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Experimental study on the cryogenic thermal storage unit (TSU) below -70 °C
Byeongchang Byeon,Kyoung Joong Kim,Sangkwon Jeong,Dong min Kim,Mo Se Kim,Gi Dock Kim,Jung Hun Kim,Sang Yoon Lee,Seong Woo Lee,Keun Tae Lee 한국초전도저온학회 2024 한국초전도저온공학회논문지 Vol.26 No.1
Over the past four years, as the COVID-19 pandemic has struck the world, cold chain of COVID-19 vaccination has become a hot topic. In order to overcome the pandemic situation, it is necessary to establish a cold chain that maintains a low-temperature environment below approximately 203K (-70°C), which is the appropriate storage temperature for vaccines, from vaccine suppliers to local hospitals. Usually, cryocoolers are used to maintain low temperatures, but it is difficult for small-scale local distribution to have cryocooler due to budget and power supply issues. Accordingly, in this paper, a cryogenic TSU (Thermal storage unit) system for vaccination cold chain is designed that can maintain low temperatures below -70°C for a long time without using a cryocooler. The performance of the TSU system according to the energy storage material for using as TSU is experimentally evaluated. In the experiments, four types of cold storage materials were used: 20% DMSO aqueous solution, 30% DMSO aqueous solution, paraffin wax, and tofu. Prior to the experiment, the specific heat of the cold storage materials at low temperature were measured. Through this, the thermal diffusivity of the materials was calculated, and paraffin wax had the lowest value. As a result of the TSU system's low-temperature maintenance test, paraffin wax showed the best low-temperature maintenance performance. And it recorded a low-temperature maintenance time that was about 24% longer than other materials. As a result of analyzing the temperature trend by location within the TSU system, it was observed that heat intrusion from the outside was not well transmitted to the low temperature area due to the low thermal conductivity of paraffin wax. Therefore, in the TSU system for vaccine storage, it was experimentally verified that the lower the thermal diffusivity of the cold storage material, the better low temperature maintenance performance.
Kim, Jhongkwon,Byeon, Byeongchang,Kim, Kyoung Joong,Jeong, Sangkwon 한국초전도저온공학회 2020 한국초전도저온공학회논문지 Vol.22 No.4
In this research, the variation of round-trip efficiency in a liquid air energy storage system (LAES) is calculated and an optimal configuration is found. The multiple stages of cold energy storage are simulated with several materials that process latent heat at different temperature ranges. The effectiveness in the charging and discharging processes of LAES is newly defined, and its relationship with the round-trip efficiency is examined. According to defined correlation, the effectiveness of the discharging process significantly affects the overall system performance. The round-trip efficiency is calculated for the combined cold energy storage materials of aqueous dimethyl sulfoxide (DMSO) solution, ethanol, and pentane theoretically. The performance of LAES varies depending on the freezing point of the cold storage materials. In particular, when the LAES uses several cold storage materials, those materials whose freezing points are close to room temperature and liquid air temperature should be included in the cold storage materials. In this paper, it is assumed that only latent heat is used for cold energy storage, but for more realistic analyzes, the additional consideration of the transient thermal situation to utilize sensible heat is required. In the case of such a dynamic system, since there is certainly more increased heat capacity of the entire storage system, the volume of the cold energy storage system will be greatly reduced.
김상권(SangKwon Kim) 한국경제연구원 2008 규제연구 Vol.17 No.2
본 논문은 삼익과 영창이 결합하였을 경우 실현할 수 있는 규모의 경제를 추정하였다. Cobb-Douglas 생산함수 추정결과 피아노산업에서 규모의 보수가 증가하는 것으로 나타났다. 구체적으로 노동과 자본이 1% 증가할 때 생산량이 약 1.2% 증가하는 것으로 추정됐다. 따라서 삼익과 영창이 기업결합 시 120~143억 원 정도의 생산비용이 절감되는 것으로 추정됐다. I estimated the expected cost-savings that might result from the merger of two piano manufacturers, Samick and YoungChang. This estimation was based upon duality between cost and production functions. The results showed that the cost-savings would amount to about 12.0∼14.3 billon won if the merger between Samick and YounChang were allowed.