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가솔린기관에서 점화장치가 연료 경제성에 미치는 영향과 매연량 감소책의 연구
柳常新,權泰憲 외1명 空軍士官學校 1979 論文集 Vol.10 No.-
An experimental study on drag reduction in the rough tubes is presented using the effective drag reducing polymer solutions. The friction factors of the rough tubes follow the maximum drag reduction asymptote for they lower Reynolds number in the turbulent flow. However, as the Reynolds number in the turbulent flow. However, as the Reynolds number is increased the rougher tube results deviate from the maximum drag reduction asymptote in smaller Reynolds number than the less rough tube results. There appears a systematic deviation from the maximum drag reduction asymptote depending on the relative roughness just as the Newtonian friction factors for the Newtonian fluid in the rough just as the Newtonian friction factors for the Newtonian fluid in the rough tubes exhibit in the turbulent region. The minor loss results in the various fittings such as elbow, tees, and gate valves are presented. The fittings have higher loss coefficients in the drag reducing polymer solutions than in the Newtonian fluid, which is quite contrary to the drag reduction phenomenon. Equivalent length of the fittings for the drag reducing polymer solutions is many times longer than that for Newtonian fluids due to the increase of the loss coefficient and the decrease of the friction factor. It can be said that the values of loss coefficients in the polymer solutions increase as the mass flow rate increase. It appears that the loss coefficients are related to another fluid of flow properties besides flow kinetic energy and shearing stress in the polymer solutions. It is spectulated that the solid-like behavior of the polymer solutions in the abruptly changing flow passage plays a significant role in increasing the loss coefficient.
점탄성 특성을 가진 폴리머용액의 난류유동 열적입구길이에 관한 실험적 연구
유상신,황태성,엄정섭 대한기계학회 1988 대한기계학회논문집 Vol.12 No.5
본 연구에서는 내경이 각각 8.5mm와 10.3mm이며 무차원길이가 각각 710과 1158인 두 개의 시험관을 사용하는 유동장치를 제작하여 시험관 입구에서부터 유체역 학적 경계층(hydrodynamic boundary layer)과 열적 경계층(thermal boundary layer)이 동시에 발달하기 시작하는 경계조건을 형성하고 관벽에서 일정한 열 플럭스(constant heat flux)를 발생하는 조건을 부여하였다. 퇴화현상(degradation)에 대하여 비교적 안정성을 가진 폴리아크라마이드(polyacrylamide) Separan Ap273을 수도물에 용해하여 제조한 폴리머용액으로 유동특성과 열전달특성을 실험하여 열적입구길이와 열전달특성 을 규명하고자 한다. Thermal entrance lengths of turbulent tube flow for viscoelastic polymer solutions are investigated experimentally in the recirculating flow system with tubes of inside diameters 8.5mm(L/D=710) and 10.3mm(L/D=1158), respectively. In the present system, the hydrodynamic and thermal boundary layers develop simultaneously from the beginning of the test section. To provide the boundary condition of constant heat flux at the wall, the test tubes are heated directly by electricity. The polymer solution used in the current study is 1000 wppm aqueous solution of polyacrylamide(Separan AP-273). The apparent viscosity of the polymer solutions circulating in the flow system are measured by the capillary tube viscometer at regular time intervals. Thermal entrance lengths vary due to the rate of degradation. The entrance lengths of degraded polymer solutions are about 500~600 times the diameter. However, the entrance lengths of fresh polymer solutions are greater than the lengths of the test tubes used in this study suggesting that thermal entrance lengths for viscoelastic polymer solutions are greater than 1100 tube times the diameters. Friction factor is almost insensitive to the degradation, but the heat transfer $j_{H}$-factor is affected seriously by degradation. Based on the present experimental data of fresh solutions a correlation for the heat transfer $j_{H}$-factor is presented.ted.
유상신,김춘식 대한기계학회 1979 대한기계학회논문집 Vol.3 No.4
An experomental study on drg reduction in the rough tubes is presunted using the drrective drag reducing proymer solutions. The friction factors of the rough tubes follow the maximum drag reduction asymptote for the lower Reynolds numbers in the turbulent flow. However, as the Reynols number is increased the rougher tube results deviate from the maximum drag rduction asymptote sooner than the less rough tube results. There appears a systematic deviation from the maximum drag reduction asymptote depending on the relative roughness just as friction factors for the Newtonian hluid inthe rough tubes exhibit in the turbulent region. The minor loss results inthe various fittings such as elbows, tees, and gate valves are presunted The fittings show higher values of the loss coefficient in the drag reducing polymer solutions than in the Newtonian fluid, which is quite contrary to the drag reduction phenomenon in the straight tubes. The eqivalent length of the fittings for the drag reducing polymer solutions is many times longer than that for Newtonian fluids due to the increase of the loss coefficient and the decrease of the friction factor. It is speculated that the solid-like behavior of the polymer solutions in the abruptly changing folw passage plays a significant role in increasing the loss coefficient.
지연에 민감한 멀티미디어 응용을 위한 재생 동기화 메카니즘
유상신,이성근,김덕진 대한전자공학회 1996 전자공학회논문지-A Vol.33 No.4
This paper aims to support delay-sensitive multimedia applications by suggesting a mechanism in which maintains almost constant end-to-end delay thus providing the optimum playout synchronization. For this task the sum of network delay and buffering delay is entiredly managed and to eliminate little delay fluctuations and instantaneous delays at a buffer and a network, a low pass filter is used. Furthermore the correction function, which is used for maintaining the buffering level ot a reference value, is a non-linear step function, unlike the existing linear and continuous function. it has a different step sizes adapting to a traffic characteristics of a network congestion. the proposed mechanism has been confirmed of it sefficiency through SLAM-II netowrk.