up to 350 rpm at the scraper rotation and over the 350 rpm, the increase rate of cooling capacity becomes gradually decreases. Therefore, it is found that the rotating speed of the scraper must be maintained at the scraper rotation speed. Figure 11: Temperature of ice slurry with seawater according to scraper rotation speed. Figure 12: IPF with respect to scraper rotation speed. a minimum of 350 rpm when designing an ice maker using the ice generator. If the rpm of the scraper is increased, the amount of ice is also increased, but the power required for rotating the scraper also increases, so that the operation energy is increased. Therefore, the performance of the entire system may be reduced, so it is preferable to maintain the rotation speed at 350 to 400 rpm. If the flow rate of the seawater into the ice generator is large, the effect on the cooling capacity with respect to the rotating speed of the scraper is reduced. It seems that as the flow rate increases, the IPF ratio decreases and the influence of increase of heat transfer due to the rotating force of the scraper becomes insignificant.