• Nuclear Engineering and Technology
• /
• 제42권4호
• /
• pp.382-393
• /
• 2010

Thermal mixing by steam jets in a pool is dominantly influenced by a turbulent water jet generated by the condensing steam jets, and the proper prediction of this turbulent jet behavior is critical for the pool mixing analysis. A turbulent jet flow induced by a steam jet discharged through a vertical upward single hole into a subcooled water pool was subjected to computational fluid dynamics (CFD) analysis. Based on the small-scale test data derived under a horizontal steam discharging condition, this analysis was performed to validate a CFD method of analysis previously developed for condensing jet-induced pool mixing phenomena. In previous validation work, the CFD results and the test data for a limited range of radial and axial directions were compared in terms of profiles of the turbulent jet velocity and temperature. Furthermore, the behavior of the turbulent jet induced by the steam jet through a horizontal single hole in a subcooled water pool failed to show the exact axisymmetric flow pattern with regards to an overall pool mixing, whereas the CFD analysis was done with an axisymmetric grid model. Therefore, another new small-scale test was conducted under a vertical upward steam discharging condition. The purpose of this test was to generate the velocity and temperature profiles of the turbulent jet by expanding the measurement ranges from the jet center to a location at about 5% of $U_m$ and 10 cm to 30 cm from the exit of the discharge nozzle. The results of the new CFD analysis show that the recommended CFD model of the high turbulent intensity of 40% for the turbulent jet and the fine mesh grid model can accurately predict the test results within an error rate of about 10%. In this work, the turbulent jet model, which is used to simply predict the temperature and velocity profiles along the axial and radial directions by means of the empirical correlations and Tollmien's theory was improved on the basis of the new test data. The results validate the CFD model of analysis. Furthermore, the turbulent jet model developed in this study can be used to analyze pool thermal mixing when an ellipsoidal steam jet is discharged under a high steam mass flux in a subcooled water pool.

• Water Engineering Research
• /
• 제3권2호
• /
• pp.93-111
• /
• 2002

In this paper, mixing characteristics and dilution of the merging buoyant discharges from array of multiple jets has been extensively studied in the hydraulic model experiments. New equations for dilution, which include the merging effects correctly, were derived. Experiments were constructed in a 20-m long, 4.9-m wide and 0.6-m deep flume, and the model diffuser was manufactured to indicate the typical characteristics of the existing ocean wastewater outfall in South Korea. Buoyant discharge from the diffuser was reproduced using heated water. Water temperature was measured using CC-Type thermocouple sensors, which were connected to a 40-channel data logger. Experimental results show that merging between ports in a particular riser is dependent upon the discharge densimetric Froude number, whereas merging between two ports which are facing each other at 90$\circ$ at the adjacent risers is dependent upon the discharge densimetric Froude number and distance from the port and port spacing. Centerline dilution increase with distance from the port outlet until two plumes has merged. However, after merging occurs, increase of the centerline dilution almost stops. Further distance from the position where merging occurs, centerline dilution increases again.

• 한국수자원학회논문집
• /
• 제38권4호
• /
• pp.313-321
• /
• 2005

항만 및 저수지에서 점착성 퇴적물의 침식 및 제거는 극도로 큰 에너지를 동반한 기계적인 배출방법으로 단지 가능할 수 있다. 소위 분사방법은 높은 전단력에도 불구하고 점착성 퇴적물을 움직이게 하는데 실효를 거두지 못하고 있다. 그러므로 본 연구는 다목적댐, 항만 그리고 호수 등에서 퇴적된 점착성 미립자들을 저감시키기 위해 기포 투입으로 침전된 미립자($Al_{2}O_3$)의 부유현상을 실험하는데 목적을 두고 있다. 실험을 통해 중요한 매개변수는 투입된 기포의 양과 침전된 퇴적물의 응고시간인 것을 알 수 있었다. 기포 투입없이 높은 pH값에서 빨리 침전되는 미립자 퇴적물(alumina)은 기포의 증가로 입자의 부유현상이 일어난다.

• 천문학회지
• /
• 제40권4호
• /
• pp.123-125
• /
• 2007

NGC 1333 is a nearby star forming region, and IRAS 4A and IRAS 4BI are low-mass Class 0 protostars. IRAS 4A is a protobinary system. The NGC 1333 IRAS 4 region was observed in the 22 GHz water maser with a high resolution (0.08") using the Very Large Array. Two groups of masers were detected: one near A2 and the other near BI. Most of the masers associated with A2 are located very close (< 100 AU) to the radio continuum source. They may be associated with the circumstellar disk. Since no maser was detected near AI, the A2 disk is relatively more active than the Al disk. Most of the masers in the BI region are distributed along a straight line, and they are probably related with the outflow. As in many other water maser sources, the IRAS 4 water masers seem to trace selectively either the disk or the outflow. Considering the outflow lifetimes, the disk-outflow dichotomy is probably unrelated with the evolutionary stage of protostars. A possible explanation may be that both the outflow-maser and the disk-maser are rare phenomena and that detecting both kinds of maser around a single protostar may be even rarer.

• 한국수소및신에너지학회논문집
• /
• 제25권4호
• /
• pp.449-458
• /
• 2014

The heat transfer phenomenon was investigated in this study when a single round water jet with the low velocity and against the direction of gravity flows to the downward facing Isothermal of definite thickness circular plate. Experimental investigation is performed for a single round jet diameter 4mm, 6mm, and 8mm with the jet velocity 2.4m/s and jet fluid temperature of $24^{\circ}C$, varied the ratio of nozzle clearance/nozzle diameter (H/D)1, 2, 3, 6, and 8, on circular plate isothermal condition with $85^{\circ}C$. The local convection heat transfer coefficient distributions are analyzed based on the visualization of jet flow field. The effects of the diameter of Nozzle, the ratio of H/D and the ratio of nozzle diameter/circular plate diameter on heat transfer phenomenon are investigated. As a results of experiment is obtained correlation equation, $Nu_r=3.18Re_r^{0.55}Pr_r^{0.4}$.

• 대한기계학회논문집B
• /
• 제28권8호
• /
• pp.895-901
• /
• 2004

Single-phase convection and nucleate boiling heat transfer were locally investigated for confined planar water jets. The detailed distributions of the wall temperature and the convection coefficient as well as the typical boiling curves were discussed. The curve for the single-phase convection indicated the developing laminar boundary layer, accompanied by monotonic increase of the wall temperature in the stream direction. Boiling was initiated from the furthest downstream as heat flux increased. Heat transfer variation according to the streamwise location was reduced as heat flux increased enough to create the vigorous nucleate boiling. Velocity effects were considered for the confined free-surface jet. Higher velocity of the jet caused the boiling incipient to be delayed more. The transition to turbulence precipitated by the bubble-induced disturbance was obvious only for the highest velocity, which enabled the boiling incipient to start in the middle of the heated surface, rather than the furthest downstream as was the case of the moderate and low velocities. The temperature at offset line were somewhat tower than those at the centerline for single-phase convection and partial boiling, and these differences were reduced as the nucleate boiling developed. For the region prior to transition, the convection coefficient distributions were similar in both cases while the temperatures were somewhat lower in the submerged jet. For single-phase convection, transition was initiated at $x/W{\cong}2.5$ and completed soon for the submerged jet, but the onset of transition was retarded to the distance at $x/W{\cong}6$ for the fee-surface jet.

• 한국지역지리학회지
• /
• 제17권2호
• /
• pp.150-166
• /
• 2011

이 연구는 장마철 남해안 호우 사례의 850hPa 면 수증기 수송의 주축 유형에 대해 우리나라의 강수량 분포 특성, 동아시아 규모의 종관 특성과 장마전선의 구조를 밝히는 것을 목적으로 한다. 그 결과 유형 A(남중국해~화남~남해안)의 경우 아열대고기압이 화남지방에까지 영향을 미치고 황해를 중심으로 뚜렷한 저압부가 나타났다. 강수량도 대체로 동서 방향으로 분포하며 지형의 영향이 잘 나타나지 않았다. 유형 B(남중국해~타이완 부근~남해안), 유형 C(북태평양~남해안)에서는 타이완 부근에 열대저기압이 자주 나타났고 북서태평양고기압은 북쪽으로 이동하였다. 남해안 부근에서만 수증기 수송 주축이 나타나는 유형 D에서는 황해에 강한 저기압이 나타났다. 주축 유형 B, C, D의 경우 강수량 분포에서 북동~남서 방향이 잘 나타나며 지형의 영향이 뚜렷하게 나타났다. 상층 제트기류는 남해안의 북쪽에서 강화되었고 하층 제트기류는 수증기 수송 주축과 거의 일치하여 나타났다. 전선의 구조를 살펴본 즉, 거의 전체 사례에서 저기압성 순환이 대류권 상층에까지 나타나는 깊은 활동전선 유형을 보였다. 이 점에서 장마는 바이우계 동안 상당한 빈도로 얕은 활동전선 유형이 나타나는 일본 남서부 지역의 경우와 차이를 나타냈다.

• 대한기계학회논문집B
• /
• 제21권9호
• /
• pp.1105-1114
• /
• 1997

The heat transfer characteristics of free surface water jet impinging normally against a flat uniform heat flux surface were investigated. This deals with the effect of three nozzle configurations (Cone type, Reverse cone type, Vertical circular type) on the local and the average heat transfer. Heat transfer measurements were made for water jet issuing from a nozzle of which exit diameter 8 mm. The experimental conditions investigated are Reynolds number range of 27000 ~ 70000( $V_{O}$=3 ~ 8 m/s), nozzle-to-target plate distances H/D=2 ~ 10, and radial distance from the stagnation point r/D ~ = 0 ~ 7.42. For all jet velocities of H/D=2, the local Nusselt number decreased monotonically with increasing radial distance. However, for H/D from 4 to 10, and for the jet velocity $V_{O}$.geq.7 m/s for Cone type nozzle and $V_{O}$.geq.6 m/s for the other type nozzles, the Nusselt number distributions exhibited secondary peaks at r/D=3 ~ 3.5. For Reverse cone type nozzle and Vertical circular nozzle, the maximum stagnation point heat transfer and the maximum average heat transfer occurs at H/D=8. But for the Cone type nozzle, the maximum stagnation and average heat transfer occurs at H/D=10, 4, respectively. From the optimum nozzle-to-target plate distance, the stagnation and the average heat transfer reveal the following ranking: Reverse cone type nozzle, Vertical circular type nozzle, Cone type nozzle.ozzle.

• 한국정밀공학회지
• /
• 제24권11호
• /
• pp.66-75
• /
• 2007

To prevent an insulator failure, an automatic cleaning and inspection robot was developed for suspension insulator strings. The robot autonomously moves along the insulator string using the clamps installed on its two moving frames. Especially, unlike the existing cleaning robots using jets of water, the robot system adopts a dry cleaning method using rotating brushes and a circular motion guide. In addition, a mechanized brush bristles and a voltage-balancing contactor are devised to increase cleaning efficiency and to prevent arc generation under live-line conditions, respectively. We confirmed its effectiveness through experiments.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2002년도 제18회 학술발표대회 논문초록집
• /
• pp.18-23
• /
• 2002

Liquid phase mixing of impinging injector is a resultant byproduct from the momentum exchange between a pair of impinging jets and penetration of opponent jet. Principal aim of the present study is revealing the liquid phase mixing mechanism of split triplet impinging injection sprays, and thus extending our understanding on this particular injection element. Overall mixing extent is estimated from patternation tests by the use of purified tap water and kerosene to simulate the real propellant components, respectively, and with the liquid jet momentum ratio, a controlling mixing parameter, in the range of 0.5 to 6.0. Emphasis is placed on the effect of liquid sheet superposition and disintegration, and the results with detailed spray visualization revealed the fact that superposed liquid sheet disintegration is the main pathway of liquid phase mixing of split triplet impinging injector to yield enhanced mixing qualities.