• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1067-1072
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• 2009

In vapor compression systems which use refrigerant as a working fluid, the oil is commonly used for compressor lubrication. Since the presence of lubrication oil can change the characteristics properties of refrigerant, the oil affects the heat transfer performance of heat exchanger to a large extent. In this paper, we focus on the effect of PVE oil experimentally on heat transfer performance of the fin-tube heat exchangers which use R410A as a refrigerant. To evaluate the heat transfer performance, the refrigerant to air type test facility chamber has been used. Fin-tube heat exchanger with grooved has been tested while according to the oil mass fraction variation from nearly zero to 1.7 wt%. It was found that the low level of oil mass fraction has an obvious effect on heat transfer performance, while the high level seems no significant influence. The influence of the oil mass fraction to heat transfer performance, however, is different between evaporation and condensation.

• Bulletin of the Korean Chemical Society
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• 제10권6호
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• pp.488-491
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• 1989

Theoretical studies on the proton transfer reaction in a formamide dimer have been done by Ab initio SCF calculation. In this study, we have shown several effects on the potential energy profile of the proton transfer in a formamide dimer, such as the effect of a basis set, the effect of a geometry optimization, and the effect of a distance between proton-donor and proton-acceptor.

• 시큐리티연구
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• 제16호
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• pp.243-264
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• 2008

우리나라 민간 시큐리티 교육과 관련된 연구들은 지금까지 주로 교육현황과 문제점 파악 및 개선에 집중되어 왔으며, 교육 참여에 따른 전이효과에 대해서는 체계적인 분석이 미흡한 실정이다. 따라서, 본 연구는 현직에 있는 민간 시큐리티 종사자를 대상으로 경비업법 제13조 1항에 의거하여 실시되는 신임 교육이 전이효과에 미치는 영향을 규명하고자 탐색적 연구를 실시하였다. 민간 시큐리티 종사자의 신임 교육이 전이효과에 미치는 영향을 보면 다음과 같다. 첫째, 시큐리티 종사자의 사회인구학적 특성에 따라 개인적 특성 교육훈련특성 업무환경, 전이효과의 차이를 검증한 결과 부분적으로 유의한 차이가 있는 것으로 나타났다. 둘째, 시큐리티 종사자의 개인적 특성이 전이효과에 미치는 영향을 검증한 결과 통계적으로 유의한 차이가 있는 것으로 나타났다. 셋째, 시큐리티 종사자의 교육훈련특성이 전이효과에 미치는 영향을 검증한 결과 통계적으로 유의한 차이가 있는 것으로 나타났다. 넷째, 시큐리티 종사자의 업무환경이 전이효과에 미치는 영향을 검증한 결과 통계적으로 유의한 차이가 있는 것으로 나타났다.

• 대한기계학회논문집B
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• 제40권4호
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• pp.237-243
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• 2016

호기성 수처리 과정의 폭기에 소요되는 에너지의 이용효율을 높이기 위해서는 물질전달 특성뿐만 아니라 소요동력에 대한 연구가 필요하다. 본 논문은 수직 2 상 유동 및 물질전달 특성에 미치는 오리피스 노즐형상과 소요동력의 영향에 대한 실험적 연구를 목적으로 한다. 측정 변수들을 이용하여 유량비, 소요동력, 물질전달 계수 그리고 물질전달 효율을 산출하였다. 소요동력이 커지면 물질전달 계수는 증가하는 반면에 유량비와 물질전달 효율은 감소하였다. 무차원 면적비가 작은 오리피스 노즐의 유량비, 물질전달 계수 및 효율이 높게 나타났다. 물질전달 특성에 미치는 유량비, 소요동력 그리고 프라우드 수의 영향을 평가하기 위한 실험식을 제시하였다.

• 설비공학논문집
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• 제14권6호
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• pp.477-484
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• 2002

A numerical investigation of the performance of the plate heat exchanger with rectangular winglet is conducted to examine the combined effect of vortex generator and louver fins. Velocity and temperature fields and spanwise averaged Nu and friction factor are presented. Enhancement of heat transfer and flow loss penalty is evident. A Parametric study of three factors (Re, angle of attack and louver angle) with levels of 5 (Re= 300, 500, 700, 900, 1100), 4($\alpha=15^{\circ}, 30^{\circ}, 45^{\circ}, 90^{\circ},$), and 4($\beta=0^{\circ}, 15^{\circ}, 30^{\circ}, 45^{\circ}$), respectively, indicates the performance defined by the ratio of heat transfer enhancement to flow loss penalty shows monotonic behavior for each parameter alone but the interactions between parameters is found to be considerable effect on the performance of heat exchanger and should be considered in design. The effect of stamping is also examined.

• 산업경영시스템학회지
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• 제31권2호
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• pp.94-103
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• 2008

This study measured technology transfer efficiency for public institutes. The study made use of DEA being one of the non-parametric linear programming to evaluate technology transfer efficiency for public institutes and to measure technology efficiency, pure technical efficiency and scale efficiency. The measurement of the technology transfer efficiency for public institutes was as follows: The cause of the technology transfer inefficiency was affected by pure technical inefficiency more than by scale inefficiency. Public institutes' RTS(Return To Scale) value varied depending upon the features of the organizations than the features of the regions. Public research institutes' RTS value is more effective than universities' RTS value. We compared the RTS group with the RTS of Projected DMU groups. The RTS group had constant returns to scale effect while the RTS of the Projected DMU had increasing returns to scale effect. The technology transfer efficiency of public institutes varied depending upon the features of the organizations and regions : The technology transfer efficiency of public institutes were as follows : public research institutes at the metropolitan area, public research institutes at the local areas, universities at the metropolitan area and universities at the local areas. In other words, the technology transfer efficiency was affected by organizational characteristics more than by regional characteristics at the place where public institutes were located.

• Advances in nano research
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• 제15권3호
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• pp.191-201
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• 2023

In order to develop better method to enhance and control the flow and heat transfer inside the radiator of electronic device, the synergistic effect of MHD nanofluids and porous medium on the flow and heat transfer in rectangular opened channel is simulated using Lattice Boltzmann method. Three nanofluids of CuO-water, Al₂O₃-water and Fe₃O₄-water are studied to analyze the influence of the type of nanofluid on the synergistic effect. The simulation results show that the porous medium can increase the flow velocity in fluid zone adjacent to the porous medium and enhance the heat transfer on the surface of the channel. Under no magnetic field, when the porosity of porous medium is 0.8, the Nusselt number is 4.46% higher than when the porosity is 0.9. Al₂O₃-water has the best heat transfer effect among the three nanofluids. At Ф=0.06, Ha=100, θ=90°, ε=0.9, Nu of Al₂O₃-water is 6.51% larger than that of CuO-water and 5.05% larger than that of Fe₃O₄-water. Magnetic field enhances seepage in porous medium and inhibits heat transfer in the bottom wall. When Ha=30 and 60, the inhibiting effect is the most significant as the magnetic field angle is 90°. And when Ha=100, the inhibiting effect is the most significant as the magnetic field angle is 120°.

• 대한기계학회논문집B
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• 제30권5호
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• pp.446-456
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• 2006

The effect of relative position of the stationary turbine blade for the fixed vane has been investigated on blade tip and shroud heat transfer. The local mass transfer coefficients were measured on the tip and shroud fur the blade fixed at six different positions within a pitch. A low speed stationary annular cascade with a single turbine stage was used. The chord length of the tested blade is 150 mm and the mean tip clearance of the blade having flat tip is 2.5% of the blade chord. A naphthalene sublimation technique was used for the detailed mass transfer measurements on the tip and the shroud. The inlet flow Reynolds number based on chord length and incoming flow velocity is fixed to $1.5{\times}10^5$. The results show that the incoming flow condition and heat transfer characteristics significantly change when the relative position of the blade changes. On the tip, the size of high heat/mass transfer region along the pressure side varies in the axial direction and the difference of heat transfer coefficient is up to 40% in the upstream region of the tip because the position of flow reattachment changes. On shroud, the effect of tip leakage vortex on the shroud as well as tip gap entering flow changes as the blade position changes. Thus, significantly different heat transfer patterns are observed with various blade positions and the periodic variation of heat transfer is expected with the blade rotation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1069-1074
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• 2004

This study investigated the effect of pressure variations on augmentation of heat transfer when the ultrasonic waves were applied. The augmentation ratio of heat transfer was experimentally investigated and was compared with the profiles of pressure distributions calculated applying a coupled finite element-boundary element method (coupled FE-BEM). As the ultrasonic intensities increase from 70W to 340W, the velocity of the liquid paraffin is found to increase as well as kinetic energy, This physical behavior known as quasi-Eckart streaming results from acoustic pressure variations in the liquid. Especially, the higher acoustic pressure distribution near two ultrasonic transducers develops more intensive flow (quasi-Eckart streaming), destroying the flow instability. Also, the profile of acoustic pressure variation is consistent with that of augmentation of heat transfer. This mechanism is believed to increase the ratio of hear transfer coefficient.

• 에너지공학
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• 제7권1호
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• pp.122-130
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• 1998

A simplified heat transfer model for the cooling capability of the AP 600 PCCS is proposed I this paper. As the PCCS domain is covered with very thin and long water film, it is phenomenologically divided into 3 regions; water entrance effect region, asymptotic region, and air entrance effect region. As the length of the asymptotic region is estimated to be over 90% of the whole domain, the phenomena in the asymptotic region is focused. Using the analogy between heat and mass transfer phenomena in a turbulent situation, a new dependent variable combining temperature and vapor mass fraction was defined. The similarity between the PCCs phenomena in the asymptotic region and the buoyant air flow phenomena on a vertical heated plate is derived. Using the similarity, the simplified heat transfer correlations for the interfacial heat fluxes and the ratios of latent heat transfer to sensible heat transfer were established. To verify the accuracy of the correlation, the results of this study were compared with those of other numerical analyses performed for the same configuration and they are well within the range of 15% difference.