• Title, Summary, Keyword: Decay Length

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

  • Kim, Hong-Jip;Lee, Kwang-Jin;Seo, Seong-Hyeon;Kim, Seung-Han;Han, Yeoung-Min;Seol, Woo-Seok
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.1
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    • pp.69-77
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    • 2005
  • To optimize and limit the axial length of the baffle of the KSR-III engine, stability rating tests using pulse gun as one of artificial disturbance devices have been done. Generally a rocket engine can be considered to be dynamically stable if a certain imposed external perturbation or pressure oscillation in rocket combustion chamber could be suppressed within a short time period. Decay time and other parameters for the evaluation of stabilization ability of an engine to external perturbation have been analyzed to quantify stabilization capacity of engine, in other words, dynamic stability margin. Baffle not covering flame zone enough which can be considered as collision region of injector wasn't be able to suppress external perturbation sufficiently. The limit of combustion stability margin of engine is assumed to be 50 mm length baffle of the KSR-III engine.

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

  • 김정호;임준형;장석헌;김규태;주진호;최세용;나완수;강형구;고태국
    • Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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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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Velocity Structure of Wall Jet Originating from Circular Orifices in Shallow Water (천해역에 방류되는 원형 다공바닥젵의 유속구조)

  • 김대근;서일원
    • Journal of Environmental Science International
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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.

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

  • Lee, Young-J.;Huh, Kang-Y.
    • Journal of the Korean Society of Combustion
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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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Studies on the Effect of Diffusion Process to Decay Resistance of Mine Props (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))

  • Shim, Chong-Supp;Shin, Dong-So;Jung, Hee-Suk
    • Journal of the Korean Wood Science and Technology
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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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CFD Analysis of a Concept of Nuclear Hybrid Heat Pipe with Control Rod (원자로 제어봉과 결합된 하이브리드 히트파이프의 CFD 해석)

  • Jeong, Yeong Shin;Kim, Kyung Mo;Kim, In Guk;Bang, In Cheol
    • The KSFM Journal of Fluid Machinery
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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.

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

  • Sung, Youl-Moon;Kim, Jong-Kyung;Park, Chung-Hoo
    • The Transactions of the Korean Institute of Electrical Engineers C
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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

  • Kim, Hong-Jip;Lee, Kwang-Jin;Seo, Seong-Hyeon;Kim, Seung-Han;Han, Yeoung-Min;Seol, Woo-Seok
    • Aerospace Engineering and Technology
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    • v.3 no.1
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    • pp.188-196
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    • 2004
  • To optimize and limit the axial length of baffle in KSR-III engine, stability rating tests using pulse gun as one of artificial disturbance devices have been done. Decay time and other parameters for the evaluation of stabilization ability of engine to external perturbation have been analyzed to quantify stabilization capacity of engine, in other words, dynamic stability margin. If baffle does not cover flame zone enough which can be considered as collision region of injector, it wasn't be able to suppress external perturbation sufficiently. The limit of combustion stability margin of engine is assumed to be 50 mm length baffle.

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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.

Micromorphological Characteristics of Buddhist Temple Woods Treated with Eire-retardant (방염 처리 고목재의 미생물 분해의 미시형태적 특징)

  • Wi, Seung Gon;Kim, Ik-Joo;Park, Young Man;Kim, Yoon Soo
    • 한국문화재보존과학회:학술대회논문집
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    • pp.27-34
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    • 2001
  • Following the recommendations made by the cultural authorities the wooden cultural properties (WCP) had been treated with fire-retardants for fire protection. However, visual inspections of some of the WCPs treated with fire-retardants showed microbial decay. The work was extended to examine the micromorphological characteristics of the WCPs in a Buddhist temple which had been treated with fire-retardant. Microscopic examination showed the presence of typical soft rot cavities along the length of microfibrils in the secondary wall. Bacterial attack was also observed by scanning and transmission electron microscopy. It is interesting that the decay patterns observed in the Buddhist temple were very similar to those observed in the waterlogged woods. Presumably chemicals in the fire-retardants used rendered the wood susceptible to attack by soft-rot and bacterial decay by causing an increase in the moisture content of wood. Further studies are needed to investigate the effect of fire-retardants used currently on the hygroscopicity and the strength of wood materials in the WCPs. Microbial attacks caused degradation of the secondary cell walls and in some cases also of the middle lamella. In addition, the cell walls in the outer parts of wood were also degraded due to weathering, and cell separation occurred from total disintegration of the middle lamella.

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