• Title/Summary/Keyword: Temperature stratification

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Prediction of Stratification Model for Diffusers in Underfloor Air Distribution System using the CFD (CFD를 활용한 바닥공조시스템 디퓨저의 성층화 모델 예측)

  • Son, Jeong-Eun;Yu, Byeong-Ho;Pang, Seung-Ki;Lee, Kwang Ho
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.29 no.3
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    • pp.105-110
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    • 2017
  • Underfloor air distribution (UFAD) is an air distribution strategy for providing ventilation and space conditioning in buildings. UFAD systems use the underfloor plenum beneath a raised access floor to provide conditioned air through floor diffusers that create a vertical thermal stratification during cooling operations. Thermal stratification has significant effects on energy, indoor air quality, and thermal comfort performance. The purpose of this study was to characterize the influence of a linear bar grille diffuser on thermal stratification in both interior and perimeter zones by developing Gamma-Phi based prediction models. Forty-eight simulations were carried out using a Computational Fluid Dynamics (CFD) technique. The number of diffusers, the air flow supply, internal heat gains, and solar radiations varied among the different cases. Models to predict temperature stratification for the tested linear bar grille diffuser have been developed, which can be directly implemented into dynamic whole-building simulation software such as EnergyPlus.

EVALUATION OF ELLIPTIC BLENDING MODEL (Elliptic Blending Model의 평가)

  • Choi Seok-Ki;Kim Seong-O
    • 한국전산유체공학회:학술대회논문집
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    • 2005.10a
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    • pp.105-110
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    • 2005
  • Evaluation of elliptic blending turbulence model (EBM) together with the two-layer model, shear stress transport (SST) model and elliptic relaxation model (V2-F) is performed for a better prediction of thermal stratification in an upper plenum of a liquid metal reactor by applying them to the experiment conducted at JNC. The algebraic flux model is used for treating the turbulent heat flux. There exist much differences between turbulence models in predicting the temporal variation of temperature. The V2-F model and the EBM better predict the steep gradient of temperature at the interface of thermal stratification, and the V2-F model and EBM predict properly the oscillation of temperature. The two-layer model and SST model fail to predict the temporal oscillation of temperature.

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Stratification Variation of Summer and Winter in the South Sea of Korea (한국 남해의 여름과 겨울철 성층 변동)

  • Lee, Chung-Il;Koo, Do-Hyung;Yun, Jong-Hwui;Kim, Dong-Sun
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.13 no.2 s.29
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    • pp.119-125
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    • 2007
  • In order to illustrate the variation cf stratification and to know the effects of the temperature and the salinity on the stratification in the South Sea of Korea, the stratification parameter defined as potential energy anomaly (PEA, $V(J/m^3)$) introduced by Simpson and Hunter (1974) was used. The oceanographic data were obtained in August 1999 and February 2000 by National Fisheries Research and Development Institute (NFRDI). V in August is generally high in offshore and low in near shore. However, in February, V in the near shore is higher than that cf the offshore due to the vertical temperature gradient between surface and bottom layer caused by the expansion of South Korean Coastal Waters (SKCW). In summer, the increase of the atmospheric heating acts on the stratification as the buoyancy forcing. In most cases, the effect cf the temperature on the stratification is stronger than that of the salinity. The temperature effect is predominantly due to the extent of the intrusion of Tsushima Warm Current into the study area. However, at stations where V is high the effect of the salinity is also significant. In winter, V is very low due to the decrease cf the buoyancy forcing, but some stations show the relatively high V due to the expansion of SKCW and salinity in winter unlike that in summer makes the stratification weak.

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Stratification related to Heat Flux in Deukryang Bay during Summer (여름철 득량만의 열속과 관련한 성층)

  • 최용규;홍성근
    • Journal of Environmental Science International
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    • v.6 no.6
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    • pp.579-588
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    • 1997
  • In order to see the stratification related to the heat flux In Deukryang Bay, the oceanographic data on July 12, 1994 and the meteorological data of Kohung and Kwangju meteorological stations were analysed. The temperature durerences between the sea surface and the near bottom were 1~3 ton spring tide (July 12, 1994) In Deukryang Bay. The temperature anomalies were high about 3t during summer In 1994. These mean that the non mixing was not effective In destroying the stratification due to the sea surface heating by the solar radition, even though it was on spring tide. The maximum solar radiation was about 600 ly/day, which was the value of the same date of oceanographic observation. The sensible and the latent heat flux which are 0~100 ly/day were not so varied during summer. The absorbed heat flux through the sea surface was mostly lost by the back radiation. which ranges are about 0~-400 ly/day. The dimensionless mixing parameter related to the buoyancy flux was 5~150$\times$$10^{-5}$. The efficiency of tidal mixing to destroy the stratecation was 0.4~0.6%.

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Thermal stratification in a horizontal pipe of pressurizer surge line (가압기밀림관의 수평배관내 열성층유동)

  • Jung, I,S,;Kim, Y.;Youm, H.K.;Park, M.H.
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.4
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    • pp.1449-1457
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    • 1996
  • In this paper, the unsteady two dimensional model for the thermal stratification in the pressurizer surge line of PWR plant has been proposed to numerically investigate the heat transfer and flow characteristics. The dimensionless governing equations are solved by using the Control Volume Formulation and SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm. The temperature profile of fluids and pipe wall with time are shown when the thermal stratification occurs in the horizontal pipe. The numerical result shows that the maximum dimensionless temperature difference is about O.514 between hot and cold section of pipe wall at dimensionless time 1,632.

Effect of an aspect ratio on thermal stratification in a solar seasonal thermal storage tank (태양열 계간 축열조 내부 열성층화에 대한 탱크 종횡비 영향 연구)

  • Kim, Seong Keun;Jung, Sung Yong
    • Journal of the Korean Society of Visualization
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    • v.18 no.2
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    • pp.28-34
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    • 2020
  • In this study, we numerically investigated the thermal stratification in solar seasonal thermal storage tanks. The vertical in/out flows were unsuitable for the thermal stratification in a large scale. The effect of an aspect ratio (AR) on the thermal stratification was investigated. When AR was less than 2, water adheres and flows along the upper wall due to buoyance and the surface effect. Thereafter, hot water flows down and a large scale vortex occurs in entire tank. For high AR, jet flows ejected from the inlet pipe impinges to the opposite wall and splits. The divided flows create two vortex flows in the upper and lower regions. These different flows strongly influence temperature and thermal stratification. The thermal stratification was evaluated in terms of the thermocline thickness and degree of stratification. Compared to ARs, the maximum degree of stratification was obtained with AR of 5 having the minimum thermocline thickness.

Reproducibility Evaluation of Stratification Using EFDC Model in Nakdong River (EFDC 모형을 이용한 낙동강에서의 성층현상 재현성 평가)

  • Choi, Hyun Gu;Han, Kun Yeun;Park, Jun Hyung
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.37 no.3
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    • pp.561-573
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    • 2017
  • Nakdong River was recently dredged with multi-functional weirs construction. Therefore, the depth was deepened and the lag time also increased. As a result, stratification occurred in some sections with deep water depth, and it also caused the increase of algal bloom phenomenon. The purpose of this study is to evaluate reproducibility of stratification in the Nakdong River by applying the EFDC model, which is a three-dimensional hydraulic and water quality analysis model proving the reproducibility of stratification phenomena in reservoirs and estuaries. In order to reproduce the Nakdong river water temperature and DO stratification, EFDC model was constructed in the downstream part of the Nakdong river and sensitivity analysis was performed on key parameters sensitive to stratification. Sensitivity analysis was used to reproduce stratification by selecting optimal parameters. The results of this study can be used as basic data for the analysis of various destratification scenarios.

Stratification and DO Concentration Changes in Chinhae-Masan Bay (진해ㆍ마산만의 성층화 및 DO 농도변화)

  • 조홍연;채장원;전시영
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.14 no.4
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    • pp.295-307
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    • 2002
  • Water temperature, salinity, and DO concentration were measured vertically in the Chinhae-Masan Bay over the course of 1 year. The characteristics of the stratification were analysed using the measured water temperature and salinity data. The vertical DO concentration changes were also analysed through consideration of the degree of stratification and the level of sediment pollution. The results of the analyses show that the thermal stratification appears just before April and disappears after October. The salinity differences between the surface and the bottom were 3.9(equation omitted), 9.3 (equation omitted), 4.3(equation omitted) in April, August, and October, respectively. The DO concentration change averaged over water depth was 2.6(mg/L) in April; 8.3(mg/L) in June: 5.9(mg/L) in August; 7.2(mg/L) in September; and 4.4(mg/L) in October. The DO concentration changes were closely related to the levels of contamination and also to the effect of the mass-transfer inhibition between the surface and bottom layers due to the thermal and density stratification.

COMPUTATIONAL FLUID DYNAMICS ANALYSIS OF THERMAL STRATIFICATION IN THE UPPER PLENUM OF THE MONJU FAST BREEDER REACTOR (몬주 고속증식로 상부플레넘에서의 열성층에 관한 전산유체역학 해석)

  • Choi, S.K.;Lee, T.H.
    • Journal of computational fluids engineering
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    • v.17 no.4
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    • pp.41-48
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    • 2012
  • A numerical analysis of thermal stratification in the upper plenum of the MONJU fast breeder reactor was performed. Calculations were performed for a 1/6 simplified model of the MONJU reactor using the commercial code, CFX-13. To better resolve the geometrically complex upper core structure of the MONJU reactor, the porous media approach was adopted for the simulation. First, a steady state solution was obtained and the transient solutions were then obtained for the turbine trip test conducted in December 1995. The time dependent inlet conditions for the mass flow rate and temperature were provided by JAEA. Good agreement with the experimental data was observed for steady state solution. The numerical solution of the transient analysis shows the formation of thermal stratification within the upper plenum of the reactor vessel during the turbine trip test. The temporal variations of temperature were predicted accurately by the present method in the initial rapid coastdown period (~300 seconds). However, transient numerical solutions show a faster thermal mixing than that observed in the experiment after the initial coastdown period. A nearly homogenization of the temperature field in the upper plenum is predicted after about 900 seconds, which is a much shorter-term thermal stratification than the experimental data indicates. This discrepancy is due to the shortcoming of the turbulence models available in the CFX-13 code for a natural convection flow with thermal stratification.

Thermal Stratification Effects Near an Interface by Horizontal Inflow of Cold Water in Thermal Storage Tank (냉수가 수평유입되는 열저장탱크의 중간 경계면 부근에서의 열성층 효과)

  • Hwang, Sung-Il;Pak, Ee-Tong
    • Solar Energy
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    • v.8 no.2
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    • pp.46-56
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    • 1988
  • This investigation concerns thermal stratification of the water due to the temperature difference (${\Delta}T=T_{\infty}-T_i$) between the mean temperature of the water in the test tank (1m wide, 1m high, 2.1m long) and the temperature of the inflow water into the tank; flow rate of circulating water and height of the sink diffuser in the test tank. The additional objectives was to observe a stratification phenomena near an interface by measuring the velosities and the temperature difference and investigate an availabilities of the better effective hot water through establishing thermocline near an interface around the bottom of the tank. Following results were obtained through the experiments. 1. When the flow rate was constant and the temperature difference (${\Delta}T=T_{\infty}-T_i$) between the mean temperature of the flow in the test tank and the temperature of the inflow water increased by 5.6, 9.5, 13.5($^{\circ}C$), obtained the better effective advantage of hot water and the stress near an interface increased gradually. 2. When the ${\Delta}T=T_{\infty}-T_i$ was constant and flow rate increased by 4.0, 4.8, 6.4, 8.0 (LPM), obtained the better effective advent age of hot water and the mean stress near an interface increased gradually. 3. When the height of the sink diffuser was 25cm from tank bottom in comparison with 50cm, obtained the better effective advantage of hot water and the mean stress near an interface increased.

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