• Title/Summary/Keyword: Air-water two-phase flow

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MOLTEN CORIUM DISPERSION DURING HYPOTHETICAL HIGH-PRESSURE ACCIDENTS IN A NUCLEAR POWER PLANT (원자로 노심 용융물의 고압분출 및 비산 현상에 대한 수치해석적 연구)

  • Kim, Jong-Tae;Kim, Sang-Baik;Kim, Hee-Dong;Jeong, Jae-Sik
    • 한국전산유체공학회:학술대회논문집
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    • 2009.11a
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    • pp.121-128
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    • 2009
  • During a hypothetical high-pressure accident in a nuclear power plant (NPP), molten corium can be ejected through a breach of a reactor pressure vessel (RPV) and dispersed by a following jet of a high-pressure steam in the RPV. The dispersed corium is fragmented into smaller droplets in a reactor cavity of the NPP by the steam jet and released into other compartments of the NPP by a overpressure in the cavity. The fragments of the corium transfer thermal energy to the ambient air in the containment or interact chemically with steam and generate hydrogen which may be burnt in the containment. The thermal loads from the ejected molten corium on the containment which is called direct containment heating (DCH) can threaten the integrity of the containment. DCH in a NPP containment is related to many physical phenomena such as multi-phase hydrodynamics, thermodynamics and chemical process. In the evaluation of the DCH load, the melt dispersion rates depending on the RPV pressure are the most important parameter. Mostly, DCH was evaluated by using lumped-analysis codes with some correlations obtained from experiments for the dispersion rates. In this study, MC3D code was used to evaluate the dispersion rates in the APR1400 NPP during the high-pressure accidents. MC3D is a two-phase analysis code based on Eulerian four-fields for melt jet, melt droplets, gas and water. The dispersion rates of the corium melt depending on the RPV pressure were obtained from the MC3D analyses and the values specific to the APR1400 cavity geometry were compared to a currently available correlation.

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Numerical Simulation of 3D Free-Surface Flows by Using CIP-based and FV-based Methods

  • Yang, Kyung-Kyu;Nam, Bo-Woo;Kim, Yong-Hwan
    • International Journal of Ocean System Engineering
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    • v.1 no.3
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    • pp.136-143
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    • 2011
  • In this paper, three-dimensional free-surface flows are simulated by using two different numerical methods, the constrained interpolation profile (CIP)-based and finite volume (FV)-based methods. In the CIP-based method, the governing equations are solved on stationary staggered Cartesian grids by a finite difference method, and an immersed boundary technique is applied to deal with wave-body interactions. In the FV-based method, the governing equations are solved by applying collocated finite volume discretization, and body-fitted meshes are used. A free-surface boundary is considered as the interface of the multi-phase flow with air and water, and a volumeof-fluid (VOF) approach is applied to trace the free surface. Among many variations of the VOF-type method, the tangent of hyperbola for interface capturing (THINC) and the compressive interface capturing scheme for arbitrary meshes (CICSAM) techniques are used in the CIP-based method and FV-based method, respectively. Numerical simulations have been carried out for dam-breaking and wave-body interaction problems. The computational results of the two methods are compared with experimental data and their differences are observed.

Landscape Design for the National Athlete Training Camp (국가대표 선수 훈련원 마스터플랜 설계경기 조경계획)

  • Kim Ah-Yeon;Yoo Seon-Keun;Oh Hyung-Seok
    • Journal of the Korean Institute of Landscape Architecture
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    • v.33 no.6 s.113
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    • pp.109-126
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    • 2006
  • As the national interest in sports has been increased over time, sports facilities and sports complex are considered more than just physical environments for training athletes or watching games. Sports facilities now become symbolic spatial devices to represent the national and cultural pride of any countries. The existing national training camp located in Taenung, Seoul is gotting outdated and degraded. The polluted air in the city risks athletes' health condition. The government planned to construct the second training camp at Jincheon, Chungbuk at the area of $2,171,910m^2$. The Korea Sports Council called for proposals to envision the future training camp, and they held a design competition from August to November, 2005. The first phase was to present the masterplan for the entire site including training buildings, outdoor training facilities, dormitories, a visitor center, a research center, education and administration buildings. Considering the size of the site, the planning process required a strong relationship between landscape and architecture. This study tries to provide general explanations on the winning proposal focused on the landscape-related issues. It also attempts to have reference points for contemporary planning and design issues to situate the project in the stream of continuing design effort to avoid the dichotomy between nature and culture. The landscape proposal for the new national taming camp suggests four main strategies; 1) The camp has two intersecting and interweaving parks which represent the natural and urban order. 2) The entire site is organized and networked by the flow of landscape called landscape ribbon in terms of topography, vegetation, and water flow. 3) The landscape is choreographed through the time and process. 4) The ecological process and the digital contents are juxtaposed in the landscape. This winning proposal is the first step to portray the national vision for the sustainable environment coexisting with sports industry. Landscape in this proposal is an active agent to network various parts of the site which enables landscape to be infrastructure. Landscape design in this proposal should be considered open-ended strategies rather than determined concrete forms and its engaging further development will be tested in following Design-Build phase.

Use of infinite elements in simulating liquefaction phenomenon using coupled approach

  • Kumari, Sunita;Sawant, V.A.
    • Coupled systems mechanics
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    • v.2 no.4
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    • pp.375-387
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    • 2013
  • Soils consist of an assemblage of particles with different sizes and shapes which form a skeleton whose voids are filled with water and air. Hence, soil behaviour must be analyzed by incorporating the effects of the transient flow of the pore-fluid through the voids, and therefore requires a two-phase continuum formulation for saturated porous media. The present paper presents briefly the Biot's basic theory of dynamics of saturated porous media with u-P formulation to determine the responses of pore fluid and soil skeleton during cyclic loading. Kelvin elements are attached to transmitting boundary. The Pastor-Zienkiewicz-Chan model has been used to describe the inelastic behavior of soils under isotropic cyclic loadings. Newmark-Beta method is employed to discretize the time domain. The response of fluid-saturated porous media which are subjected to time dependent loads has been simulated numerically to predict the liquefaction potential of a semi-infinite saturated sandy layer using finite-infinite elements. A settlement of 17.1 cm is observed at top surface. It is also noticed that liquefaction occurs at shallow depth. The mathematical advantage of the coupled finite element analysis is that the excess pore pressure and displacement can be evaluated simultaneously without using any empirical relationship.

Numerical Simulation of Tsunami Force Acting on Onshore Bridge (for Tsunami Bore) (연안교량에 작용하는 지진해일파력에 관한 수치시뮬레이션(단파의 경우))

  • Lee, Kwang-Ho;Woo, Kyung-Hwan;Kim, Do-Sam;Jeong, Ik-Han
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.29 no.1
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    • pp.46-61
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    • 2017
  • In the present work, the interaction analysis between tsunami bore and onshore bridge is approached by a numerical method, where the tsunami bore is generated by difference of upstream side and downstream side water levels. Numerical simulation in this paper was carried out by TWOPM-3D(three-dimensional one-field model for immiscible two-phase flows), which is based on Navier-Stokes solver. In order to verify the applicability of force acting on an onshore bridge, numerical results and experimental results were compared and analyzed. From this, we discussed the characteristics of horizontal force and vertical force(uplift force and downward force) changes including water level and velocity change due to the tsunami bore strength, water depth, onshore bridge form and number of girder. Furthermore, It was revealed that the entrained air in the fluid flow highly affected the vertical force.

Recent Progress in Air-Conditioning and Refrigeration Research : A Review of Papers Published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2016 (설비공학 분야의 최근 연구 동향 : 2016년 학회지 논문에 대한 종합적 고찰)

  • Lee, Dae-Young;Kim, Sa Ryang;Kim, Hyun-Jung;Kim, Dong-Seon;Park, Jun-Seok;Ihm, Pyeong Chan
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.29 no.6
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    • pp.327-340
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    • 2017
  • This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2016. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) The research works on the thermal and fluid engineering have been reviewed as groups of flow, heat and mass transfer, the reduction of pollutant exhaust gas, cooling and heating, the renewable energy system and the flow around buildings. CFD schemes were used more for all research areas. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer and industrial heat exchangers. Researches on heat transfer characteristics included the results of the long-term performance variation of the plate-type enthalpy exchange element made of paper, design optimization of an extruded-type cooling structure for reducing the weight of LED street lights, and hot plate welding of thermoplastic elastomer packing. In the area of pool boiling and condensing, the heat transfer characteristics of a finned-tube heat exchanger in a PCM (phase change material) thermal energy storage system, influence of flow boiling heat transfer on fouling phenomenon in nanofluids, and PCM at the simultaneous charging and discharging condition were studied. In the area of industrial heat exchangers, one-dimensional flow network model and porous-media model, and R245fa in a plate-shell heat exchanger were studied. (3) Various studies were published in the categories of refrigeration cycle, alternative refrigeration/energy system, system control. In the refrigeration cycle category, subjects include mobile cold storage heat exchanger, compressor reliability, indirect refrigeration system with $CO_2$ as secondary fluid, heat pump for fuel-cell vehicle, heat recovery from hybrid drier and heat exchangers with two-port and flat tubes. In the alternative refrigeration/energy system category, subjects include membrane module for dehumidification refrigeration, desiccant-assisted low-temperature drying, regenerative evaporative cooler and ejector-assisted multi-stage evaporation. In the system control category, subjects include multi-refrigeration system control, emergency cooling of data center and variable-speed compressor control. (4) In building mechanical system research fields, fifteenth studies were reported for achieving effective design of the mechanical systems, and also for maximizing the energy efficiency of buildings. The topics of the studies included energy performance, HVAC system, ventilation, renewable energies, etc. Proposed designs, performance tests using numerical methods and experiments provide useful information and key data which could be help for improving the energy efficiency of the buildings. (5) The field of architectural environment was mostly focused on indoor environment and building energy. The main researches of indoor environment were related to the analyses of indoor thermal environments controlled by portable cooler, the effects of outdoor wind pressure in airflow at high-rise buildings, window air tightness related to the filling piece shapes, stack effect in core type's office building and the development of a movable drawer-type light shelf with adjustable depth of the reflector. The subjects of building energy were worked on the energy consumption analysis in office building, the prediction of exit air temperature of horizontal geothermal heat exchanger, LS-SVM based modeling of hot water supply load for district heating system, the energy saving effect of ERV system using night purge control method and the effect of strengthened insulation level to the building heating and cooling load.

Numerical Simulation of Wave Breaking Near Ship Bow

  • Lee, Young-Gill;Kim, Nam-Chul;Yu, Jin-Won;Choi, Si-Young
    • Journal of Ship and Ocean Technology
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    • v.12 no.1
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    • pp.16-27
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    • 2008
  • The interaction between advancing ships and the waves generated by them plays important roles in wave resistances and ship motions. Wave breaking phenomena near the ship bow at different speeds are investigated both numerically and experimentally. Numerical simulations of free surface profiles near the fore bodies of ships are performed and visualized to grasp the general trend or the mechanism of wave breaking phenomena from moderate waves rather than concentrating on local chaotic irregularities as ship speeds increase. Navier-Stokes equations are differentiated based on the finite difference method. The Marker and Cell (MAC) Method and Marker-Density Method are employed, and they are compared for the description of free surface conditions associated with the governing equations. Extra effort has been directed toward the realization of extremely complex free surface conditions at wave breaking. For this purpose, the air-water interface is treated with marker density, which is used for two layer flows of fluids with different properties. Adaptation schemes and refinement of the numerical grid system are also used at local complex flows to improve the accuracy of the solutions. In addition to numerical simulations, various model tests are performed in a ship model towing tank. The results are compared with numerical calculations for verification and for realizing better, more efficient research performance. It is expected that the present research results regarding wave breaking and the geometry of the fore body of ship will facilitate better hull form design productivity at the preliminary ship design stage, especially in the case of small and fast ship design. Also, the obtained knowledge on the impact due to the interaction of breaking waves and an advancing hull surface is expected to be applicable to investigation of the ship bow slamming problem as a specific application.

Analysis of Holdup Characteristics of Large and Small Bubbles in Three-Phase Fluidized Beds by using a Dynamic Gas Disengagement Method (삼상유동층에서 동력학적 기체유출 측정방법에 의한 큰 기포와 작은 기포의 체류량 특성 해석)

  • Lim, Hyun Oh;Lim, Dae Ho;Seo, Myung Jae;Kang, Yong;Jung, Heon;Lee, Ho Tae
    • Korean Chemical Engineering Research
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    • v.49 no.5
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    • pp.605-610
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    • 2011
  • Phase holdup characteristics of relatively large and small bubbles were investigated in a three-phase(gasliquid-solid) fluidized bed of which diameter was 0.105 m(ID) and 2.5 m in height, respectively. Effects of gas(0.01~0.07 m/s) and liquid velocities(0.01~0.07 m/s) and particle size($0.5{\sim}3.0{\times}10^{-3}m$) on the holdups of relatively large and small bubbles were determined. The holdups of two kinds of bubbles in three phase fluidized beds were estimated by means of static pressure drop method with the knowledge of pressure drops corresponding to each kind of bubble, respectively, which were obtained by dynamic gas disengagement method. Dried and filtered air which was regulated by gas regulator, tap water and glass bead of which density was $2500kg/m^3$ were served as a gas, a liquid and a fluidized solid phase, respectively. The two kinds of bubbles in three-phase fluidized beds, relatively large and small bubbles, were effectively detected and distinguished by measuring the pressure drop variation after stopping the gas and liquid flow into the column as a step function: The increase slope of pressure drop with a variation of elapsed time was quite different from each other. It was found that the holdup of relatively large bubbles increased with increasing gas velocity but decreased with liquid velocity. However, the holdup showed a local minimum with a variation of size of fluidized solid particles. The holdup of relatively small bubbles increased with an increase in the gas velocity or solid particle size, while it decreased slightly with an increase in the liquid velocity. The holdups of two kinds of bubbles were well correlated in terms of operating variables within this experimental conditions, respectively.

Characterization of Groundwater Quality and Recharge using Periodic Measurements of Hydrogeochemical Parameters and Environmental Tracers in Basaltic Aquifers of Jeju Island (수리지구화학적 인자와 환경 추적자의 주기적 관측에 의한 제주도 지하수의 수질과 함양 특성 분석)

  • Koh, Dong-Chan;Cheon, Su-Hyun;Park, Ki-Hwa
    • Journal of Soil and Groundwater Environment
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    • v.12 no.4
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    • pp.60-71
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    • 2007
  • Groundwater from public wells was monitored during one year with two month interval for hydrogeochemical parameters and chlorofluorocarbons (CFCs) as environmental tracers in Jeju Island. Concentrations of major cations and $SiO_2$ show variation less than 10% whereas $NO_3$ and dissolved oxygen (DO) showed larger variation though DO variation did not change oxic or suboxic condition. $NO_3$ concentration has no consistent seasonal pattern with the largest variation of 35%. Groundwater ages determined by CFCs became temporarily younger by 5 years in October for groundwater with ages of 15 to 25 years, which can be attributed to infiltrating water in rainy season. Compared to air temperature, groundwater temperature has much smaller variation with no phase difference, which can be accounted for by a two-component model consisting of infiltrating water from surface and deeper groundwater with negligible temperature variation. The relatively small variation in groundwater age and temperature indicates that groundwater recharge through fast flow-paths is much smaller compared with basal groundwater in terms of aquifer storage.

Numerical Simulation for Tsunami Force Acting on Onshore Bridge (for Solitary Wave) (연안교량에 작용하는 지진해일파력에 관한 수치시뮬레이션(고립파의 경우))

  • Lee, Kwang-Ho;Woo, Kyung-Hwan;Kim, Do-Sam;Jeong, Ik-Han
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.29 no.2
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    • pp.92-108
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    • 2017
  • Present work shows a numerical method to analysis of interaction analysis between solitary wave and onshore bridge. Numerical simulation is carried out by TWOPM-3D (three-dimensional one-field model for immiscible two-phase flows), which is based on Navier-Stokes solver. To do this, the solitary wave is generated numerically in numerical wave channel, and numerical results and experimental results were compared and analyzed in order to verify the applicability of force acting on an onshore bridge. From this, we discussed precisely the characteristics of horizontal and vertical forces (uplift and downward forces) changes including water level and velocity changes due to the variation of solitary wave height, water depth, onshore bridge's location and type, and number of girder. Furthermore, It is revealed that the maximum horizontal and vertical forces acting on the girder bridge show different varying properties according to the number of girder, although each maximum force acting on the girder bridge is proportional to the increasement of incident solitary wave height, and the entrained air in the fluid flow affects the vertical force highly.