• Title/Summary/Keyword: mixing time

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Modified mixing coefficient for the crossflow between sub-channels in a 5 × 5 rod bundle geometry

  • Lee, Jungjin;Lee, Jun Ho;Park, Hyungmin
    • Nuclear Engineering and Technology
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    • v.52 no.11
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    • pp.2479-2490
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    • 2020
  • We performed experiments to measure a single-phase upward flow in a 5 × 5 rod bundle with spacer grids using a particle image velocimetry, focusing on the crossflow. The Reynolds number based on the hydraulic diameter and the bulk velocity is 10,000. The ratio of pitch between rods and rod diameter is 1.4 and spacer grid is installed periodically. The turbulence in the rod bundle results from the combination of a forced mixing and natural mixing. The forced mixing by the spacer grid persists up to 10Dh from the spacer grid, while the natural mixing is attributed to the crossflow between adjacent subchannels. The combined effects contribute to a sinusoidal distribution of the time-averaged stream-wise velocity along the lateral direction, which is relatively weak right behind the spacer grid as well as in the gap. The streamwise and lateral turbulence intensities are stronger right behind the spacer grid and in the gap. Based on these findings, we newly defined a modified mixing coefficient as the ratio of the lateral turbulence intensity to the time-averaged streamwise velocity, which shows a spatial variation. Finally, we compared the developed model with the measured data, which shows a good agreement with each other.

Selection of the optimum mixture condition for stabilization of Songdo silty clay (송도 지역 해양성 점토 고화처리를 위한 최적배합 조건의 선정)

  • Kim, Jun-Young;Jang, Eui-Ryong;Chung, Choong-Ki;Lee, Yong-Jun;Jang, Soon-Ho;Choi, Jung-Yeul
    • Proceedings of the Korean Geotechical Society Conference
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    • 2009.09a
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    • pp.412-419
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    • 2009
  • Large quantity of extra soils discharged from excavation site in Songdo area can be treated by hardening agents and utilized in surface stabilized layer overlying thick reclaimed soft soil deposit. Though surface layer stabilization method using cement or lime for very soft soils has been studied in recent years, but studies on moderately soft clayey silt has not been tried. The purpose of this research is to investigate optimum mixing condition for stabilizing Songdo marine soil with low plasiticity. The optimum mixing conditions of hardening agents with Songdo soil such as kind of agents, mixing ratio, initial water content and curing time are investigated by uniaxial compression test and laboratory vane test. The results indicate that strength increases with high mixing ratio and long curing time, while decreases drastically under certain water content before mixing. Finally, optimum mixing condition considering economic efficiency and workability with test results was proposed.

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Removal Characteristics of Nitrogen and Phosphorus in swine wastewater by Using Acetic acid on the SBR Process (SBR에서 아세트산을 이용한 양돈폐수의 질소·인 제거 특성)

  • Huh, Mock;Kang, Jin-Young
    • Journal of the Korea Organic Resources Recycling Association
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    • v.12 no.1
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    • pp.84-93
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    • 2004
  • This study was performed : 1) to find the suitable HRT(hydralic retention time), 2) to evaluate the effects of the ratio of mixing/aeration time and injection time of external carbon source, for the removal of organics, nitrogen and phosphorus in swine wastewater by SBR(sequencing batch reactor process), which is one of the biological treatment process. The result of this study were summarized as follows : (1) As the ratio of mixing/aeration time was higher, $NH_4{^+}-N$ removal efficiency was increased and it was increased with increasing injection time of external carbon source because nitrification was affected by denitrification microbes propagation when injection time of external carbon soruce was shorted. T-N removal efficiency was increased with increasing the ratio of mixing/aeration time and injection time of external carbon source. (2) The T-P removal efficiency showed a great difference in each operating condition, and it was increased with increasing the ratio of mixing/aeration time increased and when the injection time of external carbon source was shorted because denitrification was done with effect by denitrification microbes propagation. (3) The highest removal efficiency of organic and nitrogen were obtained by the operating condition of Run 4-1(the ratio of mixing/aeration time : 16.5/5.5, injection time of external carbon source : 15hours) and T-P were obtained by the operation condition of Run 4-2(the ratio of mixing/aeration time : 16.5/5.5, injection time of external carbon source : 3hours), and efficiency(effluent concentration)of $BOD_5$, $COD_{Mn}$, $COD_{Cr}$, T-N and T-P in the treated water was 96.1%, 87.7%, 90.6%, 86.6% and 84.5%, respectively.

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Preparation of Silica Films by Sol-Gel Process (졸-겔 법을 이용한 실리카 박막의 제조)

  • 이재준;김영웅;조운조;김인태;제해준;박재관
    • Journal of the Korean Ceramic Society
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    • v.36 no.9
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    • pp.893-900
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    • 1999
  • Silica films were prepared on Si single crystal substrates by sol-gel process using TEOS as starting materials. Films were fabricated by a spin coating technique. Sol solutions were prepared by varying the compositions of CH3OH, H2O and DMF with fixed molar ratio of TEOS=1, HCl=0.05(mol). Wetting behavior viscosity of solutions gelation time thickness of films and cracking behavior were investigated with the various solution compositions. Wetting behaviors of solutions depended on the solution compositions mixing method and mixing rate. The optimum composition of sol was TEOS : DMF ; CH3OH: H2O :HCl=1:2:4:4:0.05(mol) and the mixing rate of solution was optimized at 1 ml/min. Viscosity of solutions were controlled by choosing a reaction time(elapsed time after mixing) at a room temperature so that we could get up to 800nm thick film The surface roughness was getting poor when thickness of films was thicker than 500nm. Thickness of coated films were increased with decreasing amount of CH3OH. The best surface roughness was obtained at the content of CH3OH 4 mol. The shortest gelation time was obtained with the content of CH3OH 8 mol. Crack-free filkms were fabricated when sintered at 500$^{\circ}C$ for 1 hr with heating rate of 0.6$^{\circ}C$/min.

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An experimental study on the concentration distribution of helium and air mixture in the direct injection type engine (헬륨$\cdot$공기흡합기농도분포에 관한 실험적 연구)

  • 김봉곤;하종률;권순석
    • Journal of the korean Society of Automotive Engineers
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    • v.12 no.1
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    • pp.33-39
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    • 1990
  • This study has been conducted by experiments for distribution of concentration of helium gas, which is jetted into stationary atmosphere at the normal temperature and pressure. It is able to obtain the data for concentration of helium and air mixtures by the use of hot wire probe which has fast response. At an up stream, the concentration gradient which is attained is steep. At a down stream, the mixing time of helium and air is gradually shortened with the lapse of time in front of a jet. The arrival frequency of a jet in an unsteady area is mostly constant from 0% to 100% up to 80mm, but the time which is reaching to 100% is gradually to lengthen as a descending downstream. After starting a jet and the point of 90%, the mixing time is especially to lengthen. This reason comes from the turbulent intensity which causes for mixing of helium and air. This time difference which causes according to lengthen a jet should be considered in the design of combustion chamber.

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A study on determining the optimum mixing ratio of carbon source for anaerobic treatment (혐기성처리를 위한 탄소원의 최적 혼합비율 결정에 관한 연구)

  • 김은호;장성호
    • Journal of environmental and Sanitary engineering
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    • v.14 no.3
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    • pp.31-38
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    • 1999
  • The purpose of this study were to determine the optimum mixing ratio of sewage sludge and papermill sludge as carbon source required to SRB in treating abandoned mine drainage with natural purification wetland. If mixing sewage sludge/papermill sludge 2.0 SO42- reduced 46.2%, and then 30% in mixing ratio 0.5.Because sewage sludge was faster biodegradability than papermill sludge, effluent SCOD was 40mg/L in mixing ratio 0.5, and after that was all but regular. pH and ORP were almost neutral and -160mV, but after that was all but regular and it indicated that SRB activity was suitable. Fe removal rate was 60% in mixing ratio 2.0, and 54% in mixing ratio 0.5. In point of carbon source supply, It indicated that mixing ration 0.5 was considered as the most appropriate, because degradability of swewage sludge under short time was higher than that of papermill sludge.

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Evaluation of effect of rapid mixing intensity on chemical phosphorus removal using Al hydrolysis speciation (가수분해 산물 분포를 이용한 급속혼화강도가 화학적 인 제거 효율에 미치는 영향의 규명)

  • Kim, Seung-Hyun;Yoon, Dong-Soo;Moon, Byung-Hyun
    • Journal of Korean Society of Water and Wastewater
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    • v.25 no.3
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    • pp.367-373
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    • 2011
  • Mechanism of rapid mixing effect on chemical phosphorus removal is evaluated in this study. Assuming that chemical phosphorus removal is unaffected by mixing time, only rapid mixing intensity is evaluated. In order to find out the mechanism, it is hypothesized that rapid mixing affects the Al hydrolysis speciation, and that formation of more monomeric species ($Al^a$) results in better removal of phosphorus. According to a ferron assay, more $Al^a$ formed at higher mixing intensity than at lower intensity. Subsequent experiments revealed that better phosphorus removal was obtained at higher intensity than at lower intensity, in terms of the molar ratio of $Al_{added}/P_{removed}$. The proposed hypothesis was proved in this study. Chemical phosphorus removal is affected by rapid mixing intensity due to its effect on the Al hydrolysis speciation.

CHAOTIC MIXING IN SQUARE CAVITY FLOW (정사각형 캐비티 유동의 혼돈적 혼합 특성)

  • Le, T.H.V;Kang, S.;Suh, Y.K.
    • 한국전산유체공학회:학술대회논문집
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    • 2007.04a
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    • pp.53-57
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    • 2007
  • The quality of chaotic mixing in square cavity flow was studied numerically by CFD simulation and particle tracking technique. The chaotic mixing was generated by using time-periodic electro-osmotic flow. Finite Volume Method (FVM) was employed to get the stretching and folding field in cavity domain. With adjusting the initial condition of concentration distribution, the best values of modulation period and Peclet number which gave us good mixing performance was determined precisely. From $Poicar{\acute{e}}section$and Lyapunov exponents for characteristic trajectories we find that mixing performance also depends on modulation period. The higher value of modulation period, the better mixing performance wag achieved in this case. Furthermore, the results for tracking particle trajectories were also compared between using of Bilinear Interpolation and Higher-order scheme. The values of modulation period for obtaining best mixing effect were matched between using FVM and particle tracking techniques.

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STATIONARY $\beta-MIXING$ FOR SUBDIAGONAL BILINEAR TIME SERIES

  • Lee Oe-Sook
    • Journal of the Korean Statistical Society
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    • v.35 no.1
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    • pp.79-90
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    • 2006
  • We consider the subdiagonal bilinear model and ARMA model with subdiagonal bilinear errors. Sufficient conditions for geometric ergodicity of associated Markov chains are derived by using results on generalized random coefficient autoregressive models and then strict stationarity and ,a-mixing property with exponential decay rates for given processes are obtained.

Cholesterol Removal from Whole Egg by Crosslinked β-Cyclodextrin

  • Jeong, H.J.;Sun, H.;Chogsom, C.;Kwak, H.S.
    • Asian-Australasian Journal of Animal Sciences
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    • v.27 no.4
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    • pp.537-542
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    • 2014
  • This study was carried out to optimize cholesterol removal in whole egg using crosslinked ${\beta}$-cyclodextrin (${\beta}$-CD) and to recycle the ${\beta}$-CD. Various factors for optimizing conditions were concentration of the ${\beta}$-CD, mixing temperature, mixing time, mixing speed and centrifugal speed. In the result of this study, the optimum conditions of cholesterol removal were 25% crosslinked ${\beta}$-CD, $40^{\circ}C$ mixing temperature, 30 min mixing time, 1,200 rpm mixing speed and $2,810{\times}g$ centrifugal speed. The recycling was repeated five times. The cholesterol removal was 92.76% when treated with the optimum conditions. After determining the optimum conditions, the recyclable yields of the crosslinked ${\beta}$-CD ranged from 86.66% to 87.60% in the recycling and the percentage of cholesterol removal was over 80% until third recycling. However, the cholesterol removal efficiency was decreased when the number of repeated recycling was increased. Based on the result of this study, it was concluded that the crosslinked ${\beta}$-CD was efficient for cholesterol removal in whole egg, and recycling is possible for only limited repeating times due to the interaction of the ${\beta}$-CD and egg protein.