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대체냉매 공기조화기용 로터리 압축기의 성능향상을 위한 최적 토출계에 관한 실험적 연구
윤영,정진택,민만기,Youn, Young,Chung, Jin-Taek,Min, Man-Ki 대한설비공학회 2001 설비공학 논문집 Vol.13 No.2
R410a which is one of HFC refrigerants is being considered to be a promising replacement for R22 widely used in domestic air conditioners. The rolling piston type rotary compressors for R410a have lower energy efficiency than those for R22 because of the high pressure difference between a suction chamber and a discharge chamber in the compression mechanism. in addition, the re-expansion gas loss of the rotary compressor for R410a which occurs a ta clearance volume in a discharge port becomes larger than that for R22 due to high density of R410a refrigerant. Therefore, Pressure-Volume analyses for various design parameters of a discharge system were carried out to improve efficiency of a R410a rotary compressor. The results such as performance dta, over-compression loss, and re-expansion loss were acquired by P-V analyses and analyzed quantitatively. As a conclusion, the optimal specifications of several design parameters of a discharge system were obtained by analyzing P-V diagrams.
날개의 모서리 형상이 플래핑 운동의 공기역학적 특성에 미치는 영향
오현택(Hyun-Taek Oh),최항철(Hang-Cheol Choi),김광호(Kwang-Ho Kim),정진택(Jin Taek Chung) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Birds and insects have wings of rounded edge profiles. In the experiment, the wing of the square edge profiles had been employed. In this study, two wings which have different shapes of edge are used to investigate the aerodynamic characteristics. One wing has rounded edge profiles and the other has square edge profiles. Two half elliptic shaped wings were designed and scaled up according to the planform of a black-chinned hummingbird, Archilochus alexandri. While the wings were operated in the water, the aerodynamic forces were measured and the flow structures around the wings were visualized using the DPIV. The lift for the wing of rounded edge profiles was higher than that for the wing of square edge profiles. But drag for the wing of rounded edge profiles was lower than that for the wing of square edge profiles. Also the lift to drag ratio for the wing of rounded edge profiles at angle of attack from 0° to 40° was higher than that for the wing of square edge profiles.
날개 길이방향 유동과 날개 회전이 날개짓 운동의 공기역학적 특성에 미치는 효과
오현택(Hyun-Taek Oh),최항철(Hang-Cheol Choi),김광호(Kwang-Ho Kim),정진택(Jin Taek Chung) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.9
3-D 날개짓 운동은 왕복운동과 회전운동으로 구성된다. 3-D 날개짓 운동은 왕복운동하는 동안 날개 길이방향의 유동이 발생된다. 또한 각각의 왕복운동의 끝에서 날개 회전에 의하여 회전에 의한 순환이 발생한다. 본 연구에서는 날개 길이방향 유동과 날개 회전이 3-D 날개짓 운동의 공기역학적 특성에 미치는 영향을 알아보기 위하여 3-D 날개짓 운동과 2-D 병진운동을 비교하였다. 각각의 날개짓 운동에서 받음각과 레이놀즈수에 따라 공력을 측정하였다. 2-D 병진운동의 공력이 3-D 날개짓 운동의 공력 보다 크다. 하지만 3-D 날개짓 운동시 발생되는 양력은 왕복운동의 중반부에서 받음각 50˚까지 증가하였고 2-D 병진운동시 발생되는 양력은 받음각 30˚이상에서 감소하였다. 또한 각각의 왕복운동의 끝에서 날개 회전에 의하여 공력이 급격하게 증가하였다. In a 3-D flapping motion, the spanwise flow is generated while the wing is moved on the stroke plane. And at the end of each stroke, the rotational circulation is generated due to a wing rotation. In this study, to evaluate the effect of spanwise flow and wing rotation on the aerodynamic characteristics in 3-D flapping motion, a 3-D flapping motion was compared with a 2-D translating motion. In each flapping motion, the aerodynamic forces were measured with respect to the angles of attack and Reynolds number. The aerodynamic forces generated by 2-D translating motion were higher than those generated by 3-D flapping motion. While the lift of 3-D flapping motion was increased until the angle of attack 60˚ at mid-stroke, the lift generated by 2-D translating motion was decreased above the angle of attack 40˚ at mid stroke. Also, at the end of each stroke, the aerodynamic forces were increased rapidly due to wing rotation.
날개의 종횡비가 날개 짓 운동의 공기역학적 특성에 미치는 영향
오현택(Hyun-Taek Oh),최항철(Hang-Cheol Choi),김광호(Kwang-Ho Kim),정진택(Jin Taek Chung) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
The lift and drag forces produced by a wing of a given cross-sectional profile are dependent on the wing planform and the angle of attack. Aspect ratio is the ratio of the wing span to the average chord. For conventional fixed wing aircrafts, high aspect ratio wings produce a higher lift to drag ratio than low ones for flight at subsonic speeds. Therefore, high aspect ratio wings are used on aircraft intended for long endurance. However, birds and insects flap their wings to fly in the air and they can change their wing motions. Their wing motions are made up of translation and rotation. Therefore, we tested flapping motions with parameters which affect rotational motion such as the angle of attack and the wing beat frequency. The half elliptic shaped wings were designed with the variation of aspect ratio from 4 to 11. The flapping device was operated in the water to reduce the wing beat frequency according to Reynolds similarity. In this study, the aerodynamic forces, the time-averaged force coefficients and the lift to drag ratio were measured at Reynolds number 15,000 to explore the aerodynamic characteristics with the variation of aspect ratio. The maximum lift coefficient was turned up at AR=8. The mean drag coefficients were almost same values at angle of attack from 10° to 40° regardless of aspect ratio, and the mean drag coefficients above angle of attack 50° were decreased according to the increase of aspect ratio. For flapping motion the maximum mean lift to drag ratio appeared at AR=8.
날개 길이방향 유동이 날개짓 운동의 공기역학적 특성에 미치는 효과
오현택(Hyun-Taek Oh),최항철(Hang-Cheol Choi),김광호(Kwang-Ho Kim),정진택(Jin Taek Chung) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
Flight performance of birds and insects is superior to conventional fixed wing aircrafts at low Reynolds number regime. While they flap their wings, aerodynamic characteristics such as span-wise flow and rotational circulation are appeared on the wing. To study on the effect of span-wise flow, 3-D flapping motion was compared with 2-D flapping motion. In 3-D flapping motion, the measured lift forces were increased until the angle of attack 50° at mid-stroke. But in 2-D flapping motion, the lift forces were decreased above the angle of attack 30° at mid-stroke. Also, the mean lift to drag ratio of 3-D flapping motion is higher than that of 2-D flapping motion.
티타늄 평활관 및 전열촉진관에서 R-l34a의 관외측 풀비등 열전달 특성에 대한 연구
허재혁,윤린,정진택,문영준,김용찬,Heo Jae-Hyeok,Yun Rin,Chung Jin-Taek,Moon Young-lune,Kim Yongchan 대한기계학회 2005 大韓機械學會論文集B Vol.29 No.7
Pool boiling heat transfer characteristics of R-134a were investigated in titanium plain and low finned tubes. The diameter of test tube was 15.88 mm and the fin density was 33 fpi. Tests were conducted at saturation temperatures of $20^{\circ}C$ and $30^{\circ}C$. Heat fluxes varied from 5000 W/$m^2$ to 50,000 W/$m^2$ based on surface area of the plain tube. The pool boiling heat transfer coefficients of the titanium horizontal plain tube are lower than those of the copper plain tube by $8.2\%$. The boiling heat transfer coefficients of the low finned tube are averagely higher than those of the plain tubes by $34\%$. The average deviation of the Slipcevic correlation from the present data for the low finned tube is $20\%$.