• 한국환경농학회지
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• 제27권2호
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• pp.145-149
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• 2008

Anaerobic co-digestion of swine manure and food waste for biogas production was performed in serum bottles at various volatile solids(VS) contents and mixing ratios of two substrates(swine manure:food waste=$100:0{\sim}0:100$). Through kinetic mode of surface methodology, the methane production was fitted to a Gompertz equation. The ultimate methane production potential of swine manure alone was lower than that of food waste regardless of VS contents. However, it was appeared that maximum methane production potentials in 80 : 20 of the mixing rate at VS 3% was enhanced at 144.7%, compared to its only swine manure. The potential increased up to 815.71 ml/g VS fed as VS concentration and food composition increased up to 3.0% and 20%, respectively. The ultimate amount of methane produced had significantly a positive relationship with that of methane yield rate. Overall, it would be strongly recommended that feeding stocks use 20% of mixing ratio of food waste based on VS 3% contents when operating the anaerobic reactor on site at $35^{\circ}C$ if not have treatment of its anaerobic waste water.

• Nuclear Engineering and Technology
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• 제54권5호
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• pp.1914-1928
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• 2022

To improve the heat transfer efficiency of the reactor fuel assembly, it is necessary to accurately calculate the two-phase flow boiling characteristics and the critical heat flux (CHF) in the fuel assembly. In this paper, a Eulerian two-fluid model combined with the extended wall boiling model was used to numerically simulate the 5 × 5 fuel rod bundle with spacer grids (four sets of mixing vane grids and four sets of simple support grids without mixing vanes). We calculated and analyzed 11 experimental conditions under different pressure, inlet temperature, and mass flux. After comparing the CHF and the location of departure from the nucleate boiling obtained by the numerical simulation with the experimental results, we confirmed the reliability of computational fluid dynamic analysis for the prediction of the CHF of the rod bundle and the boiling characteristics of the two-phase flow. Subsequently, we analyzed the influence of the spacer grid and mixing vanes on the void fraction, liquid temperature, and secondary flow distribution. The research in this article provides theoretical support for the design of fuel assemblies.

• 대한기계학회논문집B
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• 제41권9호
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• pp.623-629
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• 2017

다공배플을 가진 마이크로연소기에 레이놀즈응력 난류모형을 이용하여 난류유동 및 혼합특성에 대한 수치해석 연구를 수행하였다. 다공배플은 연소실 내부에 다수의 3차원 와유동을 발생시키는 기하학적 특징을 가지고 있다. 그러한 형상특징 중에서 배플두께를 변화시킬 경우 와유동구조의 다양한 변화가 얻어졌다. 여러 와유동중에서 연료유동으로부터 생성된 와유동은 혼합도 증가에 결정적 역할을 하였다. 연소실 내부의 3차원 와유동구조는 배플두께 변화에 따른 유동의 발달상태에 의존하였다. 특히, 배플두께가 연료유입구 직경보다 작을수록 배플구멍 제트유동의 속도분포는 포물선형태에서 안장모양의 형태로 변하였다. 연소실내부의 재순환영역크기 및 혼합도는 이러한 제트유동구조에 밀접한 상관관계를 가졌다.

• 한국방재학회 논문집
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• 제9권5호
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• pp.63-68
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• 2009

본 연구에서 물 흐름에 일정한 농도로 포 소화약제를 정확하게 혼합하는 포 소화설비용 소화약제 혼합장치의 성능향상을 위하여 포소화약제의 정량 혼합특성을 분석하였다. 펌프, 탱크, 압력계, 유량계, 노즐로 구성되는 성능평가 시스템을 사용하여 개발된 프로포셔너의 성능이 실험적으로 평가하였다. 결과적으로 라인프로포셔너의 포소화약제 혼합성능은 벤츄리 효과에 의한 물유량 증가와 오리피스 단면적 증가에 따라 증가하고 오차율 $\pm4%$이내의 범위에서 물 유량과 포소화약제 양의 혼합농도 3%의 성능을 보였다. 프레셔프로포셔너의 경우 물 유량 증가와 입구압력 증가에 따라 혼합성능이 증가하고 오차율 $\pm2%$이내의 범위에서 물 유량과 포소화약제 양의 혼합농도 3%의 성능으로 분석되었다.

• Nuclear Engineering and Technology
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• 제51권5호
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• pp.1218-1230
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• 2019

A sub-channel solver, named ${\underline{S}}teady$ and ${\underline{T}}ransient$ ${\underline{A}}nalyzer$ for ${\underline{R}}eactor$ ${\underline{T}}hermal$ hydraulics (START), has been developed using the homogenous model for two-phase conditions of light water reactors. The code is developed as a fast and accurate TH-solver for coupled and multi-physics calculations. START has been validated against the NUPEC PWR Sub-channel and Bundle Test (PSBT) database. Tests like single-channel quality and void-fraction for steady state, outlet fluid temperature for steady state, rod-bundle quality and void-fraction for both steady state and transient conditions have been analyzed and compared with experimental values. Results reveal a good accuracy of solution for both steady state and transient scenarios. Axially different values for turbulent mixing coefficient are used based on different grid-spacer types. This provides better results as compared to using a single value of turbulent mixing coefficient. Code-to-code evaluation of PSBT results by the START code compares well with other industrial codes. The START code has been parallelized with the OpenMP algorithm and its numerical performance is evaluated with a large whole PWR core. Scaling study of START shows a good parallel performance.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.121-125
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• 2003

Micromixer plays an important role in Bio-MEMS or ${\mu}-TAS$. Mixing is generally generated by turbulence and interdiffusion of two fluids. Because of low Reynolds number(Re << 2000) in ${\mu}-channel$, it is difficult to generate turbulence, so mixing mainly depends on interdiffusion. Thus long channel distance is required to mix two different fluids. To reduce the channel length required for mixing, we propose the a new active ${\mu}-mixer$ that two fluids are effectively mixed in ${\mu}-channel$ by the ultrasonic wave which is generated by PZT. The ultrasonic wave is radiated into a chamber in the cross-section directional direction to interface with the two fluids. The two fluids are positioned one on top of the other. Mixing state is measured by the changing of color due to the reaction of NaOH and phenolphtalein.

• 한국진공학회지
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• 제12권S1호
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• pp.7-9
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• 2003

Solid-state reactions in Ni/Si multilayered films (MLF) with an overall stoichiometry of $Ni_2Si$, NiSi and $NiSi_2$, induced by ion-beam mixing (IBM) and thermal annealing, were studied by using spectroscopic ellipsometry and magneto-optical spectroscopy as well as x-ray diffraction (XRD). The mixing was performed with Ar+ ions of an energy of 80 keV and a dose of $1.5 x\times10^{16}$ $Ar^+$/$\textrm{cm}^2$. It was shown that the IBM induces structural changes in the Ni/Si MLF, which cannot be detected by XRD but are confidently recognized by the optical method. A thermal annealing at 673 K of the Ni/Si MLF with an overall stoichiometry of NiSi and $NiSi_2$ causes formation of the first η -NiSi phase. The first trace for $NiSi_2$ phase on the background of NiSi one was detected by XRD after an annealing at 1073 K while, according to the optical results, $NiSi_2$ turns out be the dominant phase for the annealed Ni/Si MLF with an overall stoichiometry of $NiSi_2$.

• 한국산학기술학회논문지
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• 제15권1호
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• pp.585-592
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• 2014

본 연구는 축산폐수의 혐기성 처리 시 교반의 영향에 대하여 연구자에 따라 서로 다른 결과가 보고되어 우리나라 축산폐수에 적용 시 교반의 영향을 파악할 필요가 있어 실시하였다. 4개의 혐기성 소화조를 중온 또는 고온으로 유지하면서 연속적으로 교반시키거나 교반 시키지 않고 운전하였다. 온도가 같은 경우 연속으로 교반한 반응조가 교반하지 않은 반응조의 TCOD 제거효율에 비하여 0.11-0.58% 높게 나타났다. 그리고 중온 소화조의 TCOD 제거효율이 고온 소화조의 TCOD 제거효율과 거의 같아 온도에 따른 TCOD 제거효율 간에는 큰 차이가 없었다. 연속적으로 교반한 소화조의 가스 발생량이 교반하지 않은 소화조에 비하여 1.7-4.6% 많았다. 또한 중온 소화조의 가스 발생량은 고온 소화조보다 29.1-32.1% 높고 메탄 발생량도 많았는데 이는 고온 소화조의 암모니아 저해로 인한 것으로 판단된다. 이러한 실험 결과를 종합하면 축산폐수를 혐기성으로 처리 시 중온에서 운전되고 연속적으로 교반한 반응조의 운전 조건이 더 좋은 것으로 판단된다.

• 대한수학회보
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• 제41권1호
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• pp.189-198
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• 2004

In this study we consider quantum dynamical semi-group with a normal faithful invariant state. A quantum dynamical semigroup $\alpha\;=\;\{{\alpha}_t\}_{t{\geq}0}$ is a class of linear normal identity-preserving mappings on a von Neumann algebra M with semigroup property and some positivity condition. We investigate the asymptotic behaviors of the semigroup such as ergodicity or mixing properties in terms of their eigenvalues under the assumption that the semigroup satisfies positivity. This extends the result of [13] which is obtained under the assumption that the semi group satisfy 2-positivity.

• International Journal of Concrete Structures and Materials
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• 제7권2호
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• pp.165-174
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• 2013

Portland cement concrete exposed to high temperatures during mixing, transporting, casting, finishing, and curing can develop undesirable characteristics. Applicable requirements for such the hot weather concrete differ from country to country and government agencies. The current study is an attempt at evaluating the hardened properties of the concrete exposed to hot weather in fresh state. First of all, this study reviews the current state of understanding and practice for hot weather concrete placement in US and then roadway sites with suspected hot weather concrete problems were investigated. Core samples were obtained from the field locations and were analyzed by standard resonance frequency analysis and the boil test. Based on the results, there does not appear to be systematic evidence of frequent cracking problems related to high temperature placement. Thus, the suspicious deteriorations which are referable to hot weather concreting would be due to other factors.