• Title, Summary, Keyword: Residence time

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Residence Time Effect on the Growth of ZrC by Low Pressure Chemical Vapor Deposition (저압화학기상증착법을 이용한 ZrC 성장에 잔류시간이 미치는 영향)

  • Park, Jong-Hoon;Jung, Choong-Hwan;Kim, Do-Jin;Park, Ji-Yeon
    • Journal of the Korean Ceramic Society
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    • v.45 no.5
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    • pp.280-284
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    • 2008
  • In order to investigate residence time effect on the growth of ZrC film, the ZrC films grew with various system total pressure (P) and total flow rate (Q) by low pressure chemical vapor deposition because residence time is function of system total pressure and total flow rate. Thermodynamic calculations predict that the decomposition of source gases ($ZrCl_4$ and $CH_4$) would be low as increasing the residence time. Thermodynamic calculations results were proved by investigating deposition rate with various residence time. Deposition rate decreased with residence time of source gas increased. Besides, depletion effect accelerated diminution of deposition rate at high residence time. On the other hands, the deposition rated was increased as decreasing the residence time because fast moving of intermediate gas species decrease the depletion effect. The crystal structure was not changed with residence time. However, the largest size of faceted grain showed up to specific residence time and the size of grain was decreased whether residence time increase or not.

Assessing Average Residence Time as a Physical Descriptor for Shellfish Farming Areas in Jaran Bay, Korea (자란만 패류양식해역의 물리환경 설명을 위한 평균체류시간 산정)

  • Kim, Jin Ho;Park, Sung-Eun;Kim, Youngmin;Kim, Chung Sook;Kang, Sungchan;Jung, Woo-Sung;Sim, Bo-Ram;Eom, Ki-Hyuk
    • Journal of Environmental Science International
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    • v.29 no.3
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    • pp.273-282
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    • 2020
  • Residence time is defined as the time taken for a material in a system to leave the system. The residence time characteristics in shellfish aquaculture determine the dispersion of excretion from aquaculture farms, along with the supply of food by seawater exchange. In this study, we estimated the spatial distribution of average residence time in the shellfish farming area using a particle tracking model. As a result, a relatively short average residence time of about 20 days or less was calculated in most areas, but an average residence time of more than 40 days was calculated in the inner areas. Relatively long average residence times were calculated along the west coast compared to the east coast, with the longest average residence time of more than 50 days in the northwestern areas. It can be inferred that the disturbance of the benthic ecosystem caused by shellfish farms is likely to be large because of the relatively weak dispersion of excrement from shellfish farms located on the west coast, especially in the northwest region. This distribution of average residence time is important for understanding the potential effects of seawater exchange on the environmental sustainability of shellfish farms, along with the seawater circulation characteristics of Jaran Bay.

The residence time of gas in an incinerator (소각로에서의 연소가스 체류시간)

  • Kim, Sung-Joon
    • Journal of Industrial Technology
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    • v.36
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    • pp.3-7
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    • 2016
  • The change of flue gas residence time with the location of air inlet in an incinerator is analysed. An independent numerical variable is the location of air inlet and dependant is the residence time of flue gas. The mean value of turbulence energy in a primary combustion chamber is also analysed. The flow field and the distribution of turbulence energy are investigated to evaluate their influence on the residence time of flue gas and the turbulence energy. As the position of secondary air inlet approaches to the top of primary combustion chamber, the residence time of gas and the turbulence energy become longer and larger respectively.

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Effects of Cell Residence Time Distributions in Cellular Mobile Communication Systems

  • Yeo, Kun-Min;Jun, Chi-Hyuck
    • Proceedings of the Korea Society for Simulation Conference
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    • pp.6-10
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    • 1999
  • We present a simulation result to the analysis of the effects of cell residence time distributions upon the expected channel occupancy time based on an analytic mobility model. Numerical examples show that exponential distribution provides upper and lower bound to the expected channel occupancy times of new calls and handoff calls. This fact reveals that the assumption of exponential distribution as the cell residence time distribution as the cell residence time distribution may over- or under-estimate cellular mobile systems.

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Analysis of the Gas Flow Field of Primary Combustion Chamber with the Conditions of Secondary Air Injection (2차 공기 주입 조건 변화에 따른 소형 소각로 내부의 유동장 분석)

  • Choi, Byung-Dae;Kim, Sung-Joon
    • Journal of Industrial Technology
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    • v.22 no.A
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    • pp.9-17
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    • 2002
  • This analysis is aimed to find out how the conditions of secondary air injection affects the residence time and the turbulence energy of flue gas and flow field in a small incinerator. A commercial code, PHOENICS, is used to simulate the flow field of an Incinerator. The computational grid system is constructed in a cartesian coordinate system In this numerical experiment, an independent numerical variable is the conditions of secondary air injection and dependants are the residence time of flue gas and the mean value of turbulence energy in a primary combustion chamber. The flow field and the distribution of turbulence energy are analysed to evaluate the residence time of flue gas and the turbulence energy The computational results say that the tangential injection of secondary air make the residence time much longer than the radial injection and that the radial injection of secondary make turbulence much stronger than the tangential injection.

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Flow Characteristics and Residence Time of Activated Carbon in the Cyclone for Optimized Design of an Adsorption/Catalysis Reactor (흡착/촉매 공정개선을 위한 사이클론 내 유동특성 및 활성탄 체류시간 산정)

  • Choi, Choeng-Ryul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.5
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    • pp.416-424
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    • 2007
  • In adsorption/catalytic process, numerical analysis has been performed to identify the flow characteristics of flue gas in the cyclone and to estimate the residence time of activated carbon using Computational Fluid Dynamics (CFD) technique. To consider flue gas and activated carbon particles simultaneously, Euler-Lagrangian model was employed so that residence time could be obtained from the numerical analysis directly. The numerical analysis has been performed with different three particle sizes and compared each flow characteristics with particle’ size. Fundamental flow patterns of flue gas and activated carbon particles, pressure distribution, residence time of flue gas, and activated carbon particles and distribution of activated carbon have been obtained from the numerical analysis.

Ignition Temperature and Residence Time of Suspended Magnesium Particles (마그네슘 부유 분진의 입자 체류시간과 발화온도)

  • Han, Ou-Sup
    • Journal of the Korean Institute of Gas
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    • v.19 no.3
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    • pp.25-31
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    • 2015
  • Effects of residence time on the MIT(Minimum Ignition Temperature) in suspended Mg particles are examined by using MIT experimental data and calculation results of terminal velocity. With increasing of the average particle diameter, we were able to identify that MIT of Mg dusts increased and the calculated residence time of particle decreased exponentially. Also, the influence on terminal velocity due to temperature increase increased slightly with increasing of average particle diameter.

Effect of Swirling Flow by Normal Injection of Secondary Air on the Gas Residence Time and Mixing Characteristics in a Lab-Scale Cold Model Combustor

  • Shin, D.;Park, S.;Jeon, B.;Yu, T.;Hwang, J.
    • Journal of Mechanical Science and Technology
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    • v.20 no.12
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    • pp.2284-2291
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    • 2006
  • The present study investigates gas residence time and mixing characteristics for various swirl numbers generated by injection of secondary air into a lab-scale cylindrical combustor. Fine dust particles and butane gas were injected into the test chamber to study the gas residence time and mixing characteristics, respectively. The mixing characteristics were evaluated by standard deviation value of trace gas concentration at different measurement points. The measurement points were located 25 mm above the secondary air injection position. The trace gas concentration was detected by a gas analyzer. The gas residence time was estimated by measuring the temporal pressure difference across a filter media where the particles were captured. The swirl number of 20 for secondary air injection angle of 5$^{\circ}$ gave the best condition: long gas residence time and good mixing performance. Numerical calculations were also carried out to study the physical meanings of the experimental results, which showed good agreement with numerical results.

A Study of Residence Time Calculation Methods in Decay Tank Design (감쇠탱크 설계를 위한 체류시간 계산 방법에 관한 연구)

  • Jung, Minkyu;Seo, Kyoungwoo;Kim, Seonghoon
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.29 no.5
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    • pp.220-230
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    • 2017
  • In this study we apply and compare a variety of numerical methods for calculating residence time distribution in decay tanks, a major design component in the for reducing N-16 radioactivity. Our research group has used a streamlined method using user-defined particle numbers. However, this streamlined method has several problems, including low exiting particle ratios, particle diminishing, and unphysical time distribution, among others. We utilize three numerical methods to establish residence time and time distribution (streamlined, discrete phase method [DPM], and user defined scalar [UDS]) and subsequently compare the averaged results of each. The three tests demonstrate the flow features within the decay tanks, which are then numerically simulated to enable comparison. We conclude that although each simulation predicts similar time averages, the UDS methodology provides a smoother time distribution and tracer contour plots at specific times.

A Study on Temporal-Spatial Water Exchange Characteristics in Gamak Bay using a Method for Calculating Residence Time and Flushing Time (체류시간과 교체시간 계산을 통한 가막만의 시·공간적 해수교환 특성 연구)

  • Kim, Jin Ho;Lee, Won Chan;Hong, Sok Jin;Park, Jung Hyun;Kim, Chung Sook;Jung, Woo Sung;Kim, Dong-Myung
    • Journal of Environmental Science International
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    • v.25 no.8
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    • pp.1087-1095
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    • 2016
  • The concepts of residence time and flushing time can be used to explain the exchange and transport of water or materials in a coastal sea. The application of these transport time scales are widespread in biological, hydrological, and geochemical studies. The water quality of the system crucially depends on the residence time and flushing time of a particle in the system. In this study, the residence and flushing time in Gamak Bay were calculated using the numerical model, EFDC, which includes a particle tracking module. The average residence time was 55 days in the inner bay, and the flushing time for Gamak Bay was about 44.8 days, according to the simulation. This means that it takes about 2 months for land and aquaculture generated particles to be transported out of Gamak Bay, which can lead to substances accumulating in the bay. These results show the relationships between the transport time scale and physical the properties of the embayment. The findings of this study will improves understanding of the water and material transport processes in Gamak Bay and will be important when assessing the potential impact of coastal development on water quality conditions.