• 설비공학논문집
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• 제15권12호
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• pp.1007-1017
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• 2003

An experimental study on the air-side pressure drop and heat transfer coefficient of slit fin-tube heat exchanger has been carried out. The data reduction methodology for air-side heat transfer coefficients in the literature is not based on a consistent approach. This paper focuses on new method of data reduction to obtain the air-side performance of fin-tube heat exchanger using R22 and recommends standard procedures for dry and wet surface heat transfer estimation in fin-tube heat exchanger having refrigerant on the tube-side. Results are presented as plots of friction f-factor and Colburn j -factor against Reynolds number based on the fin collar outside diameter and compared with previous studies. The data covers a range of refrigerant mass fluxes of 150∼250 kg/$m^2$s with air flows at velocity ranges from 0.3 m/s to 0.8 m/s.

• 설비공학논문집
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• 제15권3호
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• pp.220-229
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• 2003

An experimental study on the air-side pressure drop and heat transfer coefficient of slit fin-tube heat exchanger has been carried out. The data reduction methodology for air-side heat transfer coefficients in the literature is not based on a consistent approach. This paper focuses on new method of data reduction to obtain the air-side performance of fin-tube heat exchanger using R22 and recommends standard procedures for dry surface heat transfer estimation in fin-tube heat exchanger having refrigerant on the tube-side. Results are presented as plots of friction f-factor and Colburn j -factor against Reynolds number based on the fin collar outside diameter and compared with previous studies. The data covers a range of refrigerant mass fluxes of 150~250 kg/$m^2$s with air flows at velocity ranges from 0.6 m/s to 1.6 m/s.

• 한국군사과학기술학회지
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• 제10권3호
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• pp.208-216
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• 2007

As the propellant mass is being accelerated out of the gun chamber along with the projectile, a continuous pressure gradient exists between the end of chamber and the base of the projectile. For this reason, the base pressure-travel curve is very important to design a conventional gun barrel in the interior ballistics, but it is not obtained briefly by empirical or theoretical method. In this paper, a simple relation between chamber pressure and base pressure was determined by the factor of base pressure(Cb) obtained from the experimental method. The simple relation gives a reasonable prediction for the reduction of pressure between the breech and the base of projectile owing to the axial gradient in the gun tube. The predictions have been validated by the infrared screen sensor and the PRODAS(PROjectile Design and Analysis System) for interior ballistic systems. Therefore, the base pressure-travel curve could be calculated from the chamber pressure measured by piezoelectric sensor. The base pressure-travel curve obtained from the simple relation offers initial information to gun barrel designer and is used for calculation of muzzle velocity.

• 대한기계학회논문집
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• 제13권5호
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• pp.831-836
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• 1989

본 연구에서는 이에 대한 검토를 하기 위하여, Kato의 속도장을 수정하여 수치게산한 폭 증가율과 알루미늄을 재료로 실험한 결과를 비교하고, 마찰비와 판폭비 및 압하율의 변화에 따른 폭 증가율의 영향에 대하여 고찰하였다.

• 상하수도학회지
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• 제19권4호
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• pp.429-436
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• 2005

A coagulation/ultrafiltration membrane hybrid system was operated to treat river water with capacity of $0.06m^3/d$. The impact on membrane fouling by flux and linear velocity was investigated. It is known that pressure increase is proportional to flux increase. However, pressure increase was much faster than theoretical value in the pilot plant test. So it was suggested that flux was on important factor in ultrafiltration of continuous operation. Membrane fouling was decreased when linear velocity was increased. This phenomenon was found more obviously without coagulation. With the combination of coagulation and sedimentation, membrane fouling was not reduced conspicuously. Big particles formed during coagulation and sedimentation were destroyed by feed and circulation pumping, which resulted in little effect on membrane fouling reduction. The degree of destruction was similar at various linear velocities. In this study, the hollow fiber membrane was used and the system was operated in pressure type module. In case of the system used in this study, membrane fouling has been affected lightly by linear velocity variation when coagulation pretreatment was applied.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2007년도 추계학술대회
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• pp.149-154
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• 2007

This study examines the effect of acoustic excitation using forced coaxial air on the flame characteristics of turbulent hydrogen nonpremixed flames. A resonance frequency was selected to acoustically excite the coaxial air jet due to its ability to effectively amplify the acoustic amplitude and reduce flame length and NOx emissions. Acoustic excitation causes the flame length to decrease by 15 % and consequently, a 25 % reduction in EINOx is achieved, compared to a flame without acoustic excitation. Moreover, acoustic excitation induces periodical fluctuation of the coaxial air velocity, thus resulting in slight fluctuation of the fuel velocity. From phase-lock PIV and OH PLIF measurement, the local flow properties at the flame surface were investigated under acoustic forcing. During flame-vortex interaction in the near field region, the entrainment velocity and the flame surface area increased locally near the vortex. This increase in flame surface area and entrainment velocity is believed to be a crucial factor in reducing flame length and NOx emission in coaxial jet flames with acoustic excitation. Local flame extinction occurred frequently when subjected to an excessive strain rate, indicating that intense mass transfer of fuel and air occurs radially inward at the flame surface.

• 멤브레인
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• 제14권3호
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• pp.192-200
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• 2004

본 연구에서는 유기질막에 비해 안정성이 우수하고 사용수명이 긴 세라믹 막을 이용하여 혐기성 Lactobacillus 균주의 농축에 관해서 연구하였다. Cell harvesting (CH)에 영향을 주는 인자로 막투과 압력, 온도, 선속도 등에 대해 조사하였으며 세라믹 막을 이용하여 농축율 변화에 따른 플럭스와 TMP (transmembrane pressure)의 변화, 일정 VCF(volumetric concentration factor)에서 TMP변화 등의 최적조건에 관해 알아보았다. 그 결과 플럭스는 TMP, 선속도, VCF가 증가함에 따라 투과수량도 증가함을 알 수 있었다. 온도가 증가할수록 점도에 의해 초기 플럭스도 증가하지만 시간이 경과함에 따라 막 표면의 겔층의 형성으로 온도의 영향은 미미하였다. 또한 농축비 이하의 일정한 VCF에서 운전할 경우 플럭스가 안정적임을 알 수 있었다. 선속도 5 m/s, 공급액의 온도 $37^{\circ}C$, TMP 1 bar에서 6∼8 h 운전할 경우 PS 406 원액의 생균수는 4.9{\times}10^9$으로 약 8배 농축됨을 알 수 있었다.

• The Korean Journal of Physiology and Pharmacology
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• 제4권2호
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• pp.99-104
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• 2000

We investigated the action of NOS inhibitors on NOS in rats. Both of nitric oxide synthase inhibitors, $N^G$-monomethyl-L-arginine $(L-NMMA,\;3\;{\mu}M)$ or $N^G$-nitro-L-arginine methylester $(L-NAME,\;30\;{\mu}M),$ augmented phenylephrine $(PE,\;10^{-7}\;M)-induced$ contraction which was inhibited by acetylcholine (ACh) in rat thoracic aorta. This augmentation by L-NAME or L-NMMA was attenuated with the treatment of NO precursor, arginine. ACh, however, decreased the augmentation induced by L-NMMA, but not by L-NAME. Superoxide dismutase (SOD, 50 u/ml) potentiated an inhibitory effect of ACh on the PE $(10^{-7}\;M)-induced$ contraction. It has been known that platelet activating factor itself induces iNOS. Platelet activating factor $(PAF,\;10^{-7}\;M)$ inhibited PE $(10^{-7}\;M)-induced$ contraction. Pretreatment with L-NMMA (30 mM) or L-NAME (30 mM) significantly blocked the inhibitory action of PAF on PE-induced contraction. L-NMMA (100 mM) or L-NAME (100 mM) reduced nerve conduction velocity (NCV) relevant to nNOS in rat sciatic nerve. ACh attenuated the reduction of NCV by L-NMMA-, but not by L-NAME-induced reduction of NCV. These results suggest that L-NMMA and/or L-NAME have different action on three types of NOS in rats.

• 한국지진공학회논문집
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• 제16권1호
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• pp.1-12
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• 2012

이 논문에서는 뒷채움이 부실한 묻힌기초 위에 세워진 건축물의 지반증폭계수에 대한 기초묻힘으로 인한 저감계수를 산정하기 위한 연구를 비선형 의사 3D 수평지진해석이 가능한 P3DASS 유한요소 프로그램으로 수행하였다. 지반은 30m 두께로 균질하고 탄성과 점성이 있는 등방성 지반으로 단단한 암반 위에 놓인 것으로 가정하였고, 기초는 반경이 10-70m인 등가원형 강체기초로 기초묻힘은 0, 10, 20, 30m인 경우를 고려하였다. 지진해석은 노두에서 실측한 7개 지진기록의 유효지진가속도를 0.1g로 조정한 후 연약지반밑 암반에서의 지진기록을 생성하여 수행하였다. 연구 결과에 의하면, 매우 연약한 지반에 깊게 묻힌 뒷채움이 부실한 소형기초인 경우를 제외하고는 지반증폭계수가 기초묻힘비가 깊어 질수록 점진적으로 감소하고 기초크기에 따른 편차는 크지 않은 것으로 평가되었다. 따라서 뒷채움이 부실한 묻힌기초의 지반증폭계수를 설계기준에 주어진 지표면기초의 지반증폭계수에 곱해서 구할 수 있는 표준저감계수를 전단파속도와 지반종류에 따라 제안하였다. 이 표준저감계수는 지반의 평균전단파속도에 따라 보간하여 사용할 수도 있다.

• 천문학논총
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• 제17권1호
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• pp.11-14
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• 2002

Our examination of the relations of spherically symmetric accretion on a massive point object to viscous drag, neglecting gas pressure and using self-similar transformation, shows the behaviors of the asymptotic solutions? in the regions near to and far from the center. The viscosity reduces the free-fall velocity by the factor $(1\;+\;\zeta) ^{-1}$, and causes flattening in the density distribution. Therefore, the viscosity leads to the reduction of the mass accretion rate.