• Title/Summary/Keyword: Natural Circulation

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Experimental Investigation of Flow Oscillations in a Semi-closed Two-phase Natural Circulation Loop (준밀폐형 2상자연순환 회로 내에서의 유동 진동에 관한 실험적 연구)

  • Kim, Jong Moon;Lee, Sang Yong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.12
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    • pp.1763-1773
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    • 1998
  • In the present experimental study, the flow behavior in a semi-closed two-phase natural circulation loop was examined. Water was used as the working fluid. Heat flux, heater-inlet subcooling, and flow restrictions at the heater-inlet and at the expansion-tank-line were taken as the controlling parameters Six circulation modes were identified by changing heat flux and inlet subcooling conditions ; single-phase continuous circulation, periodic circulation (A), two-phase continuous circulation, and periodic circulations (B), (C), and (D). Among these, the single-phase and two-phase continuous-circulation modes exhibit no significant oscillations and are considered to be stable. Periodic circulation (A) is characterized by the large amplitude two-phase f10w oscillations with the temporal single-phase circulation between them, while periodic circulation (B) featured by the flow oscillations with continuous boiling inside the heater section. Periodic circulation (C) appears to be the manometric oscillation with continuous boiling. Periodic circulation (D) has the longer period than periodic circulation (B) and a substantial amount of liquid flow back and forth through the expansion-tank-line periodically ; this mode is considered the pressure drop oscillation. Parametric study shows that the increases of the inlet- and expansion-tank-line- restrictions and the decrease of inlet subcooling broaden the range of the stable two-phase(continuous circulation) mode.

Analysis of the Flow Rate for a Natural Cryogenic Circulation Loop during Acceleration and Low-gravity Section (극저온 자연순환회로의 가속 및 저중력 구간 유량 분석)

  • Baek, Seungwhan;Jung, Youngsuk;Cho, Kiejoo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.23 no.5
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    • pp.43-52
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    • 2019
  • Cryogenic propellant rockets utilize a natural circulation loop of cryogenic fluid to cool the engine inlet temperature before launch. The geometric information about the circulation system, such as length and diameter of the pipes and the heat input to the system, defines the mass flow rate of the natural circulation loop. We performed experiments to verify the natural circulation mass flow rate and compared the results with the analytical results. The comparison of the mass flow rate between experiments and numerical simulations showed a 12% offset. We also included a prediction of the natural circulation flow rate in the low-gravity section and in the acceleration section in the upper stage of the launch vehicle. The oxygen tank should have 100 kPa(a) of pressure in the acceleration section to maintain a high flow rate for the natural circulation loop. In the low-gravity section, there should be an optimal tank pressure that leads to the maximum natural circulation flow rate.

Preliminary Experimental Study on the Two-phase Flow Characteristics in a Natural Circulation Loop (자연순환 루프에서 이상유동 특성에 관한 예비실험 연구)

  • Kim, Jae-Cheol;Ha, Kwang-Soon;Park, Rae-Joon;Hong, Seong-Wan;Kim, Sang-Baik
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.308-311
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    • 2008
  • As a severe accident mitigation strategy in a nuclear power plant, ERVC(External Reactor Vessel Cooling) has been proposed. Under ERVC conditions, where a molten corium is relocated in a reactor vessel lower head, a natural circulation two-phase flow is driven in the annular gap between the reactor vessel wall and its insulation. This flow should be sufficient to remove the decay heat of the molten corium and maintain the integrity of the reactor vessel. Preliminary experimental study was performed to estimate the natural circulation two-phase flow. The experimental facility which is one dimensional, the half height, and the 1/238 channel area of APR1400, was prepared and the experiments were carried out to estimate the natural circulation two-phase flow with varying the parameters of the coolant inlet area, the heat rate, and the coolant inlet subcooling. In results, the periodic circulation flow was observed and the characteristics were varied from the experimental parameters. The frequency of the natural circulation flow rate increased as the wall heat flux increased.

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Experimental study on natural circulation using liquid nitrogen for superconducting applications

  • Choi, Yeon Suk
    • Progress in Superconductivity and Cryogenics
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    • v.15 no.3
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    • pp.49-52
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    • 2013
  • An experiment to investigate the natural circulation of a cryogen has been performed. The study is motivated mainly by our recent development of cryogenic cooling system for prototype superconducting cyclotron without any circulating pump. In the natural circulation loop system, a cooling channel is attached on the outer surface of the aluminium block and the liquid nitrogen passes through inside of the channel to cool the block indirectly. A cryocooler as a heat sink is located at the top to re-condense cryogenic vapor coming from the aluminium block in which electrical heater is installed as a heat source. The main dimensions are determined using the relevant analysis and the natural circulation loop is successfully fabricated. The temperature distributions in the loop are measured during initial cool-down process and in steady state, from which the modified Grashof numbers are calculated and compared with the existing correlation estimated with one-dimensional analysis for steady state flow.

The Effects of Coolant Inventory and Noncondensible Gas on the Natural Circulation in a PWR Loop System (PWR루프계통에서 냉각재 재고량 및 비응축성 가스의 자연순환에 미치는 영향)

  • Cha, Jong-Hee;Jin, Yong-Suk
    • Nuclear Engineering and Technology
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    • v.21 no.4
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    • pp.308-320
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    • 1989
  • The objective of this work is to investigate the effects of diminished primary coolant inventory and the presence of noncondensible gas during single- and two-phase natural circulation in a PWR loop model. The test model was composed of two loops with a U-tube heat exchanger in each loop. Through a series of tests, it has been confirmed that the two-phase natural circulation flow rates were greatly dependent on primary coolant inventory as previous investigators observed. The primary coolant inventory limit to maintain two-phase natural circulation was found to be the amount of the coolant necessary to keep the waterline of the coolant nozzle hole center in this model. The presence of noncondensible gas impede the single-phase natural circulation, but it did not affect the two-phase natural circulation significantly.

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PWR Hot Leg Natural Circulation Modeling with MELCOR Code

  • Park, Jae-Hong;Lee, Jong-In;Randall. K. Cole;Randall. O. Gauntt
    • Proceedings of the Korean Nuclear Society Conference
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    • 1997.10a
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    • pp.772-777
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    • 1997
  • Previous MELCOR and SCDAP/RELAP5 nodalizations for simulating the counter-current, natural circulation behavior of vapor flow within the RCS hot legs and SG U-tubes when core damage progress can not be applied to the steady state and water-filled conditions during the initial period of accident progression because of the artificially high loss coefficients in the hot legs and SG U-tubes which were chosen from results of COMMIX calculation and the Westinghouse natural circulation experiments in a 1/7-scale facility for simulating steam natural circulation behavior in the vessel and in the hot leg and SG during the TMLB' scenrio. The objective of this study is to develop a natural circulation modeling which can be used both for the liquid flow condition at steady state and for the vapor flow condition at the later period of in-vessel core damage. For this, the drag forces resulting from the momentum exchange effects between the two vapor streams in the hot leg was modeled as a pressure drop by pump model. This hot leg natural circulation modeling of MELCOR was able to reproduce similar mass flow rates with those predicted by previous models.

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Numerical study on thermal-hydraulics of external reactor vessel cooling in high-power reactor using MARS-KS1.5 code: CFD-aided estimation of natural circulation flow rate

  • Song, Min Seop;Park, Il Woong;Kim, Eung Soo;Lee, Yeon-Gun
    • Nuclear Engineering and Technology
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    • v.54 no.1
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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.

NATURAL CIRCULATION ANALYSIS CONSIDERING VARIABLE FLUID PROPERTIES WITH THE CUPID CODE (CUPID 코드의 유체 물성치 변화를 고려한 자연대류 해석)

  • Lee, S.J.;Park, I.K.;Yoon, H.Y.;Kim, J.
    • Journal of computational fluids engineering
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    • v.20 no.4
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    • pp.14-20
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    • 2015
  • Without electirc power to cool down the hot reactor core, passive systems utilizing natural circulation are becoming a big specialty of recent neculear systems after the severe accident in Fukusima. When we consider the natural circulation in a pool, thermal mixing phenomena may start from single phase circulation and can continue to two phase condition. Since the CUPID code, which has been developed for two-phase flow analysis, can deal with the phase transition phenomena, the CUPID would be pertinent to natural convection problems in single- and two-phase conditions. Thus, the CUPID should be validated against single- and two-phase natural circulation phenomena. For the first step of the validation process, this study is focused on the validation of single-phase natural circulation. Moreover, the CUPID code solves the fluid properties by the relationship to pressure and temperature from the steam table considering non-condensable gas effects, so that the effects from variable properties are included. Simple square thermal cavity problems are tested for laminar and turbulent conditions against numerical and experimental data. Throughout the investigation, it is found that the variable properties can affect the flow field in laminar condition, but the effect becomes weak in turbulence condition, and the CUPID code implementing steam table is capable of analyzing single phase natural circualtion phenomena.

An Experimental Study on the Flow Characteristics Inside an Open Two-Phase Natural Circulation Loop (개방된 2상 자연순환 회로내의 유동특성에 관한 실험적 연구)

  • 경익수;이상용
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.5
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    • pp.1313-1320
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    • 1993
  • Flow patterns inside the riser section and the effects of the heater inlet-and exit-restrictions, liquid charging level and the heater inlet subcooling on the flow characteristics inside an open two-phase natural circulation loop were studied experimentally. Three basic circulation modes were observed ; periodic circulation (A)(flow oscillations with incubation(no boiling) period), continuous circulations(stable operation mode with no flow oscillations), and periodic circulation (B) (flow oscillations with continuous boiling). The circulation rate increases and then decreases with the increase of the heating rate and the maximum circulation rate appears with the continuous circulation mode. The decrease of the inlet-restriction or the increase of the exitrestriction destabilizes the system. When the liquid charging level or the inlet subcooling decreases, the continuous circulation mode starts at the lower heating rate and the system is stabilized.

Experimental investigation of two-phase natural circulation loop as passive containment cooling system

  • Lim, Sun Taek;Kim, Koung Moon;Kim, Haeseong;Jerng, Dong-Wook;Ahn, Ho Seon
    • Nuclear Engineering and Technology
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    • v.53 no.12
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    • pp.3918-3929
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    • 2021
  • In this study, we experimentally investigate of a two-phase natural circulation loop that functions as a passive containment cooling system (PCCS). The experimental apparatus comprises two loops: a hot loop, for simulating containment under severe accidents, and a natural circulation loop, for simulating the PCCS. The experiment is conducted by controlling the pressure and inlet temperature of the hot loop in the range of 0.59-0.69 MPa (abs) and 119.6-158.8 ℃, respectively. The heat balance of the hot loop is established and compared with a natural circulation loop to assess the thermal reliability of the experimental apparatus, and an additional system is installed to measure the vapor mass flow rate. Furthermore, the thermal-hydraulic characteristics are considered in terms of a temperature, mass flow rate, heat transfer coefficient (HTC), etc. The flow rate of the natural circulation loop is induced primarily by flashing, and a distortion is observed in the local HTC because of the fully develop as well as subcooled boiling. As a result, we present the amount of heat capacity that the PCCS can passively remove according to the experimental conditions and compared the heat transfer performance using Chen's and Dittus-Boelter correlation.