• 제목, 요약, 키워드: Decay Length

검색결과 90건 처리시간 0.038초

배플 길이의 최적화를 위한 연소 안정성 평가 시험 (Stability Rating Tests for Optimization of Axial Baffle Length)

  • 김홍집;이광진;서성현;김승한;한영민;설우석
    • 한국항공우주학회지
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    • v.33 no.1
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    • pp.69-77
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    • 2005
  • KSR-III 개발과정에서 배플을 장착하여 연소 불안정 현상을 해결한 바 있으나, 추력 및 냉각과 관련된 축방향 길이에 대한 최적화 과정을 거치지는 않았다. 이에 수동제어기구로서 사용되는 배플의 축방향 길이의 최적화 및 한계를 평가하기 위하여, 축방향 길이를 작동인자로 하여 연소 안정성 여분을 평가하였다. 외부 교란 발생 장치로서 2번의 기폭이 가능한 펄스건을 사용하였다. 외부 교란에 대한 연소실에서의 응답 특성을, 감쇠 시간과 진폭비와 같은 인자를 도입하여 정량화하였다. 설계점과 탈설계점에서 시험을 수행하였으며, 분사기의 충돌점으로 생각할 수 있는 화염 영역을 감싸지 못하는 경우에는 배플의 충분한 감쇠 능력을 보장할 수 없음을 확인하였다. 따라서 연소 안정성의 여분의 경계는 KSR-III에서의 작동조건 하에서 50 mm 정도의 배플인 것으로 판단되었다.

A Control Volume Scheme for Three-Dimensional Transport: Buffer and Matrix Effects on a Decay Chain Transport in the Repository

  • Lee, Y.M.;Y.S. Hwang;Kim, S.G.;C.H. Kang
    • Nuclear Engineering and Technology
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    • v.34 no.3
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    • pp.218-231
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    • 2002
  • Using a three-dimensional numerical code, B3R developed for nuclide transport of an arbitrary length of decay chain in the buffer between the canister and adjacent rock in a high- level radioactive waste repository by adopting a finite difference method utilizing the control- volume scheme, some illustrative calculations have been done. A linear sorption isotherm, nuclide transport due to diffusion in the buffer and the rock matrix, and advection and dispersion along thin rigid parallel fractures existing in a saturated porous rock matrix as well as diffusion through the fracture wall into the matrix is assumed. In such kind of repository, buffer and rock matrix are known to be important physico-chemical harriers in nuclide retardation. To show effects of buffer and rock matrix on nuclide transport in HLW repository and also to demonstrate usefulness of B3R, several cases of breakthrough curves as well as three- dimensional plots of concentration isopleths associated with these two barriers are introduced for a typical case of decay chain of $^{234}$ Ulongrightarrow$^{230}$ Thlongrightarrow$^{226}$ Ra, which is the most important chain as far as the human environment is concerned.

고온초전도 선재의 접합 및 인덱스손실 평가 (Estimation of joint and index dissipation in HTS tape)

  • 김정호;임준형;장석헌;김규태;주진호;최세용;나완수;강형구;고태국
    • 한국초전도저온공학회:학술대회논문집
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    • pp.59-62
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    • 2003
  • We fabricated two HTS closed coils by using resistive-joint method and the joint resistance of the coil was estimated by field decay technique at 77 K. In addition, we used the Runge-kutta method for the numerical analysis to estimate the decay properties. The joint resistances were evaluated as a function of critical current of HTS closed coil and external field strength of excitation coil. It was observed that joint resistance was independent of critical current and external field strength. It was estimated that joint resistance was 8.0$\times$10$^{-9}$ $\Omega$ to 11.9$\times$10$^{-9}$ $\Omega$ for coils of contact length for 7 cm.

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간역(簡易) 처리법(處理法)에 의한 갱목(坑木)의 내부효력(耐腐效力)에 관(關)한 연구(硏究) (Studies on the Effect of Diffusion Process to Decay Resistance of Mine Props)

  • 심종섭;신동소;정희석
    • 목재공학
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    • v.10 no.3
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    • pp.166-166
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    • 1982
  • This study has been made to make an observation regarding present status of the coal mine props which is desperately needed for coal production, despite of great shortage of the timber resources in this country, and investigate the effects of diffusion process on the decay resistances of the mine props as applied preservatives of Malenit and chromated zinc chloride. The results are as follows. 1. Present status of the coal mine props Total demand of coal mine props in the year of 1975 was approximately 456 thousand cubic meters. The main species used for mine props are conifer (mainly Pinus densiflora) and hardwood (mainly Quercus). Portions between them are half and half. With non fixed specification, wide varieties of timber in size and form are used. And volume of wood used per ton of coal production shows also wide range from 0.017 cubic meter to 0.03 cubic meter. 2. Decay resistance test a) The oven dry weight decreased between untreated specimen and treated specimen has not shown any significantly, although it has shown some differences in average values between them. It may be caused by the shorter length of the test. b) The strength of compression test between untreated specimen and treated specimen has also shown the same results as shown in case of weight decrease. Reasons assumed are the same. c) The amounts of the extractives in one percent of sodium hydroxide (NaOH) between untreated and treated specimen have shown the large value in case of untreated specimen than that of treated. 3. The economical benifit between untreated and treated wood when applied in field has seen better in long tenn base in case of treated wood, although the primary cost of treated wood add a little bit more cost than that of the untreated wood.

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원자로 제어봉과 결합된 하이브리드 히트파이프의 CFD 해석 (CFD Analysis of a Concept of Nuclear Hybrid Heat Pipe with Control Rod)

  • 정영신;김경모;김인국;방인철
    • 한국유체기계학회 논문집
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    • v.17 no.6
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    • pp.109-114
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    • 2014
  • After the Fukushima accident in 2011, it was revealed that nuclear power plant has the vulnerability to SBO accident and its extension situation without sufficient cooling of reactor core resulting core meltdown and radioactive material release even after reactor shutdown. Many safety systems had been developed like PAFS, hybrid SIT, and relocation of RPV and IRWST as a part of steps for the Fukushima accident, however, their applications have limitation in the situation that supply of feedwater into reactor is impossible due to high pressure inside reactor pressure vessel. The concept of hybrid heat pipe with control rod is introduced for breaking through the limitation. Hybrid heat pipe with control rod is the passive decay heat removal system in core, which has the abilities of reactor shutdown as control rod as well as decay heat removal as heat pipe. For evaluating the cooling performance hybrid heat pipe, a commercial CFD code, ANSYS-CFX was used. First, for validating CFD results, numerical results and experimental results with same geometry and fluid conditions were compared to a tube type heat pipe resulting in a resonable agreement between them. After that, wall temperature and thermal resistances of 2 design concepts of hybrid heat pipe were analyzed about various heat inputs. For unit length, hybrid heat pipe with a tube type of $B_4C$ pellet has a decreasing tendency of thermal resistance, on the other hand, hybrid heat pipe with an annular type $B_4C$ pellet has an increasing tendency as heat input increases.

디젤 엔진 운전 조건에서 분무 연소 과정과 난류 화염 구조 특성에 대한 해석 (Characteristization of Spray Combustion and Turbulent Flame Structures in a Typical Diesel Engine Condition)

  • 이영재;허강열
    • 한국연소학회지
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    • v.14 no.3
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    • pp.29-36
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    • 2009
  • Simulation is performed to analyze the characteristics of turbulent spray combustion in a diesel engine condition. An extended Conditional Moment Closure (CMC) model is employed to resolve coupling between chemistry and turbulence. Relevant time and length scales and dimensionless numbers are estimated at the tip and the mid spray region during spray development and combustion. The liquid volume fractions are small enough to support validity of droplets assumed as point sources in two-phase flow. The mean scalar dissipation rates (SDR) are lower than the extinction limit to show flame stability throughout the combustion period. The Kolmogorov scales remain relatively constant, while the integral scales increase with decay of turbulence. The chemical time scale decreases abruptly to a small value as ignition occurs with subsequent heat release. The Da and Ka show opposite trends due to variation in the chemical time scale. More work is in progress to identify the spray combustion regimes.

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천해역에 방류되는 원형 다공바닥젵의 유속구조 (Velocity Structure of Wall Jet Originating from Circular Orifices in Shallow Water)

  • 김대근;서일원
    • 한국환경과학회지
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    • v.11 no.10
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    • pp.1039-1044
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    • 2002
  • In this study, breakwater model which has several outlet pipes to discharge water is settled in the experimental open channel and mean velocity distributions of multi wall jet are measured. The length of zone of flow establishment of wall jet is shorter than that of free jet and decay rate of jet centerline longitudinal velocity along x is linear in $0.3{leq}x/I_p{leq}17$. The rate of vertical width and lateral width spreading of multi wall jet is respectively 0.0753, 0.157.

Neutral Loop Discharge 플라즈마의 전자거동과 최적조건에 관한 기초적 연구 (A Fundamental Study on the Electron Behavior and Optimum Condition for the Formation of a Neutral Loop Discharge Plasma)

  • 성열문;김종경;박정후
    • 대한전기학회논문지:전기물성ㆍ응용부문C
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    • v.50 no.6
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    • pp.281-287
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    • 2001
  • In order to obtain guidelines for design and operation of a new plasma source by a magnetic neutral loop discharge(NLD), the electron behavior was studied experimentally and numerically. Experimentally, the magnetic field gradient was changed over a wide range, and it was found that there existed an optimum value for efficient plasma production. Analyses of the electron behavior were performed using a model that included effects of a three dimensional electromagnetic field configuration considering the spatial decay of the electric field, and the limitation to the motion of electron caused by the existence of walls and thus electron loss at wall surfaces. These three dimensional factors were found to explain the existence of the optimum magnetic field gradient. It was shown that the L dependence of the plasma production efficiency was firstly decided by the finite decay length of the electric field strength, which was further modified by electron elastic collisions with neutral atoms which drove the electron to walls. The latter effect tends to reduce the optimum value of L.

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연소 안정성 평가 시험을 통한 배플 길이의 안정성 여분 평가

  • 김홍집;이광진;서성현;김승한;한영민;설우석
    • 항공우주기술
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    • v.3 no.1
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    • pp.188-196
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    • 2004
  • 수동제어기구로서 사용되는 배플의 축방향 길이의 최적화 및 한계를 평가하기 위하여, 축방향 길이를 작동인자로 하여 연소 안정성 여분을 평가하였다. 외부 교란 발생 장치로서 2번의 기폭이 가능한 펄스건을 사용하였다. 외부 교란에 대한 연소실에서의 응답 특성을, 감쇠 시간과 진폭비와 같은 인자를 도입하여 정량화하였다. 설계점과 탈설계점에서 시험을 수행하였으며, 분사기의 충돌점으로 생각할 수 있는 화염 영역을 감싸지 못하는 경우에는 배플의 충분한 감쇠 능력을 보장할 수 없음을 확인하였다. 따라서 연소 안정성의 여분의 경계는 50mm 정도의 배플인 것으로 판단되었다.

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Experimental investigation of free and bounded presheaths in weakly magnetized plasmas

  • Kang, I.J.;Bae, M.K.;Lho, T.;Chung, K.S.
    • Current Applied Physics
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    • v.17 no.3
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    • pp.358-365
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    • 2017
  • Transports of plasmas in the edge of fusion devices have similarities in terms of formation of a free presheath and unclear explanation on the transport process relating the diffusion coefficient ($D_{\bot}$) to characteristic length of perturbing for flux tube ($L_c$). $D_{\bot}$ and $L_c$ are investigated by generating perturbations in various free presheaths due to a perturbing object located at the axial center of a linear plasma device, called DiPS (Divertor Plasma Simulator). Free presheaths are generated due to a tungsten perturbing object by changing the magnetic flux density. Bounded presheaths are also formed due to a limiting structure of a magnetic nozzle and due to the given geometry of DiPS. In terms of plasma discharge currents, radial plasma profiles were measured by using a fast scanning probe system. $D_{\bot}$ and $L_c$ within the free presheath regions were calculated by using the measured plasma parameters and compared with those of bounded presheaths near the chamber walls. Decay length of plasma density was introduced to calculation of $D_{\bot}$. To calculate the perturbation length (L) of free presheaths, a theoretical scale factor K was introduced as $L=KL_c$ using a fluid model. Normalized factor ${\delta}=D_{\bot}/D_B$, where $D_B=Bohm$ diffusion coefficient, were obtained as 8 at free presheaths and 11 at bounded presheaths.