• Smart Media Journal
• /
• v.9 no.4
• /
• pp.176-186
• /
• 2020

The size and shape of crops are diverse, and the growing environment is also different. Therefore, when one uses a drone to spray pesticides, the characteristics of each crop must be considered, and flight conditions such as the flight height and forwarding velocity of the drone should be changed. The droplet flow of pesticides is affected by various flight conditions, and a large change occurs in the sprayed area. As a result, an uneven distribution of liquid may be formed at the wake, and the transport efficiency will be decreased as well as there would be a risk of toxic scatter. Therefore, this paper analyzes the degree of distribution of pesticides to the crops through numerical analysis when pesticide is sprayed onto the selected three crops with different characteristics by using agricultural drones with different flight conditions. On the purpose of establishing a guideline for spraying pesticides using a drone in accordance with the characteristics of crops, this paper compares the amount of pesticides distributed in the crops at the wake of nozzle flow using the figure of merit, and the sum of transported liquid rate divided by the root mean square of the probability density function.

• Journal of the Korean Electrochemical Society
• /
• v.16 no.1
• /
• pp.39-45
• /
• 2013

The water management is one of the key issues in low operating temperature proton exchange membrane fuel cells (PEMFCs). The gas diffusion layer (GDL) allows the reactant gases flow to the reaction sites of the catalyst layer (CL). At high current density, generated water forms droplets because the normal operating temperature is $60{\sim}80^{\circ}C$. If liquid water is not evacuated properly, the pores in the GDL will be blocked and the performance will be reduced severely. In this study, the microchannel GDL was proposed to solve the flooding problem. The liquid water transport through 3-D constructed conventional GDL and microchannel GDL was analyzed varying air velocity, water velocity, and contact angle. The simulation results showed that the liquid water was evacuated rapidly through the microchannel GDL because of the lower flow resistance. Therefore, the microchannel GDL was efficient to remove liquid water in the GDL and gas channels.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.8
• /
• pp.21-29
• /
• 2002

In the present study, a passive control method, using a porous wall and cavity system, is applied to the shock wave/boundary layer interactions in transonic moist air flow. The two-dimensional, unsteady, compressible, Navier-Stokes equations, which are fully coupled with a droplet growth equation, are solved by the third-order MUSCL type TVD finite difference scheme. Baldwin-Lomax model is employed to close the governing equations. In order to investigate the effectiveness of the present control method, the total pressure loss of the flow and the time-dependent behaviour of shock motions are analyzed in detail. The computed results show that the present passive control method considerably reduces the total pressure losses due to the shock wave/boundary layer interaction in transonic moist air flow and suppresses the unsteady shock wave motions over the airfoil as well. It is also found that the location of the porous ventilation significantly affects the control effectiveness.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2009.05a
• /
• pp.267-274
• /
• 2009

Breakup and spray formation of pressure-swirl liquid jets injected into a low-speed convective-flow are experimentally investigated. Effects of the cross-flows on the macroscopic and microscopic spray parameters are optically measured in terms of jet Weber number and liquid-to-gas momentum ratio. The liquid stream undergoes Rayleigh jet breakup at lower jet Weber numbers and a liquid sheet isn't formed because of the weak radial velocity in the swirl jet. At higher jet Weber numbers, the macroscopic spray parameter is a very weak function of the momentum ratio but the effect of the convection on the microscopic spray parameter is significant through the secondary breakup with increasing in the liquid-to-gas momentum ratio. The convective-flow promotes bag/plume breakup and the spray formation, and its effect is more distinct at higher momentum ratio.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2010.11a
• /
• pp.177-180
• /
• 2010

Two-stage light gas gun, sorted with Ballistic Range System, is used to research spray characteristics of supersonic liquid jets. When high pressure tube was pressurized to the 135 bar, diaphragm films which composed with OHP film are ruptured. Expansion gases accelerate a projectile approximately 250 m/s at the exit of pump tube. And accelerated projectile collides with liquid storage part and liquid jets were injected into supersonic conditions. Supersonic liquid jets show the multiple jets and generate shockwave at the forward region of jets. Supersonic liquid jets of speed and shockwave angle have different value at each case. Supersonic liquid jets with minimum velocities are injected with M=1.53 at the geometry condition of L/d=23.8.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.7
• /
• pp.675-682
• /
• 2013

To verify the effect of inner- and outer-stage gas jets, a shear coaxial injector was designed to analyze the axial velocity profile and breakup phenomenon with an increase in the measurement distance. When the measurement position was increased to Z/d=100, the axial flow showed a fully developed shape due to the momentum transfer, aerodynamic drag effect, and viscous mixing. An inner gas injection, which induces a higher momentum flux ratio near the nozzle, produces the greater shear force on atomization than an outer gas injection. Inner- and Outer-stage gas injection do not affect the mixing between the inner and outer gas flow below Z/d=5. The experiment results showed that the main effect of liquid jet breakup was governed by the gas jet of an inner stage. As the nozzle exit of the outer-stage was located far from the liquid column, shear force and turbulence breaking up of the liquid jets do not fully affect the liquid column. In the case of an inner-stage gas injection momentum flux ratio within 0.84, with the increase in the outer gas momentum flux ratio, the SMD decreases. However, at an inner-stage gas jet momentum flux ratio over 1.38, the SMD shows the similar distribution.

• Journal of Korean Ophthalmic Optics Society
• /
• v.5 no.2
• /
• pp.167-173
• /
• 2000

Four glasses of $B_2O_3-Bi_2O_3-PbO-SiO_2$ (BBPS) system were prepared by melting the appropriate amounts of reagent grade oxides of $B_2O_3$, $Bi_2O_3$, PbO, and $SiO_2$ in an open crucible. The differential thermal analysis showed crystallization temperature decreased with increasing $Bi_2O_3$ or PbO content in the sample. The structures of glasses system were studied using scanning electron microscopy and Fourier transform-Infra red (FT-IR) spectroscopy. The UV cut-off and refractive index were found to be sensitive to the $Pb^{+2}$ and $Bi^{+3}$ content in the glasses. The behavior of the IR spectra of the glasses in the BP series was consistent with a role of $Bi_2O_3$ as a network former. In the BP series of glasses, the result of IR spectrum indicated that PbO behaved as a network former.

• Journal of Korean Society of Environmental Engineers
• /
• v.31 no.10
• /
• pp.933-940
• /
• 2009

To evaluate characteristics in spray flame, laminar counterflow is investigated on the effects of equivalence ratio and fuel by a two-dimensional DNS (direct numerical simulation). For the gaseous phase, Eulerian mass, momentum, energy, and species conservation equations are solved. For the disperse phase, all individual droplets are calculated by the Lagrangian method without the parcel model. n-Decane ($C_{10}H_{22}$) and n-heptane ($C_7H_{16}$) is used as a liquid spray fuel, and a one-step global reaction is employed for the combustion reaction model. As equivalence ratio increases, the fuel ignites early and the high temperature region spreads wider. The peak value of temperature, however, tends to once increase and then decreases with increasing equivalence ratio. The decrease in the peak value of temperature for the higher equivalence ratio condition is caused by the cooling effect associated with droplet group combustion. Since the evaporation of n-heptane is early, the high temperature region spreads wider than ndecane, but the peak values of temperature for both n-heptane and n-decane is almost same.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2000.04a
• /
• pp.5-5
• /
• 2000

액체 추진 로켓 엔진의 고주파 연소 불안정 관련 이론은 대체로 연소기 내부의 음향 공명 모드와 분무 연소 과정의 상호 작용을 구동 메커니즘으로 전제하며 Rayleigh Criterion의 재해석에 기초하여 불안정성 평가를 위한 매개변수를 도입하고 연소 불안정성을 예측한다. 여기에는 음향장 분석 이론, 음향 불안정 이론, 연소응답 및 기화반응 이론 등이 포함된다. 본 연구에서는 LOX/RPl 추진제 조합의 액체 추진 로켓 엔진 연소기를 대상으로 다차원 순수 음향장 해석과 연소-음향장 분석을 통해 대상 엔진의 고주파 연소 불안정 특성을 예측하였다. 수동 제어 기기인 음향공 설치에 따른 연소기의 음향장 및 연소-음향장의 특성 변화를 고찰하고 위 결과를 종합하여 음향공의 연소 불안정 억제 성능 및 대상 엔진의 연소 불안정성을 평가하였다. 연소기 형상 및 음향공 설치에 따른 다차원 순수 음향장 해석은 상용코드인 ANSYS를 사용하여 수행하였다. 내부 유체는 압축성, 비점성 유체로 유체의 평균 유동은 무시하며 위치에 관계없이 균일한 물성치를 부여하였다. 정상상태 연소과정을 가정하고 평형 화학을 이용한 분석 결과로부터 연소 기체의 관련 물성치를 결정하였다. 연소기 길이 방향, 반경 방향, 원주 방향 격자점들의 음향 특성을 주파수 영역에 대해 해석하고 3차원 음향 모드 형상을 토대로 음향장을 분석하였다. 연소-음향장 해석은 음향 불안정 이론 중 n- $\tau$ 2 매개변수 기법을 사용하였다. 연료 액적의 분무 연소 과정을 1차원적으로 가정하고 정상상태의 평형 화학 계산 결과를 이용하여 엔진의 연소면을 1차원적으로 설정하였다. 상류 연소응답과 중립 안정 곡선을 토대로 대상 엔진의 연소 불안정 특성을 분석하였다.구 분석 결과 기술적 문제점으로는 배기 가스온도가 낮은데 따른 출구 부분의 Bearing, Sealing이 문제가 될 수 있다고 판단되며 배기 가스 자체에 대기 공기중에 함유되어 있던 습기가 얼어붙는(Icing화) 문제가 발생하기 때문에 배기가스의 Icing을 방지하기 위하여 압축기 끝단에서 공기를 추출하여 배기부분에 송출할 필요성이 있는 것으로 판단되었다. 출구가스의 기체 유동속도가 매우 빠르므로 (100-l10m.sec) 이를 완화하기 위한 디퓨저의 설계가 요구된다고 판단된다. 또 연소기 후방에 물을 주입하는 경우 열교환기 및 기타 부분품에 발생할 수 있는 부식 및 열교환 효율 저하도 간과할 수 없는 문제로 파악되었다. 이러한 기술적 문제가 적절히 해결되는 경우 비활성 가스 제너레이터는 민수용으로는 대형 빌딩, 산림, 유조선 등의 화재에 매우 적절히 사용되어 질 수 있을 뿐 아니라 군사적으로도 군사작전 중 및 공군 기지의 화재 그리고 지하벙커에 설치되어 있는 고급 첨단 군사 장비 등의 화재 뿐 아니라 대간첩작전 등에 효과적으로 활용될 수 있을 것으로 판단된다.가 작으며, 본 연소관에 충전된 RDX/AP계 추진제의 경우 추진제의 습기투과에 의한 추진제 물성 변화는 미미한 것으로 나타났다.의 향상으로, 음성개선에 효과적이라고 사료되었으며, 이 방법이 편측 성대마비 환자의 효과적인 음성개선의 치료방법의 하나로 응용될 수 있으리라 생각된다..7%), 혈액투석, 식도부분절제술 및 위루술·위회장문합술을 시행한 경우가 각 1례(2.9%)씩이었다. 13) 심각한 합병증은 9례(26.5%)에서 보였는데 그중 식도협착증이 6례(17.6%), 급성신부전증 1례(2.9%), 종격동기흉과 폐염이 병발한 경우와 폐염이 각 1례(2.9%)였다. 14)

• Journal of Korean Society of Environmental Engineers
• /
• v.27 no.10
• /
• pp.1081-1089
• /
• 2005

In order to examine the application feasibility of Orimulsion fuel in a commercial boiler using heavy fuel oil, a numerical and experimental research efforts have been made especially to figure out the fundamental combustion characteristics of this fuel in a small-scale boiler. One of the notable combustion features of Orimulsion fuel is the delayed appearance of flame location with the flame shape of rather broad distribution, which is found experimentally and confirmed by numerical calculation. This kind of flame characteristics is considered due to the high moisture content included inherently in the process of Orimulsion manufacture together with micro-explosion by the existence of fine water droplets. In order to investigate the effect on the combustion characteristics of Orimulsion, a series of parametric investigation have been made in terms of important design and operational variables such as injected amount of fuel, types of atomization fluid, and phonemenological radiation model employed in the calculation, etc. The delayed feature of peak flame can be alleviated by the adjustment of the flow rate of injected fuel and the generating features of CO, $SO_2$ and NO gases are also evaluated in the boiler. When the steam injection as atomizing fluid is used, the combustion process is stabilized with the reduced region of high flame temperature. In general, the calculation results are physically acceptable and consistent but some refinements of phenomenological models are necessary for the better resolution of pollutant formation. From the results of this small-scale Orimulsion boiler, it is believed that a number of useful information are obtained with the working computer program for the near future application of Orimulsion fuel to a conventional boiler.