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공기구동 이젝터를 이용한 ABB (Air Bubble Barrier)의 기포거동 특성 연구 (Ⅱ)
서현덕(Hyunduk Seo),알리유 무사 알리유(Aliyu Musa Aliyu),김효근(Hyogeum Kim),김경천(Kyung Chun Kim) 한국가시화정보학회 2017 한국가시화정보학회지 Vol.15 No.2
To verify floatability of ABB (Air bubble barrier), we compared bubble swarm behavior with and without the air-driven ejector. Experiment was conducted using the fabricated air-driven ejector with 5 mm nozzle on the bottom of 1 m3 water tank. Reynolds number of air in the nozzle was ranged 1766-13248. We analyzed data with statistical method using image processing, particle mage velocimetry (PIV) and proper orthogonal decomposition (POD) analysis. As a result of POD analysis, there was no significant eigenmode in bubbly flow generated from the ejector. It means that more complex turbulent flows were formed by the ejector, thereby (1) making bubbles finer, (2) promoting three-dimensional energy transfer between bubble and water, and (3) making evenly distributed velocity profile of water. It is concluded that the air-driven ejector could enhance the performance of ABB.
정재훈(Jae Hoon Jung),서현덕(Hyunduk Seo),김경천(Kyung Chun Kim) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
Sweeping jet actuator is a nozzle which can switch the direction of the jet without any moving elements. Because its 2-dimensional shape and high durability, the sweeping jet actuator has drawn increasing attention to apply in industrial areas. Streamlines and streaklines are different due to the unsteadiness of oscillating jet flow. In this study, streamlines and streaklines of the sweeping jet were experimentally investigated using particle image velocimetry (PIV) and smoke visualization. Flow control has attempted to introduce a vertical thin plate on the middle of the actuator’s exit. The results show that the thin plate maintained the frequency of the sweeping jet actuator but enhanced spraying performance as increasing the portion of the flow toward vertical direction.
박판이 부착된 사각노즐에서 분사되는 Sweeping jet의 유동 및 열전달 특성
김동욱(Donguk Kim),정재훈(Jae Hoon Jung),서현덕(Hyunduk Seo),김현동(Hyun Dong Kim),김경천(Kyung Chun Kim) 한국가시화정보학회 2019 한국가시화정보학회지 Vol.17 No.2
This study investigated heat transfer and flow characteristics of a sweeping jet issued from a rectangular nozzle with a thin plate. A thin vertical aluminum plate was attached on outlet of fluidic oscillator to increase velocity of central area with Coanda effect and enhance heat transfer performance. From visualization and PIV experiments, sweeping jet with a thin plate has larger velocity distribution in center region than that of the normal sweeping jet while oscillating frequency is similar as the normal one. Thermographic phosphor thermometry method was used to visualize the temperature field and Nu distribution of plate with impinging sweeping jet with thin plate. Four Reynolds numbers and three jet-to-wall distances were selected as parameters. It is found that heat transfer performance in the low jet-to-wall spacing was enhanced as the cooled area was expanded. However, when the jet-to-wall spacing became greater than 8dh, heat transfer performance became similar due to reduced impinging velocity.
오진호(Jinho Oh),신형민(Hyungmin Shin),서현덕(Hyunduk Seo),김경천(Kyung Chun Kim) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12
Behaviors of the jellyfish subjected to bubble swarm are investigated in this study. Bubble driven steady flow is formed in a 0.5 m x 0.5 m x 0.5 m acrylic tank. Particle Image Velocimetry (PIV) is used to measure the steady flow in the tank. Surface current from bubble swarm generates a vortex near the wall of the tank and the maximum velocity of the vortex towards the bubble is about 4.5 mm/s. Two perpendicularly installed cameras capture the motion of jellyfish. Time-resolved 3-D reconstruction of the position of the jellyfish is achieved by considering angle of view. In the vortex region, the jellyfish is entrained to bubble depending on the direction of the jellyfish bell. Being entrained to bubble, the jellyfish is rotated by the vortex and swims obliquely towards direction of the jellyfish bell. The result shows that we can design bubble barrier to prevent jellyfish crown at the power plant intake.