• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.523-524
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• 2006

본 논문에서는 질소와 이산화탄소를 완충기체로 사용하는 경우의 혼합가스에 대해 가스절연설비 내부의 이물질에 의한 절연파괴특성을 모의하기 위한 침-평판 전극구조에서의 침전극 재질을 연철, 고탄소강, 스테인레스강 등으로 구성한 경우 혼합가스의 절연파괴 특성에서 나타나는 전극 재질에 의한 영향을 실험적으로 검토해 보았다. 실험 결과 연철제 전극과 고탄소강제 전극의경우에는 혼합가스의 절연파괴특성에서 유사한 N-특성이 나타남을 확인할 수 있었으나 스테인레스 강제 전극의 경우에는 다소 상이한 양상이 나타났다. $SF_6$계 혼합가스의 경우에는 순 $SF_6$의 경우와 동일하게 코로나 안정화작용에 의한 N-특성이 발현됨이 일반적인 특성으로 알려져 있으나 본 실험 결과에 의하면 침전극 재질에 따라 다소 상이한 양상이 나타날 수 있음을 관측하였다.

• Journal of the HCI Society of Korea
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• v.2 no.2
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• pp.45-51
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• 2007

Space planning is one of the popular applications of VR technology including interior design, architecture design, and factory layout. In order to provide easier methods to accommodate physical objects into virtual space planning task, we suggest applying mixed reality (MR) interface. We describe our hardware and software of our MR system designed according to requirements of the application domain. In brief, our system hardware consists of a video see-through display with a touch screen interface, mounted on a mobile platform, and we use screen space 3D manipulations to arrange virtual objects within the MR scene. Investigating the interface with our prototype implementation, we are convinced that our system will help users to design spaces in more easy and effective way.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.2
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• pp.161-167
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• 2002

In this study, external condensation heat transfer coefficients (HTCs) of two non-azeotropic refrigerant mixtures of HFC32/HFC134a and HF0134a/HCF0123 at various compositions were measured on both low fin and Turbo-C enhanced tubes of 19.0 mm outside diameter All data were taken at the vapor temperature of 39$^{\circ}C$ with a wall subcooling of 3- 8 K. Test results showed that HTCs of the tested mixtures on the enhanced tubes were much lower than the ideal values calculated by the mass fraction weighting of the pure compo- nents'HTCs. Also the reduction of HTCs due to the diffusion vapor film was much larger than that of a plain tube. Unlike HTCs of pure fluids, HTCs of the mixtures measured on enhanced tubes increased as the wall subcooling increased, which was due to the sudden break up of the vapor diffusion film with an increase in wall subcooling. Finally, heat transfer enhancement ratios for mixtures were found to be much lower than those of pure fluids.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.7
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• pp.350-359
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• 2017

Premixed burner is a very strong candidate in household condensing gas boiler burner system because it has low CO and NOx emission with high thermal efficiency. The objective of this study was to determine combustion characteristics of cylindrical premixed burner using different baffle plate and flame holes. Results showed that cylindrical premixed flame mode could be changed into lift-off flame, blue flame, red flame, and green flame with increasing equivalence ratio. In particular, blue flame was found to be very stable at heating load of 8,82~35,280 kcal/h. NOx emission was under 26 ppm between 0.775 to 0.813 of equivalence ratio. CO emission was under 58 ppm under the same equivalence ratio. Thermal efficiency, a very important index in condensing gas boiler, was found to be above 90.13% under the same equivalence region.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.2
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• pp.122-133
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• 2001

Pool boiling heat transfer coefficients(HTCs) of HFC32/HFC134a, HFC125/HFC134a, HFC32/HFC125 and HFC32/HFC125/HFC134a were measured on a horizontal smooth tube. The experimental apparatus was specially designed to simulate the real heat transfer tube with the use of the secondary fluid of water. Data were taken in the order of decreasing heat flux starting at 80kW/$m^2\; and\; ending\; at\; 5kW/m^2$ in the pool temperature at $7^{\circ}C$. Test results showed that HTCs of these mixtures were 11~38% lower than those of ideal HTCs calculated by a linear mixing rule with pure fluids、 HTCs. Experimental data were compared with Stephan & Korner, Thome, Schlunder, Thome & Shakir、s correlations only to find that those correlations were not satisfactory for all fluids. Hence, a new correlation based on the present data was proposed which could be applied even to the ternary mixture. The correlation predicts the degradation of HTCs of mixtures well, showing a mean deviation of less than 15% for all the mixture data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.2
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• pp.207-216
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• 1995

Flow and heat transfer characteristics of mixed convection heat transfer in a rectangular en-closure with various outlets are numerically investigated. The parameters considered here include Reynolds number, Grashof number and the position of outlet. The results show streamlines, isotherms, Nusselt numbers, velocity and temperature distributions. It has been shown that as Reynolds number increases, the size of cell decreases at Re$\leq$100 and increases at Re>100 for $Gr=10^4$. There is a minimum size of cells at Re=100, $Gr=10^4$. The maximum mean Nusselt number occurs at Re=400, $Gr=10^4$ and one right outlet. The mean Nusselt numbers can be formulated by the correlation equation $Nu=C{\cdot}Gr^a{\cdot}Re^b$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.5
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• pp.502-510
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• 2000

Evaporation heat transfer characteristics were studied in a horizontal tube using R22/R114 non-azotropic refrigerant mixture. the heat transfer coefficient was high in the upper part for pure refrigerants, and heat transfer coefficient was low in the lower part for refrigerant mixtures. In the low quality region where nucleate boiling was dominant, the average heat transfer coefficient was low. In the region where forced convection was dominant, heat transfer coefficient was high. Results show that the heat transfer coefficient for pure refrigerants obtained by experiments were lower than those of Yoshida et al. but agreed well with Jung et al., and Chen et al. data. But the heat transfer coefficients for refrigerant mixtures were lower about 20% than those predicted by the equation for pure refrigerant.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.4
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• pp.262-270
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• 2001

This paper deals with a prediction method for the condensation of ternary refrigerant mixture inside a horizontal smooth tube. Based on some reliable assumptions, the governing equations for the local heat and mass transfer characteristics are derived, and the prediction for the condensation of ternary zeotropic refrigerant mixtures composed of HFC32/HFC125/HFC134a, including R407C, is carried out. The local values of vapor quality, thermodynamic states at bulk vapor, vapor-liquid interface and bulk liquid, mass flux etc. are obtained for a constant wall temperature and a constant wall heat flux conditions, and the effects of the composition of HFC32/HFC125/HFC134a on heat transfer characteristics are examined. The prediction result is also compared with experimental data for condensation of ternary refrigerant mixtures. The predicted wall temperature distribution has a similar trend with experimental data but the predicted local heat transfer coefficients are 20-30% higher than the experimental data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.2
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• pp.147-154
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• 1998

This study was carried out for evaluating the interior thermal environment in KBS Open hall with large ceiling height and large space. Ventilation systems of KBS Open hall have combined mixing ventilation and downward displacement ventilation system. Temperature and velocity was measured 130 locations with low level(0.1m), mid level(0.6m) and high level(1.1m). But relative humidity was measured at 15 locations. The subjective thermal sensation was made an inquiry of occupancy at the location measured physical elements.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.4
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• pp.360-369
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• 1992

A heat pump system is constructed to evaluate its performance and heat transfer characteristics with mixtures of R22/R142b as working fluids. The heat transfer in the evaporator and the overall performance are measured and analyzed in terms of the compositions and relevant variables. Possibility of capacity modulation by changing composition is observed without degradation of heat transfer coefficients and coefficient of performance. The cooling capacity is varied continuously within 200 percent based on minimum capacity at constant compressor speed. For similar cooling capacity, COP is improved by mixing two refrigerants and shows maximum value at 60％ mass fraction of R22. Average heat transfer coefficients of mixtures decrease in comparison with pure refrigerants at similar cooling capacity and mass flow rate. However, the overall heat transfer coefficients decrease moderately. A cycle simulation is performed in order to manifest the advantages of using refrigerant mixtures, considering experimentally observed heat transfer characteristics.