• 한국추진공학회지
• /
• 제13권5호
• /
• pp.7-14
• /
• 2009

공기를 이용한 초음속 터빈 설계성능 검증방법을 해석적, 시험적으로 고찰하였다. 성능시험기 설계를 위한 터빈상사조건 및 노즐 면적비 관계를 도출하였으며 실형상 노즐을 적용한 터빈과의 성능비교를 전산유동해석 및 성능시험을 통해 수행하였다. 도출된 설계 상사조건을 이용하여 시험용 노즐 블록을 설계할 경우, 설계 성능을 정확히 예측됨을 전산 유동해석을 통해 확인하였으며 시험을 통해 검증하였다. 아울러 초음속 충동형 터빈의 설계성능 측정은 시험용 노즐 뿐 아니라 실형상 노즐을 통해서도 가능하며 이 경우 시험용 노즐의 상사 압력비와 속도비에서 설계 성능이 나타남을 확인할 수 있었다.

• 한국분무공학회지
• /
• 제25권3호
• /
• pp.111-118
• /
• 2020

This paper describes the effect of DME, biodiesel blended fuels on the macroscopic spray characteristics in a high pressure diesel injection system using Background Oriented Schlieren (BOS) method. The BOS method for visualization of impingement evaporation sprays to analyze macroscopic spray properties and evolutionary processes. In this work, the blending ratio of DME in the blended fuel are 0, 50, 100% by weight ratio. In order to investigate the macroscopic impinged spray characteristics under the various injection parameters and blending ratio. In this work, a mini-sac type single-hole nozzle injector with nozzle hole was length 0.7 mm and diameter of 0.3 mm was used. According to the result, the spray area of the collision wall increased as the DME mixing ratio increased, and the evolutionary pattern showed a stepwise increase due to the collision effect of the wall. Also, results of impinged spray area were increased according to increasing injection pressure.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
• /
• pp.682-685
• /
• 2017

본 연구는 비원형 Effervescent Type 이유체 노즐의 분사 특성을 조사하기 위한 실험적 연구를 수행하였다. 이를 위해 거의 동일한 노즐 출구 면적으로 가공한 2종류의 비원형 노즐 (E1, E2)과 1종류의 원형 노즐 (C)을 대상으로 비교 실험을 진행하였다. 이때 노즐에 장착된 Aerorator는 노즐 출구 면적과의 Aspect Ratio를 맞추기 위해 지름이 다른 3종류를 사용하였다. 따라서 각 노즐마다 3가지의 Aspect Ratio에 따라 3번의 실험을 진행하였으며, 전체 총 9종의 실험이 진행되었다. 실험은 Liquid의 유량을 고정시킨 후, 유입되는 Air의 양을 제어하며 진행하였으며, 노즐 내부 압력과 액적의 크기 (SMD)를 측정하고 노즐에서 분사 이미지를 촬영하였다. 이를 통해 3종의 노즐의 유량 계수를 압력 분무방정식과 Jedelsky 방정식을 비교 계산하였고, Jedelsky 방정식이 약 4배 정도 더 큰 값을 갖는 것을 확인하였다. 노즐에서 분사되는 SMD는 원형보다 비원형에서 더 작은 값을 갖는 것으로 나타났으며, 이는 유량 계수 값의 차이 의해 야기된 것으로 예상된다.

• 설비공학논문집
• /
• 제13권5호
• /
• pp.356-367
• /
• 2001

A numerical analysis on branch type sparger in drain tank for depressurization is performed to investigate the flow characteristics due to the change of design factor. As the result of this study, sparger\\`s flow resistance coefficient(K) is 3.53 at the present design condition when engineering margin for surface roughness is considered as 20%, and flow ratio into branch pipe ($Q_s/Q_i$) is 0.41. The correlation for calculating flow resistance coefficients as design factor is presented. Flow resistance coefficient is increased as section area ratio of branch pipe for main pipe and outlet nozzle diameter of main pipe decreasing, but the effects of branch angle and inlet flow rate of main pipe are small. As the change rate of ($Q_s/Q_i$)becomes larger, the change rate of flow resistance coefficient increases. The rate of pressure loss has the largest change as section area ratio changing. The condition of maximum flow resistance in sparger is when the outlet nozzle diameter ratio of main pipe ($D_e/D_i$) is 0.167, the section area ratio ($A_s/A_i$) is 0.1 and the branch angle ($\alpha$) is 55^{\circ}$.

• 대한기계학회논문집B
• /
• 제29권1호
• /
• pp.151-158
• /
• 2005

A characteristic of discharge for a foam spray nozzle with various parameters was investigated. The discharge patterns from a fire foam spray nozzle are important to evenly spray over a maximum possible floor area. Two parameters of a foam spray nozzle were chosen, and compared with those from the standard one. Also, in order to evaluate the performance of discharged foam agents used to protect structures from heat and fire damages, the thermal characteristics of fire-protection foams were experimentally investigated. A simple repeatable test for fire-protection foams subjected to fire radiation was developed. This test involves foam generation equipment, a fire source for heat generation, and data acquisition techniques. Results show that the bubble size of foam is increased by large inside diameter of orifice or closed air hole, but phenomenon of discharge angle and expansion ratio is opposite. For the case of the open air hole, liquid film of a circular cone discharges with formation, growth, split and fine grain. In case of the closed air hole, a pillar of foam solution discharges with that. Though the temperature gradient in the foam increases with increased foam expansion ratio. it is not change with increased intensity of heat flux.

• 대한기계학회논문집B
• /
• 제24권1호
• /
• pp.132-142
• /
• 2000

The objective of this study is to experimentally investigate the noise propagating characteristics, the noise reduction mechanism and the performance of a slotted tube attached at the exit plane of a circular convergent nozzle. The experiment is performed through the systematic change of the jet pressure ratio and the slot length under the condition of two kinds of open area ratios, 25% and 51%. The open area ratio calculated by the tube length equivalent for the slot length is defined as the ratio of the total slot area to the surface area of a slotted tube. The experimental results for the near and far field sound, the visualization of jet structures and the static pressure distributions in the jet passing through a slotted tube are presented and explained in comparison with those for a simple tube. The propagating characteristics of supersonic jet noises from the slotted tube is closely connected with the slot length rather than the open area ratio, and its propagating pattern is similar to the simple tube. It is shown that the slotted tube has a good performance to suppress the shock-associated noise as well as the turbulent mixing noise in the range of a limited jet pressure and slot dimension. The considerable suppression of the shock‘associated noise is mainly due to the pressure relief caused by the high-speed jets passing through the slots on the tube. Both the strength of shock waves and the interval between them in a jet plume are decreased by the pressure relief. Moreover, the pressure relief is divided into the gradual and the sudden relief depending upon the open area ratio of the slotted tube. Consequently, the shock waves in a jet plume are also changed by the type of pressure relief. The gradual pressure relief caused by the slotted tube with the open area ratio 25% generates the weak oblique shock waves. On the contrary, the weak normal shock waves appear due to the sudden pressure relief caused by the slotted tube with the open area ratio 51%.

• 대한기계학회논문집B
• /
• 제29권5호
• /
• pp.554-560
• /
• 2005

A new method to improve the efficiency of a hydrogen fuel cell system was introduced by using variable sonic/supersonic ejectors. To obtain the variable area ratio of the nozzle throat to ejector throat which controls the mass flow rate of the suction flow, the ejectors used a movable cylinder inserted into a conventional ejector-diffuser system. Experiments were carried out to understand the flow characteristics inside the variable ejector system. The secondary mass flow rates of subsonic and supersonic ejectors were examined by varying the operating pressure ratio and area ratio. The results showed that the variable sonic/supersonic ejectors could control the recirculation ratio by changing the throat area ratio, and also showed that the recirculation ratio increased fur the variable sonic ejector and decreased for the variable supersonic ejector, as the throat area ratio increases.

• 대한기계학회논문집B
• /
• 제20권4호
• /
• pp.1395-1405
• /
• 1996

The purpose of this experimental research is to investigate the local heat transfer characteristics in the upward free water jet impinged on a downward flat plate of uniform heat flux. The inner shape of rectangular nozzle used was sine curve type and its contraction ratio of inlet to outlet area was five. Experimental parameters considered were Reynolds number, nozzle exit-flat plate distance, and level of supplementary water. Local Nusselt number was influenced by Reynolds number, Prandtl number, supplementary water level, and distance between the nozzle exit and flat plate. Within the impingement region, the Nusselt number has a maximum value on the nozzle center axis and decreases monotonically outward from center. Outside of the impingement region, on the other hand, the Nusselt number has a secondary peak near the position where the distance from nozzle center reaches four times the nozzle width. However if nozzle exit velocity exceeds 6.2 m/s, the secondary peak appears also in the impingement region. The empirical equation for the stagnation heat transfer is a function of Prandtl, Reynolds, and axial distance from the nozzle exit. The optimum level of supplementary water to augment the heat transfer rate at stagnation point was found to be twice the nozzle width.

• 태양에너지
• /
• 제9권2호
• /
• pp.42-50
• /
• 1989

The Buoyant Jets were analysed experimentally changing flow rate (0.0291/s, 0.0371/s, 0.0451/s), ratio of nozzle tip area to throat area (aspect ratio ${\beta}$=0.4, 1.0, 1.9), and also the temperature difference (${\Delta}T=Ti-T{\infty}$) between the temperature of the inflow water into the storage tank ($1m{\times}1m{\times}3m$) and the mean temperature of the water in the storage tank were changed as $25^{\circ}C,\;35^{\circ}C$ and $45^{\circ}C$. The more aspect ratio decreased, the more the trajectories of Buoyant Jets center-line were decreased and not the more the trajectories of Buoyant Jets centerline were influenced by the increment of the difference of the temperature. The more aspect ratio decreased, the more the half widths and dilution ratio of Buoyant Jets were increased and not the more the half widths and dilution ratio of Buoyant Jets were influenced by the increment of the difference of the temperature. Fr number is the factor that can predict the flow pattern over the whole flow field. And yet for the consideration the near field of Buoyant Jets flow pattern is dominated by magnitude of momentum and buoyancy force.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.2862-2867
• /
• 2007

The steady non-reacted compressible flow field in a symmetric micro-thruster, which is used for the accurate attitude control of a satellite, is analyzed varying the nozzle pressure ratio (NPR) to investigate the plume characteristics. The nozzle throat diameter is 0.06 inch and the area ratio is 56. The recirculation region is found just behind the normal shock at the several NPRs due to the locally adverse pressure gradient along the nozzle centerline when the environmental pressure is atmospheric. This phenomenon, the cause of flow loss, is similar to the flow behind a blunt body. As NPR increases the location of Mach disk, characteristics of the normal shock, moves downstream and its strength increases. The Mach number distribution appears in a wave-type patter after the normal shock because oblique shocks are reflected on the shock boundaries especially when NPRs are very high.