• Journal of Power System Engineering
• /
• v.14 no.2
• /
• pp.5-11
• /
• 2010

분사연료의 혼합기형성과정 최적화를 통한 연소제어 기술은 디젤기관의 기관운전 및 배기특성을 향상시키기 위하여 매우 중요하다. 또한 분무의 혼합기형성 최적화를 위해서는 분사된 연료와 주위기체와의 혼합과정에 영향을 미치는 분무내부의 유동특성에 대한 연구는 필수 불가결하다. 따라서 본 연구에서는 고온 고압의 증발장에서 분무의 액상 거동에 주목하고, 그 거동특성을 통하여 증발디젤분무의 혼합기형성을 해석한다. 비정상 증발분무의 중심축에 레이저 시트광을 입사한 후, 액상분무 액적의 Mie 산란광에 의한 2차원 화상을 획득하여 증발분무 액상의 속도분포 및 와도(vorticity) 등을 구하였다. 분무의 속도분포 및 와도는 2차원 화상에 PIV법을 적용하여 계산하였다. 그림 1에 본 연구에서 구한 속도분포의 일례를 보인다. 본 연구의 결과로 상변화를 동반하는 비정상 증발장에서 구한 분무액상의 거동 특성은 상변화가 일어나지 않는 비증발장에 있어서의 분무거동특성과 유사함을 확인하였다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.11 no.1
• /
• pp.1-9
• /
• 1999

For roughened annular pipes with diameter ratios of 0.26, 0.39, and 0.56 and with Reynolds numbers ranging 13,000 to 67,000, friction factor, autocorrelation coefficients, power spectral density functions, and integral length scales for each flow condition using X-type hot wire anemometry system are experimentally investigated. Distributions of these quantities show that the times which the streamwise autocorrelation coefficients become zero first increase with decreasing the radius ratios of concentric annuli and Reynolds numbers, however the power spectra density functions increase with increasing the radius ratios and Reynolds number.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.9 no.5
• /
• pp.555-563
• /
• 1985

Two-dimensional turbulent wake flow behind a circular cylinder is investigated experimentally by suing linearized constant temperature hot wire anemometer. Turbulent fluctuations and mean velocity defects are measured in the rage of 5 dia.- 500 dia. downstream from the cylinder and for the Reynolds numbers of 2000-4000. Results with statistical treatment and digital data processing techniques are as follows: (1) The transition region from near wake to far wake is 30 dia. - 50 dia. downstream from the cylinder. (2) In the near wake, it is found that strong periodic ( f=845Hz) coherent structure exists. (3) It shows that the inertial subrange is 180Hz-2000Hz in self preservation region.

• Korean Journal of Food Science and Technology
• /
• v.32 no.6
• /
• pp.1313-1318
• /
• 2000

총고형분 함량$(TS:\;50{\sim}57%)$을 달리하여 숙성시킨 고추장의 유동특성, 정적 및 동적점탄특성을 관찰하였다. 고추장의 TS가 증가함에 따라서 점조도 지수(K)와 겉보기 점도$({\eta}_{a.5})$는 증가하였으며 유동성 지수(n)는 1보다 훨씬 낮은 0.24-0.31의 범위를 나타내어 고추장은 shear-thinning 성질을 보여주었다. 고추장의 항복응력 측정에서는 고추장의 TS가 증가함에 따라 Casson 항복응력$({\sigma}_{oc})$은 증가하는 경향을 나타내었으며, 또한 고추장의 액상 매개체인 serum 점도$({\eta}_{se})$는 고추장의 TS와 매우 좋은 상관관계$(R^2=0.97)$를 나타내었다. 고추장의 동적점탄성 실험에서는 주파수$({\omega})$가 증가함에 따라 저장탄성률(G#)와 손실탄성률(G@)은 증가하였으며 양(+) 기울기로 G#수치가 G@수치보다 높게 나타났다. 이는 고추장이 약한 겔과 같은 구조적 특성을 갖고 있으며 또한 shear-thinning 거동을 가지고 있음을 나타낸다. 정적점탄성 실험에서 고추장의 총고형분 함량에 따라서 순간탄성 변형$(J_0)$과 지연탄성변형$(J_1)$은 총고형분 함량이 증가함에 따라서 감소하였으며 점도$({\eta}_N)$와 지연시간 $({\tau}_1)$은 증가하였다. 따라서 고추장은 농도가 증가함에 따라 보다 탄력적이며 안정된 구조를 형성하고 있음을 알 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.1
• /
• pp.67-74
• /
• 2013

A jet in a crossflow (JICF) has been extensively studied because of its wide applications in technological systems, including fuel injection into a ram-combustor. However, in the case of insufficient mixing performance of the liquid jet into the crossflow, the flame in a ram-combustor is unstable. In this study, the nonuniform flame and combustion instabilities due to lack of mixing performance were experimentally investigated. By performing correlations to predict the penetration height and break-up point, the spray and mixing characteristics of JICF have been studied. In particular, the improved correlations of penetration height are proposed in two distinctive domains depending on the X/d location of the crossflow.

• The Korean Journal of Rheology
• /
• v.11 no.2
• /
• pp.143-152
• /
• 1999

Using a Rheometrics Fluids Spectrometer(RFS II), the steady shear flow and the small-amplitude dynamic viscoelastic properties of three kinds of semi-solid food materials(mayonnaise, tomato ketchup, and wasabi) have been measured over a wide range of shear rates and angular frequencies. The shear rate dependence of steady flow behavior and the angular frequency dependence of dynamic viscoelastic behavior were reported from the experimentally measured data. In addition, some viscoplastic flow models with a yield stress term were employed to make a quantitative evaluation of the steady flow behavior, and the applicability of these models was also examined in detail. Furthermore, the correlations between steady shear flow(nonlinear behavior) and dynamic viscoelastic(linear behavior)properties were discussed using the modified power-law flow equations. Main results obtained from this study can be summarized as follows : (1) Semi-solid food materials are regarded as viscoplastic fluids having a finite magnitude of yield stress, and their flow behavior shows shear-thinning characteristics, exhibiting a decrease in steady flow viscosity with increasing shear rate. (2) The Herschel-Bulkley, Mizrahi-Berk, and Heinz-Casson models are all applicable to describe the steady flow behavior of semi-solid food materials. Among these models, the Heinz-Casson model has the best validity. (3) Semi-solid food materials show a stronger shear-thinning behavior at shear rate region higher than a critical shear rate where a more progressive structure breakdown takes place. (4) Both the storage and loss moduli are increased with increasing angular frequency, but they have a slight dependence on angular frequency. The elastic behavior is dominant to the viscous behavior over a wide range of angular frequencies. (5) All of the steady flow, dynamic, and complex viscosities are well satisfied with the power-law model behavior. The relationships between steady shear flow and dynamic viscoelastic properties can well be described by the modified forms of the power-law flow equations.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.502-502
• /
• 2011

기존 연구에서는 단일 타겟으로부터 증착된 코팅층 내에 다상으로 이루어진 나노 복합구조를 형성하기 위하여, 나노 합금분말을 방전플라즈마 소결법 등으로 급속 소결하여 타겟을 제조하는 방법이 고려되어 왔다. 반면, 비정질 재료가 우수한 비정질 형성능을 가지는 경우 주조 방법에 의해서도 타겟 제조가 가능하며, 특히 최근 들어 금속 비정질 합금에서 합금의 주요 구성 원소들이 양의 혼합열을 가지는 경우, 액상 또는 과냉각 액상에서 상분리 현상이 발생한다는 것이 밝혀졌다. 이러한 사실에 기초하면, 우수한 비정질 형성능을 가지는 합금 시스템에 합금 구성 원소와 양의 혼합열 관계를 갖는 원소를 첨가함으로써, 비정질 기지 내에 화학적 불균일성을 유도하여 다상으로 이루어진 복합 구조를 형성시키는 것이 가능하다. 본 연구에서는 이러한 합금 설계법을 이용하여, 비정질 기지 내에 존재할 수 있는 불균일성 정도를 합금 조성과 주조 조건의 변화를 통하여 나노 크기에서 원자 크기까지 조절하고, 이에 따른 재료 특성과의 상관관계를 밝히고자 하였다. 이를 위하여 우수한 비정질 형성능을 가지는 Cu-(Zr, Hf)-Al 벌크 비정질 합금계에서 (Zr, Hf)과 (Y, Gd)간의 양의 혼합열 관계에 주목하여 Cu-(Zr, Hf)-(Y, Gd)-Al 벌크 비정질 형성 합금계를 설계하였으며, 이 합금계 내에서 조성과 냉각속도의 조절에 따라 나타나는 불균일성의 정도와 특성변화의 영향을 체계적으로 고찰하였다. 결과로서, Cu-(Zr, Hf)-Al 합금계에서 (Zr, Hf)을 (Y, Gd)으로 15 at.% 이상 치환한 경우, Cu-(Zr, Hf)-rich 와 Cu-(Y, Gd)-rich 비정질상으로 이상분리가 일어났으며, 이렇게 생성된 비정질-비정질 복합재는 응력 하에서 소성 변형을 거의 보이지 않았다. 반면, 5 at.% 이하로 (Zr, Hf)을 (Y, Gd)으로 치환한 경우에는 비정질 기지에 SAXS 혹은 WAXS로 확인 가능한 원자 크기의 불균일성이 나타났으며, 이 경우 비정질 합금의 점성 유동의 변화를 통해 합금의 연신 특성이 향상되었다. 특히, 본 연구에서는 비정질 기지내 불균일 제어를 통한 기계적 특성 향상을 위해서 조성 제어뿐 아니라 동역학적인 요소를 고려한 냉각속도 조절을 통한 원자단위 불균일성의 최적화가 필요함을 규명하였다. 이러한 연구 결과는 분말화 및 소결 과정을 배제하고 제조된 단일 타겟을 통해 코팅층에 다수의 합금원소를 혼합하고 나노/원자 스케일의 복합구조 형성 및 고집적화가 가능한, 타겟 모물질 설계의 새로운 방향을 제시함으로써 다기능성 복합소재 코팅층의 연구에 크게 기여할 것으로 사료된다.

• The Journal of Engineering Geology
• /
• v.20 no.4
• /
• pp.425-436
• /
• 2010

We established a stochastic 3-D fracture network system for fractured rock masses located in Il-Gwang Mine, Busan, to explore the relationship between the acidity of mine drainage and fracture geometry. A field scanline survey and borehole image processing were performed to estimate the best probability distributions of fracture geometry parameters. The stochastic 3-D fracture network system constructed for the rock masses was validated and deemed to be successful. The 3-D fracture network model was suitable for developing conceptual ideas on fluid flow in fractures at a field experimental site. An injection well and three observation wells were drilled at the field experimental site to monitor the acidity of mine drainage induced by the injection of fresh water. The field experiment, which was run for 29 days, yielded a significant relationship (with a high coefficient of determination) between the fracture geometry parameters and the acidity of mine drainage. The results show that pH increased with increasing relative frequency of fracture strike, and decreased with increasing fracture density. The concentration of $SO^{2-}_4$ decreased with increasing relative frequency of fracture strike, and increased with increasing fracture density.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.19 no.2
• /
• pp.99-108
• /
• 2014

One year long time-series current data were obtained at two stations (K1 and K2) located in the Usan Trough in the area north of Ulleungdo in the East Sea from September 2006. The observed data reveal enhanced seafloor flows in both stations with variabilities of about 20 days which is possibly governed by the topographic Rossby wave. After February 2007, strong flow in the upper layer in St. K1 appears throughout the mooring period and this is due to the passage of the warm eddy comparing with satellite sea surface temperature data. During this period, no significant correlation between the current in the upper layer and those in two deep layers is shown indicating the eddy does not affect flows in the deep ocean. It is also observed that the flow direction rotates clockwise with depth in both stations except for the upper of the K1. This implies that the deep flow does not parallel to the isobaths exactly and it has a downwelling velocity component. The possibility of the flow from the Japan Basin to the Ulleung Basin across the Usan Trough is not evidenced from the data.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.13 no.10
• /
• pp.4398-4404
• /
• 2012

This thesis was conducted a numerical analysis on the radiant heat performance according to factors of design of heat sink for cooling of the automotive LED head lamp. The heat sinks were designed with 5 different types to fit the limited internal space by formula based on an existing product (Type 1). Designed heat sinks of five types were analyzed by ANSYS CFD V12.1, and the analysis results were compared with the existing type. The results of simulation were analyzed temperature distribution and average temperature, air flow characteristic, heat flux etc. This thesis was researched on the correlation of the cooling performance according to the heat sink structure and the fin shape. Through numerical analysis, could be confirmed heat sink Type 2 as the best results.