• 대한기계학회논문집B
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• 제39권1호
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• pp.79-88
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• 2015

본 연구에서는 유한차분법(FDM)을 적용한 혼성 격자볼츠만 방법(HLBM)을 이용하여 직사각 형태를 갖는 공동형상 내 혼합특성에 대하여 수치적으로 연구하였다. 유동장은 다중 완화시간을 적용한 격자볼츠만 방법(LB-MRT)을 사용하였으며, 농도장은 두 물질의 질량은 같고 두 물질 사이의 상호작용이 없다고 가정한 Passive Scalar 방법을 사용하였다. 먼저, 정사각형과 종횡비가 2인 직사각형의 공동형상 내 유동해석 결과를 기존의 신뢰성 있는 연구결과와 비교하여 HLBM의 신뢰성을 검토하였다. 이를 토대로 다양한 종횡비를 갖는 공동형상에서 Pe수를 변화시키며 공동형상 내부에서의 혼합특성과 물질전달 형태에 대하여 파악하였다.

• 대한기계학회논문집B
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• 제37권7호
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• pp.683-693
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• 2013

본 연구에서는 혼성 격자볼츠만 방법(HLBM)을 이용하여 상판이 일정한 속도로 움직이는 공동 형상 내부에서의 혼합 특성에 대하여 수치적으로 연구하였다. 먼저, 공동 형상에서 기존의 신뢰성 있는 유동장 결과와의 비교를 통해 LB-SRT 모델과 LB-MRT 모델의 신뢰성을 검토하였다. 두 모델 모두 기존의 연구결과와 유사한 결과를 보였으나, LB-MRT 모델이 LB-SRT 모델보다 높은 Re수에서는 수치적 안정성이 높은 것을 확인하였다. 수치적 안정성이 좋은 LB-MRT 모델을 토대로 유한차분법을 적용한 HLBM을 이용하여 공동 형상 내부에서의 농도장을 수치 해석하였다. Re수와 Pe수를 변화하여 공동 형상 내부의 혼합 특성과 물질 전달 형태에 대하여 파악하였다.

• 동력기계공학회지
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• 제18권6호
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• pp.126-132
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• 2014

The P-T characteristics of mixed refrigerant in thermostatic expansion valve sensing bulb were studied using R-134a and R-410A refrigerant. The characteristics of mixed refrigerant were investigated according to pressure variation and the variation of composition ratio of R-134A and R-410A in the temperature range of $-15^{\circ}C{\sim}15^{\circ}C$. The Thermodynamic characteristic values of the mixed refrigerants were identified using the characteristic value analysis program of mixed refrigerant(Refrop v9.0, NIST). The P-T characteristics in the case of the mixing ratio of 90:10 for R-410A and R-134A were the same result as R-22. And the physical properties showed similar results with R-22. The Maximum operating pressure(MOP) of mixed refrigerant showed a tendency to decrease with decreasing the mixing ratio of additive gases($N_2$ or He) gases. The characteristics in the case of the mixing ratio of 80:1 for mixed refrigerant and additive gases were the similar result as Reference refrigerant.(R-22 MOP, Sporlan company) In addition $N_2$ and He, both showed the same results. It was able to confirm that a MOP on the thermostatic expansion valve sensing bulb can be maintained by adjusting the mixing ratio of mixed refrigerant gases and additive gases.

• 한국전산유체공학회지
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• 제11권3호
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• pp.46-51
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• 2006

This paper presents the numerical results of fluid flow and mixing in a microfluidic device for electro-osmotic flow (EOF) with an trapezoidal electrode array on the bottom wall (ETZEA). Differently from previous EOF in a channel which only transports fluid in colloidal system. ETZEA can also be utilized to mix a target liquid with a reagent. In this study we propose a method of controlling fluid flow and mixing enhancement. To obtain the flow and mixing characteristics, numerical computations are performed by using a commercial code, CFX-10, and a self-made code LBM-D. It was found that the flow near the trapezoidal electrode in the ETZEA is of 3-D complex flows due to the zeta potential difference between the trapezoidal electrode and channel walls, and as a consequence the hetrogeneous zeta potential on the electrodes plays an important role in mixing the liquid.

• 한국환경과학회지
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• 제15권9호
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• pp.897-905
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• 2006

This study has been conducted to investigate biodegradation characteristics and optimum mixing ratio for co-digestion with thermophilic acid-fermented food waste and sewage sludge using batch anaerobic digester. As the basis operating conditions for anaerobic digestion, the reaction temperature was controlled $35{\pm}1^{\circ}C$ and stirrer was set 70rpm. Thermophilic acid-fermented food waste and sewage sludge were mixed at the ratio of 10:0, 7:3, 5:5, 3:7, 0:10 and 5;5(food waste : sewage sludge) as the influent substrates. In results of co-digestion according to mixing ratio of thermophilic fermented food wastes and sewage sludge in batch mesophilic anaerobic digestion reactor, $385mL\;CH_4/g\;VS_{added}$ of methane production rate at 1:1 mixing ratio was more than that of any other mixing ratios. Compared with $293mL\;CH_4/g\;VS_{added}$ of methane production rate at 1:1 mixing ratio of food wastes and sewage sludge, pretreatment of food wastes by thermophilic acid fermentation was more effective in co-digestion with sewage sludge.

• 대한기계학회논문집B
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• 제33권7호
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• pp.527-534
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• 2009

Flame stabilization characteristics were experimentally investigated in a fuel-air cross flowing mixing layer. A combustor consists of a narrow channel of air steam and a cross flowing fuel. Depending on the flow rates of methane and air, flame can be stabilized in two modes. First is an attached flame which is formulated at the backward step where the methane and air streams meet. Second is a lifted-flame which is formulated within the mixing layer far down steam from backward step. The heights and flame widths of the lifted flames were measured. Flame shapes of the lifted flames were similar to an ordinary edge flame or a tribrachial flame, and their behavior could be explained with the theories of an edge flame. With the increase of the mixing time between fuel and air, the fuel concentration gradient decreases and the flame propagation velocity increases. Thus the flame is stabilized where the flow velocity is matched to the flame propagation velocity in spite of a significant disturbance in the fuel mixing and heat loss within the channel. This study provides many experimental results for a higher fuel concentration gradient, and it can also be helpful for the development and application of a smaller combustor.

• 한국생산제조학회지
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• 제20권5호
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• pp.535-540
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• 2011

It is well known that abrasive waterjet (AWJ) was developed as a kind of high-density energy processing technologies. AWJ is used to obtain cutting quality of various materials such as metal, ceramics, glass and composite materials within a short manufacturing time because of the characteristics of heatless and noncontact processing. However, surface roughness and dimension error like round, burr, taper vary severely according to the processing conditions such as pressure, cutting speed, orifice diameter, stand off distance and abrasive flow rate. In this paper, the effect of the shape of mixing chamber on surface quality is studied. Three types of mixing chamber - round, parabolic, elliptical - are suggested and each performance is compared to that of cylindrical mixing chamber experimentally. From the result, is proved to be the optimal mixing chamber in the aspect of surface quality the parabolic one.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.42-47
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• 2004

Air-fuel mixing and flame-holding are two important factors that have to be considered in the design of an injection system. Different injection strategies have been proposed with particular concern for rapid air-fuel mixing and flame-holding. Two representative injection techniques can be applied in a supersonic combustor. One of the simplest approaches is a transverse(normal) injection. The cavity flame holder, an integrated fuel injection/flame-holding approach, has been proposed as a new concept for flame holding and air-fuel mixing in a supersonic combustor. This paper describes numerical efforts to characterize the flame-holding and air-fuel mixing process of a model scramjet engine combustor, where hydrogen is injected into a supersonic cross flow and a cavity. The combustion phenomena in a model scramjet engine, which has been experimentally studied at University of Queensland and Australian National University using a free-piston shock tunnel, were observed around the separation region of the transverse injector upstream and the inside cavity. The results show that this flow separation generates recirculation regions which increase air-fuel mixing. Self-ignition occurs in the separation-freestream and cavity-fteestream interfaces.

• 대한환경공학회지
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• 제39권5호
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• pp.282-287
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• 2017

본 연구의 목적은 방사능 사고로 인한 오염물질 유입으로 인한 영향을 최소화하기 위한 제염제의 혼합확산장치 개발에 앞서 장치 가동으로 인한 혼합 및 확산영향을 예측하는데 있다. 유동특성분석을 위해 사용된 추적자는 방사성 동위원소는 Gy, To이며, 이를 검측하기 위해 2인치 NaI 방사선 검출기를 사용했다. 본 연구에 적용된 제염제 혼합확산장치의 임펠러는 3가지 type으로 제작하였다. 방사혼합형 임펠러는 상향류 흐름을 이용하여 수표면으로 확산이 가능하며, 최적의 조건을 찾기 위해 핀 구조를 조정하였다. 방사능 동위원소를 이용한 제염제 혼합확산장치의 유동특성을 분석한 결과, 모델별 혼합확산과 유동패턴특성을 획득하였다. Model 3 type은 별도의 Fin유도부와 보조 Fin이 구성되어 있어 다른 type의 임펠러보다 확산속도가 크고 완전혼합에 도달하는 시간이 짧게 나타났다.

• 동력기계공학회지
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• 제19권1호
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• pp.56-63
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• 2015

In this study, the exhaust characteristics of the diesel engine for the change of the mixing ratio of biodiesel fuel were quantitatively analyzed by using the numerical analysis method. As the fuel used in the experiment, the diesel and biodiesel(waste oil, soybean oil), the mixed fuel BD2(Diesel only), BD3, BD5, BD20, BD50 and BD100 were used. The injection pressure($p_{inj}$) was set to 400bar, 600bar, 800bar, 1000bar and 1200bar as the experimental variable. Also the concept of the standard deviation, Pearson's correlation coefficient and Spearman rank-order correlation coefficient based on the statistics was introduced in order to analyze the exhaust characteristics of the quantitative NOx and Soot according to the injection pressure and the mixing ratio variation of biodiesel blending fuel. It is considered that as a result of studies, for the waste oil, NOx and Soot can be simultaneously reduced through control of the mixing ratio at the regions of $p_{inj}=400bar$ and $p_{inj}=600bar$, and the Soot can be reduced without affecting on the emission of NOx at more than $p_{inj}=800bar$. For the soybean oil, NOx and Soot can be simultaneously reduced at $p_{inj}=400bar$ and the Soot can be reduced without affecting on the emission of NOx at $p_{inj}=600bar$.