• Journal of Advanced Marine Engineering and Technology
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• 제22권2호
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• pp.210-218
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• 1998

Experimental results for forced convection condensationof Refrigerant-22 and ternary Refrigerant-407c(HFC-32/125/134a 23/25/52 wt%) considered as a substitute R-22 inside horizontal micor-fin tubes are presented. The test section was horizontal double-tubed counterflow condenser with a length 4000 mm micro-fin tube having 9.53 mm OD., 0.2 mm fin height and 60 fins. The refrigerants R-22 and R-407c were cooled by a coolant circulated in a surrounding annulus. The range of parameters of mass velocity was varied from 102.1 to 301.0kg/($\textrm{m}^{2}.s$) with inlet quality 1.0. Both refrigerant R-22 and its alternative refrigerant R-407c were tested within the same range of parameters. At the given experimental conditions for R-22 and R-407c the pressure drops for R-407c were considerably higher than those for R-22 at micro-fin tubes. Over the mass velocity range tested the PF(penalty factor)was lower than the increasing ratio of heat transfer area by fins. Based on the data correlation was proposed for predicting the frictional pressure drops for R-22 and R-407c for a duration of condensation inside a horizontal micro-fin tube.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.63-64
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• 2006

Chracteristics on evaporating pressure drop of HCs refrigerants inside a horizontal tube were studied experimentally. Experimental results were presented for pressure drops of hydrocarbon refrigerants R-290, R-600a, R-1270 and HCFC refrigerant R-22 inside a horizontal double pipe heat exchanger. Three tubes with a tube diameter of 12.70mm, 9.52mm and 6.35mm were used for this study. Hydrocarbon refrigerants showed higher evaporating pressure drop than that of R-22 in all tubes. The highest pressure drop was founded in R-600a. The highest evaporating perssure drop of all refrigerants was shown in a tube diameter of 6.35mm with same mass flux. The results can be used as the basic data for the design of heat exchanger using hydrocarbon refrigerants as an alternatives.

• 설비공학논문집
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• 제14권9호
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• pp.741-748
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• 2002

The present study investigated the two-phase flow characteristics of refrigerant R-22 in T-branch with horizontal and vertical inlet tube The key experimental parameters were the orientation of inlet and branch tubes (horizontal and vertical), diameter ratio of branch tube to inlet tube (1 and 0.61), inlet mass flux (200~500 kg/$m^2$s) and inlet quality (0.1~0.4). Predicted pressure profile agreed with the measured data within 25.4%. The flow distribution ratio decreased as the mass flux increased. The flow distribution ratio decreased by 12~25% as the tube diameter ratio decreased from 1 to 0.61, and decreased by 38~47% as the orientation of branch changed from horizontal to vertical upward for horizontal inlet tubes. As the orientation of inlet tube changed from horizontal to vertical upward for horizontal branch, the flow distribution ratio increased by 15~68%, but the quality in the branch tube decreased by 28~92% due to phase separation.

• 설비공학논문집
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• 제12권3호
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• pp.309-314
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• 2000

Experimental results for heat transfer characteristics of natural refrigerants R-290, R-600a and HCFC refrigerant R-22 during evaporating inside horizontal double pipe heat exchangers are presented. The experimental apparatus is basically a vapour heat pump system, composed of a compressor, a condenser, expansion devices, a evaporator, and some other peripheral devices. The test sections were horizontal double pipe heat exchangers, which were a pair of smoothed tube, having 10.07 mm ID, 12.07 mm OD, and grooved inner fin tube, having 12.70 mm OD, 0.25 mm fin height, and 75 fins. The local evaporating heat transfer coefficients of natural refrigerants were not much affected with the mass velocity than R-22 and it could be interpreted that the local evaporating heat transfer coefficients of R-22 were increased more than those of R-290, R-600a according to the increment of mass velocity. Moreover, the maximum increment of the heat transfer coefficient was found in R-290. The average heat transfer coefficient was obtained the maximum value in R-290 and the minimum value in R-22. It reveals that the natural refrigerant can be used as a substitute for R-22. In the grooved inner fin tube, 70% of the increment of the heat transfer coefficient was obtained compared to the smoothed tube.

• 설비공학논문집
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• 제10권6호
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• pp.732-742
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• 1998

Prediction method for heat transfer coefficients in a horizontal smooth tube with forced convection condensation is proposed. In this paper, the analogy between momentum and heat transfer was applied to an annular flow regime and the logarithmic velocity distribution is applied to describe the velocity profile within the liquid film. Prediction results are compared with those of experimental ones. The test refrigerants are R113, R22, R134a, R407C(R33/R125/R134a, 23/25/52 wt%), R410A(R32/R125, 50/50 wt%) and R134a＋R123(R134a/R123, 85.5/14.5 wt%) which are used under operating conditions in a condenser of air-conditioner. The proposed prediction method shows good agreement with experimental data within$\pm 30%$ for pure refrigerants. For the mixture refrigerants including the ternary mixture refrigerant R407C, condensation heat transfer from this study are higher than those from experiments. By correcting the constant in two-phase frictional multiplier, the predicated heat transfer coefficients become similar to the experimental results.

• 무역학회지
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• 제47권2호
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• pp.47-67
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• 2022

This study is to investigate the relationships between R&D collaboration and competitive advantage in Korean international venture firms from the perspective of resource-based theory, organizational learning and network theory. The R&D collaboration is divided into vertical cooperation within the value chain and horizontal cooperation beyond value chain. The first key finding from empirical analysis is that both vertical and horizontal R&D collaborations have significantly positive impacts on technology based competitive advantages. The vertical R&D collaboration has more impacts on competitive advantages than horizontal R&D collaboration. This suggests that R&D collaboration with purchasers and suppliers plays a greater role for venture organizations' competitiveness. Second, the potential knowledge based absorption capacity and mutual goodwill trust also work significantly to reinforce the positive influences of R&D collaboration to the competitive advantage. This implies that mutual trust between partners participating in collaboration and absorption capacity within venture organizations would strengthen the effectiveness of R&D cooperation. This study provides the practical implications that the performance and effectiveness of R&D collaboration may rely on the nature of cooperation partners and internal organization capability.

• 한국해양공학회지
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• 제35권6호
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• pp.434-445
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• 2021

This paper proposes an optimal design method for an unmanned underwater vehicle (UUV) platform to overcome strong current. First, to minimize the hydrodynamic drag components in water, the vehicle is designed to have a streamlined disc shape, which help maintaining horizontal motion (zero roll and pitch angles posture) while overcoming external current. To this end, four vertical thrusters are symmetrically mounted outside of the platform to stabilize the vehicle's horizontal motion. In the horizontal plane, four horizontal thrusters are symmetrically mounted outside of the disc, and each of them has the same forward and reverse thrust performances. With these four thrusters, a specific thrust vector control (TVC) method is proposed, and for external current in any direction, four horizontal thrusters are controlled to generate a vectored thrust force to encounter the current while minimizing the vehicle's rotation and maintaining its heading. However, for the numerical simulations, the vehicle's hydrodynamic coefficients related to the horizontal plane are derived based on both theoretical and empirically derived formulas. In addition to the simulation, experimental studies in both the water tank and circulating water channel are performed to verify the vehicle's various final performances, including its ability to overcome strong current.

• 대한설비공학회지:설비저널
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• 제17권4호
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• pp.328-335
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• 1988

Natural convection in annuli between the horizontal and vertical concentric cylinders for ratio of the inner to the outer radius, $R_1$=0.85, 0.35 has been studied by the numerical analysis. Governing equations are numerically sloved by means of Successive over-relaxation methods. It is found that maximum local Nusselt number, $Nu_{1.max}$ at the inner cylinder and $Nu_{2.max}$ at the outer cylinder for $R_2$=0.35 have maxima at ${\phi}=0^{\circ}$, ${\phi}=180^{\circ}$ ${\xi}=0.4$, 1.6 for horizontal cylinder and at bottom, top for vertical cylinder, respectively. In the present study, mean Nusselt numbers at the vertical cylinder increased more than that at the horizontal cylinder by about 64% for $R_1$=0.35.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2005년도 동계학술발표대회 논문집
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• pp.256-261
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• 2005

In the present experimental study, condensation heat transfer coefficients between R404A and R152a flow in a horizontal smooth tube were compared. The outer and inner diameters of the tube were 9.52 mm and 7.55 mm, respectively, and the heated length was 1045 mm. The mass flux ranged from 150 to 400 $kg/m^{2}s$ and the test section were uniformly heated from 8 to 12. $kW/m^2$. The quality range was from 0.2 to 0.8 at the saturation temperature from 27.3 to $34^{\circ}C$. Experimental condensation heat transfer coefficients increased as the quality and mass flux increased. Modified Dobson and Chato correlation reduced the mean deviation of 5.1% for R404A and 9.4% for R152a than the original correlation$^{(2)}$.

• 기술혁신연구
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• 제23권2호
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• pp.81-100
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• 2015

본 연구는 기업이 직면한 혁신의 장애요인을 자금부족과 정보부족으로 조명하고 수직적 협력과 수평적 협력에 미치는 영향을 분석한다. 이를 위해 한국 제조업 대상으로 진행된 기술혁신조사(KIS) 자료를 이용하였다. 연구결과, 혁신의 장애요인인 자금부족은 수직적 협력에 정(+)의 관계가 있다는 가설은 지지되지 않았다. 하지만, 정보부족은 수직적 협력과 수평적 협력에 정(+)의 관계가 있다는 가설은 지지되었다. 기존 연구들은 R&D협력의 선행요인으로서 기업 내부의 활동과 관련한 논의를 진행하였으나, 본 연구에서는 이를 혁신의 장애요인으로 확장하였다. 또한, 경쟁의 구도가 기업과 경쟁사 사이의 기업 간 경쟁에서 서로 다른 협력 집단들 간의 경쟁구도로 변화함에 따라 R&D협력 유형을 범위를 수평적 협력까지 확장하여 실증 분석하였다.