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물-미립자 현탁액의 난류 열전달 향상에 관한 수치해석적 연구
정세훈,손창현 한국마린엔지니어링학회 2000 한국마린엔지니어링학회지 Vol.24 No.3
The present numerical study investigates heat transfer enhancement mechanism for suspensions of polystyrene particles in water. Numerical simulations were done for turbulent hydrodynamic fully developed flows in a circular duct with constant wall heat flux. The experimental result of microparticle suspensions show 25∼45% heat transfer enhancement over those of water. The present numerical results show the main parameter for the heat transfer enhancement of microparticle suspension in a circular duct is the change of velocity profile by the non-Newtonian fluid behavior.
초음파 진동에 의해 발생된 음향유동을 활용한 급속냉각 메카니즘
노병국(Loh, Byoung-Gook),권기정(Kwon, Ki-Jung),이동렬(Lee, Dong-Ryul) 한국소음진동공학회 2006 한국소음진동공학회 논문집 Vol.16 No.10
Acoustic streaming Induced by longitudinal vibration at 30 kHz is visualized for a test fluid flow between the stationary glass plate and ultrasonic vibrating surface with particle imaging velocimetry (PIV) To measure an increase in the velocity of air flow due to acoustic streaming, the velocity of air flow in a gap between the heat source and ultrasonic vibrator is obtained quantitatively using PIV. The ultrasonic wave propagating into air in the gap generates steady-state secondary vortex called acoustic streaming which enhances convective cooling of the stationary heat source. Heat transfer through air in the gap is represented by experimental convective heat transfer coefficient with respect to the gap. Theoretical analysis shows that gaps for maximum heat transfer enhancement are the multiple of half wavelength. Optimal gaps for the actual design are experimentally found to be half wavelength and one wavelength. A drastic temperature variation exists for the local axial direction of the vibrator according to the measurement of the temperature distribution in the gap. The acoustic streaming velocity of the test fluid in the gap is at maximum when the gap agrees with the multiples of half wavelength of the ultrasonic wave, which are specifically 6 mm and 12 mm.
조진우,이용수,유준,김세호 한국지반공학회 2006 한국지반공학회논문집 Vol.22 No.4
An experimental investigation was carried out to evaluate the strength characteristics of low cement ratio soil stabilizer. The low cement ratio soil stabilizer has been developed by the replacement of certain part of cement with by-product pozzolanic materials such as blast furnace slag, fly ash, waste gypsum and by using activator. A series of unconfined compressive strength tests were performed to investigate and obtain high-strength composite soil stabilizer with large amounts of blast furnace slag and fly ash. Test results show that there were better properties when blast furnace slag, fly ash, waste gypsum, and activator were added in proper ratio. The replacement of certain part of cement with by-product pozzolanic materials improved the strength and pore structure properties.