• 동력기계공학회지
• /
• 제2권1호
• /
• pp.25-30
• /
• 1998

In order to investigate the droplet size distribution and Sauter Mean Diameter in a ultra high pressure diesel spray, fuel was injected with ultra high pressure into the environments of high pressure and room temperature by an Electronic Hydraulic Fuel Injection System. Droplet size was measured with the immersion liquid sampling technique. The immersion liquid was used a mixture of water-methycellulose solution and ethanol. The Sauter Mean Diameter decreased with increasing injection pressure, with a decrease environmental pressure (back pressure) and nozzle diameter. Increasing the injection pressure makes the fuel density distribution of the spray more homogeneous. An empirical correlation was developed among injection pressure, air density, nozzle diameter and the Sauter Mean Diameter of spray droplets.

• 한국유체기계학회 논문집
• /
• 제11권4호
• /
• pp.45-51
• /
• 2008

The purpose of this study is to examine the effect of nozzle shape on the performance and internal flow of a cross-flow hydro turbine. CFD analysis for three kinds of nozzle shape is conducted to simulate the effect of nozzle shape. The results reveal that relatively narrow nozzle width is effective to increase the turbine efficiency and output power. Almost output power is achieved at Stage 1. Therefore, optimum design of the nozzle shape is necessary to improve the turbine performance. Recirculation flow in the runner passage decreases the turbine efficiency and output power because the flow make hydraulic loss and collision loss in the region. Air should be put into the runner passage and the recirculating flow should be suppressed by the air layer in the runner.

• Journal of Mechanical Science and Technology
• /
• 제17권6호
• /
• pp.870-878
• /
• 2003

The scale is removed from the strip by high pressure hydraulic descaling at the FSB (Finishing Scale Breaker). Recently, the spray height of nozzle has a trend to be shorter for the purpose of increasing the impact pressure by the high pressure water jet. Here, the nozzle intervals should be decided after considering the impact pressure and the temperature distribution on the strip. In other words, the minimum of impact pressure at the overlap of spray influences the surface grade of the strip due to scale and the overlap distance of the spray affects the temperature variation in the direction of the width of strip. In the present study, the impact pressure of the high pressure water jet is measured by the hydraulic descaling system and calculated with regard to the lead angle of 15$^{\circ}$ and the offset angle of 15$^{\circ}$, and then the temperature distribution and the temperature variation are calculated at the overlap distances of 0 mm, 10 mm, 20 mm, and 30 mm, respectively. The method of setting nozzle intervals is shown by utilizing these results.

• 에너지공학
• /
• 제23권4호
• /
• pp.95-105
• /
• 2014

CUPID 코드는 기기 스케일(Component scale)의 2상 유동(Two-phase flow) 해석 코드로서 다양한 2상 유동 조건의 실험 자료를 이용하여 검증되어 왔다. 특히, CUPID 코드의 CANDU형 원자로 감속재 탱크 내부 유동 해석능력을 평가하기 위해 1/4 규모 축소 실험장치의 실험결과를 이용하여 검증한 바가 있다. 본 연구에서는 이전 연구를 바탕으로 CUPID 코드를 사용하여 실제 원자로 감속재탱크 내부의 열수력 거동을 해석하였다. 감속재 탱크의 내부 구조는 아주 복잡하기 때문에 다공질 매질 방법을 적용하였으며 탱크 입구노즐 또한 기기 스케일 코드의 취지에 부합하게 아주 단순화하여 모델하였다. 해석결과의 정확성을 결정하는 가장 중요한 요소는 입구노즐의 모델 방법에 있는 것으로 나타났다. 입구노즐을 단순하게 모델하여 입구유량을 경계조건으로 부여하고 발전소 정상운전조건으로 계산한 결과, 부력에 의한 열성층화 현상이 발생하였다. 이는 전혀 타당하지 않은 것으로 입구 유동의 모멘텀을 정확하게 모의하지 않아 발생한 것이 나타났다. 이를 개선하고자 입구 유량과 운동량을 동시에 보존시킬 수 있도록 입구 노즐 면적을 축소하고 속도는 증가시켜서 계산한 결과, 사실적인 내부 유동장을 얻을 수 있었다. 결론적으로 계산 비용효과가 뛰어난 다공질 매질 방법에 입각하여 CUPID 코드를 실규모 감속재 탱크 열유동 해석에 적용할 수 있음을 보였고, 입구노즐의 적절한 모델이 가장 중요한 요소임을 확인하였다.

• 유기물자원화
• /
• 제25권2호
• /
• pp.27-31
• /
• 2017

본 연구에서는 자흡식 마이크로버블 발생장치를 운전함에 있어서 수심 변화에 의한 수압이 산소 용해율에 미치는 영향에 대하여 평가하였다. 연구결과, 흡입 공기량의 경우 수압이 증가할수록 노즐 토출부에 작용하는 힘의 증가로 감소하는 경향을 나타내었다. 산소전달계수는 수심이 증가할수록 수압 증가에 의한 흡입 공기량 감소와 반응조 용적의 증가로 감소하는 경향을 나타내었으나 수심이 증가할수록 자흡식 마이크로버블 발생장치에서 발생되는 마이크로버블의 체류시간이 증가하여 산소 용해율은 증가하는 경향을 나타내었다. 그러나 자흡식 마이크로버블 발생장치 용량에 대비하여 수심이 과도하게 깊을 경우 낮은 흡입 공기량 및 산소전달계수로 인하여 산소 용해율은 감소할 것으로 판단된다. 따라서 자흡식 마이크로버블 발생장치 운전 시 수압이 중요한 고려사항이 됨을 확인할 수 있었다.

• 한국자동차공학회논문집
• /
• 제19권6호
• /
• pp.140-147
• /
• 2011

The injection nozzle of an electro-hydraulic injector for the common rail Diesel fuel injection system is being opened and closed by movement of a injector's needle which is balanced by pressure at the nozzle seat and at the needle control chamber, at the opposite end of the needle. In this study, the slenoid actuator was considered as a prime movers in high pressure Diesel injector. Namely a solenoid-driven Diesel injector with different driving current types, as a general method driven by solenoid coil energy, has been applied with a purpose to develop the analysis model of the solenoid actuator to predict the dynamics characteristics of the hydraulic component (injector) by using the AMESim code. Aimed at simulating the hydraulic behavior of the solenoid-driven injector, the circuit model has been developed as a unified approach to mechanical modeling in this study. As this analytic results, we know the suction force and first order time lag for driving force can be endowed in solenoid-driven injector in controlling the injection rate. Also it can predict that the input current wave exerted on solenoid coil is the dominant factor which affects on the initial needle behavior of solenoid-driven injector than the hydraulic force generated by the constant injection pressure.

• 한국분무공학회지
• /
• 제18권1호
• /
• pp.55-60
• /
• 2013

In this study, injection flow rates and material of the solenoid sealing of the injectors were improved for the development of a di-methyl Ether(DME) common-rail system. To deliver the same amount of energy provided by injection pressure of diesel $P_{inj}$ = 160 MPa, the DME injectors need to have larger diameter of nozzle hole and more No. of hole at low injection pressure of $P_{inj}$ = 40~50 MPa. The simplified nozzle flow model, which takes account of nozzle geometry and injection condition, was employed in order to design the concept of a injector nozzle such as No. of hole, diameter of hole and diameter of needle seat, etc. Injection amount and rate were tested by diesel and DME test stand. As a result, the diameter of nozzle hole were enlarged by 0.25 mm. The diameter of the orifice in the high pressure line was increased by 1.0 mm to maintain hydraulic force in the nozzle. The material of the solenoid sealing was changed to HNBR, which was strong against the corrosive. Experimental results showed that the injection amount of the DME injector drastically increased by 191.9% comparison to that of diesel at $P_{inj}$ = 40 MPa.

• International Journal of Safety
• /
• 제3권1호
• /
• pp.15-19
• /
• 2004

A new tower internal, which is called CSE, is presented. The CSE is composed of a nozzle perforated in its bottom along the entire periphery and equipped with a multi vane axial swirler at the inlet and hollow cylindrical separator at the outlet of the nozzle. According to the experimental work for obtaining the necessary hydraulic information of the CSE, which is used for preliminary design of a separation column, the CSE showed a stable operation over the wide rage of gas/liquid ratio. However, it caused large pressure drop due to the high gas velocity which should carry liquid droplets through the element. The high pressure drop may cause problems in energy recovery and the application of the CSE can be limited to the high pressure columns. Assuming that the tray efficiency of the CSE is the same with the existing separation columns, the results of the column design showed the size reduction of the column diameters by 30 to $40\%$ and investment cost saving, depending on operating conditions. The application of the CSE to separation column may also contribute to the de-bottlenecking the existing column.

• International Journal of Fluid Machinery and Systems
• /
• 제10권1호
• /
• pp.47-53
• /
• 2017

Surface pressure integration and momentum method were respectively performed to evaluate the impeller thrust and the system thrust of a contra-rotating axial flow water jet propulsion, and an interesting phenomenon so-called thrust paradox was revealed. To explain the paradox, the impeller thrust and the system thrust were physically and theoretically analyzed, the results show that the impeller thrust is head involved and is determined by the hydraulic parameters upstream and downstream the impeller, while the momentum method depicted by a classic equation is valid simply under the best efficiency point. Consequently, the role of a water jet propulsion nozzle was deduced that the nozzle is mainly to limit the flow rate that crosses the impeller and to assure the system working under the best efficiency condition apart from its ability to produce momentum difference. Related mathematical formula expressed the nozzle diameter is the dominant variable used to calculate the working condition of the water jet propulsion. Therefore the nozzle diameter can be steadily estimated by the former expression. The system thrust scaling characteristics under various speeds were displayed lastly.

• Membrane and Water Treatment
• /
• 제10권4호
• /
• pp.307-311
• /
• 2019

The ejector type microbubble generator, which is the method to supply air to water by using cavitation in the nozzle, does not require any air supplier so it is an effective and economical. Also, the distribution of the size of bubbles is diverse. Especially, the size of bubbles is smaller than the bubbles from a conventional air diffuser and bigger than the bubbles from a pressurized dissolution type microbubble generator so it could be applied to the aeration tank for wastewater treatment. However, the performance of the ejector type microbubble generator was affected by hydraulic pressure and MLSS(Mixed Liquor Suspended Solid) concentration so many factors should be considered to apply the generator to aeration tank. Therefore, this study was performed to verify effects of hydraulic pressure and MLSS concentration on oxygen transfer of the ejector type microbubble generator. In the tests, the quantity of sucked air in the nozzle, dissolved oxygen(DO) concentration, oxygen uptake rate(OUR), oxygen transfer coefficient were measured and calculated by using experimental results. In case of the MLSS, the experiments were performed in the condition of MLSS concentration of 0, 2,000, 4,000, 8,000 mg/L. The hydraulic pressure was considered up to $2.0mH_2O$. In the results of experiments, oxygen transfer coefficient was decreased with the increase of MLSS concentration and hydraulic pressure due to the increased viscosity and density of wastewater and decreased air flow rate. Also, by using statistical analysis, when the ejector type microbubble generator was used to supply air to wasterwater, the model equation of DO concentration was suggested to predict DO concentration in wastewater.