스크래퍼형 이중관식 증발기를 적용한 해수 제빙장치의 성능 특성

Abstract

Ice has been considered as effective storage material for temperature around 0℃, because of the latent heat due to phase change. In recent years, researches on the slurry ice which has a lower freezing point and fluidity have been conducted using concentrated brines. Because of high energy density, slurry ice is often used to comfort cooling of buildings, food processing, and preservation. However, studies about ice making devices that make slurry from the seawater are insufficient. Therefore, in the fishing boat, fresh water flake ice is loaded on the fishroom in advance and it is used for storage of fishes. It causes degradation of fishes’ freshness and quality. The main purpose of the present study is to provide basic data for seawater slurry ice maker through the experimentation. In the present study, performance characteristics of seawater slurry ice maker are investigated experimentally with the scraped surface double tube evaporator, which can provide ice making amount stable at relatively high evaporating temperature. The experimentations are conducted under various operating conditions; inlet temperature, salinity, and flow rate of seawater, scraper rotation speed, evaporating temperature, and inlet temperature of cooling water. The main results are summarized as follow : (1) The produced slurry ice is a liquid form with white fluidity and the diameter of ice particle is 0.2mm to 0.3mm. (2) The section, where the stable ice making is possible, is determined depending on the inlet temperature and the flow rate range of seawater. By controlling the flow rate of seawater, the Ice packing factor(IPF) of the system can be adjusted to 0.3 ~ 14.7%. (3) The IPF increases as speeding up the scraper, but when the scraper speed is high, the optimum COP exists at low flow rate and when the scraper speed is low, the optimum COP exists at high flow rate. Therefore, it is considered that each scraper speed has optimum COP as flow rate. (4) IPF, Ice making amount, and cooling capacity rise when the salinity decreases. On the other hand, since the compressor power consumption does not affected by the salinity, the COP increases as the salinity decreases. Also, in the same IPF, the higher salinity makes the lower temperature of the ice. Therefore, adjusting the salinity before ice making is required to match proper temperature of the catch and it will have a positive effect on maintaining freshness. (5) The IPF increases in case that the evaporating temperature decreases and increment of the cooling water temperature. But as the cooling water temperature increases, the COP decreases from 3.09 to 2.32. It is considered that condensing pressure change affects the compressor power consumption. Seawater is directly used in condenser as cooling water on board. The temperature of the seawater varies according to seasons, and as a result, the IPF and COP of the system are changed. Consideration is required for this relations. Optimum operating conditions for the seawater ice slurry maker are established through experiments. These results will be considered as important data for designing a slurry type seawater ice maker.