• Journal of the Korean Institute of Gas
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• v.12 no.1
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• pp.48-53
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• 2008

The condensation heat transfer coefficients of R-22 and R-410A in a small diameter tube were investigated. The main components of the refrigerant loop consist of a receiver, a variable-speed pump, a mass flowmeter, an evaporator (preheater), and a condenser (test section). The test section consists of smooth, horizontal copper tube of 3.38 mm outer diameter and 1.77 mm inner diameter. The refrigerant mass fluxes varied from 450 to $1050\;kg/(m^2s)$ and the average inlet and outlet qualities were 0.05 and 0.95. The main results were summarized as follows : the condensation heat transfer coefficient also increases with increasing mass flux and quality. The condensation heat transfer coefficient of R-410A was slightly higher than that of R-22. Most of correlations proposed in the large diameter tube showed significant deviations with experimental data except for the ranges of low quality and low mass flux.

• The Journal of Advanced Prosthodontics
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• v.9 no.4
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• pp.252-256
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• 2017

PURPOSE. This in vitro study aimed to analyze and compare the reproducibility of zirconia and lithium disilicate crowns manufactured by digital workflow. MATERIALS AND METHODS. A typodont model with a prepped upper first molar was set in a phantom head, and a digital impression was obtained with a video intraoral scanner (CEREC Omnicam; Sirona GmbH), from which a single crown was designed and manufactured with CAD/CAM into a zirconia crown and lithium disilicate crown (n=12). Reproducibility of each crown was quantitatively retrieved by superimposing the digitized data of the crown in 3D inspection software, and differences were graphically mapped in color. Areas with large differences were analyzed with digital microscopy. Mean quadratic deviations (RMS) quantitatively obtained from each ceramic group were statistically analyzed with Student's t-test (${\alpha}=.05$). RESULTS. The RMS value of lithium disilicate crown was $29.2\;(4.1){\mu}m$ and $17.6\;(5.5){\mu}m$ on the outer and inner surfaces, respectively, whereas these values were $18.6\;(2.0){\mu}m$ and $20.6\;(5.1){\mu}m$ for the zirconia crown. Reproducibility of zirconia and lithium disilicate crowns had a statistically significant difference only on the outer surface (P<.001). The outer surface of lithium disilicate crown showed over-contouring on the buccal surface and under-contouring on the inner occlusal surface. The outer surface of zirconia crown showed both over- and under-contouring on the buccal surface, and the inner surface showed under-contouring in the marginal areas. CONCLUSION. Restoration manufacturing by digital workflow will enhance the reproducibility of zirconia single crowns more than that of lithium disilicate single crowns.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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• pp.180-186
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• 2001

The condensation heat transfer coefficients of pure refrigerants R-22, R-134a, and a binary refrigerant mixture R-410A flowing in a small diameter tube were investigated. The experiment apparatus consists of a refrigerant loop and a water loop. The main components of the refrigerant loop consist of a variable-speed pump, a mass flowmeter, an evaporator, and a condenser(test section). The water loop consists of a variable-speed pump, an isothermal tank, and a flowmeter. The condenser is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. The test section consists of smooth, horizontal copper tube of 3.38mm outer diameter and 1.77mm inner diameter. The length of test section is 1220mm. The refrigerant mass fluxes varied from 450 to 1050kg/(㎡$.$s) and the average inlet and outlet qualities were 0.05 and 0.95, respectively. The main results were summarized as follows ; in the case of single-phase flow, the heat transfer coefficients increase with increasing mass flux. The heat transfer coefficient of R-410A was higher than that of R-22 and R-134a, and the heat transfer for small diameter tubes were about 20% to 27% higher than those predicted by Gnielinski. In the case of two-phase flow, the heat transfer coefficients also increase with increasing mass flux and quality. The condensation heat transfer coefficient of R-410A was slightly higher than that of R-22 and R-134a. Most of correlations proposed in the large diameter tube showed significant deviations with experimental data except for the ranges of low quality and low mass flux.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.911-918
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• 2002

Evaporation heat transfer coefficients of carbon dioxide($CO_2$), R-22, and R-134a in a horizontal smooth tube were measured and analyzed as a function of heat flux, mass flux, and evaporating temperature. The experiments were carried out by varying heat flux from 10 to 20 $kW/m^2$, mass flux from 170 to 340 $kg/m^2s$, and saturation temperatures of 5 and $10^{\circ}C$. It was found that the heat transfer coefficient of $CO_2$ decreased with a rise of quality due to an earlier liquid-film dryout as compared to R-22 and R-134a. Averaged heat transfer coefficients of $CO_2$ were 22-63% higher than those of R-22 and R-134a at all test conditions. The effects of mass flux and heat flux on averaged heat transfer coefficients were much greater in $CO_2$ than in R-22 and R-134a. When comparing $CO_2$ test results with the correlations in the literature, the existing models yielded large deviations at medium and high qualities. Therefore, a generalized correlation for $CO_2$evaporation heat transfer needs to be developed by including the effects of dryout phenomenon.

• Korean Chemical Engineering Research
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• v.49 no.1
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• pp.35-40
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• 2011

The low caloric LNG, which didn't meet the gas interchangeability of Korea, has been imported from 2005 winter season. Amount of this LNG imports has been increased from year to year. In the near future, very low caloric LNG (calorific value ${\leq}$ 9,500 kcal/$Nm^3$) such as CBM, Shale LNG will be imported large amounts. For this reason, we need a method for monitoring live calorific values(CV) of LNG in each storage tank to supply gasified LNG with interchangeable CV at LNG receiving terminal. This study was conducted to develope the method for measuring the live CVs of LNG in each storage tank using LNG densitometer. For this purpose, the accurate correlation between CV and density of LNG was derived and the uncertainty of this method was evaluated and also the measuring system for CVs was constructed at LNG receiving terminal. To verify this method, the results of measurement using this method were compared with the field data of LNG analysis and the results showed that the deviations were 0.17~0.47%.

• Atmosphere
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• v.25 no.4
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• pp.707-718
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• 2015

This study investigates the characteristics of turbulent fluxes observed at Ieodo Ocean Research Station (IORS) in autumn 2014. The 10 Hz IORS data is quality controlled and calculated to be the 30 minutes turbulent fluxes. The quality control consists of five steps: a weather check, Vickers and Mahrt (VM) sequential check, VM parallel check, flag check, and direction check. Since the IORS is an open-sea station with no orographic influence, there are no significant diurnal variations for the turbulent fluxes and 10 m wind speed. According to stabilities, the unstable and semi-unstable states appear more than 28% and 70% in autumn, respectively and they have strong winds of over $10m\;s^{-1}$. In addition, the turbulent fluxes increase with increasing wind speed. In particular, the latent heat flux and its deviations are clearly shown because the latent heat flux is influenced by the change of both the sea surface roughness and wave height induced by the wind. To demonstrate the changes of the turbulent fluxes before and after typhoon, Vongpong (1419), which is the most intense typhoon affecting the Korean Peninsula in 2014, is considered. The turbulent flux fluctuates in accordance with the location of Vongpong. The turbulent fluxes have a large (small) variation when Vongpong approaches (retreats) at the IORS. The overall results represent that the IORS data helps us understand physical processes related to air-sea interaction by providing the valuable and reliable observed data.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.2
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• pp.175-181
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• 2014

A four-link mechanism consisting of torsion bars is used for opening the trunk lid in most midsize sedans. When the weight of the lid is in equilibrium with the spring force exerted by torsion bars, the lid stops opening at a pop-up height. However, the actual pop-up height has large deviations from the specified height even with the same parts in the same car model, which leads to quality issues. Automotive manufacturers have experienced this deviation problem despite much effort to resolve it. In this research, we developed a multi-body dynamics model for the analysis of pop-up deviation of a trunk lid with torsion bars, which can simulate the actual pop-up motion of the trunk lid by considering kinematic constraints of the motion and friction forces in joints. We could also determine the most important factor that governs the pop-up height by sensitivity analysis of all parts. The developed system can be used for the analysis of other trunk lid systems to control the tolerance of parts.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.9
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• pp.1245-1252
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• 2001

The condensation pressure drop for pure refrigerants R-22, R-134a, and a binary refrigerant mixture R-410A flowing in a small diameter tube was investigated. The test section is a counterflow heat exchanger with refrigerant flowing in the inner tube and coolant flowing in the annulus. The test section consists of 1220 [mm] length with horizontal copper tube of 3.38 [mm] outer diameter and 1.77 [mm] inner diameter. The refrigerant mass fluxes ranged from 450 to 1050 [kg/(㎡$.$s)] and the average inlet and outlet qualities were 0.05 and 0.95, respectively. The main experimental results were summarized as follows : In the case of single-phase flow, the pressure drop of R-134a is much higher than that of R-22 and R-410A for the same Reynolds number. The friction factors for small diameter tubes are higher than those predicted by Blasius equation. In the case of two-phase flow, the pressure drop increases with increasing mass flux and decreasing quality. The pressure drop of R-134a is much higher than that of R-22 and R-410A for the same mass flux. Most of correlations proposed in the large diameter tube showed enormous deviations with experimental data. However, the correlation predicted by Honda et al showed relatively good agreement with experimental data for R-134.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.34 no.2
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• pp.153-159
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• 2016

Rivers refer to either natural or artificial structures whose primary functions are flood control and water conservation. Due to recent localized torrential downpours led by climate change, large amounts of eroded soil have been carried away, forming deposits downstream, which in turn degrades the capacity to fulfill these functions. To manage rivers more effectively, we need data on riverbed erosion and deposition. However, environmental factors make it challenging to take measurements in rivers, and data errors tend to prevent researchers from grasping the current state of erosions and deposits. In this context, the aim of the present study is to provide basic data required for river management. To this end, the author made annual measurements with a Real-time Kinematic-Global Positioning System (RTK-GPS) and a total station in Pats Cabin Canyon, Oregon, United States, and also prepared thematic maps of erosion and deposition thickness as well as water depth profiles based on a GIS spatial analysis. Furthermore, the author statistically analyzed the accuracy of three dimensional (3D) measurement points and only used the data that falls within two standard deviations (i.e. ±2σ). In addition, the author determined a threshold for a DEM of Difference (DoD) by installing measurement points in the rivers and taking measurements, and then estimated erosion and deposition thickness within a confidence interval of ±0.1m. Based on the results, the author established reliable data on river depth profiles and thematic maps of erosion and deposition thickness using pre-determined work flows. It is anticipated that the riverbed data can be utilized for effective river management.

• Journal of the Korean Society of Clothing and Textiles
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• v.22 no.5
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• pp.664-675
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• 1998

The purpose of this study was to isolate the observational error included in plane photogrammetric data and suggest more accurate and suitable method for body shape measurement. Three experiments were carried out in this study. First of all, the variables which can be obtained from photogrammetric method were selected among the data which can be measured improperly by direct measurement or showing large deviations between the samples. Secondly, the height, the width and the depth of 50 subjects were measured by plane photogrammetry. The result showed that plane photogrammetric data contain significant observational error even for the same variables, as the angle of which photos had been taken changes. Therefore, in order to reduce the observational error and to measure the human body accurately, three-dimensional measurement, stereo photogrammetry was employed in the last experiment. As it is important to isolateonly the observational error by plane photogrammetry and to exclude the accidental error caused by movement of human body subject, body shape model(manikin) was used as subject. The result showed that the average observational error by plane photogrammetry was more than 4 cm in the height, 0.85-1.29cm in the width and 0.49cm in the depth. In conclusion, it is not adequate to use the height obtained from plane photogrammetric data as human body measurement data. And the width and the depth should be used cautiously, even though they are relatively less significant, the error still can make some difference on clothing construction.