• Nuclear Engineering and Technology
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• 제54권1호
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• pp.72-83
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• 2022

This paper presents a numerical investigation of two-phase natural circulation flows established when external reactor vessel cooling is applied to a severe accident of the APR1400 reactor for the in-vessel retention of the core melt. The coolability limit due to external reactor vessel cooling is associated with the natural circulation flow rate around the lower head of the reactor vessel. For an elaborate prediction of the natural circulation flow rate using a thermal-hydraulic system code, MARS-KS1.5, a three-dimensional computational fluid dynamics (CFD) simulation is conducted to estimate the flow rate and pressure distribution of a liquid-state coolant at the brink of significant void generation. The CFD calculation results are used to determine the loss coefficient at major flow junctions, where substantial pressure losses are expected, in the nodalization scheme of the MARS-KS code such that the single-phase flow rate is the same as that predicted via CFD simulations. Subsequently, the MARS-KS analysis is performed for the two-phase natural circulation regime, and the transient behavior of the main thermal-hydraulic variables is investigated.

• 한국재난정보학회 논문집
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• 제18권1호
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• pp.163-172
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• 2022

연구목적: Li-ion 배터리의 효율적인 열관리 기술을 확보하기 위하여 Single&-phase 침지 냉각 기술을 적용한 시스템의 실험을 통하여 적용가능성을 확인하고자 하였다. 연구방법: LG-Chem에서 생산된 JH3 파우치 셀을 사용하여 14S2P 모듈을 제조하여 미국 카길사에서 생산된 식물성계 냉각유체에 침지한 후 0.3C~1C 속도로 충방전을 시행하여 열분포를 확인하였다. 연구결과: 침지냉각 기술로 배터리 모듈을 40℃ 이하의 온도로 관리할 수 있으며, 침지액의 분자구조 변화가 없다는 결과를 도출하였다. 결론: 침지냉각 방식이 Li-ion 배터리 열관리에 적용 가능함을 확인하였다.

• 한국항공우주학회지
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• 제35권9호
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• pp.805-815
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• 2007

단일추력의 정상 작동 상태의 액체 로켓 엔진 시스템 모듈화 프로그램을 작성하기 위한 선행 연구로 엔진 주요 구성품들에 대한 성능설계 프로그램을 작성하였다. 주요 구성품으로는 추력실, 원심형 펌프, 충동형 터빈, 재생 냉각 채널 등이 고려되었다. 복잡성을 피하기 위하여 열역학적 관계식 및 비점성 이론을 바탕으로 한 여러가지 관계식들과 간략한 수학적 모델을 사용하였다. 본 논문에서는 도출된 결과를 정성적으로 살펴보고, 주요 설계 파라미터를 바꿔가면서 구성품의 작동특성 변화에 대한 경향성을 검토함으로써 일반적인 구성품 설계 이론에 부합하는가를 확인하였다.

• 한국소음진동공학회논문집
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• 제22권12호
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• pp.1184-1190
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• 2012

This study is focused on the experimental analysis of the noise induced by phase change of refrigerant at the entrance of capillary tube. The refrigerant is usually two-phase condition when it flowed into the capillary tube. At the entrance of capillary tube, the phase condition of refrigerant is formed by sub-cool control. If it has sufficient sub-cool temperature, all of the vapor refrigerants turned to liquid, which means there is only liquid. Otherwise, the gas is coexisted. Based on this theory, we experiment on each case by changing sub-cool temperature using refrigerant-supplying equipment. The noise level is measured for each case and compared.

• 대한기계학회논문집
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• 제18권9호
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• pp.2404-2412
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• 1994

A mathematical model has been developed for predicting kinematic, thermal, and solidification histories of atomized droplets during flight. Liquid droplet convective cooling, recalescence, equilibrium-state solidification, and solid-phase cooling were taken into account in the analysis of the solidification process. The spherical shell model was adopted where the heterogeneous nucleation is initiated from the whole surface of a droplet. The growth rate of the solid-liquid interface was determined from the theory of crystal growth kinetics with undercooling caused by the rapid solidification. The solid fraction after recalescence was obtained by using the integral method. The thermal responses of atomized droplets to gas velocity, particle size variation, and degree of undercooling were investigated through the parametric studies. It is possible to evaluate the solid fraction of the droplet according to flight distance and time in terms of a dimensionless parameter derived from the overall energy balance of the system. It is also found that the solid fraction at the end of recalescence is not dependent on the droplet size and nozzle exit velocity but on the degree of subcooling.

• 전기학회논문지
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• 제58권1호
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• pp.132-136
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• 2009

Recently, for improvement of the magnetic field of high temperature superconductor (HTS) apparatus, many studies investigating on operating in the range of $20{\sim}65\;K$ with liquid helium or the conducting method using cryocooler are actively reviewed. Also, the cooling method using solid nitrogen as cryogen is being suggested. Since the nitrogen has very large specific heat in solid state, it is expected that it can be operated for a long time without a continuous supply of cooling energy. However, there are still insufficient data on the characteristics of solid nitrogen such as thermodynamic properties and liquid-solid phase change. Especially, there was almost no study done on the electrical insulation properties of solid nitrogen so far. In this study, solid nitrogen to find the electrical characteristics was made by using cryocooler and cryostat, and investigated the flashover discharge and breakdown. The results of this study will be useful as a basic data for electrical insulation design of the HTS system using solid nitrogen as cryogen.

• 한국초전도ㆍ저온공학회논문지
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• 제23권4호
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• pp.35-38
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• 2021

Conventional direct current (DC) rotating machines are usually used for crane and press machine using high torque in metal and steel industries, because of a constant output power along variable rotating speed. A general DC motor with permanent field magnets could not increase a magnetic flux density at a gap between armature coils and field magnets. However, a superconducting DC motor has field magnets composed with high temperature superconducting (HTS) coils and it could increase the magnetic flux density at the gap to over 10 times than those of a general DC motor by control the excitation current into HTS coils. The superconducting DC motor could be operated with extremely high torque and constant output power at a low rotational speed. In this paper, a 500 W superconducting DC rotating machine was conceptually designed with a LN₂ (Liquid Nitrogen) cooling method and the operation characteristics results of HTS field magnets were presented. The two no-insulation HTS magnets for a 500 W superconducting DC rotating machine were fabricated. The excitation current for the HTS magnets could be controlled from 0 to 40 A. This test results will be available to design large-sized HTS magnets for a number of hundred kW class superconducting DC rotating machine under LN₂ cooling system.

• 한국초전도ㆍ저온공학회논문지
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• 제11권1호
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• pp.16-19
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• 2009

Recently, for improvement of the magnetic field of high temperature superconductor (HTS) apparatus, many studies investigating on operating in the range of $20{\sim}65K$ with liquid helium or the conducting method using cryocooler is actively reviewed. Also, the cooling method using solid nitrogen as cryogen is being suggested. Since the nitrogen has very large specific heat in solid state, it is expected that it can enable long time operation without a continuous supply of cooling energy. However, there is still insufficient data on the characteristics of solid nitrogen such as thermodynamic properties and liquid-solid phase change. Especially, there was almost no study done on the electrical insulation properties of solid nitrogen so far. In this study, solid nitrogen to find the electrical characteristics was made by using cryocooler and cryostat, and investigated the flashover discharge and breakdown. The results of this study will be useful as a basic data for electrical insulation design of the HTS system using solid nitrogen as cryogen.

• 설비공학논문집
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• 제18권6호
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• pp.518-525
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• 2006

The present experiments have been performed for obtaining the melting heat transfer characteristics of micro-encapsulated solid-liquid phase-change material and water mixture slurry flow in a circular tube heated with constant wall heat flux. The phase change material having a low melting point was selected for a domestic cooling system in the present study. The governing parameters were found to be latent heat material concentration, heat flux, and the slurry velocity. The experimental results revealed that the increase of tube wall temperature of latent microcapsule slurry was lower than that of water caused by the heat absorption of fusion.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2005년도 동계학술발표대회 논문집
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• pp.193-198
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• 2005

The present experiments have been performed for obtaining the melting heat transfer characteristics of micro-encapsulated solid-liquid phase change material and water mixed slurry flow in a circular tube heated with constant wall heat flux. The phase change material having a low melting point was selected for a domestic cooling system in the present study. The governing parameters were found to be latent heat material concentration, heat flux, and the slurry velocity. The experimental results revealed that the increase of tube wall temperature of latent microcapsule slurry was lower than that of water caused by the heat absorption of fusion.