• Nuclear Engineering and Technology
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• 제30권5호
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• pp.424-434
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• 1998

RELAP5/Mod3.1 code was assessed with the semiscale experiment S-NC-3, and S-NC-4, which simulated the two-phase natural circulation and reflux condensation for the SBLOCA of PWR, respectively . Test S-NC-3 and S-NC-4 calculation results showed that RELAP5/Mod3.1 quite well describes the influence of steam generator secondary side heat transfer degradation on both two-phase natural circulation and reflux condensation. A comparison between the calculated and measured two-phase mass flow rate in test S-NC-3 shows good agreement for primary mass inventory more than 92%. And RELAP5/Mod3.1 have a good mass flow rate prediction capability for the transient such as S-NC-4 except some flow oscillations. The reflux flow rate for S-NC-4 test is under predicted, and the overall results verify that the correct prediction of the reduced liquid level appears to be required for the correct calculation of the overall phenomena.

• Membrane and Water Treatment
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• 제10권5호
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• pp.321-330
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• 2019

The objective of this study was to examine the recovery of the power plant cooling tower blowdown water (CTBD) by membrane distillation. The experiments were carried out using a flat plate poly vinylidene fluoride (PVDF) membrane with a pore diameter of $0.22{\mu}m$ by a direct contact membrane distillation unit (DCMD). The effects of operating parameters such as transmembrane temperature difference (${\Delta}T$), circulation rate and operating time on permeate flux and membrane fouling have been investigated. The results indicated that permeate flux increased with increasing ${\Delta}T$ and circulation rate. Whereas maximum permeate flux was determined as $47.4L/m^2{\cdot}h$ at ${\Delta}T$ of $50^{\circ}C$ for all short term experiments, minimum permeate flux was determined as $7.7L/m^2{\cdot}h$ at ${\Delta}T$ of $20^{\circ}C$. While $40^{\circ}C$ was determined as the optimum ${\Delta}T$ in long term experiments. Inorganic and non-volatile substances caused fouling in the membranes.

• 한국수소및신에너지학회논문집
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• 제29권6호
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• pp.635-641
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• 2018

To select the operating condition of 0.5 MWth chemical looping combustion system, minimum fluidization velocity, transition velocity to fast fluidization and solid circulation rate were measured using mass produced new oxygen carrier (N016-R4) which produced by spray drying method for 0.5 MWth chemical looping combustion system. A minimum fluidization velocity decreased as the pressure increased. The measured transition velocity to fast fluidization was 2.0 m/s at ambient temperature and pressure. The measured solid circulation rate increased as the solid control valve opening increased. We could control the solid circulation rate from 26 to $93kg/m^2s$. Based on the measured minimum fluidization velocity and transition velocity to fast fluidization, we choose appropriate operating conditions and demonstrated continuous solid circulation at high pressure condition (5 bar-abs) up to 24 hours.

• Nuclear Engineering and Technology
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• 제52권12호
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• pp.2789-2802
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• 2020

Small Modular Reactors (SMRs) are attracting wide attention due to their outstanding performance, extensive studies have been carried out for lead-based fast reactors (LFRs) that cooled with Lead or Lead-bismuth (LBE), and small modular natural circulation LFR is one of the promising candidates for SMRs and LFRs development. One of the challenges for the design small modular natural circulation LFR is to master the natural circulation thermal-hydraulic performance in the reactor primary circuit, while the natural circulation characteristics is a coupled thermal-hydraulic problem of the core thermal power, the primary loop layout and the operating state of secondary cooling system etc. Thus, accurate predicting the natural circulation LFRs thermal-hydraulic features are highly required for conducting reactor operating condition evaluate and Thermal hydraulic design optimization. In this study, a thermal-hydraulic analysis code is developed for small modular natural circulation LFRs, which is based on several mathematical models for natural circulation originally. A small modular natural circulation LBE cooled fast reactor named URANUS developed by Korea is chosen to assess the code's capability. Comparisons are performed to demonstrate the accuracy of the code by the calculation results of MARS, and the key thermal-hydraulic parameters agree fairly well with the MARS ones. As a typical application case, steady-state analyses were conducted to have an assessment of thermal-hydraulic behavior under nominal condition, and several parameters affecting natural circulation were evaluated. What's more, two characteristics parameters that used to analyze natural circulation LFRs natural circulation capacity were established. The analyses show that the core thermal power, thermal center difference and flow resistance is the main factors affecting the reactor natural circulation. Improving the core thermal power, increasing the thermal center difference and decreasing the flow resistance can significantly increase the reactor mass flow rate. Characteristics parameters can be used to quickly evaluate the natural circulation capacity of natural circulation LFR under normal operating conditions.

• KIEAE Journal
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• 제16권6호
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• pp.167-172
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• 2016

Purpose: The solar water heater with natural circulation has been used for several decades in the world as it is automatically operated without a pump and controller and is easy to maintain and repair. After the subsidy was offered from 2012, the solar water heater with natural circulation is becoming increasingly popular in Korea. Recently, the development of a wall-integrated solar water heater, which improves the applicability of buildings and prevents the overheating in the summer, is being developed. On the other hand, the design and performance evaluation data of solar water heaters are very inadequate, and analysis of heat and flow is required to develop a new type of solar water heater. Method: Therefore, in this study, we proposed a new simplified system analysis model that reflects heat and pressure loss from the test results of KS B ISO 9806-1 (Solar collector test method), assuming that the collector is a simple pipe system, the validity of which was verified through experiments. Result: As a result, first, the RMSE of the system circulation flow rate and the average temperature of the inlet and outlet of the collector according to the experimental results and the simulation are 0.05563 and 0.88530, respectively, which are very consistent. Secondly, the mass flow rate is increased linearly with the increase of the solar radiation, and the mass flow rate is 0.0104 ~ 0.0180kg/s in the range of $200{\sim}380W/m^2$ of solar irradiance. Compared with the test flow rate 0.0764kg / s of the test collector, it showed a level of less than 20%.

• Journal of Animal Science and Technology
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• 제49권2호
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• pp.279-286
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• 2007

반응물을 연속적으로 내부 순환시키는 생물막 연속회분식모래여과 공정을 고안하고 외부 탄소원이 전혀 사용되지 않는 조건하에서의 돈사폐수 처리특성을 평가하였다. 수직형과 경사형 모래여과조에서의 NOx-N 부하량에 따른 탈질율은 각각 19%와 3.8%로 수직형에서 5배 정도 높은 효율을 보임에 따라 수직형태의 모래여과조를 생물막 연속회분식 공정과 연계하여 운전하였다. 처리공정을 HRT 15일, 내부순환율 105L/hr.m3, 평균 암모니아성 질소 부하량 54g/m3.d 조건에서 운전하였을 때 STOC, NH4- N, TN의 처리효율은 각각 75%, 97%, 85%이었다. 생물막 연속회분식 반응조와 모래여과조간의 내부순환으로 TN의 제거효율이 약 14%증진되는 것으로 나타났으며 얻어진 질소제거효율 증진은 주로 모래여과조에서의 탈질에 의한 것으로 밝혀졌다. 또한 용해성 인의 경우 내부순환이 수행되지 않았을 시에는 유출수내 농도가 오히려 증가하였으나 내부순환시에는 약 57% 정도가 제거되는 것으로 나타남에 따라 반응물의 내부순환이 용해성 인의 제거효율 증진에도 기여함을 알 수 있었다. 시스템에서의 질소제거 양상을 분석해본 결과 최종 유출수내의 NH4-N은 부하량 60g/m3.d 수준에서 약 20mg/L 이하로 비교적 일정하였고 부하량이 100g/m3.d. 이상의 수준으로 상승함에도 80% 이상의 질소 제거효율을 보였다. 그러나 부하량 100g/m3.d 수준 이상에서부터 처리효율이 감소하는 것으로 나타나 외부탄소원이 전혀 사용되지 않는 운전조건에서의 질소의 적정 부하량은 약 100g/m3.d 정도인 것으로 판단되었다.

• Ocean and Polar Research
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• 제44권4호
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• pp.269-285
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• 2022

The interaction between ocean and ice shelf is a critical physical process in relation to water mass transformations and ice shelf melting/freezing at the ocean-ice interface. However, it remains challenging to thoroughly understand the process due to a lack of observational data with respect to ice shelf cavities. This is the first study to simulate the variability and circulation of water mass both overlying the continental shelf and underneath an ice shelf and an ice tongue in the Terra Nova Bay (TNB), East Antarctica. To explore the properties of water mass and circulation patterns in the TNB and the corresponding effects on sub ice shelf basal melting, we explicitly incorporate the dynamic-thermodynamic processes acting on the ice shelf in the Regional Ocean Modeling System. The simulated water mass formation and circulation in the TNB region agree well with previous studies. The model results show that the TNB circulation is dominated by the geostrophic currents driven by lateral density gradients induced by the releasing of brine or freshwater at the polynya of the TNB. Meanwhile, the circulation dynamics in the cavity under the Nansen Ice shelf (NIS) are different from those in the TNB. The gravity-driven bottom current induced by High Salinity Shelf Water (HSSW) formed at the TNB polynya flows towards the grounding line, and the buoyance-driven flow associated with glacial meltwater generated by the HSSW emerges from the cavity along the ice base. Both current systems compose the thermohaline overturning circulation in the NIS cavity. This study estimates the NIS basal melting rate to be 0.98 m/a, which is comparable to the previously observed melt rate. However, the melting rate shows a significant variation in space and time.

• 한국수소및신에너지학회논문집
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• 제28권4호
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• pp.384-391
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• 2017

Effects of operating variables on solid circulation rate were measured and discussed using two-interconnected circulating fluidized bed system at ambient temperature and pressure. OCN 706-1100 particles were used as oxygen carrier. The measured solid circulation rates increased as the lower loop seal gas flow rates and the solid height in the fuel reactor increased. Suitable operating conditions to avoid choking of the air reactor were confirmed. Continuous long-term operations of steady-state solid circulation were also demonstrated at two different conditions based on the operating window.

• 에너지공학
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• 제8권2호
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• pp.233-241
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• 1999

온수생산을 위하여 기존의 강제순환식이 아닌 자연순환식 회로를 이용한 대형 온수생산 시스템을 개발하였다. 그리고 이 시스템의 설계와 성능평가를 위한 시뮬레이션 프로그램을 개발하여 실용화 가능성을 제시하였다. 실제규모의 성능실험에서 주어진 기하학적 조건하에 시스템이 정상상태 운전 시 보일러 가열량(695㎾)일 때, 급수 유량이 0.3$\ell$/s 로 일정하게 순환함을 보였다. 그리고, 비정상상태로 작동 할 경우 순환유량이 0.4~0.6 $\ell$/s 로 시스템이 불안정함을 실험을 통해 확인하였다. 개발된 프로그램과 대형의 온수생산 시스템의 성능평가의 비교.검증을 통하여 시뮬레이션 프로그램을 이용한 시스템 설계에 적용될 수 있음을 보였다.

• Nuclear Engineering and Technology
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• 제33권4호
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• pp.397-408
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• 2001

A marine reactor shows very different thermal-hydraulic characteristics compared to a land- based reactor. Especially, study on the variation of flow field due to ship motions such as inclination, heaving and rolling is essential since the flow variation has great influence on the reactor cooling capability. In this study, the natural circulation characteristics of integral type marine reactor with modular steam generators were analyzed using computational fluid dynamics code, CFX-4, for inclined conditions. The numerical analyses are performed using the results of natural circulation experiments for integral reactor which are already conducted at Seoul National University. From the results, it was found that the flow rate in the ascending steam generator cassettes increases due to buoyancy effect. Due to this flow variation, temperature difference occurs at the outlets of the each steam generator cassettes. which is mitigated through downcomer by thermal mixing. Also, around the upper pressure header the flow from descending hot leg goes up to the ascending steam generator cassettes due to large natural circulation driving force in ascending steam generator cassettes. From this result, the increase of How rate in the ascending steam generator cassettes could be understood qualitatively.