• Title/Summary/Keyword: Temperature stratification

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Experimental Research for Identification of Thermal Stratification Phenomena in The Nuclear Powerplant Emergency Core Coolant System(ECCS). (원전 비상 노심냉각계통 배관 열성층화 현상 규명을 위한 실험적 연구)

  • Song, Dho-In;Choi, Young-Don;Park, Min-Su
    • Proceedings of the KSME Conference
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    • 2001.11b
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    • pp.735-740
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    • 2001
  • In the nuclear power plant, emergency core coolant system(ECCS) is furnished at reactor coolant system(RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, it occurs thermal stratification phenomena in case that there is the mixing of cooling water and high temperature water due to valve leakage in ECCS. This thermal stratification phenomena raises excessive thermal stresses at pipe wall. Therefore, this phenomena causes the accident that reactor coolant flows in reactor containment in the nuclear power plant due to the deformation of pipe and thermal fatigue crack(TFC) at the pipe wall around the place that it exists. Hence, in order to fundamental identification of this phenomena, it requires the experimental research of modeling test in the pipe flow that occurs thermal stratification phenomena. So, this paper models RCS and ECCS pipe arrangement and analyzes the mechanism of thermal stratification phenomena by measuring of temperature in variance with leakage flow rate in ECCS modeled pipe and Reynold number in RCS modeled pipe. Besides, results of this experiment is compared with computational analysis which is done in advance.

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A Study on Thermal Stratification Characteristics and Useful Rate of Hot Water in Thermal Storage Tank during Hot Water Extraction Process (온수 추출과정 동안 축열조 내의 열성층 특성 및 온수 이용률에 관한 연구)

  • 장영근;박정원
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.6
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    • pp.503-511
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    • 2002
  • Heat flow characteristics during hot water extraction process was studied experimentally. Data were taken at various outlet port type for the fixed inlet port type, inlet-outlet temperature differences and mass flow rates. In this study, the temperature distribution in a storage tank and an outlet temperature were measured to predict a degree of stratification in the storage tank, and a useful rate of hot water was analysed with respect to the variables dominating a extraction process. Experimental results show that the degree of stratification and useful rate of hot water are all high in a low flow rate in case of using modified distributor I (MDI) as the outlet port type.

An Experimental Study on Thermal Stratification of Pressurized Plenum Underfloor Air Distribution System during Cooling (가압식 바닥급기 시스템의 여름철 성층화 경향에 관한 실험적 연구)

  • Kim, Dong-Hee;Yu, Ki-Hyung;Cho, Dong-Woo;Seo, Jung-Seok;Han, Sung-Phil
    • Proceedings of the SAREK Conference
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    • 2007.11a
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    • pp.340-345
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    • 2007
  • The underfloor air distribution system has been attracting to architects and building owners as one of valuable system for the renovated and newly office building. In this paper, we discussed the thermal stratification profile of pressurized plenum underfloor air distribution(UFAD) according to indoor setting temperature, diffuser number, diffuser type. For this, the space of office building(H corp.) is selected for measuring the air volume of underfloor diffuser and vertical temperature profile. As a result, the thermal stratification profile is influenced by the number and type of the underfloor diffuser and thermal storage character of the underfloor. Whereas indoor setting temperature have a lower significant impact on thermal stratification.

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SIMULATION OF THERMAL STRATIFICATION IN INLET NOZZLE OF STEAM GENERATOR

  • Ji, Joon-Suk;Youn, Bum-Su;Jeong, Hyun-Chul;Kim, Sang-Nyung
    • Nuclear Engineering and Technology
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    • v.41 no.3
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    • pp.287-294
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    • 2009
  • Due to thermal hydraulics phenomena, such as thermal stratification, various events occur to the parts of a nuclear power plant during their lifetimes: e.g. cracked and dislocated pipes and thermally fatigued, bent, and damaged supports. Due to the operational characteristics of the parts of the steam generator feedwater inlet horizontal pipe, thermal stratification takes place particularly frequently. However, the thermal stress due to thermal stratification at the steam generator feedwater inlet horizontal pipe was not reflected in the design stage of old plants(Kori Unit No.1, 2, 3 and 4, Yeonggwang Unit No. 1 and 2, and Uljin Unit No. 1 and 2; referred to as old-style power plants hereinafter). Accordingly, a verification experiment was performed for thermal stratification in the horizontal inlet nozzle steam generator of old-style plants. If thermal stratification occurred in the horizontal pipe of an old-style power plant, numerical analysis of the temperature distribution of the pipes and fluids was conducted. The temperature distributions were compared at the curved part of the pipe and the horizontal pipe before and after the installation of the improved thermal sleeves designed to alleviate thermal stress due to thermal stratification. The thermal stress reduction measure was proven effective at the steam generator inlet horizontal pipe and the curved part of the pipe.

NUMERICAL ANALYSIS OF THERMAL STRATIFICATION IN THE UPPER PLENUM OF THE MONJU FAST REACTOR

  • Choi, Seok-Ki;Lee, Tae-Ho;Kim, Yeong-Il;Hahn, Dohee
    • Nuclear Engineering and Technology
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    • v.45 no.2
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    • pp.191-202
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    • 2013
  • A numerical analysis of thermal stratification in the upper plenum of the MONJU fast breeder reactor was performed. Calculations were performed for a 1/6 simplified model of the MONJU reactor using the commercial code, CFX-13. To better resolve the geometrically complex upper core structure of the MONJU reactor, the porous media approach was adopted for the simulation. First, a steady state solution was obtained and the transient solutions were then obtained for the turbine trip test conducted in December 1995. The time dependent inlet conditions for the mass flow rate and temperature were provided by JAEA. Good agreement with the experimental data was observed for steady state solution. The numerical solution of the transient analysis shows the formation of thermal stratification within the upper plenum of the reactor vessel during the turbine trip test. The temporal variations of temperature were predicted accurately by the present method in the initial rapid coastdown period (~300 seconds). However, transient numerical solutions show a faster thermal mixing than that observed in the experiment after the initial coastdown period. A nearly homogenization of the temperature field in the upper plenum is predicted after about 900 seconds, which is a much shorter-term thermal stratification than the experimental data indicates. This discrepancy may be due to the shortcoming of the turbulence models available in the CFX-13 code for a natural convection flow with thermal stratification.

Seasonal characteristics of thermal and chemical stratification in Lake Paldang (팔당호의 계절별 열적 및 화학적 층화 특성)

  • Son, Ju Yeon;Park, Jin Rak;Noh, Hye Ran;Yu, Soon Ju;Im, Jong Kwon
    • Journal of Korean Society on Water Environment
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    • v.36 no.1
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    • pp.1-13
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    • 2020
  • The purpose of this study was to investigate the thermal and chemical stratification in Lake Paldang 2013-2018 weekly using Schmidt's stability index (SSI) and the index of chemical stratification (IC-i). The annual average for SSI was 19.1 g cm/㎠ with the maximum value of 45.3 g cm/㎠ in the summer and the minimum value of 4.8 g cm/㎠ in fall-winter showing seasonal differences as well as increased vertical mixing in the summer. The lake stability increased higher in 2016 as compared with the other period. The most influential factors of thermal stratification were temperature and heavy rainfall. Especially, high water temperature and a prolonged residence duration caused by reduced rainfall and inflows could result in an increase of the stratification period. While decreasing inflow and outflow at the end of the rainfall, the thermal stratification was restrengthened within 7-14 days, and then stabilized rapidly before the rainfall. IC-DO increased with high air temperature in the spring and fall-winter. However increasing sunshine duration and residence time and decreasing rate of outflow caused an increase of IC-DO in the summer. Rainfall (less than 800 mm/year) and discharge (less than 200 CMS) significantly declined in 2015 resulting in IC-DO (0.77) increased more than three times over the other years and bottom water hypoxia occurred. The SSI and IC-i used in this study could be applied to other lakes to understand changes in stratification and mixing dynamics.

EVALUATION OF TURBULENCE MODELS FOR ANALYSIS OF THERMAL STRATIFICATION (열성층 해석 난류모델 평가)

  • Cho, Seok-Ki;Kim, Se-Yun;Kim, Seong-O
    • Journal of computational fluids engineering
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    • v.10 no.4 s.31
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    • pp.12-17
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    • 2005
  • A computational study of evaluation of current turbulence models is performed for a better prediction of thermal stratification in an upper plenum of a liquid metal reactor. The turbulence models tested in the present study are the two-layer model, the shear stress transport (SST) model, the v2-f model and the elliptic blending mode(EBM). The performances of the turbulence models are evaluated by applying them to the thermal stratification experiment conducted at JNC (Japan Nuclear Corporation). The algebraic flux model is used for treating the turbulent heat flux for the two-layer model and the SST model, and there exist little differences between the two turbulence models in predicting the temporal variation of temperature. The v2-f model and the elliptic blending model better predict the steep gradient of temperature at the interface of thermal stratification, and the v2-f model and elliptic blending model predict properly the oscillation of the ensemble-averaged temperature. In general the overall performance of the elliptic blending model is better than the v2-f model in the prediction of the amplitude and frequency of the temperature oscillation.

Stratification of American Ginseng Seed: Embryo Growth and Temperature (미국삼 종자의 매장처리 : 배 성장과 온도)

  • John, T.A.Proctor;Dean, Louttit
    • Journal of Ginseng Research
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    • v.19 no.2
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    • pp.171-174
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    • 1995
  • Freshly harvested American ginseng (Panax quinquefolium L.) seeds were stratified at two locations over each of three years. Seed development and temperature in the stratification boxes were investigated until the seed was removed 12 months later and direct-seeded in the field. During stratification and seeding (14 months) three embryo stages were identified. In Stage I of 250 days (Sept. to mid-May) embryo length increased from about 0.5 to 1.0 mm: in Stage II of 100 days (mid-May to late Aug. when seeded) length increased to 2.0 mm and in Stage III (late Aug. to late Nov.) length increased to 5.3 mm. Excerpt split width could also be placed in three stages. Changes in embryo length correlated with embryo endosperm length ratio. Insertion compression tests showed that the excerpt softened rapidly in late Stage II and throughout Stage III. The stratification box temperatures at all depths (10, 25 and 50 cm) never exceeded -2$^{\circ}C$ even when the air temperatures dropped to -13$^{\circ}C$ and were, therefore not damaging to the seeds.

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Numerical Analysis of Thermal Stratification and Turbulence Penetration into Leaking Flow in a Circular Branch Piping (원형 T분기배관 내 누설유동의 열성층화와 난류침투에 관한 전산해석적 연구)

  • Han, Seong-Min;Choi, Young-Don
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1833-1838
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    • 2003
  • In the nuclear power plant, emergency core coolant system(ECCS) is furnished at reactor coolant system(RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can be occurred due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack(TFC) accident. In the present study, when the turbulence penetration occurs in the branch piping, the maximum temperature differences of fluid at the pipe cross-sections of the T-branch with thermal stratification are examine

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Study of Thermal Stratification into Leaking Flow in the Nuclear Power Plant, Emergency Core Coolant System (원자로 비상 냉각재 누설에 의한 열성층의 비정상 특성에 관한 연구)

  • Han Seong-Min;Choi Yong-Don;Park Min-Soo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.3
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    • pp.202-210
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    • 2006
  • In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can be occurred due to coolant leaking in the check valve. The thermal stratification produces excessive thormal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, when the turbulence penetration occurs in the branch pipe, the maximum temperature differences of fluid at the pipe cross-sections of the T-branch with thermal stratification are examine.